If you try to go on a trip in your automobile, you are not going to get very far if there are no gasoline stations to feed your auto. Or restaurants to feed you. Or auto repair shops. This is what is called infrastructure. In the same way, if you want a rocketpunk future, you are going to need some infrastructure in space or your spacecraft are not going to get very far either.

Having said that, creating these pieces of infrastructure will be very expensive. It will be difficult to fund them. And you can be sure that whoever manages to build them will have iron control over who is allowed to use said infrastructure. And how much will be charged as a fee to use it.

It is possible to use spacecraft without any of this infrastructure, but it will be much more difficult. The owners of the infrastructure will probably adjust the fees so it will be cheaper to use their services, but only barely.

And of course an entertaining series of future histories can be postulated using various initial conditions. Does one national government have a monopoly? Two or more governments? Does one privately owned corporation have a monopoly? Two or more corporations? Or a several governments and several corporations?

From the invited address of Salter Wherry to the United Nations General Assembly, following establishment of Salter Station in a stable six-hour orbit around the Earth, and shortly before Wherry withdrew from contact with the general public:

Nature abhors a vacuum. If there is an open ecological niche, some organism will move to fill it. That's what evolution is all about. Twenty years ago there was a clear emerging crisis in mineral resource supply. Everybody knew that we were heading for shortages of at least twelve key metals. And almost everybody knew that we wouldn't find them in any easily accessible place on Earth. We would be mining fifteen miles down, or at the ocean bottom. I decided it was more logical to mine five thousand miles up. Some of the asteroids are ninety percent metals; what we needed to do was bring them into Earth orbit.

I approached the U.S. Government first with my proposal for asteroid capture and mining. I had full estimates of costs and probable return on investment, and I would have settled for a five percent contract fee.

I was told that it was too controversial, that I would run into questions of international ownership of mineral rights. Other countries would want to be included in the project.

Very well. I came here to the United Nations, and made full disclosure of all my ideas to this group. But after four years of constant debate, and many thousands of hours of my time preparing and presenting additional data, not one line of useful response had been drafted to my proposal. You formed study committees, and committees to study those committees, and that was all you did. You talked.

Life is short. I happened to have one advantage denied to most people. From the 1950s through the 1990s, my father invested his money in computer stocks. I was already very wealthy, and I was frustrated enough to risk it all. You are beginning to see some of the results, in the shape of PSS-One—what the Press seems to prefer to call Salter Station. It will serve as the home for two hundred people, with ease.

But this is no more than a beginning. Although Nature may abhor a vacuum, modern technology loves one; that, and the microgravity environment. I intend to use them to the full. I will construct a succession of large, permanently occupied space stations using asteroidal materials. If any nation here today desires to rent space or facilities from me, or buy my products manufactured in space, I will be happy to consider this—at commercial rates. I also invite people from all nations on Earth to join me in those facilities. We are ready to take all the steps necessary for the human race to begin its exploration of our Universe.

It was past midnight by the time that Jan de Vries had read the full statement twice, then skipped again to the comment with which Salter Wherry had concluded his address. They were words that had become permanently linked to his name, and they had earned him the impotent enmity of every nation on earth: "The conquest of space is too important an enterprise to be entrusted to governments."

From Between The Strokes Of Night by Charles Sheffield (1985)

Surface to Orbit Boost

For most missions, almost half of the delta-V budget is used up in the first 160 kilometers or so, the lift-off from Terra's surface into Low Earth Orbit. This is the reason behind Heinlein's "halfway to anywhere" comment. In dollar terms, the Russian Proton would cost about $5000 per kilogram boosted into LEO while the Space Shuttle would cost about $18,000 per kilogram. Actually if you factored in all the shuttle's design and maintenance costs, the real price was closer to $60,000 per kilogram. NASA was hoping that the shuttle would cost more like $1,400/kg (in 2011 dollars), though part of the over-run was due to the multi-year interruptions in launches following Shuttle failures.

Infrastructure that help reduce the cost include Lofstrom loops, laser launchers, Marshall Savage's Bifrost Bridge, and the famous Space Elevator.

See the section on Laser Launching below.

Orbital Propellant Depots

As the delta-V for a mission goes up, the amount of propellant required goes up exponentially (or looking at it another way: the amount of payload shrinks exponentially). Large amounts of propellant are expensive, but the higher the mass-ratio the higher the likelihood that the spacecraft will not be resuable. Propellant expense is bad enough, but that's nothing compared to having to build a new spacecraft for each mission. Increasing the mass ratio means things like making the walls of the propellant tanks thin like foil, and shaving down the support members so they are fragile like soda straws. With such flimsy construction it does not take much normal wear-and-tear to turn the spacecraft into junk.

Having a propellant depot at the mid-point of a round-trip mission cuts the required delta-V in half. Instead of the spacecraft having to lug enough propellant to go to Mars then return to Terra, it only carries enough for half the trip but re-fuels (re-propellants, or re-remasses) at the halfway point. And when you are dealing with exponential growth, cutting the delta-V in half cuts the propellant amount much more than half.

Indeed, Rick Robinson noticed that with access to an orbital propellant depot, most cis-Lunar and Mars missions are well within the delta-V capabilities of a sluggish chemical rocket engine. You do not have to use a nuclear thermal rocket. Hop David noticed this as well. Dr. Takuto Ishimatsu's ISRU optimization algorithm calculated that NASA's Mars Reference Mission was more optimal with no NTR but with ISRU ("optimal" defined as "requiring less mass boosted from Terra into LEO").

This is also an argument for orbital propellant depots in Low Earth Orbit. Remember that once the rocket has traveled from Terra's surface into LEO, you are "halfway to anywhere". This means for a one-way trip, LEO is the mid-point of the mission.

Now to make this work, in addition to the depots you will need sources of propellant and tankers and lighter to keep the depots filled up. Water and hydrogen propellant is available in such places as the lunar poles, asteroids, and perhaps the Martian moons Phobos and Deimos. Dr. Takuto Ishimatsu developed an algorithm to optimize placement and supply of ISRU orbital depots.

Examples of tankers include Kuck Mosquitos, Zuppero Water Ships, and Zuppero Lunar Water Trucks.

Early Days - economics of private space services

Next up: in-space refueling. The first and most obvious customer is NASA; an orbital fuel depot would allow them to launch satellites on smaller LVs or launch larger satellites, allowing a choice between savings on the LV and increased capabilities on the spacecraft. That could mean buying an Atlas 401, Zenit, Soyuz, H-IIA or Falcon 9 instead of an Atlas 551, Ariane 5, H-IIB or Delta 4(5,4). Perhaps less obvious, Russia would see a significant benefit from a LEO depot in the plane of the Baikonur launch site. Vehicles would refuel in order to plane-change to an equatorial orbit for GEO deployment. Further into the future a fuel depot would be essential for the smooth operation of tugs and satellite tenders, serving as a buffer between fuel launches and fuel used in missions.

I think the current leader is Boeing with their in-development ACES vehicle using integrated fluids management. However, they are focused on LOX/LH2 propellant; few customers today have cryogenic upper stages. Hypergolic fuels require a different set of technologies and would most likely require shipping expendable supplies of a pressurant, either nitrogen or helium, but they have a larger potential market right now as hypergolics are typically used for satellite stationkeeping and orbit changes. The third fuel category is inert gases (argon, xenon) for ion engines; these can be stored as compressed gases or cryogenic liquids.

I think a near-term possibility is simply to ship water. It is dense, relatively inert and can be used as a life support consumable or as a propellant after electrolysis. It has a high surface tension and can be wicked out of a bulk tank in microgravity without pressurants or membranes. There are cubesat-scale thrusters available today that separate water over time, accumulating a charge of gaseous O2 and H2 using small amounts of power, then ignite that fuel in a high-efficiency engine. If future satellites were to adopt this technology for RCS and stationkeeping then they could nearly double their Isp while eliminating toxic fuels and cutting down to a single storage tank. Beyond the near-term possibilities, a water depot operator would be able to buy water from any LEO cargo provider as well as any asteroid mining company, relying on the proven launch capabilities today while safely and cheaply allowing for a riskier but cheaper future supply.

Interorbital Exchange - part 1: cis-lunar space

     This entry covers cis-lunar space. The topic of lunar mining and fuel supply has a rich field of information available and I cannot claim to know all of it, but hopefully this will show how we can begin to harvest most of our propellant instead of shipping it from Earth.

     First let's establish some basics:

     I assume that we will develop zero boiloff cryogenic storage, reliable cryogenic fluid transfer and reliable cryogenic engine restart. Vehicles will be designed to last 20-30 years, but generally are planned to be replaced every 10 years. Obsolete systems will keep operating until they fail, providing some bonus production capacity.

     The Moon's surface gravity is 1.62m/s², about 16.5% of Earth gravity.
     It takes about 1.87km/s of dV to land or take off from the equator. Only a little more is needed for the poles.
     Another 0.64km/s will take you from low Lunar orbit to EML1 (Earth-Moon Lagrange Point One).
     Low orbits around the Moon are not stable so you should not park anything important there.

     Large amounts of water ice are available at the south pole and most likely at the north pole as well.
     Plenty of metal oxides are available (including iron, aluminum and titanium), but carbon is rare.
     In some locations the mantle interface material (KREEP) is accessible at the surface; this rock is rich in incompatible elements like phosphorus, potassium, rare earths and radioactives.

     Low Earth orbit takes anywhere from 9.4 to 10 km/s of dV to reach.
     Each launch site has a specific, most-efficient inclination. Changing inclinations is very expensive.
     From any low-Earth orbit, EML1 is 3.77km/s away.
     From Kennedy Space Center LEO, geosynchronous orbit is 4.33km/s away. It's only 3.9km/s from an equatorial orbit.
     Earth escape is 3.22km/s away.
     EML1 is the balance point between Earth and the Moon, the place where the gravity of each body cancels out.
     From EML1, a craft with a heatshield can get to any low Earth orbit for 0.77km/s.
     Without a heatshield, 3.77km/s is required.
     A similar maneuver can use the Earth as a slingshot, departing from EML1 with a little nudge into any inclination and then burning at closest approach for best use of the Oberth effect.
     From EML1, geosynchronous orbit is only 1.38km/s away.

     Putting all of that together:
  • The best place for a fuel depot is at Earth-Moon Lagrange Point One (EML1). Fuel can be harvested at the harvester's pace, shipped to the depot at the tanker's pace and accumulated for later use. Fuel is shipped to LEO only as needed and into the correct inclination.

  • The surface to EML1 tanker needs to use chemical engines to overcome the Moon's gravity. It must carry about 4.6km/s of fuel, though the second half of the trip is empty and requires much less fuel. My reference tanker is 5.5 tons, cryogenic with zero boiloff and can deliver 29 tons of propellant from the Lunar surface to EML1, then land at the harvester. Each trip burns just under 34 tons, so the harvester must produce about 2.2kg of propellant for each kg in EML1.

  • The EML1 to LEO tanker can use either chemical or ion engines. The low thrust option requires a very different trajectory and a dV of about 7km/s, plus a lot of onboard power. This can be a competitive option but initially it would be simpler to use the same tanker for each leg. Because the vehicle needs to aerobrake, it requires a reusable heatshield. The same tanker design is used, but it is launched with a dual-use shroud of about 6.3 tons that is kept with the vehicle. This trip delivers 44 tons of propellant at a cost of 19 tons. So, for each kg in LEO the harvester has to produce 3.1 kg. That lines up fairly well with other sources suggesting 75 tons to be harvested for 25 tons in LEO.

     The harvester is an unknown quantity. There are several concepts (including one of mine), but I will use a more generic NASA number of 10kg propellant per kg of harvester per year, with 10% spares. That means if we want to harvest 100 tons of fuel per year we need to send 10 tons of equipment to start and 1 ton of spares for each year. This was for a Mars ISRU system with rover/excavator and integrated power systems. A Lunar system would be much simpler since it would only be melting and filtering water ice then electrolyzing it, so it is possible the equipment will produce far more propellant than this estimate.
     Cheap propellant in LEO is useful for missions to other planets or moons. It is also useful for supplying a LEO station with water and stationkeeping fuel. Satellite servicing tugs could base out of EML1 with a ready supply of fuel and easy access to all inclinations. If commercial satellites were modified to use a water electrolysis thruster system for stationkeeping then they could be launched empty to EML1 for less dV than a direct launch to GEO. A fill of fuel at EML1 and a 1.4km/s nudge would place the satellite in GEO with decades of stationkeeping thrust available. As a bonus, the upper stage of the launch system could be refueled and repurposed. Lastly, water is extremely useful for manned operations as radiation shielding, drinking water and a reserve source of oxygen.

     An example of why the interorbital exchange would be useful is NASA's Mars Design Reference Mission (DRM). Each manned trip requires three flights (one crew and two cargo), each using around 190 tons of fuel. Just the fuel would require 9 Block 1 SLS launches or 6 of the 105-ton launches; being generous we're talking about at least $4.5 billion. This is 570 tons of propellant over 2.1 years, or about 267 tons per year at around $7.9 million per ton. A full campaign of three flights to Mars would cost $13.5 billion in fuel. With lunar ISRU we can save at least $4.7 billion as described below (potentially over $9 billion) and gain a sustainable supply of propellant in EML1/LEO with minimal Earth mass.
     An ISRU plant with this capacity would mass at least 83 tons and consume about 18 tons of spares per Mars opportunity. A modified version of my tanker could land perhaps 17 tons of cargo on the Moon for about 62 tons of fuel; this would require two Falcon Heavy flights (~$300 million) or an SLS block 1 flight with two additional Falcon 9 refueling flights (~$850 million). This initial 15-ton plant (with 1 year of spares and a 500-kg dextrous robot for remote repair operations) would provide the first ISRU fuel as a proof of concept. The cargo lander would be refueled and returned to LEO two months later with plenty of lunar samples. (3 tons of samples, 25 tons of fuel.) At this point the whole architecture can be validated and the final ISRU design can be settled. Until this step happens we have to use some pessimistic numbers (as below), but there is the possibility that the pilot plant will be many times more productive than expected as it will be running a much simpler refining process.
     A standard tanker with dual-use shroud (11.8t empty) would be launched with a Falcon 9. Another standard tanker with 43.5 tons of fuel would be launched on a Falcon Heavy, transfer 27.8 tons of fuel to the shrouded tanker and then head to the Moon and land by the ISRU plant. The shrouded tanker would travel to EML1. At this point fuel can be transferred all the way to LEO; without a proper depot there are some inefficiencies, so only about 40 tons are delivered in each shrouded tanker (requiring two standard tanker flights to fuel up). Fortunately this is enough for the outbound trip of a cargo tug.
     The first shipment of 40 tons would take the rest of the year to produce and would be delivered to the cargo tug in LEO, allowing it to deliver a 22-ton payload to the Lunar surface. (Payload would be a second 15-ton ISRU plant, two years of spares for both plants and 1 ton of other cargo.) This could be a Falcon Heavy carrying two payloads or one of several competing options. After 30 days of surface operation the cargo tug returns to LEO (again, 3 tons of samples and 25 tons of fuel).
     The next 40 tons of fuel take a bit over five months to produce and allow the cargo tug to bring the next 22-ton package. Return fuel for the tug would take three weeks.
     At this point the infrastructure on the moon is producing 1.25 tons of fuel per day. Each cargo trip takes less and less time to refuel (3.4 months, then 2.6 months, then 2 months). A proper depot at EML1 and three more ISRU packages round out the system. The depot is 300-ton capacity, about 20 tons of hardware and delivered to EML1 by a Falcon Heavy. In total the buildup phase takes two years and two months, almost exactly one synodic period. 90 tons of ISRU hardware is on the surface with an annual production of 900 tons and spares requirements of 9 tons. This system can deliver 289 tons of fuel to LEO every year, or 617 tons per Mars synodic period. The target of 570 tons is met with an extra 47 tons of fuel for delivering spares.
     A total of seven Falcon Heavy flights are required, plus one Falcon 9. Let's call this $1.1 billion in launch costs over 26 months. Let's also assume that spares are supplied as 11-ton packages by Falcon 9, two per synodic period. A third assumption is that we will need to replace about 20% of the system every period (at a conservative 10-year lifespan for components), so we budget a Falcon Heavy flight for $150 million. That's an operational cost of about $250 million per period. In the first synodic period the fuel in LEO will cost $2.2 million per ton in launch costs. Each additional period will cost only $405,200 per ton in launch costs.

     The cost of all that hardware is difficult to estimate. Let's look at two very different systems and get a ballpark figure. The BA-330 expandable space station module from Bigelow is estimated to mass about 22 tons and cost about $250 million, or about $12 million per ton. By contrast, the Iridium NEXT constellation of 72 satellites is expected to mass 57.6 tons in total and cost $2.4 billion (not counting launch costs), or about $42 million per ton. The comsats include costs like bandwidth leases and operations, but let's use that figure anyway as a first approximation. The startup phase requires 131 tons of hardware, or about $5.5 billion. Extended operation will replace about 10% of that hardware per year at a cost of about $550 million. This ignores the significant commonalities between systems; all the propulsion units are identical, all tankers identical other than the cargo adapter and all six 15-ton ISRU plants are identical.
     This gives us the second part of fuel costs: capital expense. Each ton of fuel in LEO in the first period costs $9.8 million, with additional periods costing $890,000. These numbers assume we do not spread the capital costs over five periods, but front-load the entire bill into the first launch season. The first Mars caravan would cost $6 billion instead of $4.5 billion in fuel, but the next one would pay only $1.4 billion. A campaign of three flights to Mars would save about $4.7 billion in fuel costs. As a budget line item, the cis-lunar fuel network would cost NASA or a private operator $375 million per year once established.
     What if, instead, a cost-effective hardware program is used that is closer to the BA-330 in terms of cost per kg? Now our 131 tons of hardware only costs about $1.6 billion with annual replacement costs of $160 million (or per-period costs of $342 million). Under this assumption, the startup phase would cost $2.7 billion with operational costs of $592 million per period ($278 million per year). Propellant would cost $5.34 million per ton in the first period and $960,000 per ton thereafter. NASA would save about nine billion dollars on three Mars flights, and would even save about $1.2 billion on the first flight.

EML-1: the next logical destination

The first Earth-Moon Lagrange point, or EML-1, offers a number of key advantages that make it an ideal destination for activities in cislunar space. Over the near-term, however, its utility is constrained by a lack of physical infrastructure. This can change if our approach to space moves away from destinations and towards a strategy of enabling capabilities.

Talk abounds of going beyond Earth orbit, although once beyond low Earth orbit (LEO) what happens next becomes a little fuzzy in most discussions. This need not be the case, as capabilities can be built from the very first test of a trans-LEO vehicle. Some sample test runs:

  1. Out to GEO: Given launch locations of likely US crewed vehicles, the mission could involve a plane change to geostationary (perhaps through a bi-elliptical transfer for extra-credit), close-approach to a “zombiesat”, and perhaps even retrieval of some old hardware for forensic analysis.
  2. Free-return trajectory: A loop around the Moon to give the heat shield a workout on the return. Perhaps some maneuvering out around the Moon. How close can they shave the rear-end of the Moon at perilune?
  3. EML-1 visit: The main purpose would be to establish a halo orbit. Once there, it would make sense to drop off a package of instruments that could serve a number of purposes.

Instrumental to the use of EML-1 is the concept of the halo orbit. It is a technique that allows an object to orbit an empty space, typically a Lagrange point, as with SOHO, WMAP, Genesis, the future JWST, and others. The best, though inapt, way to think about it is as a sort of gyroscopic effect, as with a bicycle wheel, where the hub is on the line connecting the centers of gravity of two objects (like the Earth and Moon), and the satellite is on the wheel. The action of the orbit helps to keep the object in place; some station keeping is required, but at a level orders of magnitude less than the ISS.

The EML-1 neighborhood is good for looking not only outward, but also back in towards Earth. EML-1 is a naturally clutter-free environment, since space junk doesn’t normally have station-keeping capability, as well as a “high ground” that allows observation not only of the Earth but also everything that’s orbiting around the Earth out to GEO. Instruments could be placed there for the specific purpose of keeping an eye on the traffic in cis-GEO space. By the same token, it is also ideal for looking at the Moon, and serves as a natural gateway to the entirety of the Moon’s surface. Bigelow Aerospace has proposed using EML-1 as an aggregation point for modules to be emplaced on the Moon’s surface using Armadillo Aerospace rockets for the descent. As far back as 1986 a Lunar Spaceport was envisioned as a kind of motel/gas station/warehouse/restaurant/garage for space travelers.

The Moon is still a bit in the future, though, as there are still a lot of things to consider on the Earth side of EML-1. One of the key advantages of staging at EML-1 is, as Brad Blair notes, “its ability to fall into various inclinations without a major [delta-V] penalty, thus increasing the number of customers that could be reached by a small set of vehicles and systems elements.”. What this means is that the inclination you end up in in LEO is set by how you depart from EML-1.

If you picture the Earth-Moon system, and the line connecting their centers of gravity, EML-1 is about 85 percent of the way to the Moon. Trace an ellipse from the EML-1 point down around the Earth and back up to EML-1. Put the perigee close enough to Earth and you can even get some aerobraking. This ellipse can be assumed to be in the orbital plane of the Moon. Now, rotate that ellipse around the Earth-Moon axis. This means that every inclination of LEO orbit is accessible, from the 28.5° of Kennedy Space Center, to the 51.6° of ISS, to even polar orbits, although the latter suffer from more delta-V penalty by virtue of the Earth’s oblateness.

If all of the LEO inclinations are available from EML-1, then it is also true that any LEO inclination can get to EML-1. This means that the ISS can serve as a staging point for missions to EML-1 in the nearer term, and later stations in different inclinations can also reach EML-1 as they come online. There is no need to wait to get started. As soon as a crew vehicle comes online it can start staging from ISS to EML-1, first as test-runs, then as missions to emplace as well as service, upgrade, and refuel assets. By the time crewed facilities are emplaced there will already be regular traffic to the location.

One question often raised is “What would a crew do at EML-1?” There are a myriad of answers:

1) In terms of propellant, it is cheaper to go from EML-1 to GEO and back to EML-1 than it is merely to go from LEO to GEO. Over the long term, it makes sense to stage GEO operations from EML-1. What kind of operations? The easiest answer is salvage, given the hundreds of tonnes of scrap circulating in GEO. Crews could fall down to GEO, spend a few days retrieving defunct equipment like failed satellites, and then return to EML-1 to process it. Whatever could be reused in some way is unknown, but the real value is in the forensic analysis of how the satellite weathered in the GEO environment over a known period of time. That kind of information allows for better satellite design.

2) EML-1 is an on-ramp to what are known as the InterPlanetary Superhighways (IPS). These are a network of ridges and ripples in space created by the gravitational effects of the planets and Sun. A satellite pushed onto the IPS will travel very, very slowly along this network to its destination, where it can kick itself into a halo orbit around a Lagrange point and collect data. Locations of interest would include the Sun-Mars L-2 and Sun-Jupiter L-1, to observe the Asteroid Belt; the Sun-Venus equilaterals at L-4 and L-5 to provide communications relay when Mars is on the other side of the Sun from Earth; Sun-Saturn L-2 to look at the Kuiper Belt; Sun-Neptune L-2 to look at the Oort Cloud; Sun-Mars L-1 as a waypoint on the way to Mars and the Asteroid Belt; Sun-Earth L-1 to watch the Sun; Sun-Earth L-2 to watch the stars. The key is that all of these instruments would also be able to return via the IPS to EML-1 for regular maintenance and servicing. As more probes are added to the network, instead of thrown into the void, there will be an increasing stream of probes in need of work.

3) The time lag from EML-1 to the Moon and back is much less than that for Earth-Moon. As a result, it is a better location for safe teleoperation of robots on the lunar surface.

4) As lunar activities ramp up, there will be an increasing need for freight handling of goods destined for the Moon, as well as those from the Moon. Early lunar exports are likely to be low-value-added goods such as oxygen, water, raw regolith, and some metals, but as more capabilities are established the exports will start creeping up the value-added chain: foodstuffs from lunar greenhouses, crafts created by the locals from local materials, increasingly sophisticated entertainment like dance and music, and so forth.

5) EML-1 is an ideal location to aggregate mission components for a trip to an asteroid. Fuel can come from the Moon, while spacecraft come from Earth. Someone’s going to have to put all of that together.

6) A facility at EML-1 can serve as a communications node for lunar operations to overcome the line-of-sight issue. Additionally, with solar sails “pole-sitting” above the north and south lunar poles, communications with the far side can be established.

7) Port services. While probes returning on the IPS will end up in the neighborhood of EML-1, they will need to be picked up. Same thing with freeflyer platforms sent on low-energy trajectories around the Moon for production runs. A space tug would be a good tool to have, and someone has to fly it.

These are just a few ideas, which can easily be expanded. If a crew can fall down to GEO for a servicing run, it can also fall down to HEO, MEO, and LEO for servicing missions. If an asteroid mission can be assembled at EML-1, so too can a Mars mission. If crews are salvaging dead satellites and kick stages from GEO, they may be able to cobble together the parts for other missions, selling the result to whomever wants to buy a space probe.

From EML-1: the next logical destination by Ken Murphy (2011)
Interorbital Exchange - part 2: Mars cargo

     This entry covers near-term resources on and near Mars and how they might be transported.
     I assume the propellant network described in part 1 has been built, or at least that lunar propellant is available at Earth-Moon Lagrange Point One (EML1).
     The short version of the below is that using hardware similar (or identical) to the part 1 Lunar infrastructure, cargo to and from Mars becomes relatively cheap.
     A set of three NASA-reference mars missions could have their cargo requirements filled for a total of $11.4 billion (including fuel).
     Nitrogen and argon from Mars could be as cheap as $400 per kg at EML1.

     Again, let's start with the basics.

     Mars has a surface gravity of 3.711m/s² or 37.6% of Earth gravity, and a surface rotation of about 0.24km/s.
     Mars is blessed with a thin atmosphere, mostly carbon dioxide but with useful amounts of nitrogen and argon.
     Martian soils are rich in perchlorates and relatively rich in water.
     The north and south poles have permanent ice caps, mostly water ice under a layer of frozen CO2.
     CO2 slabs violently sublimate in the spring, making the edges of the ice caps fairly dangerous in this season. Otherwise the dust storms are not a serious threat.
     Takeoff and landing requires 4.1km/s; drag can save as much as 2.4km/s of this on landing.
     Mars has two moons, Phobos and Deimos. Both are believed to be captured asteroids, probably C-type.
     From EML1, Mars transfer costs 0.74km/s. Mars capture costs 0.9km/s and the move to low Mars orbit costs 1.4km/s. Trip total is just over 3km/s.
     From low Mars orbit, reaching Phobos costs 1.4km/s and reaching Deimos costs 1.9km/s.
     Launch opportunities to or from Earth (using a Hohmann transfer orbit) occur every 2.135 years, or about 26 months.

     Taking all of this together we want a surface location near the equator and a depot in low orbit. If we find significant amounts of water at either Phobos or Deimos then we want a mining outpost there. It would be nice if we could set up a Phobos-anchored tether for orbit changes.

     Getting cargo to Mars is slow and expensive. The post in part 1 used NASA's Mars Design Reference Mission (DRM) as a baseline to show how in-situ resource utilization (ISRU) could save money on fuel. Let's look at other ways to save.
     For starters, let's use the same cargo tug as described in part 1. This is a 5.5 ton dry vehicle that would deliver 50 tons of payload to EML1 using 77 tons of Lunar fuel and a reusable 15-ton (fueled) drop tank. The tug and payload would refuel with 63 tons of lunar fuel and continue on to Mars with fully propulsive capture to low orbit. These tugs can be used as fuel tankers between Phobos and LMO and can also be used to return cargo to Earth (up to 52 tons to EML1 all propulsive).
     Once cargo is in low Mars orbit, a different vehicle is needed to land it. The cargo tugs are capable, but multiple atmospheric landings in Mars gravity are out of reach. Instead, let's use the Access to Mars SSTO ferry (Strickland, Gopalaswami). This is a 30-ton dry mass, reusable SSTO cargo ferry for moving payloads to and from the Martian surface. The vehicle is 14 meters in diameter, which poses a problem; we would need a larger-diameter booster, a way to assemble the vehicle in orbit or a way to launch such a wide payload on an existing rocket. The design could probably be scaled down, but extrapolating the performance of a smaller version is not trivial. I will assume the problem is solved without specifying how. If reliable fuel is available from Phobos then the lander might be redesigned to refuel both in LMO and on the surface, allowing it to carry more payload each way.
     The cargo lander is intended to fuel up, launch to orbit (with 5 tons of payload or excess fuel), collect a 25-ton payload and land. Repeat as needed. Each 50-ton tug payload would require two lander trips. NASA's reference mission involves 80 tons of cargo to the surface, so two such flights would be required. Note that the ~40-ton DAV would not be required at all; a crew version of the lander can ferry crew to and from the surface. That suggests that a single 50-ton payload could include all of the required surface habitat, science equipment, power, rovers, food, etc. The first mission would require a cargo lander and crew lander as well as an orbital depot, so the first mission would require three 50-ton cargo flights to establish infrastructure along with the surface cargo. Each additional mission would require only one cargo flight.
     Each lander flight requires 95 tons of fuel, and each mission requires two flights (one 25-ton cargo, one 20-ton cargo + crew). This 190 tons requires about 9 tons of ISRU plant and 2 tons of spares. The Phobos ISRU plant should provide 15 tons of fuel for each lander. We might also send a single tug flight back to Earth each period for a cost of 63 tons of propellant from Phobos. That totals about 7.4 tons of ISRU plant and 1.6 tons of spares. A cargo tug can haul fuel from Phobos to the LMO depot, delivering 37.2 tons per trip at a cost of 25.8 tons of fuel.

     So, let's compare this to the baseline NASA plan over the course of three missions to Mars. The first trip requires three cargo flights to establish the orbital depot, Phobos ISRU base, tanker fleet and lander fleet. A habitat, science payload, ISRU facility, food and other supplies are delivered to the surface. Total cost is two landers (60 tons), three tugs (16.5 tons), 420 tons of Lunar fuel, a ~15-ton depot (200-ton capacity) and 16.4 tons of ISRU plant (with 3.6 tons of spares). That leaves 55 tons of payload available for the surface mission, with the understanding that the surface ISRU system will provide sufficient water and buffer gas.
     As a first-mission flight, the fuel alone will cost $2.24 billion. Using a middle of the road estimate of $30 million per ton for hardware (including surface payloads) that's almost exactly $5 billion. Launch costs would be three Falcon Heavy and a Falcon 9, about $500 million. Total mission cost, $7.75 billion. Note that this does not include the crew launch, transit habitat or crew recovery; these will be discussed in a later post.
     Future flights would require a single cargo flight, 55.5 tons of hardware ($1.67b) and 140 tons of lunar fuel ($135m). All other components are reusable and already present. Total pricetag for the cargo end is $1.8 billion for each additional mission. After about the fifth mission some of the infrastructure hardware will need scheduled replacement, so this cycle of one expensive mission and four cheap missions could continue indefinitely or the replacement costs could be spread across multiple missions. Still, $11.4 billion for three missions to Mars is cheap compared to $2.5 billion for MSL/Curiosity (which was money well spent) or the $156 billion for Apollo to put men on the moon.

     Looking past the baseline, the Mars surface base is able to supply nitrogen for breathing gas and argon for electric engine fuel. This can be carried back to EML1 in a reusable cargo tug that paid for itself by delivering its first payload to Mars orbit. The same tug can be reused multiple times. Ultimately the cost of shipping along this route is the cost of spares and replacement of the various ISRU bases, depots and tugs. With Earth launch costs in the $3 million per ton range, any advantage is worth pursuing. Cargo from Mars costs about 126kg of spares to Mars per ton delivered to EML1. Cargo to Mars costs about 76kg of spares to the Moon per ton delivered to LMO. Of course each trip requires the use of a cargo tug costing anywhere from $66-$165 million but in terms of ongoing costs we're looking at 6.78 tons from Earth to support a 50-ton cargo from Mars, a better than 7:1 ratio. Another way to say it is for $20 million in launch costs we can get 50 tons of argon and nitrogen (or Mars core samples or Phobos turnings, etc.) at EML1 for use elsewhere once the system is established, a savings of at least $130 million.

Lunar Orbital Facility Location Options

For travel throughout cislunar space, I’ve long been an advocate of having depots on both ends of the journey. The LEO depot provides a refueling stop at the first practical point after leaving the ground, and also a spot for bringing vehicles back from lunar space for refueling for their next trip out. The lunar orbit depot plays a similar role for flights to/from the lunar surface, as well potentially, as being a staging location for departures into interplanetary space. By launching from a lunar facility near the top of earth’s gravity well, it’s both possible to use low-thrust trajectories in and out of cislunar space, as well as to do an earth swingby with a departure burn at apogee for high-thrust departures taking maximum advantage of the Oberth effect.

One important question however has been where to place the lunar orbital facility.

Lunar Orbital Facility Orbit Options
A recent FISO telecon presentation by Ryan Whitley and Roland Martinez of NASA JSC describes and discusses several of these staging orbit options. I’ll be reposting snapshots of a few of their slides to introduce the orbits, but here you can find their full presentation:

They discuss most of the commonly cited options including Low Lunar Orbit, Frozen Orbits, L2 Halo Orbits, Distant Retrograde Orbits, and a more recently discovered option, Near Rectilinear Orbits.

This slide shows some of the smaller lunar orbit options and descriptions (click for larger image):


And this slide shows some of the larger lunar orbit options, with descriptions (click for larger image):


And this slide shows all of the orbits relative to each other to give you a better idea of what they look like (click for larger image):


Comparison of Options

While Whitley and Martinez in their FISO telecon focus on evaluating the various staging orbits from the standpoint of NASA missions using the Orion capsule, they still provide a lot of useful information for evaluating options for the location of a lunar orbital facility/depot. To me, some of the considerations for locating a lunar orbital facility are:

  • How frequently do you have opportunities to travel from a LEO facility to the lunar facility, and how frequently you can travel the other direction?1
  • How much delta-V does it take to go between the facility and LEO and the facility and the lunar surface?
  • How long is the transit between the location and the lunar surface?
  • How useful is the orbit for supporting deep space missions?
  • How hard is it to reach various lunar surface destinations from the lunar orbital facility location?
  • What is the thermal environment like in the orbit?
  • And how much of the lunar surface to destination delta-V can be provided by some sort of propellantless lunar launch scheme2?

Based on these considerations, I’d like to focus the rest of this post on the pros and cons of the two options I consider most interesting–L2 Halo Orbits and Near Rectilinear Orbits.

Pros and Cons of EML-2 Halo Orbits
EML-2 orbits have been my favorite option ever since learning about the low delta-V cost of reaching them via powered lunar swingbys. They have a lot going for them, including:

  • One of the lowest delta-V stopping points in the lunar vicinity, requiring only ~3.43km/s of delta-V from LEO.
  • Easy access to/from a LEO facility on every LEO-lunar or lunar-LEO window.
  • Any-time access to/from anywhere on the lunar surface.
  • Low stationkeeping delta-V3
  • Benign and cold thermal environment4
  • Continuous communications with Earth, and most of the farside of the Moon.
  • Good staging point for both deep-space and lunar missions.
  • Could become a starting location for a lunar space elevator.

But EML-2 does have a few drawbacks:

  • Long LEO-EML2 and EML2-LEO transit times5 for the low delta-V powered-swingby option.
  • Long EML2 to lunar surface (and vice versa) travel times6
  • It wasn’t clear that a propellantless lunar launch option located at either pole could launch easily to EML2. An elliptical orbit from such a launcher would have its line of apsides pass through the launch location, which would be orthogonal to the Moon-EML2 line. You could launch into a polar LLO, and then do multiple burns from there to EML2, but the propellantless launch option would only provide the first leg of the trip (surface to LLO).

The long trip times mean that the vehicles taking people between LEO and EML2 and between EML2 and the Moon will require much more extensive life support and accommodations than would be needed if the trip were shorter. That will drive up the dry mass of those systems, and by extension the propellant and overall cost of moving people to and from EML2.

Pros, Cons, and Questions Regarding Near Rectilinear Orbits
Starting several months ago, some of my astrogator friends started telling me about NASA’s interest in Near Rectilinear Orbits for exploration missions. After all the talk about Distant Retrograde Orbits, this sounded a bit like the “flavor of the week” syndrome, but the FISO presentation helps explain some of the allure of such orbits:

  • Only slightly higher delta-V to/from LEO to NROs compared to LEO to EML27.
  • Because the NRO orbit’s perilune is only 2000km from the Moon’s surface, once per 6-8 day orbit, the orbit lines up so that the travel time between NROs and the lunar surface drops to 0.5 days.
  • Powered swingby trajectories between LEO and NROs take approximately 5 days each direction, instead of 9-11 for EML2.
  • Slight lower delta-V between NROs and the lunar surface compared to EML2.
  • The NRO is close enough to an elliptical polar orbit that it might be possible for a polar base to use propellantless launch techniques to fling payloads nearly into NRO, with possibly only minor adjustments and raising the perilune with a burn near apolune half an orbit later8

The benefits of shorter transit times are pretty important, but there are still a couple of relative drawbacks and open questions:

  • While it’s possible to get from LEO to a given NRO orbit during every lunar injection window, the NRO facility will be at different points in its orbit during each window, which may make a first-orbit rendezvous either infeasible or it might cost additional delta-V. I’d want to get this resolved, because while this isn’t an issue for one-off, ground-launched missions like the NASA folks were thinking of, this would be a real issue for reusable spaceship flights between a LEO and NRO facility.
  • Likewise, departures from the NRO may not be in the optimal part of the orbit for the Earth return maneuver when the timing is right to return to the plane of the LEO facility. This isn’t a problem if you’re doing a direct return, but once again is a big pain in the neck for reuse of space hardware. Once again this is something I’d want to analyze more before settling on an NRO orbit.
  • Additionally, the NRO facility has LOS with one lunar pole about 86% of the time (while heading out and coming back from apolune), but only sees the other facility for a brief period near perilune. If you’re planning on using propellantless launch methods to send stuff from a polar lunar settlement to the NRO facility, it’s going to be in an NRO with apilune on the opposite side of the moon from your lunar settlement, meaning you’ll only be in contact briefly for maybe 1 day out of a week.
  • Because the perilune is only 2000km, the heating environment is going to be warmer than EML2, with slightly higher boiloff, but this is probably only a minor difference–it should still be tons easier to keep cryo boiloff low in an NRO than in LEO.

While NRO orbits have some really interesting characteristics, I’d really want answers to those first two concerns before I’d pick it for the location of a lunar orbital facility. If you can’t get to it on a regular basis from a given LEO depot without having to do complicated trajectories, or paying big penalties in flight duration or delta-V, then that would likely outweigh the benefits. If on the other hand, it’s not a big deal to adjust the trajectory on the way to and from the NRO facility to enable rendezvous with the facility regardless of where it is within its orbit when the LEO to lunar launch window opens, then it could be a really interesting location for a lunar transportation node. I’ll have to see if I can get some of my astrogator friends to weigh in on those questions. Until then I’m probably still more of a fan of EML-2, in spite of the annoyingly long transit times.

[Update 1: After speaking with an astrogator friend who’s been looking at NROs to support lunar missions, he thinks it might be possible to put an NRO facility in an orbit whose period is synchronized with the average time between launch windows from the LEO facility. If that works, that would mean the NRO facility would be in approximately the same part of its orbit during each trip to/from the Earth. There are questions of if you can make an NRO orbit with a long enough period (~9 days) to make that work, and if the NRO facility could be made to line up both for arrivals and departures from/to Earth, but hopefully he’ll have more opportunity to dig into that further later this year.]

  1. Due to the orbital motion of the Moon and nodal regression of a LEO facility, you get optimal lunar departure and/or return options about every 7-9 days IIRC. The choice of lunar orbital facility location may constrain this further.
  2. Lunar Slings, Mass Drivers, Launch Loops, etc. All the stuff I was supposed to write about in my “The Slings and Arrows of Outrageous Lunar Transportation Schemes” series that I still need to finish
  3. <10m/s/yr
  4. About 10x lower LOX/LH2 boiloff rate than LEO. In fact with passive insulation you can completely surpress LOX boiloff and even freeze oxygen at EML-2
  5. 9-11 days
  6. 3-5 days
  7. 3.58km/s vs 3.43km/s
  8. Which you’d also want to be the burn that brings you to rendezvous with the NRO facility
From Lunar Orbital Facility Location Options by Jonathan Goff (2016)

Kuck Mosquito

Kuck Mosquitoes were invented by David Kuck. They are robot mining/tanker vehicles designed to mine water propellant from icy dormant comets or D-type asteroids and deliver it to an orbital propellant depot.

Form follows function. So it is unsurprising that the Kuck Mosquito resembles an Enterobacteria phage T4 virus. Only difference is that the virus is injecting, while the Mosquito is sucking out.

Because LEO is drier than the driest desert, there is money to be made by importing water from nearby worlds. The closest hydrated body to LEO, speaking in delta-v terms, is the moonlet Deimos (closer than the Earth, closer than Luna.) See “The Deimos Water Company” by David Kuck of Oracle, Arizona for details.

Kuck mosquito — As icy dormant comets or D-type asteroids are warmed by the sun, they accumulate an outer anhydrous lag layer. An in-situ mining robonaut called the Kuck mosquito is designed to drill through this layer, inject steam, and pump out the water in the core. Some of the water is electrolyzed for fuel for a small H2-O2 chemical engine. To gain a secure foothold, thermal lances melt into the substrate. The targeted bodies must have a cometary matrix of not less than 30% ice. There is a danger of catastrophic fracture of the subsurface mantle layer due to the tensile forces generated by the pressurization. Dave Kuck, “The Exploitation of Space Oases,” Princeton Conference on Space Manufacturing, Space Studies Institute, 1995

(ed note: in the game, Kuck Mosquitos have 220 kilonewtons of thrust and a specific impulse of 460 seconds. The water bag masses 40 metric tons because that is the standard measurement in the game.)

From High Frontier game by Philip Eklund (2010). Atomic Rocket Seal of Approval.

In 2007 it is difficult to maintain a space station in Low Earth Orbit (LEO). Before we can hope to colonize asteroids we need a better way to get out of LEO.

Kuck mosquitoes (designed by David Kuck of Oracle, Arizona) are small, unmanned craft that consist of not more than a drill, a heating element, and a bag house to store extracted volatiles. (ed note: it will also require a source of electricity. Maybe an RTG or solar cell array)

Sending small Kuck mosquitoes to Near Earth Asteroids to retrieve water and fuel is more doable than manned missions.

A few Kuck mosquitoes returning to earth orbit with full bag houses would make LEO much more hospitable.

These mosquitoes could be tankers for LEO fuel depots. LEO fuel would make manned spaceflight to the moon, Mars and asteroids much less difficult.

From Kuck Mosquito by Hop David (2007)
Kuck Mosquito
PropulsionH2-O2 Chemical
Specific Impulse450 s
Exhaust Velocity4,400 m/s
Wet Mass350,000 kg
Dry Mass100,000 kg
Mass Ratio3.5
ΔV5,600 m/s
Mass Flow49 kg/s
Thrust220,000 newtons
Initial Acceleration0.06 g
Payload100,000 kg
Length12.4 m
Diameter12.4 m

Deimos, the outer moon of Mars, is possibly the most accessible source of water to LEO. Lewis has shown the delta-V to go from LEO to Deimos is less than that needed to land on Earth's Moon. Partial loss of velocity at Mars might be obtained by a shallow dip into the Martian atmosphere. The delta-V to return from Deimos to HEEO (Highly eccentric Earth orbit) is very small. The travel time is roughly two years. The Moon may be used as an aid to accelerate and decelerate a vehicle as it leaves LEO and arrives at HEEO. Shallow penetration of the Earth's atmosphere may be used to loose velocity and aid in capture into HEEO.

Bodydelta-V Surface to LEO (m/sec)time of flight (d)delta-V LEO to Surface (m/sec)time of flight (d)

(ed note: the important part is LEO to Deimos Surface is deltaV=1800 m/s and 270 days transit, Deimos Surface to LEO is deltaV=5600 m/s and 270 days transit.)

A disadvantage of Deimos is the 26 month delay between launch opportunities.

Fanale calculates that ice should exist at a depth of 100 meters at the equator and at a depth of 20 meters at the poles of Deimos. Thus, the drilling equipment proposed in 1995 by Kuck should be able to reach ice at or near the poles, but not near the equator.

To move 100 tonnes of water ice from Deimos to LEO will require 250 tonnes of water ice for propellant (Z). Thus, in order to leave Deimos 350 tonnes must be propelled from the surface. A 1,000 cubic meter collection bag should be large enough to contain the 350 tonnes of ice, cuttings & other precipitates.

(ed note: 100 metric tons payload + 250 metric tons propellant implies mass ratio of about 3.5, since engine and structural mass are a small fraction of this (e.g, by the table below, the drilling equipment is 0.3 metric tons). If it electrolyzes the propellant into O2 and H2 and burns it as chemical fuel with a specific impulse of 450 seconds, this would give a delta-V of around 5,500 m/s or so.)

Table 1. Mass of Drill and equipment for the Deimos version of the drill presented in "Exploitation of Space Oases" presented at Princeton May 1995. The total mass is in grams. The drill pipe is titanium for lightness and chemical resistance to corrosion.
Down The Hole Hammer Drill, Titanium drill pipe & accessories
L (mm)OD (mm)ID (mm)Weight (grams)NumberWeight (grams)Ti
Hammer DTH210162333699No
Under-reamer Guide782049.43148.2Yes
Casing Shoe21241610160No
Collar Pipes1000434013741013740Yes
From The Deimos Water Company by David Kuck (1997)

The images below are details of the "Spider" water harvester carried by the Robot Asteroid Prospector. It performs much like the business end of the Kuck Mosquito.

Optimizing Depot Placement

Takuto Ishimatsu's Ph.D. thesis is titled Generalized multi-commodity network flows : case studies in space logistics and complex infrastructure systems (abstract here). Basically: manually chosing where to place in-situ resource allocation depots so as to get the maximum benefit is a very very hard problem. Wouldn't it be nice to create a computer program that could automatically find the optimum solution?

This is very relevant to our interests.

For the Apollo missions NASA used a "carry-along" strategy, where all vehicles and resources traveled with the crew at all times. Along with the horrific propellant cost to boost all of this from Terra into LEO. For the International Space Station NASA adopted a "resupply" strategy. This also has horrific boost cost plus it requires a close resupply source (Terra).

The resupply strategy ain't a gonna work for a Mars mission (as Terra gets further and further away), so the conventional view was to use a carry-along strategy. Dr. Ishimatsu examined NASA's Mars Design Reference Architecture 5.0 (plus addendum 1 and 2).

As you know from reading this section the way to avoid the horrific boost costs is in-situ resource utilization: travel light and live off the land. The problem is figuring out what is the best placement of in-situ mining, refining, and orbital depot assets.

Dr. Ishimatsu's software determined that using lunar propellant mines and tankers would cut the cost of the conventional NASA Mars mission by a whopping 68 percent!

It is very similar to the military. The old bromide is that amateurs talk about battle tactics while professionals talk about logistics. Well, deep space exploration is going to require a well-planned logistics strategy as well.

Dr. Ishimatsu examined several prior solutions, but all either were not scaleable as the mission complexity increased, required the user to pre-define the logistics network (i.e., solve the problem manually), or were not capable of doing optimization with no human input.

Dr. Ishimatsu used Dale Arney and Alan Wilhite's technique of modeling space system architectures using graph theory. The nodes are physical locations in space wihle the arcs (connections between the nodes) are possible movements or transports between nodes. Note that arcs are one-way, an arc going from node A to node B is totally different from an arc going from node B to node A. This is because one can, for instance, use aerobraking to traverse an arc going from LEO to Terra's Surface, but one cannot use aerobraking to go from Terra's surface into LEO.

To allow for the optimal solution, it is best to include as many nodes and arcs as possible. The optimizer obviously cannot use arcs and nodes that are not present. If the optimal solution requires use of a missing node or arc, it will not be found.

One peculiarity is that you use an arc that starts and ends on the same node to model a node that is a resource processing facility. This is required in order to allow the optimizing mathematics to work. These are called a "graph-loop", "self-loop" or a "buckle".

Another peculiarity is having several arcs between a given pair of nodes. For instance, if the mission could move items between node A and node B by either chemical rockets or nuclear thermal rockes, each rocket type would have its own arc between node A and node B. This is because the two rocket types have different specific impulse and thus different propellant consumption. Additional arcs will be required for the same rocket type if it has different delta V usage choices. For instance, a nuclear thermal rocket can do either an economical burn with a long time of flight or an expensive burn were more propellant was expended in order to reduce the time of flight. There will also be an additional arc where aerocapture is possible.

Basically the multiple arcs allow the optimization to explore multiple mission choices. One choice per arc.

These multiple arcs between a given pair of nodes are called "parallel arcs."

For logistics calculation, you state the mission as a set of demands at certain nodes in the network. A demand for "plantISRU" at the LSP node corresponds to a lunar mission to transport an in-situ resource allocation industrial plant to the lunar south pole.

Dr. Arney modeled the propellant required in a mission as costs on a given arc. But Dr. Ishimatsu found it more useful to model the propellant required for all subsequent stages of the mission as payload on a given arc. In addition, since in-situ resource allocation (ISRU) allowed propellant and other resources to be generated at other nodes besides Terra, it made sense to model propellant as commodities included in the flow variables rather than as costs like Dr. Arney did. This allows formulating the problem as a multi-commodity network flow, with some commodities coming from Terra and others from ISRU sites.

The optimization problem becomes finding the best routes in the network that satisfies the mission demands while also meeting certain constraints (i.e., figuring out which nodes and arcs to use). The result will tell you "where to deploy what."

The program is trying to optimize TLMLEO, which is Total Launch Mass from Terra to Low Earth Orbit (LEO) required to set up the entire logistics network. The program is trying to find the solution with the lowest TLMLEO.

Note that there are lots of other things that could be optimized for, but this system only optimizes TLMLEO. Other things that might be optimized include:

  • Development, Test, and Evaluation cost of the various components (ISRU and orbital propellant depots will require lots of expensive R&D)
  • Number of rendezvous and refueling events (the more, the higher the chance of a malfunction or accident)
  • Complexity (the more complicated, the more potential points of failure)

For the nitty-gritty mathematical details of the optimization, please refer to Dr. Ishimatsu's thesis. It contains lots of calculus and matric algebra which makes my head hurt. There are matrix multiplications for flow equilibrium, flow transformation, and flow concurrency.

As a case study, Dr. Ishimatsu ran NASA's Mars Design Reference Architecture 5.0 through his software.

In the model, everything that travels from node to node is a "commodity", even the crew. The 20 commodities are listed in the table below. Each commodity has a flow and demand all measured in kilograms.

  • Crew
    • crew (traveling to Mars)
    • crewRe (returning to Terra)
  • Resources
    • hydrogen
    • oxygen
    • water
    • methane
    • carbonDioxide
    • food
    • waste
  • Infrastructure
    • habitat
    • plantISRU
    • sparesISRU
  • Transportation
    • vehicle
    • inertLOXLH2
    • inertLOXLCH4
    • inertNTR
    • tankLOX
    • tankLH2
    • tankLCH4
    • aeroshell

Commodity "crew" represents the crew traveling from Terra to Mars while "crewRe" represents the crew returning to Terra. A self loop on Mars transforms crew into crewRe, enforcing the rule that the mission is a round trip. This is a mathematical trick that allows the optimization math to work.

The Resources catagory includes the rocket propellants, crew provisions, and crew wastes.

The Infrastructure catagory includes habitation facilities, ISRU industrial plants, and ISRU spares.

The Transporation catagory includes vehicles, propulsive elements, and non-propulsive elements. "InertX" means "rocket engine utilizing propellant X" while "TankX" means "tank full of propellant X. The three engines are: chemical liquid oxygen + liquid hydrogen, chemical liquid oxygen + liquid methane, and nuclear thermal rocket. Note that NTR can use any of the three tanks as propellant, the others require tanks of each of their named propellants. For NASA reasons, the NTR is not allowed for lift-off or landing on a planet, and aerocapture is allowed for unmanned cargo missions but not allowed for manned missions.

Solar electric rockets were not included because they require a different way of defining the arc parameters.

For the Mars mission it requires a demand for "habitat" at GC and a demand for "crewRE" at PAC. This translates into a mission to send a crew of six and a surface habitat to Mars Gale Crater, the crew becomes crewRE (crew ready to return to Terra) on Mars after a 540 day stay, which forces a mission to send the crewRE from Mars to Terra Pacific Ocean Splashdown.

Dr. Ishimatsu used the graph below, which does show the self-loops but only shows a single arc even when parallel arcs are present. Otherwise the diagram would be an unreadable mess. The full graph has 16 nodes and 598 arcs. There are self-loops at LSP (Lunar south pole), DEIM (Deimos), PHOB (Phobos), and GC (Mars Gale Crater).

ISRU availability/technology have the folloiwng assumptions:

  • Lunar ISRU can produce O2 from regolith or H2O from water ice at a rate of 10 kilograms per year per unit plant mass while requiring spares of 10% of plant mass per year.
  • Mars ISRU can acquire CO2 from the atmosphere or H2O from water ice with the same production rate and spares requirement as those for lunar ISRU.
  • Mars CO2 can be converted into CH4 and H2O via the Sabatier reaction or can be converted into O2 via solid oxide electrolysis.
  • Electrolysis of H2O and pyrolysis of CH4 are assumed to be available along with lunar/Mars ISRU

All these chemical reactions are modeled as an optional self-loop.

First, a "baseline" problem is defined and sent through the program for a solution. This is a simplified problem whose solution will be used to measure the results of altering various parameters. Among other things the baseline problem has the propulsion system modeling simplified. For the details about the baseline problem, please refer to Dr. Ishimatsu's thesis

Dr. Ishimatsu rubs salt in the wound by cheerfully telling us "Using MATLAB 8.3 (R2014a) with CPLEX 12.6 on an Intel R CoreTM i7-2640M CPU at 2.80 GHz, one run of the optimization model takes approximately 12 seconds for preprocessing and 1.2 seconds for optimization (TLMLEO minimization)." He did a test validation by constraining the model to NASA's Mars Reference Mission, the results were practically identical.

The baseline solution has a TLMLEO of only 271.8 metric tons, a 68% savings from the NASA Mars Reference Mission NTR scenario, and a 78.3% savings from NASA's chemical/aerocapture scenario.

Then the user can alter various propulsion parameters and measure the results against the baseline solution. The other parameters and assumptions remain the same. The surprise here is that NASA's Mars Reference Mission's reliance on nuclear thermal rockets is sub-optimal. LOX/LH2 chemical engines are superior, if you include ISRU (which NASA did not). The massive amounts of oxygen and hydrogen produced by the Lunar ISRU more than makes up for the relatively low specific impulse of the chemical rocket.

The arc from Kennedy Space Center (KSC) to Low Earth Orbit (LEO) has by far highest delta V cost: 9.8 km/s. This is the mathematical way to model Heinlein's "Halfway to Anywhere" observation. The emergent property produced by optimization is the need for in-situ resource utilization.

Now the user can alter various ISRU availability scenarios and measure the results against the baseline solution. The other parameters and assumptions remain the same.

Example: Depot into Story Plot

For the science fiction author writing about a solar system future, things like orbital propellant depots might be more than just the background of the story. With a little effort, they can help a bit with the plot as well. A good way to start is to remember "everything old is new again", that is, find a historical analogy and set it in the science fiction future. Keeping in mind that current events are "historical" as far as the future is concerned. Here is an example:

This is an article from magazine, about how self-driving trucks are going to decimate the economies of small towns in suddenly non-strategic locations.

Self-Driving Trucks Are Going to Hit Us Like a Human-Driven Truck we drove by town after town, we got to talking about the potential effects self-driving vehicle technology would have not only on truckers themselves, but on all the local economies dependent on trucker salaries. Once one starts wondering about this kind of one-two punch to America’s gut, one sees the prospects aren’t pretty.
     We are facing the decimation of entire small town economies, a disruption the likes of which we haven’t seen since the construction of the interstate highway system itself bypassed entire towns...
     ...We can’t stop there though, because the incomes received by these 8.2 million people create the jobs of others. Those 3.5 million truck drivers driving all over the country stop regularly to eat, drink, rest, and sleep. Entire businesses have been built around serving their wants and needs. Think restaurants and motels as just two examples. So now we’re talking about millions more whose employment depends on the employment of truck drivers. But we still can’t even stop there.
     Those working in these restaurants and motels along truck-driving routes are also consumers within their own local economies. Think about what a server spends her paycheck and tips on in her own community, and what a motel maid spends from her earnings into the same community. That spending creates other paychecks in turn. So now we’re not only talking about millions more who depend on those who depend on truck drivers, but we’re also talking about entire small town communities full of people who depend on all of the above in more rural areas. With any amount of reduced consumer spending, these local economies will shrink...
     ...This is where we’re at and this is what we face as we look towards a quickly approaching horizon of over 3 million unemployed truckers and millions more unemployed service industry workers in small towns all over the country dependent on truckers as consumers of their services.
     The removal of truckers from freeways will have an effect on today’s towns similar to the effects the freeways themselves had on towns decades ago that had sprung up around bypassed stretches of early highways. When the construction of the interstate highway system replaced Route 66, things changed as drivers drove right on past these once thriving towns. The result was ghost towns like Glenrio, Texas.
With the patience that carved the Grand Canyon over eons, nature reclaims Glenrio, where the clock stopped with the bypass of Route 66. The replacement of Route 66 with a four-lane superhighway that allowed motorists to zip past rather than wander through ultimately allowed Glenrio to decline.

To transpose this situation into one's science fiction future, you have to look for analogies. Cargo spacecraft are obviously trucks, orbital propellant depots are gas stations. The positioning of the depots is like Route 66, optimized for the spacecraft and destinations. The small towns are boom-towns that grew up around the depots, maybe even growing into orbital colonies.

Then we transpose the historical events:

  1. Orbital propellant depots are established so as to allow cheap chemical rockets access to transport goods too and from points in the inner solar system. This is the network of automobile gasoline stations on Route 66.

  2. boom-towns spring up to relieve spacecraft crews of accumulated flight pay burning a hole in their pockets.

  3. The boom-towns grow into Star-Towns, maybe even becoming a full orbital colony. The gas stations on Route 66 have become small towns.

  4. Now some disruptive technology throws a monkey wrench into the works.
    Historically it was the network change of switching from Route 66 to the national highway system, bypassing the gas station towns.
    Currently it is the self-driving trucks that need less gasoline, and certainly do not need sleeping motels, restaurants, or brothels.
    In our science fiction future, the network can be changed by, say Beams-R-Us setting up routes for cheap laser thermal rockets. The self-driving trucks are similar to the advent of nuclear rockets (requiring less propellant) or unmanned rockets (requiring no sleeping, fancy food, or prostitutes).

  5. Deprived of their revenue stream, the boom-towns and orbital habitats start dying, becoming ghost towns like Glenrio, Texas.

Such an emotionally-charged situation can drive a science fiction story plot.

The locals are going to be very angry at whoever invented the disruptive technology which doomed their town. An employee of Beams-R-Us who is stupid enough to visit such a dying boom-town is likely to get beat up in some dark corridor, maybe even suffer a tragic air-lock "accident."

Hot-heads living in the town might be tempted to stage something drastic in order to draw media attention to their plight. Terrorist actions are easy when one has access to so many concentrated forms of energy.

On the street, it is "rats deserting a sinking ship" time. Desperate individuals will do almost anything to board a spacecraft bound for someplace better.

The local government will be frantic to find a new revenue stream. If they cannot find a legal one, the solar system underworld has lots of illegal ones.

And of course there will be a few stubborn crazy-coot old-timers who refuse to leave, haunting the empty modules.

In my effort to transpose the situation, I had to play fast and lose with some inconvenient particulars. Master Artist William Black's pointed out a few items I swept under the rug. But the point is the technique of finding analogies allowing one to transpose a past or current situation into the future. Try reading a few historical or current news items with this in mind and see what you can come up with.

     I don't think boomtowns would spring up around propellant depots, rather propellant depots will be an asset positioned by volatiles mining outfits—which operate extraction sites and send product to the depots, which may be at some distance from the extraction sites.
     Propellant depots will be positioned at the site of large scale in-space activities, not the center of the activity, but part of the infrastructure supporting it.
     I don't see propellant depots existing in isolation. There will not be truck-stop towns in space, which I think are an artifact of physical highways.
     I see asteroid mining boomtowns as distinctly different phenomena from their historical namesake here on Earth, the primary difference being mobility.
     The asteroid mining boomtown moves where the resources are, just like the mining outfits will do. When the strike dries up the boomtown moves, along with the core set of corporate operations, right on to the next site.
     I see propellant depots being end-user distribution points, the depots will be clustered anywhere there is large scale in-space operations, resource mining or manufacturing and freight transfer points— like gateway stations at EML2, or at Phobos and Deimos, Ceres, elsewhere as well, but you see what I am getting at.

The Lost Fleet

Regarding the "orbital depots" bit, the boomtown going bust when bypassed sounds a lot like the Lost Fleet series.

In the backstory, there's a "jump" type FTL with limited range—jump from one system to another in the web, then on and on. But midway through a hundred-year interstellar war, both sides figure out and build incompatible implementations of the same new "hypernet"—basically a Stargate thing. Important systems get on the hypernet, and all the systems that were only important because ships had to pass through on their way to someplace really Until a Lost Fleet stuck behind enemy lines has to head back to their home space by the old-fashioned jump network after they get lured into a trap using the key to the enemy hypernet.

Pretty fun read, and sort of a macro version of the same situation. The series explores some of the different ways such systems might fail.

From a comment by Rob Davidoff (2016)


3-D Printing

3-D printing is also known as "additive manufacturing". This is because the object is created by adding blobs of new material, instead of the conventional method of starting with a block of material and carving away the unwanted bits (for example, as done by a CNC router).

This was a mind-blowing concept when Keith Laumer used it in his 1981 novel Star Colony, but with the advent of hobbyist 3-D printers it is now considered trendy but not impossibly futuristic.

Corporations will be angered by 3D printers: if you thought the RIAA went ballistic about digital music piracy and the MPAA was freaking out about movie file sharing, you ain't seen nuthin' yet. Manufacturers are going to start foaming at the mouth about digital object piracy. I predict even more draconian Digital rights management laws.

There is already in the real world people who are stirring up trouble by making blueprints that will 3D print plastic "ghost" firearms with no serial numbers. They are trying to strike a blow for Libertarianism, but they might just wind up making 3D printers illegal. Angry corporations are one thing, angry governments are even worse.

And if you take a super-duper 3-D printer and hook it up to a super-duper 3-D scanner, you have a Star Trek Replicator. Which will create unintended consequences.

But I digress.

NASA is interested in 3-D printing because Every Gram Counts. It would be a valuable savings in mass if a spacecraft did not have to carry spare parts for every conceivable thing that might break, but could instead only carry a 3-D printer and the raw material. You do not have to waste payload on spare parts you might never need. And the computer blueprints have zero mass.

Most currently available 3-D printers only print with one material (generally some kind of plastic). Innovators are frantically working on printers that can handle multiple materials. This is vital for printing, say, an electric motor or an electronic circuit. Currently available printers deposit blobs of material, in the future they will deposit on an atom-by-atom basis.

In September 2014, SpaceX delivered the first zero-gravity 3-D printer to the International Space Station (ISS). On December 19, 2014, NASA emailed CAD drawings for a socket wrench to astronauts aboard the ISS, who then printed the tool using its 3-D printer.

As a proof-of-concept, Markus Kayser created the Solar Sinter. He noted that in the deserts of Terra, there is a lack of useful artifacts but unlimited amounts of sunlight and sand. The Solar Sinter is a computer controlled magnifying glass that 3-D prints by melting layers of sand. There are many planets and moons where such a tool would be incredibly useful.

Architecture Et Cetera (A-ETC) is working on Project SinterHab. This will use microwaves to fuse Lunar dust in order to 3-D print habitat modules for a Lunar base.

Foster + Partners is working with the ESA to make a 3-D printed lunar base. Lunar soil is mixed with magnesium oxide to produce the material. Layers are bound by being sprayed with a binding salt in a controlled pattern. The binding salt turns the material into a stone-like solid.

A 3-D printer can also be used as the "assembler" component of a Santa Claus Machine.


"I am a physicist. I specialize in the field of molecular structures. As you know, practically all of the raw materials used in industry today are synthesized from artificially transmuted elements—using techniques originally perfected on Mars." The Assassin nodded, keeping his eyes fixed on the professor. Brozlan went on: "The synthetic compounds used today are amorphous in nature—they do not possess any highly organized internal structure. Essentially the processes just turn out vast quantities of some particular kind of molecule, without assembling the molecules together into any higher level of organization." He took a long breath and then said: "An area of research that I was involved in some time ago had to do with taking the idea one step further."

"To produce a full range of materials needed on Mars, it was not sufficient to just synthesize or import unstructured molecules in bulk," Brozlan resumed. "We needed to be able to duplicate, say, the crystal lattice structures of many metal-base compounds, or the polymer chains of organic substances—things that are abundant on Earth but totally lacking back there."

"I'd have thought that that's where you'd use traditional processing methods," the Assassin muttered. He didn't mind talking as long as it was he who was asking the questions. It could only be to his ultimate advantage to know more about what was going on.

"On Earth, yes," Brozlan replied. "Primary raw materials are cheaper than they've ever been, because they're now synthetic. From those primary materials, things like steel, rolled alloys, fabricated goods, and so on must still be produced in much the same way as they've always been. Hence the costs are much the same as they've always been, and by the time they get to Mars that means expensive."

"If you ship it all up from Earth," the Assassin agreed. "But why bother? Why not just set your own processing plants up right there?"

"We could have done that." Brozlan nodded. His face creased into a frown. "But somehow we were not satisfied with that idea. We had a virgin planet with no set ways or traditions to uphold. It seemed unsatisfactory simply to follow slavishly the methods that had evolved on Earth. We could have spent fortunes copying all of Earth's industrial complexes on Mars only to find them obsolete before they went into production. You see, we were convinced that there had to be a better way."

The Assassin thought for a moment and looked puzzled. "How?" he asked at last. Brozlan's eyes glinted. He replied:

"Consider any form of component that is used in the construction of a larger assembly . . . the parts of a machine, for example. How is the component made? Answer—we take a lump of whatever material we need and cut away from it all the excess to leave the shape that we require. That forms the basis of just about every machining process that is used traditionally. Cut away what you don't want to leave behind what you do want."

"Okay." The Assassin shrugged. "What other way is there?"

"Deposition!" Brozlan peered at him intently as if expecting some violent reaction. The Assassin looked back at him blankly. Brozlan explained: "Instead of cutting material away to leave the part, we deposited material to build the part up!"

"You mean like electrolytic forming? That's not new."

"The idea isn't," Brozlan agreed. "But the way we were doing it was. You see, electrolytic forming works only with certain metals. We were working with every kind of molecule."

"You mean you could build up something out of anything—any substance at all?" The Assassin looked astounded.

"Exactly! And it didn't have to be all from the same kind of molecule, either. We could mix them together any way we chose.' For instance, we could produce a solid block that was phophor-bronze at one end and polythene at the other, with a smooth transition from one to the other in between. It opened up a whole new dimension in engineering design possibilities. The whole process was computer-controlled. A designer could develop a program to create any part he wanted out of any material he chose or any combination of materials—molecule by molecule if he really wanted to go down to that level of detail and if he had the patience and the processor power to handle it."

"Molecule by molecule .. ." The Assassin's face registered undisguised disbelief. "That's incredible . . ."

"Nevertheless, it worked," Brozlan told him. "There have been experimental plants on Mars operating for years now, turning out goods that are higher in quality and far cheaper to produce than anything' that could ever come out of the factories of Earth—even things normally processed from organically derived substances, such as paper, oils, fats, sugars . . . you name it."

"Oil . . . food . . . paper ... all synthesized from transmuted elements?" The Assassin gaped as his mind struggled to take it all in. "Why have we never heard of such things?"

"Politics." Brozlan sighed. "By that time there was a different brand of thinking among the higher echelons of the Federation government. Ambitious and unscrupulous men were taking over. They did not see these discoveries as potential benefits.for all mankind, but only as a means toward furthering their own designs by securing full economic autonomy. They began to see themselves as undisputed rulers over a thriving and self-sufficient world. Those purposes would be served better if Earth were allowed to lag behind, with its industries unable to compete against the newer Martian ones. The Federation authorities assumed tight control over our work and placed a strict security blanket over everything. That was why few people knew about what we were doing. That was also where the movement for Martian independence had its origins. Only a handful of individuals stand to gain, and not in the ways that are popularly believed."

"Interesting, isn't it, Hadley?" the colonel came in, spinning suddenly on his heel to face the bed. "But if you think that's hard to swallow, wait until you hear the next bit." He nodded at Brozlan, who continued:

"That was just one aspect of the research work going on at that tune. Another aspect was Dr. Franz Scheeman's work on structural scanning with neutrino beams. You see, Scheeman developed a method for scanning a material object, inside and out, and for extracting from the transmitted beams a complete encoding of the arrangement of atoms and molecules within the object. It was analogous to the way in which an old TV camera encoded the information contained in a visual scene." Brozlan took a deep breath. "The real breakthrough came when we combined Scheeman's technique with the molecular-deposition process that we have just been talking about!"

Silence reigned for a long tune while the Assassin digested the professor's words. Then his eyes widened slowly and transfixed Brozlan with a dumbfounded, unblinking stare.

"You're joking . . ." the Assassin breathed at last.

"A solid-object camera!" the colonel confirmed for him. "Yes, Hadley, you've got it. They could scan an object and derive a complete structural code for it. From that code they could generate a computer program to control the deposition process. Result—a perfect analog, a molecule-by-molecule copy of the original. And, of course, if they could make one they could just as easily make as many as they liked. Think of it, Hadley . . ."

The Assassin thought about it. Raw materials in abundance at negligible cost and the ability to transform them into any object for which an original already existed—it would be the Golden Age come true. Something in his expression must have betrayed what was going through his mind.

The colonel nodded and continued. "But think of some of the deeper implications, too. What would happen if somebody suddenly introduced that kind of technology into a complex and established economy like Earth's? Suppose that once you'd built the prototype of, say, a domestic infonet terminal"—he pointed to the bedside console—"you could churn out a million of them, all for peanuts. What would happen to the conventional electronics industry then? What about the components industry that supplies it? What would happen to the industries that supply all the parts—the plugs, sockets, metalwork, moldings, and all that kind of thing? And then what about the service industries that depend on all those in turn ... office equipment, furnishings, data processing, real estate, and so on through the list? How could they survive if half their customers and half their business went to the wall?" The colonel spread his arms wide in the air. "All finished, Hadley. Total collapse. How could you cope with ninety-five percent of a planet's population being suddenly redundant? How could a global economy, with its roots buried in centuries of steady evolution, survive an upheaval like that?"

"You see," Brozlan added, "That is exactly what the Federation government wanted to do. They wanted to rush full-speed into setting up a huge Martian industrial conglomerate based on the new technology, flooding Earth's markets with goods at giveaway prices."

"Earth would have been ruined," Barling interjected. "Or at best would have faced the prospect of existing as a very second-rate entity, dependent on a new rising star."

From Assassin by James P. Hogan (1978 )
The Killing Star

(ed note: the intruders have entered the solar system and are systematically committing genocide on the species known as Man. For asteroid colonies, an alien laser broadcast subtly reprogrammes the 3D printer to create a deadly infective substance that destroys technology. This would not kill on the habitable planet Terra, but sabotaging the technology of an asteroid colony will destroy all life support)

SOMETHING LIKE A LIGHTHOUSE BEACON WAS SWEEPING the solar system. On Ceres, the first cluster of gamma-ray telescopes picked it up and passed the signal to the station's computer net with a red tag for instant analysis. Within a microsecond, one of the most highly advanced brains ever built by the hand of man had undergone a subtle change in programming and, against all previous instructions, sent an ominously less subtle program change on a hairline beam of laser light to one of the gamma-ray telescope robots.

And still within that part of a second, the robot began to respond. Its multiple brains had been designed to predict the consequences of any action— from lifting a rock to constructing a new furnace— and then to decide the appropriate action at lightning speed by committee voting. Even without a human presence, the machine was capable of manufacturing a gamma-ray telescope, or anything else it was instructed to supply.

Antlike in appearance, it was more like a colony of machines than an entity of its own—just as its creator had intended. It had been built from and by a hive of smaller, simpler machines, which still circulated inside it like motile cells through a dense matrix of connective pathways. There were workers of many shapes and sizes, and what could even be called "drones" and "egg-laying queens." Each was so intensely social, and so intimately connected to the robot's circuits, that if it were isolated from the rest of the hive, it could no more function on its own than an ant cast out of its hill or a human marooned on an island, and it quickly "died." Like an anthill, or the Ceran colony itself, every robot hive met all the essential criteria of an organism.

One half second after the laser flashed into its eyes, the hive sensed a loss of some essential material it had been programmed to produce—a loss that, left unaccounted for, would have violated its first directive and allowed the human colony inside Ceres to come to harm.

The material in question had never existed before on Ceres, or anywhere else in the solar system; but the hive did not know that it was being deceived, that it was not acting on orders given it by human beings. Egoless, incapable of friendships or emotional ties, free of conscious sympathies and antipathies, without overt motives or concealed ones, the hive's brains and workers responded so fast that it was already fashioning the right tools and had already located the right chemicals before Ed Bishop could even begin to notice that a problem was developing.

By the time the maglev had shuttled him from Isak's home to the north pole, a pressurized tent had already sealed off his stricken, half-eaten robot from the rest of Ceres, a phone line had already connected the tent to the colony, and a system of laboratory modules was already being trucked to the site.

The tent itself enclosed a fully equipped "clean room." Bishop had entered through an airtight; glove box that fit him like a space suit, and in the ; center of the room one of the robots was melting in the warming air. It occurred to him then—too late—that no one should have been allowed to pressurize the chamber or heat the air. A second robot had stood on the far side of the room, ready to assist him. Now both machines lay in melting heaps, and Bishop found himself alone and afraid, abandoned by his crew, as he retreated to a module whose hull was twisting out of shape and leaking air. He tightened his suit helmet, hoping to buy himself a few more minutes of life, and began his final report to Isak.

There was very little he could say that was new to the president. One of the machines had been tricked into producing a substance that, for lack of a better name, Bishop had come to call a "molecular virus" or "template"—with which it had promptly infected itself.

Isak had replayed the images over and over on his pad: Bishop's robot on the floor of the tent, being eaten as if by a mighty cancer, breaking open like a poorly constructed beehive, thousands of microrobots spilling out of the rent across its abdomen, writhing and melting; Bishop's robot assistant placing samples under the scopes; and then, after an hour or two, the scopes themselves seizing up and flaking apart. .. and then the robot assistant.

The scopes had lasted long enough to show, with brutally realistic computer animation, what was happening. Most chemical reactions released their excess energy as heat: random, chaotic molecular motion. Every schoolgirl knew that every chemical compound had a specific melting point, at which the motion became so distorted that the crystalline structure broke down and individual molecules drifted off in different directions. The template molecule, when it came into contact with a ceramic composite, a carbon-metallic alloy, or with almost any substance likely to be manufactured by civilized beings, rearranged its crystal structure in such a way that the old melting points were drastically altered. Superconductors failed to function. Mechanical parts either became brittle or liquefied at room temperature. On the face of each crystal in the "tissues" of the stricken robot molecules were rearranging identically and transmitting a pattern of molecular recoil to every neighboring crystal— which vibrated and softened in turn.

"To get the ball rolling, the robot need only have innocently manufactured a few milligrams of this stuff," Bishop said. He was breathing hard inside his helmet, speaking quickly now, and Isak detected a touch of panic in his voice. "When all this got started, that's all there was—less than a gram. Then we had the whole robot and the scopes and then another robot crumbling to pieces—tons of the stuff lying around. How do you contain something like that? Sooner or later it was bound to get out. Sooner or later it should even get to the Intruders."

"But that seems an unlikely hope," Sargenti added. "They would have built-in protection, some sort of half-life. Otherwise they'd have to worry about meteorite impacts flicking bits of contaminated dust off Ceres and one of their ships coming in contact with it."

"If this had happened on Earth," Bishop said, "they could have counted on the winds to spread template dust to every continent. All the towers and skylines would have vanished. Obviously that wasn't enough. They wouldn't have been happy just knocking Earth back to the Stone Age and leaving the Acropolis, Renaissance cathedrals, Mayan temples, and the forests still standing. But here on Ceres, where we depend on high-tech for everything—even the air we breathe—the template is the perfect Final Solution." He stopped and took a deep breath. "One other thing. I'm afraid it's gotten through the material in my suit and into me. From the feel of it, I'd say even the iron and calcium in our bodies is vulnerable."

There was a popping sound behind Bishop, and the room fogged as the air pressure dropped.

From The Killing Star by Charles Pellegrino and George Zebrowski

Santa Claus Machine

The Santa Claus Machine is sort of a technological version of Aladdin's Lamp or a Cornucopia. Basically it is a Star Trek Replicator that uses in-situ resources as feedstocks. More crudely it is a mass spectrometer feeding a 3D printer.

If you are trying to set up a base or colony on a desolate moon or planet, a Santa Claus Machine could be the difference between success and failure. The less equipment and prefab base you have to bring and the more stuff you can manufacture with local resources, the better.

As with any such thing, it has two parts: a disassembler and an assembler. This is because there are two basic operations possible in the universe, analysis and synthesis. That is, breaking one large object into smaller parts, or assembly smaller parts into one larger object. The ancients called this "solve et coagula" (e.g., written on the arms of the Sabbatic Goat in the famous illustration by Eliphas Levi).


The disassembler breaks down the input material into atoms, then sorts the atoms by element and isotope. This provides the raw materials needed by the assembler.

In most Santa Machine designs, the disassembler is a fusion torch attached to a mass spectrometer (in this context the fusion torch has nothing to do with the similarly named "torchship").

You shovel rocks, dirt, and other regiolith into the hopper of the fusion torch. The input matter is flash heated to a temperature of about 15,000 K by the awesome power of thermonuclear fusion, disassembling all the compounds into individual atoms and ionized atoms at that. You now have all the atoms separated in a plume of ultra-high temperature plasma.

There are many proposed ways of sorting the atoms into bins for each individual element and isotope. The most commonly mention method is using a mass spectrometer.

Atoms have inertia, like anything else that is matter. And like all other matter the more mass an atom has, the more inertia is has. So if the atoms are moving in one direction in a atomic beam, if you give each atom a shove to the right with a given strength push the atoms with less inertia will be nudged off course more than the atoms with more inertia. Without the push all the atoms in the beam will strike the target point. The shove with smear the target point to the right. If you nudge enough, the target will smear into a row of points, one for each element. Nudge it more and the points will separate further into points for each isotope of each element.

All you have to do is put a collection bin at each target point and they will fill up with pure isotopes. But do be careful about the bins for fissionable isotopes. Allowing a critical mass to accumulate will have unfortunate consequences.

Mass spectrometers generally use a magnetic or electrostatic field to give atomic beam a shove.

Keep in mind that what you get out depends upon what you load into the input hopper. If the asteroidal regiolith you are shoveling in contains no uranium, none is going to show up in the collection bins. You might have to import isotopes that are absent in your location.

Just imagine how useful the fusion torch+mass spectrometer combo would be for recycling the mountains of trash filling up our real life land-fills. The entire blasted world is impatiently waiting for somebody to tame fusion power.

Also note that this technology makes it easy to refine uranium ore into weapons grade uranium, which will make the astromilitary and the authorities extremely nervous. Current enrichment techniques such as gas centrifuges require the resources of an entire nation the size of Iran. A fusion torch could do in your garage.


The assembler takes atoms from the disassember's output, and puts them together according to the user selected blueprint.

This will basically be advanced versions of the 3D printers and rapid prototyping machines available now. Instead of just handling one material (typically plastic) they will be capable of printing in multiple materials. They will accept as feedstock the elements and isotopes from the disassembler, and either chemically create the required compounds or just print the compounds by alternating the atoms.

Early crude versions will print blobs of paste composed of compounds created from the atom feedstocks, much as a commercial 3D printer makes objects out of molten plastic. Later advanced versions will assemble the object atom by atom.

The limits will be

  1. the chemical elements required from the disassembler for object currently being printed (does the local regiolith have all that is necessary?)
  2. the availability of blueprint files for the desired object (are the blueprints illegal?)
  3. the speed of printing the object (if it takes ten years to print, forget it)
  4. the supply of fusion fuel to power the fusion torch (though with fusion you are talking gigawatts per centigrams/seconds of fuel)

Faster printers will be more expensive, because that's the way it always is.

Some blueprints will be illegal (e.g., DIY nuclear warhead) and of course will be readily available anyway from data smugglers and on the dark web. There might be illegal blueprints which on the surface look innocent, but combining part 23 of the dust precipitator plan with part 17 of the air conditioner plan creates a working submachine gun.


The human consequences of the singularity reverberated endlessly, too. The exiles hadn’t simply been dumped on any available world; in almost all cases, they’d been planted in terrain that was not too hostile, showing crude signs of recent terraforming.

And the Eschaton had given them gifts: cornucopias, robot factories able to produce any designated goods to order, given enough time, energy, and raw materials. Stocked with a library of standard designs, a cornucopia was a general-purpose tool for planetary colonization.

Used wisely, they enabled many of the scattered worlds to achieve a highly automated postindustrial economy within years. Used unwisely, they enabled others to destroy themselves. A civilization that used its cornucopia to produce nuclear missiles instead of nuclear reactors—and more cornucopias—wasn’t likely to outlast the first famine, let alone the collapse of civilization that was bound to follow when one faction or another saw the cornucopia as a source of military power and targeted it. But the end result was that, a couple of hundred years after the event, most worlds that had not retreated to barbarism had achieved their own spacegoing capabilities.

Newpeace had been settled by (or, it was more accurate to say, the Eschaton had dumped on the planet) four different groups in dispersed areas—confused Brazilian urbanites from Rio; ferocious, insular, and ill-educated hill villagers from Borneo; yet more confused middle-class urban stay-at-homes from Hamburg, Germany; and the contents of a sleepy little seaside town in California.

Each colony had been plonked down in a different corner of the planet’s one major continent—a long, narrow, skinny thing the shape of Cuba but nearly six thousand kilometers long—along with a bunch of self-replicating robot colony factories, manuals and design libraries sufficient to build and maintain a roughly late-twentieth-century tech level McCivilization, and at ten-meter-tall diamond slab with the Three Commandments of the Eschaton engraved on it in ruby letters that caught the light of the rising sun.

From IRON SUNRISE by Charles Stross (2004)

Needless to say the invention of a Santa Claus Machine will have a drastic effect on the economy of your civilization.

And other things too. I've already mentioned how the powers-that-be will be concerned with giving rock-rats the ability to manufacture weapons of mass destruction and refine kilogram lots of weapons grade fissionables. And I'm sure the futuristic equivalent of the MPAA and RIAA will be furious with Joe Asteroid wallpapering their habitat dome with atom-level perfect copies of the Mona Lisa. Not to mention how angry the banks will be with a device that can crank out undetectable counterfeits of coins, bills, cheques, and other legal documents.

Of course things get astronomically worse if a Santa Claus Machine can produce copies of itself. Now you've got a freaking Von Neumann self-replicating machine on your hands.

I have a feeling that Santa Claus Machines will always be under military guard, much like the beam propulsion lasers controlled by the Laser Guard. The Santa Guard will place the machine at the site of a future base/colony, and watch what is manufactured like a hawk. If a colony builder submits a blueprint for something questionable, they are liable to be apprehended by the Santa Guard and questioned.

In the far future Santa Claus Machines might be equipped with a law-abiding artificial intelligence. If the user asks it to make a nuclear warhead, the machine will refuse and call the cops.

Trope-a-Day: Matter Replicator

Matter Replicator: The cornucopia machine or autofac, which can build matter into pretty much any object that you want and have – or can write – a recipe for.

Sadly, they are required to obey the laws of thermodynamics and conservation of mass-energy. They also tend to incorporate – especially in larger models designed to build larger objects – arrays of specialized nanofactories and macro-scale tools, and require plenty of energy and specialized appropriate feedstocks for whatever it is you want them to build (so mining, refining, recycling, bactries, and the rest of the industrial supply chain haven’t gone away quite yet). You can make them increasingly general-purpose in these areas at the cost of greater inefficiency – field autofacs are a lot less elegant and more energy-hungry and expensive to run than standard household models.

Living things generally have to be grown in a medical vat instead; simply because most of them tend to die when only half-printed. Yes, this is exactly as gross as it sounds. (Also, some dead organic matter – well, let me put it this way. While you can print up a steak in an autofac, steak is still made in carniculture vats, because first, self-replicating steak is cheaper, and second, it gets boring eating the exact same steak hundreds or thousands of times. Similar although aesthetic considerations are why vatwood is generally preferred to directly replicated wood – although vatwood planks are seen as input to larger autofacs.)

Nonetheless, they’re more than good enough for post-material scarcity purposes.

Things That Make Things

Since we’ve just passed the Matter Replicator trope, and since it may be relevant to an upcoming FAQ question, I thought I’d throw out some definitions relating to such things that may make things clear. Well, clearer.

A nanofac is the basis of nanofacturing technology. Think of it as essentially a 3D printer which can handle arbitrary molecular components with single-atom resolution. (It doesn’t have to: a lot of the time it can simply place pre-assembled multi-atom components picked out of its feed, but the point is that it can.) While it can use free-floating assembler nanites as part of its operation, the vast majority of the work is done in a supercooled vacuum chamber by an array of distant descendants of the atomic force microscope. The materials supply it needs is fed to it as a suspension of molecular components called nanoslurry available in a variety of forms, supplied as a utility from a central nanosource that makes the stuff from raw materials and recycles the return feed of all the stuff that the nanofacs don’t use.

Most important to note is that a nanofac is not a discrete thing you can buy itself – it’s just the term for the central construction array as a module.

What you can buy, on the other hand, is a cornucopia, which is a general-purpose construction device that comes in sizes ranging from desktop-printer-sized (the ubiquitous nanoforge) to dishwasher/fridge size. These are common household, etc., appliances, packaged as vending machines by companies like Valuematic Vending, and are basically a user interface/power supply/etc. wrapped around an appropriate nanofac. They can make pretty much anything you can describe in a recipe, or conceptual seed, to give it its formal name, although if it’s something too big to fit into its vacuum chamber what you’ll get is a heap of parts over several runs which you have to assemble manually following the v-tags after you get them out. (They may or may not bond permanently once you do this.)

A specialized cornucopia, on the other hand, is a fabber. These exist because in nanofacturing, there’s essentially a scale with versatility at one end and efficiency at the other. A cornucopia is a magical device that can make everything, but isn’t the fastest or most efficient way to make anything in particular.

So there are fabbers, which trade off that ability for greater speed and efficiency and customized user-friendliness in doing one particular thing. So while you want a cornucopia available to you, certainly, what you want in your wardrobe is a clothing fabber, in your kitchen is a food fabber, in your sickbay is a pharmafabber, in your wet bar is a cocktail fabber, etc., etc.

And finally, it’s worth noting that assembling things atom by atom, or molecule by molecule, is not actually a terribly efficient way to do things in the first place. It works fine for small objects, sure, where the convenience outweighs the inefficiency, and especially for those made out of lots of tiny components with fine detail to assemble. But large things, especially large things with large areas of relatively homogeneous structure, you really don’t want to make that way.

Which is where autofacs come in. An autofac is a automated assembly system that contains an array of nanofacs for making individual detailed components, but which also contains lathes and drills and presses and kilns and extruders and all manner of other macroscale manufacturing-process equipment, along with plenty of motile robots whose job is to do the assembly of all the different outputs of these processes into the end product. (So they take in nanoslurry for the ‘facs, but also metal ingots, ceramic powder, plastic granules, etc., etc., as their raw materials.)

These vary in size from the relatively modest autofacs you’ll find in most neighborhoods, belonging to companies like Ubiquifac, whose job is to construct large goods people have ordered on-line at a point relatively local to them for immediate delivery, up through larger factories – such as the ones that take nanoslurry and sheet metal in at one end and have finished vehicles drive out the other – all the way to truly giant many-square-miles really-can-build-anything complexes like the Hive.

It’s FAQing Time!

Yes, folks, it’s that time again for the first time when I answer y’all’s background questions!

We have one question this month. James Sterrett asks:

What precursor elements do autofacs require for fabrication? The same elements in the same proportions as the finished product (plus waste etc), or can they synthesize required elements?

Well, now, that’s an interesting question with quite a complicated answer, inasmuch as autofacs are rather complicated things in themselves..

Let me first suggest that this might be a good time to re-read Things That Make Things, since it covers a lot of the terminology I’m about to be throwing about.

So let’s start at the small end, with one of the most common working parts of an autofac, and which is also the core component of a cornucopia, including the ubiquitous desktop nanoforge, the portable nanolathe, and the specialized fabbers.

These, themselves, can’t synthesize elements, or indeed produce any other part of their feedstock – which is to say, you can’t just throw trash into them and have them rearrange it into what you want (you need specialized disassemblers for that, that are hardened to the job. Throw trash into a cornucopia, you have a good chance of wrecking the delicate internal components). They’re just glorified 3D printers. They’re absolutely dependent on a supply of feedstock, which is called nanoslurry.

(One exception to this is that you can also get what is called a nanobrick, which is basically dehydrated nanoslurry and formed together with a mass of simple assemblers. You use it together with a programming nanolathe for field construction, after mixing it with a suitable solvent, usually water, to form a nanopaste. But that’s not what we’re talking about here.)

Nanoslurry itself is a complex suspension of materials useful in nanoconstruction, designed to make it as easy and efficient as possible for nanofacs to pick out the bits they need. It comes in a variety of different kinds and grades, most of which are intended for one specialized industrial application or another. Standard-grade, which is what is shipped out as a public utility down municipal nanopipe systems, comes in two forms, informally referred to as “gray” and “green”.

The nanopipe you have plugged into your domestic cornucopia, for that matter, is actually a four-pipe system. The first supplies gray nanoslurry – which is water, long-chain alcohols, sulphur and nitrogen compounds, a suspension of iron and copper oxides, heavy metals, silicates, acetats, nanograins of industrial plastics, ceramics, and alloys, and prefabricated molecular components, or to put it another way, everything you might need to perform “common mechanosynthetic applications”. The second supplies green nanoslurry, which is specialized towards organic synthesis applications – what this means, of course, varies from world to world. And the third is the special-order pipe, which gets aliquots of specialized feedstock shot down it upon request, because while you may occasionally need, say, 2.1 g of technetium, it’s something specialized enough that there’s no point in including it in the regular feedstock.

(The fourth is the return pipe, that pumps what’s left after the nanofac has picked out what it needs back to the nanosource for recycling.)

And what the nanofacs need is, well, exactly what elements are in the finished product. (Plus a certain degree of in-process waste that ends up squirted down the outgoing pipe back to the nanosource.)

So, so far, we’ve just pushed the problem back to the nanosource; after all, nanoslurry doesn’t exist in nature, so it has to be manufactured. Which is what nanosources do: out of a variety of sources. Air mining, for worlds with atmospheres that have useful components. The bactries of chemical companies, refining volatile asteroid-liquor into useful chemicals with bacterial aid. Giant metal ingots shipped from smelters, which are reduced to slurry components. Reclaimed and purified chemicals from recycling plants and biocleaning cascades. In short, from the ends of all the conventional supply chains. Larger autofacs, like the Hive, will usually have their own nanosource(s) to produce all the specialized feedstocks that they want, especially since autofacs use a bunch of those raw materials elsewhere in their non-nanotech manufacturing processes.

So now we’ve just pushed the question back another level, haven’t we, to “can the people the nanosources use as suppliers synthesize elements?”

To which the answer is, finally: yes, but they usually don’t.

Nucleosynthesis is possible. There’s an entire engineering discipline, alchemics, that specializes in this sort of thing. But it’s neither cheap nor convenient, inasmuch as it still involves banging nucleons together and trying to get the wee buggers to stick, a process that tends to involve particle accelerators and nucleonic furnaces and isotopic separators and mucking about at absurdly high energy densities and low efficiencies. That said, it is now regular non-experimental engineering, and a large enough autofac might well include the equipment.

…but economically, it is almost always cheaper to dig the stuff up and have it shipped to you for nanosource processing than try to manufacture it on site from other elements. Nature’s production process may be slow and uncomfortably explosive for anyone within a couple of hundred light-years, but, damn, does it have economies of scale.

This effect is only amplified, of course, by the fact that alchemics equipment is also what you use to produce gluonic string, muon metals, and various other kinds of exotic matter that genuinely don’t occur in nature anywhere. Now that’s what you call comparative advantage!

Self-replicating Machine

A self-replicating machine or Von Neumann device is an independent robot that can create a duplicate of itself from materials scavenged locally. The little monsters can multiply exponentially (i.e., like cancer) so it is best you have some kind of control or kill switch on them.

They are used when you have a really big job, so you want the robot work force to scale itself up to a size suitable to the task. For example: covering the entire equator of the planet Mercury with solar power cells in only a few years. Or sending robot space probes to every planet in the entire galaxy.

Of course it can be weaponized as either an anti-ship or planetary attack weapon.

Self-replicating machine

A self-replicating machine is a type of autonomous robot that is capable of reproducing itself autonomously using raw materials found in the environment, thus exhibiting self-replication in a way analogous to that found in nature. The concept of self-replicating machines has been advanced and examined by Homer Jacobsen, Edward F. Moore, Freeman Dyson, John von Neumann and in more recent times by K. Eric Drexler in his book on nanotechnology, Engines of Creation and by Robert Freitas and Ralph Merkle in their review Kinematic Self-Replicating Machines which provided the first comprehensive analysis of the entire replicator design space. The future development of such technology is an integral part of several plans involving the mining of moons and asteroid belts for ore and other materials, the creation of lunar factories, and even the construction of solar power satellites in space. The possibly misnamed von Neumann probe is one theoretical example of such a machine. Von Neumann also worked on what he called the universal constructor, a self-replicating machine that would operate in a cellular automata environment.

A self-replicating machine is an artificial self-replicating system that relies on conventional large-scale technology and automation. Certain idiosyncratic terms are occasionally found in the literature. For example, the term "clanking replicator" was once used by Drexler to distinguish macroscale replicating systems from the microscopic nanorobots or "assemblers" that nanotechnology may make possible, but the term is informal and is rarely used by others in popular or technical discussions. Replicators have also been called "von Neumann machines" after John von Neumann, who first rigorously studied the idea. However, the term "von Neumann machine" is less specific and also refers to a completely unrelated computer architecture that von Neumann proposed and so its use is discouraged where accuracy is important. Von Neumann himself used the term universal constructor to describe such self-replicating machines.

From the Wikipedia entry for Self-replicating machine

(ed note: "rollers" are Lunar cargo hauling vehicles, with built-in pressurized habitat modules)

     “That reminds me of something I’ve been meaning to ask," Ben said, a little embarrassed and eager to change the subject. “Why are rollers so cheap? You’ve kept telling me that machines are expensive on the Moon. We bought a used one, but even the new rollers I priced were cheap. I'm not arguing with the price—but there’s a contradiction there.”
     Garrison thought for a moment. “Okay, lemme see if I can explain it. Suppose you wanted to sell eggs on the Moon. What would you import, eggs or chickens?”
     “Chickens, of course,” Ben said. “Or probably fertilized eggs, let ’em hatch here.”
     “Minor detail. A fertilized egg is just a chicken in compact packaging. But the point is the same. Since eggs are something everyone can use, it’s worth shipping in a whole egg factory—that is, the chicken—rather than importing the finished product, the egg. You sell a million eggs cheap and make your money on volume. Now, suppose you wanted to important caviar. What do you ship in—the fish eggs or the sturgeon?”
     “The caviar, obviously.”
     “Right. Not only is the fish harder to take care of than a chicken, but a lot fewer people are going to want the product. So if you’re going to make a living selling caviar on the Moon, you’re not going to have much volume. You send the price through the roof to compensate.”

     Garrison took a sip of his beer and went on. “What’s expensive on the Moon are the caviar machines, things you only need a few of if you need them at all. Specialized high-tech stuff. Like the automated ID booth you were expecting. Or maintenance robots. Or luxury items, like those automatic hairdressers that were such a big fad when we were in New York. They’d cost too much, so the Conners get along without them and tell themselves they're better olf without them. If we ever get back to Central, ask Mrs. Lombroska her opinion of automated hotel systems. That’s the caviar stulf.
     “What we've been riding in is a chicken’s egg. There are thousands of rollers around, because some UNLAC lab on Earth designed a whole roller factory. They built it, shipped it here, switched it on, and stepped back. It s been cranking out rollers ever since. They’ve tweaked up the design a few times, and they put out a few different models for dilferent jobs. Cargo versions, oversize jobs like that big guy out front. Besides dialing in what model to make, they just leave the factory alone. Which makes rollers cheap. Basic supply and demand.

     “The kicker is that the factory is totally automated, right down to raw materials. I got a tour of it once. They have robot bulldozers that feed dirt into the hopper of a soil-cracker, and dedicated long-distance robot haulers that supply ore for lunar-rare elements like nitrogen from nearby mines. They fabricate the parts right from raw materials. Robot labor assembles it. They call it a half-von Neumann machine.”
     “Meaning what?"
     “A von Neumann is any machine capable of replicating itself. Then the relicas replicate themselves, and soon you’re up to your keister in von Neumanns. There have been some gimmicky lab gadgets that could copy themselves but no one has ever built a worthwhile true von Neumann. A half-von Neumann can endlessly duplicate a machine simpler than itself. ”
     “They can’t do that with an entire roller, Ben protested. “It’s too complex.”
     “You open up that control panel when we re back aboard and see how many parts there are in it. They ve got the things boiled down to absolute simplicity."

     Ben frowned for a second. “Wait a minute. Solar powered factory, right?”
     “So they've got free power. And they’re getting the raw materials essentially for free, digging the dirt out of the ground and refining it; Robots mine the raw materials and build the rollers, so you don’t have any labor costs. Power, material and labor free. Aside from the cost of building the factory, it doesn’t cost them anything to make the rollers! So what do they base the cost on?”
     “ ‘The value of a thing is that which it will bring,’ ” Garrison quoted. “They sell for whatever the market will bear. At the moment, the market is flooded, so rollers are cheap. Another good run of immigration, and thesupply will dry up. Or else they can just turn off the factory for a while until it’s needed again, and drive the price up a bit. But you've spotted a real problem there. How do you run an economy when things of value cost nothing to produce? The roller plant is an example, not an exception. Lots of common items on the Moon are produced that way.”
     “So how do they run the lunar economy?”
     Garrison shrugged. “UNLAC? I think they just ignore it and hope it will go away. I mean, Christ, you’ve got a whole planet here that doesn’t even have its own currency. Instead we use everyone else’s money—and half of that is in confetti-denominations. From an economic standpoint, the whole Moon is sheer chaos, but it works somehow. I think the policy people are afraid that if they try to fix it, people will notice it can’t possibly work, even though it's been working for years. Confidence would collapse, and the whole place would go to hell in a hand basket.”

(ed note: Garrison is asking about why deep-drilling gear is being hauled to the Lunar farside)

     “Why do they need deep-drill gear for way the hell out there?’ Garrison asked.
     “Laser array. ”
     “The comm laser array they’re building out there.”
     “Right, we’d heard about that," Garrison replied. “But what do comm lasers have to do with deep-drill mining?”
     “They're shipping a whole laser factory out there, and they need a bunch of materials that aren’t available on the surface. It’s the old factory that built the Nearside array."
     “A whole factory just to build a few comm lasers?” Ben objected.
     Garrison shrugged. “You have to put the factory somewhere. Cheaper to ship it than haul the final products halfway around the Moon, even if you only need a few lasers.

     “They need more than a few,” Mohammed said. “With the space traflic density they’re projecting, they'll need to track maybe two, three dozen comm-targets at once—most of the interplanetary shipping, plus the Settlements on Mars, the Belt, and the inner and outer planets. Plus you need back-ups for all of those, and you have to have lasers at several frequencies for various dull reasons. Right off the bat, they’ll need about a hundred frequency-tunable comm laser units. More with eventual expansion, and for replacement of broken units. Makes sense to build them on the spot. Besides which, the laser units aren't small. Each comm laser unit will be self-contained. Each one with its own solar cells and storage coils and pointing mechanism and so on.

     “If they had built ’em at Central Colony, and shipped ’em from there, maybe I’d have been able to fix two of them on my roller at a time. Shipping two per trip, and one trip a month, it would take over four years to get ’em all out there. That would cost UNLAC plenty, more so if they hired several oversize rollers to get it done faster. There aren’t that many outsizers around, and they cost plenty to hire. It’s cheaper, faster, and easier to ship a robot factory out there. In fact, most of the factory is already out at Farside Station. The deep-drill mining gear is the last component to go in.”

From FARSIDE CANNON by Roger MacBride Allen (1988)
Rapid Bootstrapping Of Space Industry

(ed note: A self-replicating lunar factory (SRLF) would dramatically accelerate the rate of space industrialization. The problem is establishing the first one. A "seed" hardware has to be developed, then delivered to the lunar surface.

A 1982 study figured you'd have to deliver about 100 metric tons of seed hardware, basically the mass of an entire SRLF. This is far too much mass to deliver, short of an Orion Drive spacecraft. This can be reduces a bit by using 3D printing, but not enough.

A more drastic measure to reduce the seed mass is to avoid full "closure." A SRLF with full closure can totally replicate itself using local materials. A SRLF lacking full closure would require some of the components for the new machine to be shipped from Terra. The main missing item is the local manufacture of computer chips and electronics. A chip fabrication unit requires many tons of seed mass. The advantage of shipping computer chips from Terra is drastically lowered seed mass and faster SRLF replication time (since it doesn't have to make a new chip fab). The disadvanage is lack of full closure does not scale. As more SRLFs are produced, Terra will have to boost more and more computer chip mass.

The paper proposes a new approach: "bootstrapping."

The seed mass for the initial SRLF is low (about 12 metric tons) because the seed will only be able to create equipment that is much more primitive and crude than the seed, say 1700s-era technology. The 1700s tech will construct new equipment that was 1800s-era tech. The 1800s tech will construct 1900s-era tech and so on. It will bootstrap itself until it reaches the point of being an actual full closure SRLF. It will then start cranking out daughter factories and space industrialization goes into high gear. According to their mathematical model, the fully developed 7th generation SRLF will have a total mass of about 100 metric tons, which is in close agreement with the 1982 study. But this is from only 12 metric tons shipped from Terra, instead of 100 MT. Abet with several years of tech advancement.)

Once successfully bootstrapped, a robotic network can access, process, transport, and utilize the solar system’s resources for mankind’s benefit. Appropriately designed robots will not have the problems traveling the vast distances of the solar system that humans have, and they can set up the infrastructure that will enable us to follow. Within the first several decades a vital industry could be established on the Moon and in the asteroid belt using technologies that are for the most part only modestly advanced beyond today’s state-of-the-art. After that, human outposts, laboratories, and observatories can spring up everywhere between the Kuiper belt and Mercury. It can grow exponentially and provide mankind the ability to do things that today are only dreams...

...There are several additional strategies to reduce the launch mass of a seed replicator. The first is to identify and use only the simplest system capable of replication. The second is to avoid full “closure”. Closure is the ability to replicate all aspects of the system in space so that nothing further is required from Earth to build replicas. Nearly full closure is vastly easier to achieve than full closure (Freitas and Gilbreath 1980), because the manufacture of electronics and computer chips requires heavy, high-tech equipment that would be expensive to launch from Earth and would command much of the industry’s resources during replication. However, incomplete closure results in very high launch masses later as the industry grows exponentially, as we show below. A third strategy, which to our knowledge has not been discussed in the literature, is to begin with a simpler, sub-replicating system and evolve it toward the self-replication capability. In this strategy, the evolving system might never become a “self-replicator” even after it reaches full closure, because each generation can continue creating something significantly more advanced than itself. This is the strategy adopted here.

The first hardware sent to the Moon will be high-tech equipment built on Earth. However, the high launch costs demand that it be mass-limited so it will have insufficient manufacturing capability to replicate itself. It will construct a set of crude hardware made out of poor materials, so the second generation is actually more primitive and inefficient than the first. The goal from that point is to initiate a spiral of technological advancement until the Moon achieves its own mature capabilities like Earth’s. This evolving approach will provide several benefits. First, industry on the Moon can develop differently than on Earth. The environment, the manufacturing materials, the operators (robots versus humans), and the products and target markets are all different. Allowing it some reasonable time to develop will allow it to evolve an appropriate set of technologies and methods that naturally fit these differences. Second, the evolving approach supports the development of automation so that industry can then spread far beyond the Moon. The technological spiral will develop the robotic “workers” in parallel with the factories. It will also improve automated manufacturing techniques such as 3D printing. The third and probably most important benefit is the economic one. As we show here, a space economy can grow very rapidly, and it will quickly require massive amounts of electronics and robotics unless there is full closure. The tiny computer chips alone become too expensive to launch within a few decades as the industry grows exponentially, and therefore we will quickly need lithography machines on the Moon to make the computer chips. The evolving approach sends only a small and primitive set of machines as “colonists”, and the nascent lunar industry develops over time – but still rapidly – toward the full sophistication that Earth cannot afford to launch...

...So the objective is for the first robotic “colonists” on the Moon to fabricate a set of, say, 1700’s-era machines and then to advance them steadily through the equivalent of the 1800’s, 1900’s, and finally back into the 2000’s. We argue that this can be accomplished in just a few decades. There are reasons why this technological spiral will be both easier and faster than when we accomplished it on Earth. First, the majority of the technology does not need to be re-invented. The knowledge will be provided by technologists on Earth. Second, the Earth will provide material support in the early stages. We will send teleoperated robots and complex electronic assemblies prior to achieving closure. On the other hand, there will be new challenges. For example, we must gain experience in the lunar environment to learn how to adapt terrestrial technologies to it...

...For the concept of lunar industry presented here we do not think the term “self-replicator” is appropriate and so we will avoid the term. A self-replicator is by definition self-contained with all of its parts co-located in a complete set. That entire set fabricates a new complete set that is situated in a new location before the next replication cycle begins. This is unlike industry or biology on Earth: neither businesses nor industries are self-replicators. Although biological species are self-replicators, they require a vast number of other species in a highly networked ecology to survive, and the ecology does not operate on a synchronized replication cycle. We think the networked complexity of these examples is the more successful topology for space industry because it is the one that naturally occurs and hence is probably the more efficient and adapted for survival, as well as the more easily bootstrapped through an evolutionary process. We therefore avoid any requirement that the various hardware assets remain together in a closed set, and we allow instead for transportation to develop naturally between multiple, specialized production sites. Thus, lithography machines to make computer chips can be located in just one laboratory on the Moon, and their products can be transported to other sites for incorporation into robots and machines. The original facility to house that equipment can be built larger than necessary to allow for expansion and to gain economies of scale...

The set of assets within each generation is described below. To be conservative, we usually assume that each asset is retired at the end of its generation so that only the more modern assets of the new generation are involved in producing the generation after that (except as noted below for solar cells and robonauts). This is overly conservative, but it allows that hardware failures could disable some new assets that are unable to be repaired while assets from the prior generation continue to operate to take their place.

In Generation (“Gen”) 2.5, the use of the decimal place (rather than incrementing to 3.0) indicates that the assets of Gen 2.0 and Gen 2.5 are added cumulatively rather than retiring the Gen 2.0 hardware. We do this because it is necessary to vastly diversify materials manufacturing as quickly as possible, and this is accomplished by creating Gen 2.5 hardware that is no more sophisticated than Gen 2.0 although capable of making different materials.

The technologies needed for mining, chemical processing, and metallurgy are for the most part already existent in Earth’s industry. The feasibility of adapting them to the lunar environment has been and is currently being demonstrated by the wide variety of successful space utilization projects described elsewhere in this issue of the journal.

Excavators. The excavators will travel between the digging site and the resource processing site, delivering sufficient lunar regolith each hour to maintain production rates of the other assets. The details of the excavators are unimportant. In our modeling we assumed for specificity that they are small and operate in a swarm. They may also be fitted with paving attachments (Hintze and Quintana 2012).

Chemical plants for volatiles. Dry regolith or an ice/regolith mixture will be deposited into hoppers and then fed into chemical plants. Electrical power for the processes is augmented with thermal power from solar concentrators. One type of chemical plant will be concerned with producing gases and liquids. These fluids will include oxygen, hydrogen, water, hydrocarbons such as methane, and (in more advanced generations) solvents for industrial processes. So far, NASA has developed and field tested only basic oxygen production systems, including hydrogen reduction and carbothermal systems. More complex chemical processes have been developed for terrestrial applications, and by adapting the lessons-learned from the lunar projects it should not be difficult to adapt the other processes to the lunar case, too. For specificity, we have described the chemical plants using particular masses, power levels, and production rates after examining several sources of data. These include analyses of lunar chemical plants (Mendell 1985, Taylor and Carrier 1993) and the actual construction and performance of lunar chemical plants that our team and collaborators have recently field tested on Mauna Kea in 2008 and 2010 (Boucher et al. 2011; Captain et al. 2010; Gustafson et al. 2010a; Gustafson et al. 2010b; Muscatello et al. 2009). The specifics are not too important as we will vary these numbers over wide ranges to demonstrate general feasibility of the bootstrapping process. Gen. 3.0 and subsequent will have larger throughputs than the earlier generations, and they will gain from economies of scale by building much larger chemical plants rather than reproducing a large number of smaller plants (Lieberman 1987; Gallagher et al. 2005). However, to be conservative we ignore the economies of scale and instead describe the chemical plants as though they were units identical to the originals. These represent “units” of chemical processing capability in larger plants rather than standalone assets.

Chemical plants for solids. Chemical plants are also needed to produce plastics and rubbers from the lunar polar ice. This is possible because we now know that the ice contains large quantities of carbon molecules (CO, CO2,…) as well as nitrogen-bearing and hydrogen-bearing molecules (Colaprete et al. 2010; Gladstone et al. 2010). These materials may be needed for gaskets, seals, and insulators, for example. Later diversity will introduce sheet materials, fabrics, and layered and complex materials. Again, economies of scale are ignored in the model to be conservative.

Metal and Ceramics Refinery. It will be crucial to manufacture metals and metal-oxide ceramics and to improve the properties of the various alloys with subsequent generations. Processes to do this from lunar soil have been described (Rao et al. 1979; Jarrett et al. 1980; Sargent and Derby 1982; Lewis et al. 1988; Stefanescu et al. 1988; Landis 2007; Lu and Reddy 2008), and some development work is on-going by our colleagues and collaborators. Notionally, the early generations in our model will produce crude “mongrel alloys” by electrowinning or other methods. Hardware constructed from those alloys will need to be massive to add strength to make up for their poor mechanical properties. (This will be partially offset by the reduced forces in low lunar gravity.) Subsequent generations of metal refineries will add processes and material streams to improve the mechanics of the materials. Oxygen and other gases produced by metal refining will be sent to the chemistry plants. Electrical power is augmented with thermal power collected by solar concentrators.

Manufacturing. Additive manufacturing will have two forms: 3D printers that make parts that are small enough to fit inside the printer, and larger units that move about robotically and add material onto large structures external to themselves. The printers may eventually have multiple material streams including metals and plastics to make complex assemblies in a single pass. However, the earlier generations will require import from Earth of the most complex assemblies, such as electronics packages and the assembly robots. Furthermore, “appropriate technology” will mandate the design of simpler assets that can function without too many complex or miniaturized components, simplifying their manufacture and reducing imports. To achieve the final generations, the additive manufacturing technologies require advancement beyond the current state of the art. However, gains are being made rapidly and it is very likely the advancements will support the bootstrapping strategy presented here.

Solar Cell Manufacturer. Power will be provided mainly by solar cells. Ignatiev et al. (2001) and Freundlich et al. (2005) have shown how these may be manufactured on the Moon even in the earlier, more primitive generations of lunar industry. For specificity, we have described the mass, power, and throughput of the solar cell manufacturers as per those earlier studies. We show that these devices in the first and subsequent generations produce far more available power than needed by the following generation. This excess power capacity grows exponentially. We assume that solar cells are added cumulatively from one generation to the next. Failure of solar cells by radiation damage and micrometeoroids has not been modeled explicitly, but can be deducted from the exponentially growing excess.

Power Station. In the first generation, a power station is included in the mass of hardware shipped to the Moon. This station includes power conditioning, docking stations, and cabling to manage and distribute the solar power. It might also include a small nuclear reactor to support human presence and as a backup system to support re-bootstrapping in case of system failure.

Robonauts. Robotic astronauts, or “robonauts”, will perform the assembly and maintenance tasks. The name is borrowed from a particular robot developed by General Motors and the NASA Johnson Space Center, with the assumption that robonauts in future lunar industry will be the direct descendants of the current ones. The number of robonauts must grow rapidly as the industry itself grows. At first the robonauts are imported from Earth. To keep the strategy slightly more economical, they are not retired with each subsequent generation. Beginning with the third generation their structural components are made on the Moon, while Earth continues to send their cameras, computers, motors, and sensors. Eventually they are made completely on the Moon.

At first the robonauts will be teleoperated from Earth. The approximately 2.5 second round-trip communication time delay can be managed even for fine motor tasks, such as screwing parts together by hand, by having a teleoperator on Earth interact with a virtual world that models the robonaut and its environment rather than interact with the reality itself. The robonauts on the Moon will mimic the behaviors they observe in the virtual reality as closely as possible using existing levels of robotic autonomy. Resynchronization will occur in the virtual world using a rubric designed to prevent operator confusion. Similar schemes are being developed for telesurgery with large communication latency (Haidegger and Benyó 2003). This will make teleoperation manageable for lunar operations, but it will require a growing and expensive workforce of teleoperators on Earth plus sufficient communications bandwidth, and it will not be extensible to the asteroid main belt or beyond. Therefore, with each generation, progress will be made toward full autonomy.

Table 1 describes the autonomy in terms developed by Hans Moravec (Moravec 1999; Moravec 2003). Moravec’s “insect” level is when robots perform simple pre-programmed responses to sensor inputs. Many machines operate at the insect level today. The “lizard” level is when robots identify objects functionally to guide their motor tasks. Lizard-level robotics is already appearing in laboratories on Earth and is making steady progress toward greater capability. “Mouse” level is when the robots learn and improve the performance of their tasks through simple positive and negative feedback. This is important because human industry is only adapted to terrestrial conditions, but learning robots can adapt it to the multitude of environments they will experience in the solar system. “Monkey” level is when the robots maintain a mental model of the world including other agents. This provides them with insight into the intent of other agents as well as foresight. “Human” level is when the robots have the mental ability to reason abstractly, generalizing from specific learning situations to a broader class of applications, and thus to make decisions in the face of the unexpected. These higher levels of robotics will be necessary in the distant future when, for example, a robotic construction crew is building a science lab on Pluto, many hours of time delay away from human help. Extrapolating the computing speed of small, inexpensive microprocessors that are commercially available, we expect by the year 2023 they will reach the speed Moravec predicted as necessary to support human-level robotics. Even if Moore’s Law ended today, that computer power is easily achieved by paralleling inexpensive microprocessors and by other advances planned by computer chip manufacturers (Gargini 2005). On-going advances in robotic software and artificial intelligence present a very optimistic picture that these levels of robotics will be achieved as Moravec predicted, with lizard-level occurring by 2020, mouse-level by 2030, monkey-level by 2040, and human-level by 2050. Only mouse-level is needed by the end of bootstrapping on the Moon, but depending on how fast the strategy is carried out the robotics sent to the asteroid belt may be at the monkey-level or higher.

Electronics Manufacturing. In the baseline model, when Gen. 2.5 is fabricated its assets include some electronics manufacturing machines. Those machines themselves are built with electronics imported from Earth, and they are capable of making only the crudest and simplest of electronics components such as resistors and capacitors, which will not be miniaturized or efficient. Gen. 3.0 and subsequent possess a greater diversity of electronics manufacturing machines with increasing sophistication. By Gen. 5.0 we aim to have basic lithography machines on the Moon, built using computer chips sent from Earth, so that by Gen. 5.0 all computer chips can be made in space. The early computer chips will lack the transistor density of chips made on Earth, but they will be adequate for “appropriate technology” in space. Later generations (not modeled here) continue spiraling the sophistication of space industry so that eventually the lithography machines and computer chips match the best of Earth’s.

(ed note: the reseachers then created a mathematical model to determine how rapidy the lunar industry would grow. Maximum production rate "Max." is when the plants run full bore trying to make the next generation. Reduced production rate "Red." is when the plants pause manufacturing to allow other tasks, such as technological advancement, manufacturing experiments, or to allow slow robotnauts to catch up assembling parts. "Red." reduces the manufacturing rate by one-half. As it turns out, the reduced rate is the minimum necessary to meet survival and growth goals. Once the SRLF reaches the final generation, it can switch over to Max rate thereafter.)

Self-replicating spacecraft


In theory, a self-replicating spacecraft could be sent to a neighbouring planetary system, where it would seek out raw materials (extracted from asteroids, moons, gas giants, etc.) to create replicas of itself. These replicas would then be sent out to other planetary systems. The original "parent" probe could then pursue its primary purpose within the star system. This mission varies widely depending on the variant of self-replicating starship proposed.

Given this pattern, and its similarity to the reproduction patterns of bacteria, it has been pointed out that von Neumann machines might be considered a form of life. In his short story, "Lungfish", David Brin touches on this idea, pointing out that self-replicating machines launched by different species might actually compete with one another (in a Darwinistic fashion) for raw material, or even have conflicting missions. Given enough variety of "species" they might even form a type of ecology, or – should they also have a form of artificial intelligence – a society. They may even mutate with untold thousands of "generations".

The first quantitative engineering analysis of such a spacecraft was published in 1980 by Robert Freitas, in which the non-replicating Project Daedalus design was modified to include all subsystems necessary for self-replication. The design's strategy was to use the probe to deliver a "seed" factory with a mass of about 443 tons to a distant site, have the seed factory replicate many copies of itself there to increase its total manufacturing capacity, over a 500-year period, and then use the resulting automated industrial complex to construct more probes with a single seed factory on board each.

It has been theorized that a self-replicating starship utilizing relatively conventional theoretical methods of interstellar travel (i.e., no exotic faster-than-light propulsion, and speeds limited to an "average cruising speed" of 0.1c.) could spread throughout a galaxy the size of the Milky Way in as little as half a million years.

Implications for Fermi's paradox

In 1981, Frank Tipler put forth an argument that extraterrestrial intelligences do not exist, based on the absence of von Neumann probes. Given even a moderate rate of replication and the history of the galaxy, such probes should already be common throughout space and thus, we should have already encountered them. Because we have not, this shows that extraterrestrial intelligences do not exist. This is thus a resolution to the Fermi paradox – that is, the question of why we have not already encountered extraterrestrial intelligence if it is common throughout the universe.

A response came from Carl Sagan and William Newman. Now known as Sagan's Response, it pointed out that in fact Tipler had underestimated the rate of replication, and that von Neumann probes should have already started to consume most of the mass in the galaxy. Any intelligent race would therefore, Sagan and Newman reasoned, not design von Neumann probes in the first place, and would try to destroy any von Neumann probes found as soon as they were detected. As Robert Freitas has pointed out, the assumed capacity of von Neumann probes described by both sides of the debate are unlikely in reality, and more modestly reproducing systems are unlikely to be observable in their effects on our Solar System or the Galaxy as a whole.

Another objection to the prevalence of von Neumann probes is that civilizations of the type that could potentially create such devices may have inherently short lifetimes, and self-destruct before so advanced a stage is reached, through such events as biological or nuclear warfare, nanoterrorism, resource exhaustion, ecological catastrophe, or pandemics.

Simple workarounds exist to avoid the over-replication scenario. Radio transmitters, or other means of wireless communication, could be used by probes programmed not to replicate beyond a certain density (such as five probes per cubic parsec) or arbitrary limit (such as ten million within one century), analogous to the Hayflick limit in cell reproduction. One problem with this defence against uncontrolled replication is that it would only require a single probe to malfunction and begin unrestricted reproduction for the entire approach to fail – essentially a technological cancer – unless each probe also has the ability to detect such malfunction in its neighbours and implements a seek and destroy protocol (which in turn could lead to probe-on-probe space wars if faulty probes first managed to multiply to high numbers before they were found by sound ones, which could then well have programming to replicate to matching numbers so as to manage the infestation). Another workaround is based on the need for spacecraft heating during long interstellar travel. The use of plutonium as a thermal source would limit the ability to self-replicate. The spacecraft would have no programming to make more plutonium even if it found the required raw materials. Another is to program the spacecraft with a clear understanding of the dangers of uncontrolled replication.

Applications for self-replicating spacecraft

The details of the mission of self-replicating starships can vary widely from proposal to proposal, and the only common trait is the self-replicating nature.

Von Neumann probes

A von Neumann probe is a spacecraft capable of replicating itself. The concept is named after Hungarian American mathematician and physicist John von Neumann, who rigorously studied the concept of self-replicating machines that he called "Universal Assemblers" and which are often referred to as "von Neumann machines". While von Neumann never applied his work to the idea of spacecraft, theoreticians since then have done so.

If a self-replicating probe finds evidence of primitive life (or a primitive, low level culture) it might be programmed to lie dormant, silently observe, attempt to make contact (this variant is known as a Bracewell probe), or even interfere with or guide the evolution of life in some way.

Physicist Paul Davies of Arizona State University has even raised the possibility of a probe resting on our own Moon, having arrived at some point in Earth's ancient prehistory and remained to monitor Earth (see Bracewell probe), which is very reminiscent of Arthur C. Clarke's The Sentinel.

A variant idea on the interstellar von Neumann probe idea is that of the "Astrochicken", proposed by Freeman Dyson. While it has the common traits of self-replication, exploration, and communication with its "home base", Dyson conceived the Astrochicken to explore and operate within our own planetary system, and not explore interstellar space.

Oxford-based philosopher Nick Bostrom discusses the idea that future powerful superintelligences will create efficient cost-effective space travel and interstellar Von Neumann probes.


A variant of the self-replicating starship is the Berserker. Unlike the benign probe concept, Berserkers are programmed to seek out and exterminate lifeforms and life-bearing exoplanets whenever they are encountered.

The name is derived from the Berserker series of novels by Fred Saberhagen which describe a war between humanity and such machines. Saberhagen points out (through one of his characters) that the Berserker warships in his novels are not von Neumann machines themselves, but the larger complex of Berserker machines – including automated shipyards – do constitute a von Neumann machine. This again brings up the concept of an ecology of von Neumann machines, or even a von Neumann hive entity.

It is speculated in fiction that Berserkers could be created and launched by a xenophobic civilization (see Anvil of Stars, by Greg Bear or could theoretically "mutate" from a more benign probe. For instance, a von Neumann ship designed for terraforming processes – mining a planet's surface and adjusting its atmosphere to more human-friendly conditions – might malfunction and attack inhabited planets, killing their inhabitants in the process of changing the planetary environment, and then self-replicate and dispatch more ships to attack other planets.

Replicating seeder ships

Yet another variant on the idea of the self-replicating starship is that of the seeder ship. Such starships might store the genetic patterns of lifeforms from their home world, perhaps even of the species which created it. Upon finding a habitable exoplanet, or even one that might be terraformed, it would try to replicate such lifeforms – either from stored embryos or from stored information using molecular nanotechnology to build zygotes with varying genetic information from local raw materials.

Such ships might be terraforming vessels, preparing colony worlds for later colonization by other vessels, or – should they be programmed to recreate, raise, and educate individuals of the species that created it – self-replicating colonizers themselves. Seeder ships would be a suitable alternative to Generation ships as a way to colonize worlds too distant to travel to in one lifetime.

From the Wikipedia entry for Self-replicating spacecraft
The Ring of Charon

“Figured out what?” Sondra asked. “A theory about what?”

“About what the Charonians are,” she said.

“They’re von Neumanns. That’s it. That’s got to be it.”

“That’s what?”

“The answer, the explanation. The key to it all.

Not all by itself, but it’s a start.” Marcia stood up, still holding the pages of the message, and stared off into space, carefully thinking it all out. “It makes sense,” she said. “They’ve got to be von Neumanns.”

“Will you please quit saying ‘von Neumanns’ and explain what they are?” Sondra demanded.

“It’s very simple,” Marcia said. “How did we miss it? A von Neumann machine is any device that can exactly duplicate itself out of locally available raw materials. A toaster that could not only toast bread but build more toasters out of things found in the kitchen would be a von Neumann toaster. It’s a very old concept, named for the scientist who dreamed it up.

“But von Neumann’s real idea was to build a von Neumann starship,” Marcia said. “A robot explorer that could fly from one star system to another, explore the system—and then duplicate itself a few dozen times, maybe mining asteroids for materials. It would send out new von Neumanns, duplicates of itself, from there. Then each new exploration robot would travel on to a nearby star, duplicate itself, and start the cycle again. Each machine would report back to the home planet on what it found. Even given a fairly slow transit speed between stars, you could explore a huge volume of space in just a few hundred years. Traveling, exploring, reproducing, over and over again.”

Von Neumann Machine. Any machine that can precisely duplicate itself. A Swiss army knife that included a Swiss-army-knife-making attachment would be a von Neumann machine.

From The Ring of Charon by Roger MacBride Allen (1990)
A Life for the Stars

He was saying to Frad: "The arrangements with the machinery are cumbersome, but not difficult in principle. We can lend you our Brood assembly until she replicates herself; then you reset the daughter machine, feed her scrap, and out come City Fathers (computers) to the number that you'll need—probably about a third as many as we carry, and it'll take maybe ten years. You can use the time feeding them data, because in the beginning they'll be idiots except for the computation function.

From A Life for the Stars by James Blish (1962)

Space Plastic

Plastics are organic polymers, which means they are composed of huge chains of carbon and hydrogen molecules. The raw materials can be found in carbonaceous asteroids and in the hydrocarbon lakes of the Saturnian moon Titan.

Inside the closed ecology of a spacecraft's or base's CELSS some of the carbon and hydrogen can be diverted to brewing up some plastics. The source can be from carbon dioxide in the air or from agricultural waste.

Bootstrapping Space: Plastic

I've mentioned several times that plastic can be produced from agricultural waste and/or CO2.

 The plastic of interest is polyethylene, or rather ultra high molecular weight polyethylene (UHMWPE, UHDPE, polyethene or trade names Spectra or Dyneema). It is formed of very long single chains of carbon, so the unit formula is CH2. This material is a thermoplastic, melting around 130 °C (or less if it contains solvents and/or crystalline defects). In normal use it should be kept between -150 °C and about 80 °C, so in-space applications will typically require a protective coating such as thin-film aluminum.

 So, we will assume we have available a quantity of ethanol (C2OH6) from other processes. Fermentation of sugar and/or cellulose is one possible source, as is syngas fermentation. It does not have to be perfectly pure; ethanol-water eutectic produced by distillation is acceptable. See the link for chemical structure and other data. This is passed through a fluidized bed reactor with alumina or zeolite dehydration catalyst that removes one molecule of water from each molecule of ethanol, yielding ethylene (C2H4) at high purity. The catalyst has to be regenerated periodically to recover the water and remove carbon and trace contaminants. The ethylene can be stored in high-pressure tanks.

 An alternative is to use the reverse water gas shift reaction to convert H2 and CO2 to CO; with additional H2 added this is syngas. The H2 would come from electrolysis of water. If methane is available it can be used with some O2 to produce syngas directly. Apply the methanol process, then apply something like the Mobil methanol to gasoline process to yield ethylene. Proper choice of zeolite will yield pure gaseous ethylene.

 The ethylene can be polymerized using titanium tetrachloride as a catalyst. This process has been used commercially for 60 years and currently yields high-quality resin with masses of 5.5 to 6 x10^6 grams per mol and contaminants of titanium (<40 ppm), aluminum (<20 ppm) and chlorine (<30 ppm), a total of 110 grams of catalyst lost per ton of plastic {UHMWPE biomaterials handbook, Steven M. Kurtz; chapter 2, tables 2.1 and 2.2}. Of these, chlorine is the hardest to replace unless there are convenient chloride salt deposits available; even so, 10kg of chlorine would be sufficient for 333 tons of plastic. The catalyst also requires magnesium chloride and a structural scaffold (usually microporous silica beads, sometimes zeolite or activated carbon), both of which can be completely recovered. The catalyst must be activated with triethylaluminum (TEA); this material is very dangerous and also useful as a rocket igniter. It can be produced using metallic aluminum, hydrogen gas and ethylene gas; if no TEA is available to jump-start the reaction then a small amount must be made using another process involving lithium hydride or ethyl chloride.
 A related catalyst, metallocene titanium, zirconium or hafnium chloride is used in solution with methylaluminoxane (MAO). Recent work has developed related catalyst systems using MAO; it is also very dangerous and is related to TEA. Synthesizing metallocene looks straightforward, but the input materials are fairly complex.
 These reactions can be terminated by hydrogen, so care must be taken to avoid any excess hydrogen gas in the ethylene or catalyst bed (particularly avoid water gas shift). The reactions normally occur in a solvent which does not react with the catalysts; this allows the catalyst active sites to remain exposed as the polymer molecules are carried away. Details about separation of metallocene from solvent appear to be kept secret, but supported catalyst in solvent should be straightforward as a continuous process.

 Solvents are a tricky question. The ideal solvent will be an organic oil which can be extracted from biomass, can dissolve PE, boils above 150 °C, does not thermally polymerize below that temperature and is nontoxic. Orange oil (mixed terpenes) fit that description, but the yield of terpene per m² of growing area is so low that it is disqualified for use in space. Proven solvents are xylene and toluene. This is an input that requires additional research; plant oils, silicone oils and possibly alcohols should be examined. Prototype production of PE could use Earth-sourced solvents while demonstrating the process is feasible, as could projects with a specific mass of plastic as a goal (early tethers for example).

 The product of this polymerization process is purified to contain only long-chain polymer and solvent. If necessary this can be done by centrifuge but the proportion of shorter chains and branches should be very low with these catalysts. Solvent is removed until the concentration of polymer is around 20% by mass. This results in a gel which is loaded into a ram extruder or similar heat and pressure device with spinneret holes. As the gel is passed through these holes the molecules are drawn into alignment; the resulting gel fibers are cooled and passed through water or ethanol to gradually remove the rest of the solvent as the fiber is drawn further. This gel spinning causes a very high degree of alignment and crystallization and can even reduce lattice defects; this is the secret of the incredibly high strength of Spectra fibers. The fiber is eventually wound onto a bobbin and then heat treated to drive off any remaining solvent and to further improve strength. Individual fibers are woven into yarn which is then used as needed. Again, fibers that will be exposed to space or to monatomic oxygen (low-Earth orbit) should be coated with a protective layer such as vapor deposited aluminum or a UV and oxygen resistant polymer film.

 For bulk use the freshly made polymer will have all solvent removed, yielding a powder that can be pressed into pellets for later use or pressed directly into shape. The powder can be melted under inert gas or redissolved in solvent and cast or extruded into the necessary shapes; pellets can sometimes be difficult to redissolve without shredding or patience.

 The bulk plastic is suitable for cutting boards, artificial joints, low-friction or low-wear contact surfaces, storage containers for water or moderate acids / bases, lightweight mechanical parts like rollers, cams, gears, etc., etc. Extruded rods can be used in 3d prototyping machines for additive manufacturing.

 The fiber is suitable for composite overwrap pressure vessels, tensile reinforcing members (including in regolith blocks), habitat hulls, meteoroid hull patches, cut-resistant cloth, ballistic armor, sutures and space tether strands.

Actually doing any of this would require the services of a good process chemist / chemical engineer at the least (plus possibly other engineers) to set up the various reactions, required equipment and input streams. Many of these processes if operated in batch mode will have unreacted or partially reacted inputs, and all of the processes will have some byproducts; these materials will need to be destroyed, most probably in a wet gasifier (supercritical water + O2 reactor) to recover the C, H and O. Any trapped catalyst material will find itself in the ash/salts, so any metals in the waste stream will end up as oxides or chlorides. Because the inputs are generated slowly, the overall process does not need to be particularly time-efficient as long as it is reliable, low-maintenance and low-mass-loss. For edge cases where a large supply of water and methane or CO2 are available a different solution might be used that takes less time but more manual effort.
From Bootstrapping Space: Plastic by Chris Wolfe (2015)


What sort of space clothing will space colonists wear? Something lightweight, to save on mass. No spandex, please.

Clothing is difficult to manufacture in microgravity, from growing the plant fibers to spinning, weaving, dying, and tailoring. All of those processes are much more difficult when things are floating around. This will limit the supply of available clothing, and make them expensive.

On the ISS, the crew wears garments made of cotton. These have a tendency to shed lint which can clog up ISS machinery and air filters. They are experimenting with Merino wool shirts and polyester shorts, which are lighter and do not shed lint.

The clothing might be treated with anti-microbial agents to make them odour resistant, since a microgravity clothes washer is so problematic that the ISS does not have one. On the ISS, clothing is worn and re-worn without washing until they get too stinky. Then they are put on the next cargo supply ship to burn up in re-entry. Actually, in microgravity, clothing does not actually touch the wearer's body as much as it does under Terra's gravity. For a crew of six, the ISS requires about 400 kilograms of clothing per year.

In classic Star Trek, the laundry renders the clothing back down to its chemical components, filters out the dirt, then refabricates the clothing. Nowadays we would think in terms of a 3D printer. Later versions of Star Trek would use unobtanium "replicators", but they have unintended consequences.

There are two basic ways to enable textiles to kill microbes. The first is to coat the fabric in a liquid solution that contains metals like silver ions; metal oxides like copper oxide; or compounds of ammonium. The other way is to impregnate the threads themselves with these kind of antimicrobial agents. Some testers said that the clothing would not stink, but it did tend to get noticeably heavier the more times it was worn. Presumably from the accumulation of perspiration and cast-off skin cells.

The ISS solution of "rely upon resupply from Terra" for the clothing problem won't work for a Mars Mission. Terra will be too far away, so you'll have to carry all the required clothing. In and effort to reduce the clothing payload NASA commissioned the UMPQUA Research Company in 2011 to produce the Advanced Microgravity Compatible Integrated Laundry System. The prototype worked on a vomit comet test flight, but UMPQUA is trying reduce the unit's water and power supply requirements.

The Advanced Microgravity Compatible, Integrated Laundry (AMCIL) is a microgravity compatible liquid / liquid vapor, two-phase laundry system with water jet agitation and vacuum assisted drying.

Umpqua Research Company previously developed a complete microgravity compatible Single Phase Laundry System (SPLS). Single-phase operation during the wash cycle facilitated microgravity compatible fluidics and eliminated problems associated with foams. Pulsed water jets were utilized to agitate the clothing. Drying was achieved with microwave assisted vacuum drying followed by a tumble cycle that greatly enhanced softness in the previously vacuum pressed clothing. Tumbling was achieved by an array of three air jets, two to generate a cyclonic effect and a third to induce tumbling by blowing perpendicular to the plane of rotation. This concept was successfully demonstrated during a KC-135 microgravity simulation flight.

The proposed AMCIL concept will build on the SPLS technology and incorporate key design improvements to reduced water requirements and lower power consumption. Specific advancements include a redesigned wash cycle that consumes less water and reduces power demand.

The Phase I effort will demonstrate the feasibility of the microgravity compatible liquid / liquid vapor, two-phase washing concept in a laboratory scale system. A complete, automated prototype unit that incorporates the system parameters established during the Phase I tests will be designed, fabricated, and tested during the Phase II program.

Skirts or kilts are discouraged because [a] it is difficult to impossible to keep them in a modest position in free fall, and [b] if the decks are open gratings instead of solid floors, people on the next deck down will be treated to an up-skirt view. No panchira allowed.

NASA ISS astronauts wear clothes with lots of pockets and strips of velcro, as a handy place to carry gear.

In Larry Niven's Protector, the Belters of the asteroid belt spend most of their lives inside their space suit. They have a tendency to paint their suits in extravagant colors. One of the characters had Salvador Dali's Madonna of Port Lligat on the front of their suit. In an interesting psychological quirk, Belters also tend to be nudists when in a pressurized environment. This could also be a response to the difficulty of making clothing, or a reaction to the how expensive clothing is.

Shipping Clothing

I'd waived clearance while still under ascent thrust on our original trajectory to a 200-kilometer parking orbit. Our delta-vee margin was excellent even though the Tomahok was running with a full cargo bay of—would you believe it?—cotton underwear.

Clothing wears out, and we hadn't established any clothing industry in space yet. Spinning, weaving, dyeing, and tailoring are ancient technologies, but they were among the last to be adapted to the weightlessness of space. As for cotton, one of the Commonwealth's primary products, nobody has yet developed an artificial fiber quite as comfortable.

We had a lot of leeway in changing our flight path because the Tomahok had "bulked-out" before she "grossed-out"—the hold was filled long before maximum weight was attained.

From Manna by Lee Correy (G. Harry Stine) 1983

APPAREL. The clothing worn in most of the KNOWN GALAXY, at least that worn by EARTH HUMANS, is for the most part extremely dull, or in very bad taste. Usually both. At least, this is the case in HOLLYWOOD SCIFI, and so far as I can tell from book covers, in most written SF as well. The general norm, especially for advanced societies, is essentially long underwear; the most common alternative is a jumpsuit, equally unflattering and harder to get into or (especially) out of.  These may be tarted up - as in the era c. 2000 CE - with racing stripes, corporate-logo-style swooshes, and so forth. But no matter what you do to them, basically they are all butt-ugly. To be sure, a babelicious actress will still look good, especially since her outfit is invariably skin-tight and low-cut. But she'd look good in anything, and even better in a more flattering costume.

Things are slightly better when WARFARE is involved (which may be why it is so common). Uniforms tend to follow 20th century CE practice, more or less, and so are at least crisp if still basically long underwear. Original Trek did go boldly where no one has gone since, putting the female crew members in those miniskirts. Alas, the feminists did away with that. Their logic might be impeccable, as Spock would say, but 'tis still a pity.

The one social system in the Known Galaxy that allows people to actually look good is NEOFEUDALISM. In Neofeudalist cultures (at least in the ruling class), the men get to wear that most dramatic of male costume accessories, a sword, while the women are all a major eyeful in long, tight, low-cut dresses. There is simply no way to look better without looking tacky. This of course is achieved in the final, decadent stages of the FIRST EMPIRE, when the women - at least those of the Imperial Court - run around looking like the Victoria's Secret catalog. But when you see that much flesh on display, you know that the FALL OF EMPIRE is at hand.

On the whole, ALIENS WITH FOREHEAD RIDGES get to dress better than Earth Humans. The same odd rule applies as with Earth Humans, though; on the whole, the more civilized they are the worse they dress. In general, Space SF Apparel is in a bad way. Give us some help here, people! With at least billions, maybe trillions of intelligent, civilized beings throughout the Known Galaxy, someone ought to be able to come up with a few decent outfits.

From The Tough Guide to the Known Galaxy by Rick Robinson
Trope-a-Day: Space Clothes

Space Clothes: Averted; even in space, people just wear regular clothes. (Sure, they have lots of pockets, but that’s not specific to spacer culture.) The only difference is that the pure-skirt option is eliminated for both sexes (because microgravity), and the cloaks have to come with MEMS and occasional microfan thrusters to let them manage themselves as people move.

And spandex is not used for regular, day-to-day clothing anywhere. Even not in space.

Bootstrapping Clothing

 One of the basic necessities not yet mentioned is clothing.

 Most clothing is made, not surprisingly, of cloth. That in turn is made of woven threads, which are made either of plastic, animal hair or plant fiber.

 I'm going to eliminate animal fibers simply on an efficiency basis. The varieties of animals that are raised for fur (sheep, rabbits, goats, yaks) can also produce meat and milk, but are much less efficient than purpose-bred varieties. Sheep are probably the best all-round performers (~5.4kg wool per animal per year eating about 2kg/day of feed), but we can still do much better than that. Of course any incidental fur, skin, etc. will be used for filling, lining, leather and such, but we cannot assume there will be enough of that material to clothe everyone.

Read on for the rest. This turned out to require a lot more growing space than I would have thought, 10.26m² per person.

 Plastic has many benefits. Some routes to plastic production don't involve living organisms as a bottleneck. Others use byproducts of food production. Depending on the choice of plastic the resulting fabric can be quite strong, durable and chemical-resistant. Dyes can be incorporated directly into the fibers for simpler, more durable coloring. Plastics can also have drawbacks like static buildup or melting, and tend to be degraded by UV exposure.
 On Earth, the main clothing fibers are nylonpolyurethane (as Spandex), acrylicrayon and polyester. Nylon and polyurethane are fully synthetic, typically at the end of a long chain of processes that start with benzene. Acrylic is also fully synthetic, most commonly encountered as cheap knitting yarn. Rayon is a cellulose polymer that typically starts life as wood or bamboo fiber; it is considered semisynthetic even though it is just as heavily processed as nylon. Polyester refers to a family of plastics, some of which are found in nature. Notable polyesters include PET (PET as Dacron, BoPET as Mylar), Vectran and PLA.
 Notice that none of those are my favorite plastic, polyethylene. I suspect PE fabric for clothing would be uncomfortable, with no stretch and a slightly oily feel. Excellent as an outer layer in a protective garment but terrible for underwear.

 Plant fibers also have many benefits. Softness and durability are at the forefront. Natural fibers tend to withstand flexing better than synthetic fibers. These tend to char rather than melt. They also have a softer feel. On the other hand, natural fibers are more difficult to dye and can be more labor-intensive to produce.
 On Earth the main clothing fibers are cotton, flax (linen) and hemp. All three are grown for their fibers and seeds; the seeds can be eaten, milled into flour or pressed for oil. All three are suitable for hydroponic cultivation, mechanical harvesting and mechanical processing.

 Regardless of type, the various fibers are spun into yarns. Often the yarn is composed of several different fibers in order to combine desirable properties. For example, it is very common to include a few percent Spandex with cotton or nylon to produce a yarn with some elastic response.

 From yarn, some types of clothing are knitted directly. Machine-knit sweaters and socks are common. Other types require that the yarn is woven into fabric, which is then cut and sewn. One key variable is the weight of the fabric, typically specified in ounces per yard or grams per square meter. I'll be using GSM / grams per square meter. For example, a thin t-shirt might use 100 gsm material while a resort hotel might offer super-thick 800 gsm bath towels. I've used values below that are in the middle of the range for each fabric type.

 Fabric amounts are handled oddly in the US. People specify some number of yards of length, but often fail to mention that it's not square yards. Fabric is typically sold in widths of 45" or 60" (sometimes 32"). If a pattern calls for 2 yards of 45" fabric, that's actually 2.5 square yards. I've listed values below in square meters. I used a variety of sources; there was one excellent sewing blog with tables for the first three items, then I found a pattern for coveralls. For the bath and bedroom items I used actual dimensions, added an allowance for hems and converted to metric.

Typical fabric requirements:
pants, 1.5-4.2m² (2.5m² avg.) x 250gsm = 625g
shirt, 0.7-3.4m² (2m² avg.) x 150gsm = 300g
dress, 1.3-7.7m² (3m² avg) x 200gsm = 600g
coveralls, 4.3-6m² (5.3m² avg.) x 350gsm = 1855g
sheet (queen): 6m² x 150gsm = 900g
sheet (full): 5m² x 150gsm = 750g
blanket (single-layer fleece): 7m² (90x110"/ 230x280cm) x 350gsm = 2450g
quilt (2-layer without filling): 14m² (90x110"/ 230x280cm) x 200gsm = 2800g
pillowcase: 1.4m² x 150gsm = 210g
napkin: 0.4m² x 200gsm = 80g
towel (face / washcloth): 0.1m² x 350gsm = 35g
towel (hand): 0.4m² x 350gsm = 140g
towel (bath): 0.9m² x 500gsm  = 450g (also worth a read)

 Let's assume each person has a full set of bedding and bath linens, a blanket, a napkin and one week of clothing. The linens come to 20.2m² of various weights, 4.865kg. Clothing depends a lot on the person's size, preference and occupation; I will add the first four values and divide by three to get an 'average' mass for a day's clothing. This is likely to be high as I doubt that a third of the crew will need heavy denim coveralls for daily work. Still, that comes to 29.9m² or 7.887kg for seven outfits. That's 12.75kg in total; add a bit of leeway for knits and undergarments (~1.5kg), thread, sizing, etc. and call it 15kg per person. Specifics may differ; I'm assuming a full-size bed and all single people. A couple could use the same sheet and bathroom set. A more regimented facility might use Navy-style hot bunks and hot air drying after bathing to cut most of the linens. I suppose wealthy tourists might want more amenities.

 These things wear out. Socks and undergarments typically last perhaps half a year. Outerwear lasts 1-3 years depending on circumstances, so let's use one year. Bedding and bath items can last many years, but let's call it three. Heavy-duty work outfits like denim coveralls might last a decade or might wear out in three months; call it one year. On an annual basis using these numbers each person needs about 12.5kg of replacement fabric. These estimates are a bit conservative; many people replace their clothing far less often than this and only when they are actually worn through. I assume that the 'replaced' garments may not necessarily be discarded and people may simply build up a wardrobe over time. Sufficient space could be available to store 2-3 weeks worth of clothing, while worn or damaged pieces would be used as rags or as fiber sources for filter paper.

 Let's look at yields. I simply don't have enough information available to predict the material requirements for plastics, so this will focus only on natural fibers.

 Cotton can be grown at 1000-1500 lb per acre in open fields. In a hydroponic environment with no pests and tight nutrient control it should be possible to significantly exceed that mark, but let's use 1500lb/ac for this estimate. 4047m² per acre gives us about 0.37lb per m² or about 168g/m². Estimates range from 150-180 days for a growth cycle, so let's use 165 days. That works out to almost exactly 1 gram per square meter per day. Each person needs 34.25 grams per day, which would require 34.25m² per person. If we use a record yield of 6.31 bales per acre, that would be 3,536kg/ha or 354 grams per m² or 2.15g/m² per day > ~16m² per person. Seed production is about 1.62 x cotton production, or 3.48g/m² per day.
  Flax can be grown to yield over 1800kg/ha or 186g/m². Growth cycle is 90-125 days (in Canada), so we will use 108 days. That gives 1.72g/m² per day or 19.89m² per person.
 Hemp has yielded 6 tonnes of fiber per hectare or 600g/m² (again, Canada). Growth cycle is 70-90 days for fiber only (80) or 110-150 days (130) for dual crop. Using the dual crop number we get 4.62g/m² per day or 7.4m² per person. Seed production is about 0.7g/m² per day.

 Based on those numbers it sounds like a mix of 2:1 hemp and cotton would be ideal. That would be 4.93m² per person of hemp and 5.33m² per person of cotton to produce a total of 12.5kg of fiber. The process would co-produce about 1.25kg of hempseed and 6.77kg of cottonseed plus another few kg of plant waste.

It's worth mentioning that the record land yields tend to be twice the high averages, if not more, for most crops; even so, hydroponic methods can often surpass the record yields simply by preventing stress. Crops that have not been optimized for performance (like flax and hemp) have the potential to double or triple their yields given a dedicated breeding project. Have a look at dwarf rice and wheat yields vs. the varieties that existed before the 60's for an example of this in action. In other words, within a decade any number I post here will be obsolete as long as someone is actively developing the potential of these species. I think a combination of longer 'useful life' assumptions for clothing and improved hydroponic yields could cut the required area down below 3m² per person. That research and breeding could be applied to commercial crops on the ground, providing improved incomes for farmers around the world.

Bamboo has bast fibers, similar to flax and hemp. Most things referred to as 'bamboo fiber' are actually rayon made with bamboo as a feedstock, but true bamboo fiber is possible. The raw material is high in lignin, so processing is often a combination of mechanical chopping and chemical or enzyme boosted bacterial retting. Lots more details here:

The tenacity of those fibers is less than half that of cotton. The resulting cloth won't be as durable or tough, but still falling between wool and rayon. That is to say, still useful and with a reportedly pleasant feel.

The yield of bamboo basts can be as high as 53 tonnes per hectare (5.365kg/m² or 14.7g/m² per day). As long as the net fiber yield is at least 15% of the gross bast mass then it is competitive with cotton. If it is over 31% then it is competitive with hemp.

yield source:

If we look back a ways (1909), at least one author noted yields as high as 44 tons per acre (an eye-popping 98.6 tonnes per hectare) and fiber yields as high as 44%.

source: Congressional Serial Set: pulp and paper investigation hearings. 1 January 1909. (available free)

Let's go with the modern optimistic yield (while noting that high-intensity hydroponics can almost certainly double that value) and a fiber yield of, say, 38%. That would give a fiber yield of 5.6g/m² per day or about 6.1m² per person. The plants require a three-year lead time and a third of the stand is harvested each year. Waste from this process would be suitable for paper or fuel alcohol.

I think the main drawback would be that bamboo grows very tall. A dwarf species could be found that grows to 4m after three years, but it's not certain the yield numbers would still apply. Even so, that's about 25m³ per person. Cotton by contrast grows to perhaps 130cm. Allowing 20cm for lighting and nutrient systems, that same 4m space could house two stacked crops. If a mild dwarf variety of cotton was developed that matured to 110cm or less, three stacked crops could occupy the same space and would become competitive again on a floor-space and volume basis.

Another drawback is that bamboo requires several years to develop for this purpose. Peak fiber yields occur at three years. Peak structural strength is typically seen around 5 years. For paper pulp or wattle it can be taken at 1-2 years.

Those drawbacks are certainly opposed by several advantages unique to bamboo. It's a structural material, can be used similar to wood (buttons, flooring, furniture) and resists bacterial and fungal attack. Bamboo resists high-pH environments and can be embedded in concrete; it could serve as the tension member in a reinforced regolith-block construction if metal is scarce.

John Powell: Beta cloth is also a good candidate for durable outer wear. It's non-flammable, completely recyclable and made from silica fibers, a major component of lunar regolith. The Apollo/Skylab spacesuits used it.

Chris Wolfe: Excellent idea. I'd probably not want to wear that against the skin and there's a potential inhalation hazard from shed fiber fragments, but as an outer layer with heat and chemical resistance it would be very useful for engineering coveralls. Equipment to make silica fibers would also be useful for making rockwool insulation and rooting media.

From Boostrapping Space: Clothing by Chris Wolfe (2015)

Solar Power Stations

Solar Power
PlanetSol Dist
☿ Mercury0.3876.6779,121
♀ Venus0.7231.9132,613
⊕ Terra1.0001.0001,366
♂ Mars1.5200.433591
⚶ Vesta2.3620.179245
⚵ Juno2.6700.140192
⚳ Ceres2.7680.131178
⚴ Pallas2.7720.130178
♃ Jupiter5.2000.03751
♄ Saturn9.5800.01115
♅ Uranus19.2000.0034
♆ Neptune30.0500.0012

Space-based solar power (aka "Powersat") is one of those concepts that make one think about idealistic hippy futurists in the 1970's drunk on the idea of MacGuffinite that is also ecological and green. It is solar energy on steroids. By placing the solar collectors in orbit you get all the solar energy since ground based solar collectors can only gather the frequencies that our atmosphere is transparent to, and are hampered by rain clouds and/or the fact that it is nighttime.

You can get almost unlimited amounts of green energy: no nasty coal, oil, natural gas, or uranium is required. Groovy, man!

The fact that none of these exist today tells you that the difficulties are overwhelming.

At Terra's orbital distance from Sol the solar power flux is abotu 1,366 watts per square meter. Due to the inverse square law the power increases the closer you get to Sol (see table). And vice versa as well.

But we do not care about such stations, since other than being a species of MacGuffinite, it has nothing to do with spacecraft, right?

Au contraire! Read on to see how solar power stations can be a boon to spacecraft.

Beamed Power

Let me take a minute to talk about solar moth rockets.

Remember the fundamental rule of rocket design: Every Gram Counts. The motivation behind the solar moth is "just imagine how much mass we could save if we eliminated the rocket engine from the design! Using the "magnifying glass incinerating an ant" principle, the solar moth utilizes a large mirror to focus the heat from the sun on the propellant, energizing it so it rushes out the exhaust bell, resulting in thrust.

It is a pity that solar energy is so diffuse around Terra's orbit. To really get worth-while amounts of heat, the solar moth will need huge mirrors. Which sort of eliminates the mass advantage of removing the engine.

That's where the powersat comes in. Have a powersat send power in a beam of microwaves and give the solar moth a microwave rectenna to receive the electrical energy! You will be using Beam-powered propulsion. The electricity can be used to heat the propellant. Suddenly your pathetically weak solar moth will be a super-powered muscle machine.

This will also work nicely with ion-drive, VASIMR, or other electrically powered propulsion. The nuclear power plants required have a huge mass penalty, this would eliminate that problem. Some comedian joked that the main problem with ion drives is designing an electrical extension cable millions of miles long. Well, using beamed power this is pretty much the same thing.

Microwaves are difficult to focus, and the conversion from electricity to thermal energy has unavoidable inefficiencies. It would be nice to beam thermal energy instead of electrical energy. Can do: replace the microwave with a laser! Now you can use the same lightweight mirror on a solar moth, but with the much more intense radiant energy of a laser. It will be a laser thermal rocket. You can also use it on a solar sail craft and make it into a high-powered laser or photon sail. The advantage is that your delta-V capacity will be incredibly large. The disadvantage is that you are at the mercy of whoever owns the powersat.

If your laser thermal rocket is renting laser time from Beams-R-Us, you better make sure that your bill is paid up. Otherwise they will pull the plug and your rocket will suddenly be powerless, and on a one-way ticket to nowhere. You might be able to limp along using solar power instead of the laser from Beams-R-Us, but I would not bet your life on it.

And make sure you stick closely to the flight plan you filed with Beams-R-Us, or they might have a problem keeping the beam aimed at you.

Beams-R-Us might purchase their own laser thermal or laser sail ships. They will then be like a rail-road company, owning both the trains and the rails they run on.

As a matter of fact, the solar collector on the powersat will be much more effective if it was closer to the sun than Terra's orbit. Say: the orbit of Mercury. Now we're cooking!

Beam Power and Range

The report Fusion Energy for Space Missions in the 21st Century had an informative analysis on a proposed beam-powered spacecraft system, tucked away in Appendix B: An Alternative Strategy for Low Specific Power Reactors Powering Interplanetary Spacecraft, Based on Exploiting Lasers and Lunar Resources.

If you are in a hurry, skip to the end of this segment to see the chart showing laser power and range.

They started by examining a standard mission to Mars, and how chemical propulsion resulted in travel times that would exceed the astronaut's career limits on radiation exposure. Cyclers (with their more massive levels of radiation shielding) were rejected as a solution because they force the round trip periods to be inconveniently long four-year cycles.

A better solution would be a more powerful rocket engine. One that was strong enough to reduce the trip time so that the radiation dosage would be acceptably low (even with the spacecraft's lower level of radiation shielding).

The analysis assumed a radiation dose limit of chronic 5 rem/year (0.05 sievert) and acute 25 rem/incident (0.25 sievert). It assumed that spacecraft radiation shielding would still result in an exposure of 0.1 rem per day (0.001 sievert). This means that the astronauts would receive 25 rems in only 0.7 year (250 days).

So the spacecraft would have to be capable of making a round trip to Mars in only 0.7 year. Of course this means the astronauts will have to retire at the end of the mission.

The report then starts looking at a 0.33 year (4 month) one-way mission. This would only result in a radiation exposure of 12 rem (0.12 sievert). It would require the engine to have a minium specific power (αp) of 10 kWe/kg (ten kilowatts of electrical power per kilogram of engine). How they arrived at that figure is a bit complicated, see the report for details.

For a 1,000 metric ton initial vehicle mass the engine would need about 129 MWe output (engine mass of 12.9 metric tons at 10 kWe/kg)

The little NASA spacecraft in the center of the diagram receives beam power from an inflatable foil mirror focused on a photocell receiver.

The inflatable foil mirror has a diameter of about 1,000 m (one kilometer!) and an areal mass of 10-2 kg/m2. A=πr2 so the mirror has a surface area of about 785,000 m2. Times the areal mass means the foil mirror has a mass of about 7,850 kilograms (7.9 metric tons).

The photocell receiver has a diameter of about 100 m and an areal mass of 1 kg/m2. 7,850 m2 and a mass of 7,850 kilograms. In case you are interested, this represents a diamond film semiconductor 100 μ thin film voltalic array along with support structure. The dark non-laser side has heat radiators to get rid of the 10 kWth/m2 waste heat (see below).

We want the mirror+photocell combo to have a specific power of 10 kWe/kg for our 4 month Mars trip.

Each square meter of photocell is fed by 100 square meters of mirror. 1 square meter of photocell has a mass of 1 kg. 100 square meters of mirror has a mass of 1 kg. So each square meter of photocell represents 1 + 1 = 2 kg worth of mirror+photocell.

So in order for the mirror+photocell to have αp=10 kWe/kg, each square meter of photocell needs to be fed 20 kW of laser light. 20 kW divided by 2 kg equals the desired 10 kW/kg.

But that is only if the photocells were 100% efficient at converting laser light into electricity. The report assumes they are actually only 70% efficient (with an ultraviolet laser beam with a wavelength between 100 and 200 nanometers). Therefore they will need 30 kW/m2 of laser light (20 × 0.70) in order for αp=10 kWe/kg. In case of emergency, the diamond film semiconductor photocell can use solar energy at about 2% efficiency. This would probably be about 0.2 kWe/m2 at Terra orbit, raw solar energy is about 1.366 kW/m2.

The inflatable foil mirror probably has an efficiency of about 90%.

Since the 30 kW of laser power fed to each square meter of photocell comes from 100 square meters of foil mirror, each square meter of foil mirror needs to feed 30,000 W / 100 = 300 W of laser light to the photocell array.

The point of all this is that the specified NASA spacecraft needs the incoming laser beam to have a power density of 300 watts per square meter and have a spot size of at least one kilometer in diameter.

Unlike the diagram above, the report is of the opinion that it makes more sense to base the laser station on Luna instead of Terra. Lack of atmosphere (so you can use laser beams in the vacuum frequencies, like ultraviolet c), and access to Lunar Helium-3 for fusion plants (though that is more or less a Chimera). And it would also work on a Solar Power Station.

Desired characteristics:

  • 100 megawatt-level high average power
  • High conversion efficiency (20% to 40%)
  • High specific power (≥1 kWe/kg)
  • Tunability to any desired wavelength (Free Electron Laser)
  • Laser intensity at emitter 100 kW/m2

You want to use a free-electron laser so the beam frequency can be tuned. This allows laser to be adjusted to wavelength optimal for the photocell receiver of that particular spacecraft.

Laser intensity at emitter 100 kW/m2 in order to balance beam losses using optical coatings with radiative cooling.

The emitter would be large, to limit diffraction losses and to allow adequate cooling (otherwise intensity becomes too many kilowatts per square meter and the emitter melts). Probably an array of thin hexagonal wafer mirrors, each supported by three computer controlled actuators. It would have an areal mass of about 40 kg/m2.

Note that these specs are for a single laser emitter that might be dedicated to a Mars mission for four months. Beams-R-Us will probably have an antenna farm full of these lasers. The more lasers, the more clients they can service simultaneously. More clients can be added by, say, having a given laser alternate boost periods between two clients. Scheduling might become tricky.

As previously mentioned, the astromilitary will be alarmed at the prospect of civilian ownership of huge batteries of ship-killing laser death-ray turrets. There might be a move to put Beams-R-Us under military control.

Given the lunar-base transmitter intensity of 100 kW/m2, and the spacecraft photocell receiver needing 30 kW/m2 of laser light, it is possible to make an equation relating the average laser power PL and the range between transmitter and receiver R. If you are going to change either of those variables the equations will need tinkering with.

Well, if you were running Beams-R-Us, you'd want to know how much energy each laser will require, and the maximum range a customer can be at, wouldn't you?

The other main variable is on the spacecraft, the ratio of the diameter of the inflatable foil mirror Dr to the diameter of the photocell receiver Df. The ratio is Dr/Df.

Dr = diameter of inflatable foil mirror
Df = diameter of photocell receiver
Dr/Df = ratio of mirror diameter to photocell diameter (10.0 in our sample ship)
R = range
λ = laser wavelength
PL = average laser power. Note in first two equations this is in watts, in third it is megawatts (200 MW in our sample ship)
3×104 W/m2 = 30 kW/m2, needed laser energy density at photovoltaic array
0.9 = efficiency of inflatable foil mirror (90%)
x1/2 = square root of x

So for the first equation:

Dr = (Dr/Df) * sqrt((4/π) * ((0.9 * PL)/(3×104)))

Dr = 10.0 * sqrt((4/π) * ((0.9 * 2×108)/(3×104)))

Dr = 870 m ≈ 1000 m diameter of inflatable foil mirror

Second equation:

Df = sqrt((4/π) * ((0.9 * PL)/(3×104)))

Df = sqrt((4/π) * ((0.9 * 2×108)/(3×104)))

Df = 87 m ≈ 100 m diameter of photocell receiver

Third equation is used to draw the chart below. Each diagonal λ line is plotted by choosing a constant value for λ then stepping along the X-axis with various values for R, using R and λ to calculate the Y-value PL

Given the requirement of a 1,000 metric ton initial vehicle mass on a Mars 4 month mission needing an engine with 129 MWe output, an inflatable foil collector with an efficiency of 90% and a photocell receiver efficiency of 70%, the required UV laser beam power is 200 MW. 129 / (0.9 * 0.7) ≈ 200 MW.

As indicated on the chart by dotted lines, the intersection of the Mars trip line and the λ=0.16 μM (UV) line is at the 200 MW average laser power point. Longer wavelengths would require a higher laser power, or several laser stations enroute to decrease the range requirement. A laser station on, say, Phobos would cut the range requirement in half. The ship would use a laser station based on Luna up to the half-way point, then switch to Phobos station.

Power Beaming Equations

Power beaming is clearly central to space-based solar power concepts. Here I will provide a quick overview of my understanding of power beaming, the various equations involved, typical example calculations.

If power beaming were efficient and cheap, I believe space-based solar power would be quite viable even for grid power. However it’s not, and that largely has to do with the distances involved AND the fact that you need to convert energy multiple times, with losses along the way. The distances involved aren’t a complete show-stopper, since you can solve that problem just by operating at a large enough scale. However, the conversion inefficiencies (and the need to dump waste heat, etc) is not going to go away simply by operating at greater scale (although it helps).

The first equation we need is the diffraction limit. Roughly speaking, the spot size of a transmitted beam (microwave or laser) is:

Spot size = distance-to-spot * wavelength / (aperture diameter)

This is close enough for an order-of-magnitude estimate. More detailed work to follow.

But if we have a satellite out in Geosynchronous orbit (36,000 km altitude) transmitting power at roughly 10GHz (3cm wavelength, the shortest wavelength that still penetrates readily through the atmosphere) with an antenna 300m in diameter (NRO SIGINT/ELINT satellites are rumored to be that big, but maybe only around 100m in diameter), you’d have a spot size on the order of:

3.6×107m * 3×10-2m / (3×102m) = 3.6×103m or 3.6 km in diameter

…turns out that not all the energy of your beam is contained in this diameter (“Where’s that factor of 1.22,” you cry), but that’s a halfway decent start (and you’d need an infinitely wide aperture to collect all the energy in the beam…). 3.6km is obviously huge. The biggest full-aperture dish ever built is the half-way finished Chinese Arecibo clone at 500m. Still, there are ways to tweak this.

With a laser operating at 1micron, in medium-Earth-orbit (10,000 km) with 1 meter diameter optics needs only a:

1×107m * 1×10-6m / 1m = 10m diameter receiver to receive the vast majority of the beam’s energy. This is much, much better, obviously. You could put a 10m diameter receiver on top of a tethered airship or drone or something that allows you to transmit it to the ground without interference from clouds.

Or heck, use it to power high-altitude aircraft… but that’s a whole ‘nother blog post! (And suffice it to say, there are lots of caveats about laser transmission of energy, too.)

From Power Beaming by Chris Stelter (2015)

Power beaming stations might well be dual purpose, the space age equivalent of the military frontier posts of the American west.

The military purpose would be to protect Earth from infalling asteroids or whatever military threat develops in deep space, but they pay for themselves by beaming power to cooperative targets like friendly shipping or energy receivers mounted on NEOs. Unless there is a red alert, shipping takes priority and even if the beam is interrupted, the ships continue to coast on predictable orbits and can be picked up after the interruption is resolved (repairs made, asteroid vapourized etc.)

Life in Fort Heinlein revolves around maintaining the solar energy arrays and maintaining the tracking systems, and life will be pretty tedious. Daily routine includes system checks and battle drills, and screw-ups get to go out and polish the mirrors under the first sergeant's unforgiving gaze. A secondary economy of service providers (saloons and whorehouses) will grow around the "fort" to service the crew, and other business might set up shop as well, everything from contractor repair depots to futures traders monitoring ship traffic and energy consumption.

Lightweight ships tapping into this system have torch like performance, economy traffic might go by cycler (although the "taxis" might need torch like performance to match the cycler or slow down to orbital velocity after dropping off) and bulk traffic will still go by low cost transfer orbits.

Laser Power Transmission

This and similar proposals on power and propulsion generated a great deal of speculation and study in the 1970s. These activities, although generally incomplete and sometimes contradictory, identified several themes:

  • Lower cost power and propulsion is key to the development of near-Earth space.
  • Solar- and nuclear-powered lasers have the characteristics for high payoff in space applications.
  • Expensive transportation applications show high potential for cost reduction through the use of remote laser power.
  • Economical power beaming in space requires multiple customers who cannot use available (solar photovoltaic) power sources.
  • High laser conversion efficiency is a key power-beaming challenge.
  • NASA laser power requirements are very different from those of DOD and DOE, but NASA can benefit from the breadth of basic research generated by the programs of other agencies.

From the studies, then, a general set of requirements are emerging for beaming power by laser to currently envisioned space missions. First, the laser must be capable of long-term continuous operation without significant maintenance or resupply. For this reason, solar- and nuclear-powered lasers are favored. Second, the laser must supply high average power, on the order of 100 kW or greater for applications studied so far. For this reason, continuous wave or rapidly pulsed lasers are required.

Since solar energy is the most available and reliable power source in space, recent research designed to explore the feasibility of laser power transmission between spacecraft in space has focused on solar-pumped lasers. Three general laser mechanisms have been identified:

  • Photodissociation lasing driven directly by sunlight
  • Photoexcitation lasing driven directly by sunlight
  • Photoexcitation lasing driven by thermal radiation

Solar-Pumped Photodissociation Lasers

Several direct solar lasers based on photodissociation have been identified, including six organic iodide lasants that have been successfully solar pumped and emit at the iodine laser wavelength of 1.3 micrometers. (See figure 40 for a possible application of such a laser.) Another lasant, IBr, has been pumped with a flashlamp and lased at 2.7 μm with a pulsed power of hundreds of watts. One organic iodide, C3F7I, and IBr have been investigated intensively to characterize their operation. Several reports on experimental results and modeling have been published. An important characteristic of the photodissociation lasers under consideration is that they spontaneously recombine to form the lasant molecule again. Both C3F7I and IBr do this to a high degree, permitting continuous operation without resupplying lasant, as is generally required for chemical lasers. In addition, C3F7I absorbs almost no visible light and thus remains so cool that it may require no thermal radiator except the pipe that recirculates the lasant. A variety of other lasants offering increased efficiency are under study.

Solar-Pumped Photoexcitation Lasers

Another group of direct solar-pumped lasers rely on the electronic-vibrational excitation produced by sunlight to power the laser action. Two systems are being actively studied. The first is a liquid neodymium (Nd) ion laser, which absorbs throughout the visible spectrum and emits in the near-infrared at 1.06 μm. This lasant has lased with flashlamp pumping and is currently being tried with solar pumping, since calculations indicate feasibility. A second candidate of this sort is a dye laser, which absorbs in the blue-green range and emits in the red, near 0.6 μm. These lasers offer good quantum efficiency and emission that is both of short wavelength and tunable. However, the lasers require extremely high excitation to overcome their high threshold for lasing, and the feasibility of achieving this with concentrated sunlight is still a question for further research.

Indirect Photoexcitation Lasers

Photoexcitation lasers driven by thermal radiation produced by the Sun are termed indirect solar-pumped lasers. The lower pumping energy implies longer wavelength emission than with photodissociation lasers. Two lasers, the first blackbody-cavity-pumped laser and a blackbody-pumped transfer laser, work on this principle. Molecules such as CO2 and N2O have lased with emission wavelengths between 9 μm and 11 μm. These lasers are inherently continuous wave and have generated powers approaching 1 watt in initial laboratory versions, with blackbody temperatures between 1000 K and 1500 K. While such lasers, powered by solar energy, may be used in space, they also offer great potential for converting to laser energy the thermal energy generated by chemical reactions, by nuclear power, by electrical power, or by other high- temperature sources.

From Laser Power Transmission by Edmund J. Conway. Collected in Space Resources NASA SP-509 vol 2

The laser power needed to accelerate the 82,000 ton interstellar vehicle at one percent of earth gravity was just over 1300 terawatts. As is shown in Figure 5, this was obtained from an array of 1000 laser generators orbiting around Mercury (which has 6.7 times the solar flux compared to Terra's orbit). Each laser generator used a thirty kilometer diameter lightweight reflector that collected 6.5 terawatts of sunlight and reflected into its solar-pumped laser the 1.5 terawatts of sunlight that was at the right wavelength for the laser to use.

When fed the right pumping light, the lasers were very efficient and produced 1.3 terawatts of laser light at an infrared wavelength of 1.5 microns. The output aperture of the lasers was 100 meters in diameter, so the flux that the laser mirrors had to handle was only about 12 suns. The lasers and their collectors were in sun-synchronous orbit around Mercury to keep them from being moved about by the light pressure from the intercepted sunlight and the transmitted laser beam.

The 1000 beams from the laser generators were transmitted out to the L-2 point of Mercury where they were collected, phase shifted until they were all in phase, then combined into a single coherent beam about 3.5 kilometers across. This beam was deflected from a final mirror that was tilted at 4.5 degrees above the ecliptic to match Barnard's elevation, and rotated so as to always face the direction to Barnard.

The crew to construct and maintain the laser generators were housed in the Mercury Laser Propulsion Construction, Command, and Control Center. The station was not in orbit about Mercury, but hung below the "sunhook," a large ring sail that straddled the shadow cone of Mercury about halfway up the cone.

The final transmitter lens for the laser propulsion system was a thin film of plastic net, with alternating circular zones that either were empty or covered with a thin film of plastic that caused a half-wavelength phase delay in the 1.5-micron laser light. (During the deceleration phase, when the laser frequency was tripled to produce 0.5-micron green laser light, the phase delay was three half-wavelengths.) This huge Fresnel zone plate acted as a final lens for the beam coming from Mercury. Since the focal length of the Fresnel zone plate was very long, the changes in shape or position of the billowing plastic net lens had almost no effect on the transmitted beam. The zone plate was rotated slowly to keep it stretched and an array of controllable mirrors around the periphery used the small amount of laser light that missed the lens to counteract the gravity pull of the distant Sun and keep the huge sail fixed in space along the Sun-Barnard axis.

From ROCHEWORLD by Dr. Robert E. Forward
The Pirates of Rosinante

(ed note: this is a laser thermal rocket energized by powerful lasers on an L5 colony)

The next item on the agenda was the laser-powered high-acceleration tug, otherwise referred to as the ultra-fast optical system, UFOS having more dash and elan than LPHAT. Corporate Susan made the presentation it had worked up with Skaskash and Lady Dark.

"The basic idea isn't bad,” said Cantrell. “How would you keep the lens oriented normal to the laser when you start to move the engine to a different orientation?"

"We have a pair of pipes at the equator of the sphere, pumping water in opposite directions,” said Corporate Susan. “Also, inside the sphere, under the photovoltaic surface, are two pairs of circular loops, set flush with the surface and at right angles to each other. Each pair pumps water in a counterrotary direction. The pumps are all controlled, so the UFOS is gyroscopically stabilized in three planes."

"I see,” Dornbrock said. “How do you move the engine around on the surface of the geodesic sphere?"

"The sphere rests on this little egg cup here,” said Corporate Susan. “The egg cup is a plastic perforated surface. When we want to move, we pressurize the surface, and the geodesic sphere floats on an air cushion. Then the mechanical hands around the perimeter of the egg cup orient the engine while the sphere stays put, or the engine stays put and the hands reorient the sphere, depending on how you work the gyroscopic pumps."

"Wouldn't you lose a lot of air pressurizing the perforated surface?” Corporate Forziati asked.

"No, actually,” Corporate Susan replied. “We have built a little valve into each perforation which only operates when the surface is depressed by the weight of the element of the sphere in contact with it.” A diagram flashed on her telecon screen for a moment.

"Thank you,” Forziati said. “And when you are not under thrust, weight is no problem and you don't pressurize. Very good."

"On the other end of the egg cup,” Bogdanovitch said, “where you have the engines and the tanks for the reaction mass, you have a long cable supporting the warship. Couldn't you have the ship on an egg cup, too?"

"No,” Corporate Susan replied. “The engines are thrusting against the geodesic sphere, which rests on top of the egg cup. The warship must keep its center of mass in line with the axis of thrust. Put it on the sphere with its own egg cup, and it would have to stay lined up with the engines—on the other side—which means the sphere would have to be built stronger, and heavier."

"And it would get in the way of the big laser beam,” Cantrell added.

"Then how does the warship stay out of the jet of ions?” asked Bogdanovitch.

"It rotates at the end of its cable,” said Corporate Susan, “and makes a little circle around the jet of uranium ions which provide the main thrust. The jet of boron and hydrogen is flared off, simply to provide electrical neutrality, but it also provides a tiny bit of thrust, which can be used to offset the wobble the ship would otherwise cause by swinging around the main jet."

"I don't understand,” Marian said.

Corporate Susan dissolved into a diagram. “Consider the vector diagram of the force exerted by the cable supporting the ship,” said the computer. “Most of it runs through the axis of thrust, but there is a small component going at right angles to that thrust. The boron and hydrogen, flared off with the excess electrons from the decaply ionized uranium, can be adjusted to exactly balance that small component. The flare—a very soft jet—would be in the same plane as the ship, and pointing in the same direction, to push where the ship is pulling."

"The jet—the flare, I mean, turns with the cable?” asked Marian.

"Of course,” said Corporate Susan.

"Orange and green,” said Marian. “Very pretty. What color is the uranium jet?"

"Hard X-ray,” Skaskash said. “It would probably be dangerous for two or three hundred kilometers."

"That might be an idea whose time has come,” Cantrell said at last. “Any more questions? No? Shall we build it? ... It seems to be unanimous."

"I have a model at the shop you can use. I'll have the changes you wanted put on, and you can use that, if you want."

"How big is it?"

"Not big—” Ilgen stretched his arms. “Maybe a meter and a half. Did you decide what ship you wanted with it?"

"The Alamo. We need to impress people, and the Alamo is the biggest thing we've got."

"Right, Charlie. I'll throw in a model of the Alamo to the same scale. The UFOS plus the Alamo figures to go seven to eight times as fast as any cruiser."

Cantrell whistled softly.

"I'll tell the Navy,” he said. “That ought to make them very happy."

From The Pirates of Rosinante by Alexis Gilliland (1982)
Early Days - economics of private space services

Last on my list is beamed power, which arguably does not belong in an 'early days' roundup. The usual example is a solar power satellite network beaming power down to the surface. Other uses include long-range power (probably laser) to a vehicle or satellite for propulsion and short-range power (probably RF) between a carrier satellite and payload cubesats or other small craft.

The SPS concept has been thoroughly explored over the decades. All necessary technologies exist and have been demonstrated. Environmental impact studies have been performed. The main barrier now is launch costs, which can be overcome by low-cost reusable LVs and / or the use of material harvested in space. As long as human civilization continues to use electricity there will be a market for SPS power on the surface. As the impact of human-induced climate change grows, the demand for power that does not threaten our species will continue to grow.

This kind of baseload power is further into the future but there are near-term applications. In particular, electric space tugs would benefit from a constellation of modest-sized SPS craft. Instead of carrying large solar panel arrays, a tug could carry just the rectenna and power conditioning equipment necessary to receive beamed power. This hardware would be lighter and much more resistant to radiation, allowing for a longer service life for LEO-GEO tugs. The reduced mass would make the tug more fuel-efficient, while a proper network of satellites would allow full-time operation of the tug's ion engine without requiring large battery packs. This same network of satellites could provide peak power to other assets with intermittent high power demand, particularly to a low-orbit space station that periodically does energy-intensive materials processing or uses electric engines for reboost / CAM. A further set of customers might include satellites intended only for short missions; formation flights of cubesats for example would benefit from requiring a smaller mass (and lower price) of rectenna than they would have required in solar panels.

A 'retrofit' option would be an SPS network that beams power using IR or visible lasers rather than RF. The specific frequency would be one that solar cells can efficiently convert. The SPS would simply lase the solar panels of the client craft, providing power when the sun is not available or increasing power while the craft is lit. This is significantly less efficient than RF but it would work on existing satellites and at longer ranges.

Spacecoaches and Beamed Power

The spacecoach is a design pattern for a reusable solar electric spacecraft, previously featured on Centauri Dreams here and developed in A Design for a Reusable Water-Based Spacecraft Known as the Spacecoach (Springer Verlag), which I wrote with Alex Tolley. It primarily uses water as its propellant. This design has numerous benefits, chief among them the ability to turn consumables, ordinarily deadweight, into working mass.

The recent announcement of the Breakthrough Starshot project, which aims to use beamed power to drive ultra lightweight lightsail probes on interstellar trajectories, is of note. This same infrastructure could be used to augment the capabilities and range of spacecoaches (or any solar electric spacecraft), while providing a near-term use for beamed power infrastructure as it is developed and scaled up.

The spacecoach design pattern combines a medium sized solar array (sized to generate between 500 kilowatts and 2 megawatts of peak power at 1AU) with electric propulsion units that use water as propellant (and possibly also waste streams such as carbon dioxide, ammonia, etc). We found that, even when constrained to these power levels, they could fly approximately Hohmann trajectories to and from destinations in the inner solar system. Because consumables are converted into propellant, this reduces mass budgets by an order of magnitude, and effectively eliminates the need for an external interplanetary stage, all while greatly simplifying the logistics of supporting a sizeable crew for long duration missions (more consumables = more propellant).


The primary constraint for space coaches, especially if you want to travel to the outer solar system, is available power. This is an issue for two reasons. First, solar flux drops off by 1/r2, so at Jupiter, a solar array will generate roughly 1/25th the power as it does at Earth distance. Second, trips to more distant locations will typically require a greater delta V (and thus higher exhaust velocity to achieve this with a given amount of propellant). The amount of energy required to generate a unit of impulse scales linearly with exhaust velocity, so the net result is the ship’s power requirements are increased, all while the powerplant’s power density (watts per kilogram of solar array) is decreased.

Testing Beamed Power

Beamed power infrastructure would enable space coaches and solar electric spacecraft in general to operate at higher power levels for a given array size, which would enable them to operate at higher thrust levels, and to utilize higher exhaust velocities to maximize delta V and propellant efficiency. This means they would be able to accelerate faster, achieve higher delta-v, while using less propellant. In effect beamed power to SEP spacecraft will give their operators the equivalent of a nuclear electric power plant (without the nukes).

A spacecoach built for solar only operation would be able to serve as a testbed for beamed power. For example, a space coach departing Earth orbit could be illuminated with a beam that increases its power output by a small amount, say 10% (large enough to make a measurable difference in performance, yet small enough that major modifications are not required to the ship as it just experiences slightly brighter illumination while in beam). At higher light levels, this technique could also be used to simulate lighting and heat loading conditions expected at the inner planets while remaining in near Earth space. Note also that lasers can be tuned to the absorption wavelength(s) of the photovoltaic material, greatly improving conversion efficiency (and reducing heat gain per unit of power delivered). An even cheaper way to build out and test power beaming infrastructure will be with satellites and probes that utilize solar electric propulsion.

The pathway to a system based primarily on beamed power then becomes one based on incremental improvements, both for the ground based facilities and for the ships. This would result in near term applications for the beamed power facilities while the much more technically challenging aspects of the starshot project are sorted out. Meanwhile, satellite and space coach operators could test ships with ever higher levels of beamed power until they hit a limit (heat rejection is probably the main limit to how much power can be concentrated per unit of sail area, as this is similar to concentrated photovoltaics).

The chart below illustrates the power/performance curve by showing the amount of impulse that can theoretically be generated per megawatt hour using electric propulsion, as a function of exhaust velocity. Real world performance will be somewhat lower due to efficiency losses, but this shows the relationship between thrust, ve and power. We see that impulse per MWh varies from 72,000 kg-m/s (ion drive, ve ~ 100,000 m/s) to 1,400,000 kg-m/s (RF arcjet, ve ~ 5000 m/s). A Hall Effect thruster, a flight proven technology, would yield about 300,000 kg-m/s per MWh. Compare this to pure photonic propulsion, which would yield only 12 to 24 kg-m/s per MWh. Clearly photonic propulsion will be necessary to achieve a delta v of 0.2c, but for more pedestrian applications such as satellite orbit raising, launching interplanetary probes or cargo ships from LEO to BEO (beyond earth orbit), electric propulsion will work well at power levels many orders of magnitude lower than what’s required for a starshot.


Driver for an Interplanetary Infrastructure?

Closer to home there could be lots of opportunities to sell beamed power to space operators. It’s costly to launch large payloads beyond low earth orbit (which isn’t cheap in the first place). Meanwhile, payload fairings limit the size of self-deploying solar arrays, which limits the use of electric propulsion for satellites and probes. If one could launch spacecraft with small solar arrays to LEO, and then use beamed power to amplify their power budget they could use electric propulsion to boost themselves to their desired orbits or interplanetary trajectories within a reasonable time frame. The beamed power infrastructure can also be built up incrementally. Early systems would beam 100 kilowatts to 10 megawatts of power to targets measuring meters to tens of meters in diameter. This should be readily achievable, and can be scaled up from there in terms of power output, beam precision, etc. The result: lower costs per kilogram to deliver a payload to its destination or desired orbit compared to all chemical propulsion.

This could make electric propulsion for transit from LEO to GEO and beyond an attractive option. Meanwhile, the power beaming operator would accrue lots of operational experience with beam shaping, tracking objects in orbit, etc, all things that will need to be mastered for the starshot project, while providing an economic foundation for the power beaming facilities during the buildup to their intended purpose.

In fact, one can imagine the starshot project becoming a profitable LEO to BEO (beyond earth orbit) launch operator in its own right. The terrestrial power beaming infrastructure is one component. A standardized “power sail” that can be fitted to many different payloads, from geostationary satellites to interplanetary probes, is another. The power sail would consist of a self-deploying solar array that is sized to work well with beamed power, heat rejection gear, and electric propulsion units. It would use beamed power during its boost phase to rapidly accrue velocity for its planned trajectory, and then as it leaves near Earth space, would transition to use ambient light as its power source from there. Meanwhile these power sails would provide an evolutionary path from conventional spacecraft to solar electric propulsion to the nanocraft envisioned for purely photonic propulsion.

As a starting point, it would be interesting to conduct ground based vacuum chamber tests to see how a variety of PV materials respond to being illuminated with concentrated laser light tuned to their peak absorption wavelengths. What do the conversion efficiencies look like? How much waste heat is generated? How do the materials perform at high temperatures in simulated in-beam conditions? Building on that one can imagine experiments involving cubesats to validate the data from those experiments in real world conditions, and if that all works out, one could scale up from there to build out beamed power infrastructure for use by many types of solar electric vehicles.

Ambitious R&D projects have a way of generating unintended side benefits. It’s possible that the starshot initiative, in addition to being our first step toward the stars, will also make great contributions to travel and exploration within the solar system.

From Spacecoaches and Beamed Power by Brian McConnell (2016)

Powersat Weapons

About this point all but the hopelessly dull are thinking "wait just a darned minute, what are the military applications?" Pretty good, actually. Have you ever heard of a Laser Combat Mirror? The laser-propulsion mirror eliminates most of the mass of the engine, the laser combat mirror eliminates most of the mass of a laser cannon. This will free up payload mass in the space warship so it can carry more of other kinds of weapons.

As the range increases the powersat beam rapidly becomes too diffuse to do damage due to diffraction. But a warship sporting a laser combat mirror can focus the seemingly harmless diffuse beam into an eye-searing ship-destroying pin-point. Again much in the same way that sunlight is too diffuse to harm ants, unless a naughty boy uses a magnifying glass to focus it into an ant-destroying death ray.

Powersat's weapon potential is so effective that they will probably be nationalized, removed from civilian hands, and turned over to the military.

And even without a fleet of warships with laser combat mirrors, a powersat all alone is a pretty fair orbital laser weapon. Without laser combat mirrors the range is limited, but within that range, whoo boy can they vaporize the heck out of enemy spacecraft, space assets, and even torch ground targets. Their huge solar panels make them fragile, but they can do plenty of damage before they are neutralized.

Not quite green ecological hippy anymore, is it?


G. Harry Stine's (writing as Lee Correy) wrote a rocketpunk novel called Manna. In the novel, the military branches of the space-faring nations would like to put five gigawatt High Energy Laser (HEL) satellites in orbit. Using fancy techniques they are powerful enough to get their weapon laser beam through Terra's atmosphere and incinerate targets on the ground.

The trouble is the militaries want the HEL beamer satellites to be stealthy. The root of the trouble is that a five gigawatt HEL beamer containing a +five gigawatt power source is about as stealthy as a New York 4th of July fireworks display.

If only the power source could be at some distance from the HEL beamer, sending the energy by electromagnetic waves. You know, the same way a powersat sends microwave energy to ground power stations... hmmmmmmm.

That would work, the HEL beamers could be stealthy little dastards with no nuclear power plant, but rapidly unfurling a powersat reception antenna when it came time to zap something.

Now comes a bigger problem. Nobody can build any powerstats.

Why? Well, no corporation is going to embark upon a multi-billion dollar project like a powersat without insurance. And no insurance company is going to underwrite a multi-billion dollar installation which becomes a military target the instant it redirects its power beam from a power station in order to energize a HEL beamer. Especially a military target so huge, easy to hit, and incredibly fragile as a powersat.


How to solve the problem? Well, since it is an insurance problem, there should be an insurance solution.

Through a series of international agreements, the Resident Inspection Organization (RIO) was formed. This international group regularly inspected all powersats, and insured that they stayed pointed at ground power stations. In exchange, the insurance companies would underwrite the powerstats. If any powersat started to energize something that might be a stealthed HEL beamer, RIO would sound the alarm to all the astromilitaries, presumable giving the military units enough time to blow the living snot out of the powersat.

Naturally the astromilitary of Nation Alfa would be angry at RIO squealing when astromilitary Alfa tried to energize one of their HEL beamers. But astromilitary Alfa would be vary grateful if RIO squealed about astromilitary Bravo, Charlie, Delta or Echo doing the same thing.

     "I'm worried about RIO's reaction," Captain Kevin Graham remarked from the space port. "Our captains are concerned that PowerSat, InPowSat, and InSolSat powersats could have their power beams diverted to the American beam weapon stations on orbit . . . and we know where every one of them is stationed even though the Aerospace Force tried to hide them in inclined Clarke orbits."
     That was Top Secret information! How had the League of Free Traders found these battle stations, shrouded as they were with hard stealth technology?
     Ursila Peri reported from L-5, "I don't know if the powersat crews would carry out an order to redirect power beams to military battle stations. Whether the Aerospace Force has plans for a military takeover of the powersats is another matter, but such an attempt would put them in confrontation with the RIO teams on the powersats."...
     ...Vaivan went on, "Sandy, energy war isn't difficult to understand. Most low-tech countries will continue to do business with us in spite of any embargo or boycott. We provide value received and take very little off the top. The Tripartite may try to invoke sanctions against our customers by pulling their powersat plugs, but we'll be there with another plug. And we have a space port, space lift capability, primary metals and plastics industries, and the lunar mine and smelter at Criswell Center. You haven't see that yet, but it's just a lunar mine and smelter. Commonwealth Glaser's capable of supplying powersat electricity to anyone the Tripartite cuts off because they're now building powersats with lunar materials at a much faster rate than the Tripartite companies."
     "They'll react," I warned.
     "They'll go after your powersats."
     "In the face of international law and the Resident Inspection Organization? The insurance trusts won't stand for it," Wahak maintained. "Those trusts are controlled by the Tripartite, but not even a consortium of all the Tripartite banks could possibly cover the insurance losses. And there won't be any because the insurance trusts will place a rather strong damper on any military powersat takeovers. Then RIO will drive in the bung."
     "RIO teams are un-armed," I reminded him.
     "We'll see what happens when everybody shows their cards. RIO will have to become the first Space Patrol whether they want to or not because circumstances will force it ... and so will we."...
     ..."How much capacity has been dropped off the powersat net?" Ali tried to get back on track.
     "Fourteen gigawatts," Shaiko reported. "The cut-offs in­volved split beams, so no powersat is totally off-line, but One-Zero-Five-East and Six-Zero-East have near-zero loads."
     I didn't like that. "Which powersats will have near-zero if they pull the plug on Annom, Nireg, and Sorat?" I asked.
     Shaiko consulted a nearby display before replying, "Two-Zero-East and One-Zero-Five-East."
     "That drops One-Zero-Five-East down to zilch, doesn't it?" I observed.
     "Any load left on One-Zero-Five-East if Annom and Sorat go off?"
     "What are you worried about, Sandy?" It was Vaivan who caught my concern.
     "A ten gigawatt powersat can pump a big laser, Vaivan," I explained. "A high-energy laser—they're called hell beamers from their acronym, H-E-L—is limited in beam power density and range only by its energy source. If it's a self-contained unit, the space facility is large and vulnerable. But if a hell-beamer's energized remotely, it's small and hard to identify. Powersat One-Zero-Five-East could put its ten gigawatts into a hydrogen-fluoride hell-beam station to punch a beam right down to surface from GEO!"
     This was obviously news to them. Rayo Vamori broke the silence, "Is there a battle station over us?"
     "The Aerospace Force has them over all parts of the world in sixty-degree inclined geosynchronous orbits. Kevin Graham's captains have spotted them."
     Ali said slowly, "I'd better pay Peter Rutledge a visit."
     I went with Ali to the Resident Inspection Organization's headquarters, GEO Base Zero. Ali needed a pilot, and he wanted me to meet those upon whom the delicate stability of space power depended.
     I'd never known any RIO people. They kept to themselves as an anational paramilitary organization with a tradition of non-involvement. They had to be aloof. Thanks to RIO, there hadn't been a conflict in space since the Sino-Soviet Incident.
     Ali wanted to make certain that RIO knew what was happening with the powersats. He was also covering his anatomy by insuring that Powersat One-Zero-Five-East or any other powersat didn't get its power beam redirected to a hell-beamer.
     The approach to RIO Headquarters was a two-man job. The first challenge from RIO came at a thousand kilometers. We answered with the proper transponder code. Then we had to close at no more than ten meters per second, matching orbits and station-keeping ten klicks behind at zero closure rate. There we were thoroughly scanned. Once we proved we were sweet, pure, and unrefined as well as incapable of swatting a bee in revenge for being stung, they put a RIO pilot aboard. She strapped into the jump seat between Ali and me and flew the ship. It was rather disturbing to sit next to someone wearing about twenty kilos of Comp-X around her waist. From her accent as she reported on her comm set to RIO Approach, she was Japanese. I knew she wouldn't hesitate to self-destruct and take the ship and the two of us with her if we tried to ram GEO Base Zero...
     ..."He had to be. How much do you know about RIO and how it's run, Sandy?"
     "Only what I've read, which was reasonably extensive be­cause the Academy wanted future officers to understand RIO not as an adversary, but as a potential obstacle."
     The Resident Inspection Organization had been the factor which permitted the powersat network. Without non-national or international inspection, who was to know whether or not a powersat also contained a hell-beamer? Who could have ascer­tained whether or not an attack satellite was hidden in the structures of the photovoltaic panels? And who'd be sure that the power beam wouldn't be diverted—as Ali and I now feared— from the ground rectenna to an otherwise passive and silent hell-beamer satellite? Could someone really pirate the pilot beam that kept the power beam phased on the rectenna and then concentrate several power beams on an Earth or space target, even though the power density of a single powersat beam is only one-fifteenth that of a microwave oven?
     These questions left unanswered posed a military threat which in turn made a powersat a military target because nobody could take chances if an armed conflict appeared imminent.
     A powersat is a terribly vulnerable thing—square kilometers of solar panels and bus bars carrying megawatts of power. No businessman, entrepreneur, financier, banker, or investor would have risked a worn penny on a powersat that was a certain target in the opening moments of any future war. Neither Lloyd's nor Macao's would or could have underwritten the insurance re­quired for the long-term financing.
     Obviously, a non-political international inspection organization was required. But how could it be organized, financed, and operated to insure that it remained non-national? That had been an enormous problem.
     But technology always creates the new social organizations necessary to finance, manage, and control it.
     People hacked away at the problem until RIO was organized at the Hartford Convention. RIO was formed with the funding from the groups who'd lose the most if a powersat were attacked as a military target, whether it was an actual threat or not. The damage or destruction of a multi-billion dollar powersat would be an expensive loss to the insurance underwriters.
     The world needed space power and the insurance consortiums were the critical bottleneck. Whether or not there were economic pressures applied is a moot point today because the fraction of a percent that was tagged onto the kilowatt-hour consumer electric bill amounted to billions of dollars in insurance premiums which in turn more than paid for the 2,000 RIO inspectors and specialists with their independent communications and transportation systems.
     Rutledge had been accurate in using the sentry as the analogy for RIO.
     A lot of people didn't understand that an unarmed RIO was considered to be very effective. If a resident team or one of the ubiquitous spot inspection teams under the command of Rutledge found something unusual, there were two options open to the team leader: (a) report it covertly to RIO Headquarters for evaluation there; or (b) in a real emergency communicate the military activity to everybody. In the latter case, it was then important for RIO to get out of the line of fire.
     Because of its unique anational character and novel operational methods, RIO often acted in strange and unfathomable ways. Unarmed as they were, they posed no military threat to |anyone. But the threat of their capability to saturate the comm/info network with the danger cry of the watch dog was a sure and certain restraint on military space activities. I suspected—and knew in some cases—that RIO had intelligence operations which penetrated deeply into nearly every military organization in the world. It wouldn't have surprised me, either, if their intelligence activities also embraced the world of commerce.
     A lot of military planners had spent a lot of time and effort drafting plans and programs for circumventing RIO. The Aerospace Force—whose job was ostensibly to keep and guard the peace, too—had a continual highly-classified think-tank activity going on "should it be necessary to activate such plans and programs." But the job of any military service is to ensure the security of its nation...

From Manna by G. Harry Stine (1983)

Hyperpower Stations

There are just some industrial applications that demand power approaching Kardashev Type I levels. Hyperpower stations will supply you with massive amounts of power (along with a massive electricity bill).

At the orbital radius of the planet Mercury the solar flux is about 9,121 watts per square meter, a whopping 6.7 times the 1,366 W/m2 available at Terra's orbital radius. So a ten kilometer square solar photovoltaic array that was 100% efficient would crank out about one terawatt of power.

Titanic solar power stations covering huge areas on the surface of Mercury or Luna are called "Asimov Arrays", name bestowed by James Powell and Charles Pellegrino after Isaac Asimov pointed out several serious errors in their design. Such as "You do know that Mercury is not tidally braked with respect to the Sun, do you not?"

Do keep in mind that it is not mandatory for the solar cells to be mounted on Mercury, they can be orbital. You could even place them closer to the sun if you really need the power. The only problem is that light pressure will tend to push them away, Mercury's gravity can anchor them.
An Asimov Array of solar power stations around the lunar equator could supply the all the energy needs of inhabited Terra. The power would be beamed to Terra using microwaves.
There is 2.0 × 1013 watts (20 terawatts) potential between Jupiter and Io. This can be harvested with electrodynamic tethers.
Alternatively, you mount lasers on copper rods and launch them from Io at Jupiter. As the rods cut the magnetic lines of force they generate electricity. This is converted into laser light and beamed back to Io. Rod is destroyed when it hits Jupiter, but so what, they are cheap.
Saturn, Uranus, and Neptune have atmospheres rich in Helium-3, useful for 3He+D fueled fusion reactors (although there is some evidence that Saturn only has 1/5th the 3He of the others). This can be harvested by atmospheric scooping. Jupiter has 3He as well, but the heavy gravity makes it uneconomical to harvest. You need a freaking solid core NTR to boost the harvest into Jovian orbit.
Naturally huge arrays of fusion power plants are going to require a huge supply of fusion fuel nearby.

“Getting the power may not cost us that much after aIl,” said Tuna ("Richard Tuna" is actually Charles Pelligrino). “Not when you consider where computer science and robotics are headed during the next fifty to seventy years. A few days ago, at Brookhaven, we came to realize that it may cost us only the expense of developing about thirty small, self-replicating factories—which build factories, which build factories—which, when they reach a certain population density, switch over from building factories to building solar panels. We simply send them like a viral infection tolthe planet Mercury, and carpet one hemisphere with panels. You’d get more than fifty thousand times the U.S. energy budget there.”

“Mercury rotates!” Colby called out.


“Sorry, Richie,” Colby said, “but you can’t build your panels on one hemisphere only, because Mercury rotates. Where have you been? People have known that for ten years. I’m sure it rotates. Have I introduced you to the natural resource? Ask him.”

“He’s right,” said Dr. Isaac Asimov. “Mercury rotates with aperiod of about three months, and the energy received per square foot, when Mercury is most distant from the Sun, is seven times what Earth receives. It goes up to ten times during closest approach. The interesting thing is that the one-eighty-degree and zero-degree longitudes do become gravitationally locked, alternately, during apihelion, and are exposed to the Sun almost three times longer than the longitudes ninety degrees away from them.”

“Oh, no,” Tuna groaned, flushing with embarrassment. “I don’t believe it. We have to redesign the whole thing.”

“Please,” Asimov said, raising his hands above his head, as if to show that he bore no weapons. “Don’t blame me. I didn’t make Mercury rotate. Better to find out now than when you get there and look up in the sky and—‘Hey! Why is the Sun moving?’ ”

Tuna groaned. “I don’t believe I missed that. We can redesign it, though. We’ll just have to cover a bit more surface area, and perhaps send three times as many machines to get the project started … make sure at least one cluster of them is in sunshine at any given moment…”

“And you’ll certainly want to test and perfect the machines on the Moon first,” added Asimov. “You know, it’s just one more argument for building a permanent Moon base. By the time you perfect solar panel builders for Mercury, you’ll already be beaming large quantities of clean energy down to Earth from the Moon…” He paused and smiled. “Incidentally, I wrote a science fiction story, way back in 1940, about an interrupted array of panels around the Moon’s equator (I have yet to figure out which story this is. The closest I can find is Reason). So if you ever do build the thing, Richard, you can call it the Asimov Array.”

“We can?”

“I insist on it.”

(ed note: The following is from the technical appendix to the novel.

Keep in mind that this was written in 1993 so adjust US dollars and national power consumption for inflation)

The technology for producing antimatter using particle accelerators is presently under development at American and European laboratories. At CERN’s seven-kilometer-circumference synchrotron near Geneva, Switzerland, antiprotons are routinely produced by firing a high-energy beam of protons into a block of tungsten. A trillion (1012) antiprotons can be created in this way. A trillion antiprotons may sound like a lot, but they contain the potential annihilation energy of only three hundred joules (roughly equivalent to the “bang” from a cap gun), and the CERN facility gets slapped with a $40,000 electric bill every time the accelerator is turned on (more like $68,000 US in year 2017).

Clearly, simpler and more efficient accelerators are needed. Machines with the proper requirements are presently under development in the United States (and soon to be under intensive development in Japan) for use in fusion reactor research.

“As an example,” explains physicist George Mueller, “in one design being studied, the particle accelerator will produce short bursts of protons with a power beam of 1014 watts, about one hundred times the present power output of the entire world! (in 2013 the world's average energy consuption was about 12.3×1012 watts, 1014 is still one hundred times as much) Of course, since the machine will be operated in 10-8-second bursts, the average power is very much lower.”

The natural location for antimatter factories, in view of their large power requirements, is in space, where continuous and, from an industrial perspective, limitless solar power is available. “Using the solar flux at the Earth’s distance from the Sun,” adds Mueller, “a light collector about three hundred kilometers on a side could provide the power for a 1014-watt factory (9×1010 m2. Solar flux at Terra orbit is 1,366 W/m2. At 100% efficiency that is 1.2×1014 watts).

If the efficiency of antiproton production from each high-energy proton in the initial beam could be made as high as 0.1 percent (efficiency of 0.001.) [presently Hiroshi Takahashi is predicting higher efficiencies] (Dr. Robert Forward thinks realistically it will be more like 0.0001)

…then this machine would produce 1020 antiprotons per second (each antiproton requires 1.5×10-10 Joules, 1.2×1014 watts at efficiency of 0.001 can produce 7.98×1020 antiprotons per second),…

…or about one kilogram of antimatter per month.” (antiprotons have a mass of 1.7×10-27 kilograms. At a rate of 1020 antiprotons/sec 1 kilogram would take 69 days or 2.3 months)

From our earliest brainstorming sessions emerged proposals for a solar panel array, in orbit around Earth, covering an area in excess of ten thousand square kilometers. Even if it should one day become economically feasible to mine, refine, and transport materials from the Moon to Earth orbit, such an array would literally become a gigantic solar sail, requiring a considerable expenditure in thrust (presumably from rockets that would have to be refueled from somewhere) just to keep it from blowing away on the solar wind.

Our attention tumed elsewhere, to a power source more firmly anchored, yet overlooked, perhaps because it is so large that no one noticed it before. If we are correct, the planet Mercury is destined to become the most valuable piece of real estate in the solar system.

Presently, we are eyeing self-replicating, solar-panel-building machines. If humanity plays its cards right, prototypes could be tested on the Moon near 2020, and the rewards that the descendants of these first machines can bring—cheap, clean, and unlimited power for all mankind—are yet another argument for a permanent Moon base. Using the materials available at the lunar surface, they will build solar panel farms, and new solar-panel-building machines. In time, the farms will girdle the Moon’s equator to form the Asimov Array (named, exactly as described in Chapter 4, after an early contributor to the concept). The Asimov Array will provide power for Earth.

However, we dare not use that power for producing and storing large quantities of antimatter on the Moon, or anywhere near Earth, because even a single kilogram of the stuff—a mere handful—carries the explosive potential of forty hydrogen bombs, along with the moral responsibilities that go hand in hand with the possession of such power. (1 kilogram of antimatter + 1 kilogram of matter will make about 1.8×1017 joules, about 43 megatons. B83 nuclear bomb has highest yield of any in US nuclear arsenal, it has a maximum yield of 1.2 megatons. So 43 MT is about thirty-six hydrogen bombs)

Once perfected, the descendants of the original Asimov Array robots can be sent like a viral infection to the planet Mercury. Assembling replicas of themselves from the substance of their host, their first half decade of habitation will be a latent, incubation phase, during which most of the solar panels manufactured by the machines will be used to power an ever-accelerating chain reaction of machines building more self-replicating machines. As their population approaches a predetermined critical density, more and more of them cease reproduction and join to form solar panel factories, with the result that almost three decades after the arrival of the original twenty or thirty machines, uncountable square kilometers of generator, with an area the size of Rhode lsland being added daily.

When Mercury is farthest from the Sun, each panel will receive 6.7 times as much solar energy as it would receive on the surface of the Moon. This figure rises to fully ten times the lunar surface value as the planet’s eccentric orbit dips twenty-four million kilometers nearer the Sun. In time, self-replicating machines will carpet the Mercuran landscape from pole to pole with solar panels, giving mankind more than 50,000 times the present U.S. electrical energy budget, a power capable of launching at least two interstellar missions per year.(1990 U.S. annual electrical output 2.7×1016 Joules. ×50,000 = 1.3×1021 Joules. Divided by 2 per year = 6.7×1020 Joules = 7.5 kilogram antimatter per interstellar mission.)

Using self-replicators, the world’s future energy problems and even the excess energy required for relativistic flight can be solved for a very small initial investment: the cost of developing as few as a dozen ancestral machines on the Moon. Of course, we should not trouble ourselves to begin immediate development. They would be too expensive to build today, and too inefficient if built from the equipment now at hand—just as a trans-Atlantic airline service and videocassette recorders, though technologically feasible, would have been prohibitively expensive to build in 1925. We must wait, not only for technology to catch up with the idea, but for the idea to become economically viable.

From FLYING TO VALHALLA by Charles Pellegrino (1993)

The main dome of Ganymede City covered three square kilometers of the moon's surface. Here on the top level, the observation screens covered the interior of the dome; they could be turned on individually, or en masse to show a panorama of sky and surrounding terrain. A direct view would have left the observation level with too little shielding against the leakage of solar radiation trapped by Jupiter's magnetic field; even though Ganymede City sat in the moon's radiation shadow, the aboveground portion was protected, as an added precaution, by meters of water in the outer shell, piped in from the nearby ice field. Natives called Ganymede City "the big igloo,” because of the liquid that was kept frozen in its insulating space. In addition to the physical shielding against stray radiation and occasional meteors, the Laser-Fed Fusion Reactor powered the super conducting units which cast a magnetic shield over the domes.

Ganymede plowed through a sea of death; but despite this, ships had visited all the Galilean satellites by 2015. Built at the Martian space docks on Phobos and Deimos, the water- and magnetically-shielded tin cans, as the ships came to be called, had penetrated into Jupiter's radiation belts, setting up research bases on Callisto and Ganymede, as well as temporary facilities on a few of the close-in rocks whipping around the edges of the gas giant’s atmosphere.

To make power for building the first underground living quarters, the tin cans had deployed a giant sun mirror. The collector was no more than a few molecules thick, but its huge size and focusing capacity made up for the fact that the sun's intensity was only about four percent of what it was in the vicinity of earth (51 W/m2 instead of 1,366 W/m2).

While Ganymede City's first levels were being built, a mass driver track had been constructed beyond what was now the tug port. Using the three-kilometers-per-second escape velocity from the Jovian moon, the track began to toss copper ingots toward Jupiter, whose escape velocity was twenty times greater; this large energy difference was expressed in the form of eddy currents of electricity forming in the copper as it rushed through Jupiter's powerful magnetic field; these were lased back to Ganymede by a small disposable unit, continuing right up to the moment when the ingot hit the atmosphere for a final, dramatic surge of electricity. Current flow was evened out by storage facilities at the receiving station on Ganymede.

As a result of this and other systems, Ganymede became one of the energy-self-sufficient places for science, attracting research and development from earth. The solar mirror was still working; the lofter still threw ingots into Jove's face; and a second fusion LFR had recently been completed.

Ironically, Sam thought, success on Ganymede had slowed the building of facilities on Saturn's moons, as well as delaying development of the larger asteroids such as Ceres. A whole system of worlds waited to come alive out here, offering conditions for industry and research, room for a civilization to grow.

From MACROLIFE by George Zebrowski (1979)

Hyperpower Uses

Here are a few industrial applications that require hyperpower stations.

Interstellar Mission Laser Sail
Such as in Rocheworld, which needed an outrageous 1,300 terawatts.
Solar system wide network of laser power transmission and laser thermal rocket energizers.
Project Daedalus
This slower-than-light unmanned starship would get up to 0.12 c and cruise for 46 years before flashing through the Barnard's Star system frantically snapping pictures. It would require 30,000 metric tons of Helium-3, harvested from Jupiter's atmosphere over a 20 year period. It also needs 20,000 metric tons of deuterium, but you can get that out of seawater.
Antimatter Creation
Installations producing commercial quantities of antimatter, which are hideously inefficient power hogs. In Michael McCollum's Thunderstrike antimatter is used as super-duper rocket fuel and to move valuable asteroids to more convenient locations. Pelligrino and Powell's Valkyrie and Frisbee's starship use antimatter as starship fuel. But antimatter has a thousand and one uses, it will be a valuable commodity.
Antimatter distribution is administered by the Antimatter Guard.
Valkyrie Antimatter Starship
These ultralight starships can deltaV up to 0.92c and back down to zero. But my slide rule says they'll need about 4,200 metric tons of antimatter.
Frisbee Antimatter Starship
This brute can delta V up to 0.125c and back down to zero, with an acceleration of 0.01 g. And the freaking thing is 700 kilometers long (not meters, kilometers). It will require 159,450 metric tons of antimatter liquid hydrogen, because it ain't no ultralight starship. 500 kilometers of the ship is just heat radiators.

Fission Fuel Plant

Atomic Rockets need Atomic Fuel. Raw uranium or thorium ore is worthless as fuel for your nuclear thermal rocket or nuclear power reactor (the same goes for nuclear weapons). The stuff the asteroid miners haul in will have to be enriched before it can be used as fuel.

Common power reactors require enrichment from 1% to 20%, fast-neutron power reactors and nuclear thermal rockets need 20% to 85%, above that is the weapons-grade fissionables needed for nuclear weapons, SNRE Peewee engines, Orion pulse units, and nuclear salt water rockets burning 90% UTB.

Enrichment requires a sizable high-tech factory, they will have to be strategically placed around the inhabited solar system. Along with security forces provided by the astromilitary of a select group of nations, to ensure that none of the weapons-grade plutonium gets stolen (the Nuke Guard).

It is a lamentable fact that fission engine fuel elements clog up with nuclear poisons and stop working while there is still lots of fuel in them. After about 15% of the fuel is burnt (85% unburnt) the rod stops fissioning. Since is it a criminal waste of scarce fuel to throw the rod away when 85% is still yet to be used, you have to take it to a nuclear reprocessing plant. The plant will filter out all those nuclear poisons and use the unburnt fuel to make new fuel rods. A distressing by-product is lots of weapons-grade plutonium, which the Nuke Guard will also have to deal with.

Obviously reprocessing will only be needed for solid core and closed-cycle gas core NTRs. Other nuclear rockets blow the nuclear fuel out their tail pipes, burnt and unburnt.

There will have to be reprocessing plants strategically placed around the inhabited solar system, perhaps inside enrichment plants. Perhaps with a network of fuel transport ships shuttling fuel rods (fresh and spent) between plants and spaceports for convenience. Said ships will undoubtedly be a part of the Nuke Guard.

Tether Propulsion


A momentum exchange tether is a kind of space tether that can be used as a launch system, or to change spacecraft orbits. Momentum exchange tethers create a controlled force on the end-masses of the system due to centrifugal acceleration. While the tether system rotates, the objects on either end of the tether will experience continuous acceleration; the magnitude of the acceleration depends on the length of the tether and the rotation rate. Momentum exchange occurs when an end body is released during the rotation. The transfer of momentum to the released object will cause the rotating tether to lose energy, and thus lose velocity and altitude. However, using electrodynamic tether thrusting, or ion propulsion the system can then re-boost itself with little or no expenditure of consumable reaction mass.

A non-rotating tether is a rotating tether that rotates exactly once per orbit so that it always has a vertical orientation relative to the parent body. A spacecraft arriving at the lower end of this tether, or departing from the upper end, will take momentum from the tether, while a spacecraft departing from the lower end of the tether, or arriving at the upper end, will add momentum to the tether.

From the Wikipedia entry for MOMENTUM EXCHANGE TETHER

A good low-mass way to prevent cables from failing catastrophically is to use Hoytethers (cables that are elongated Hoytubes). Strengthening a cable by increasing its diameter quickly becomes too expensive in terms of mass. A Hoytether on the other hand is a low mass network of redundant cables that fails gracefully.

Momentum exchange Hoytethers were featured in the novel Saturn Rukh by Robert L. Forward.


A momentum exchange tether is a long thin cable used to couple two objects in space together so that one transfers momentum and energy to the other. A tether is deployed by pushing one object up or down from the other. Once the two objects are separated by enough distance, the difference in the gravitational force at the two locations will cause the objects to be "pulled" apart. This is called the "gravity gradient force". The tether can then be let out at a controlled rate, pulled by the tension caused by the gravity gradient force. Once the tether is deployed, if there are no other forces on the tether it will have an equilibrium orientation that is aligned vertically. There are a number of different concepts for momentum exchange using tethers. Some general categories are:

A bolo is a long rotating cable anywhere in space that is used as a "momentum-energy bank". It could be used to "catch" a payload coming from any given direction (in its plane of rotation) at any given speed (less than its maximum tip speed), and then some time later, "launch" the payload off in some other direction at some other speed. A gravity gradient stabilized bolo orbiting some planet has the property that if the tether is cut, then one-half an orbit later, the separation distance between the two masses is seven times larger than the initial separation. This can be used to deorbit the lower mass, or throw the upper mass to a rendezvous or to escape.

(ed note: momentum-energy bank is just like a financial bank, only using momentum instead of money. You can put momentum in by catching a spacecraft and take momentum out by launching a spacecraft, but the important point is you cannot take out more momentum than the blasted bank currently contains. This means you need a strategy to balance deposits and withdrawals of momentum.

The most common strategy is to have two bolos, for example one at Terra orbit and one at Mars orbit. Each bolo lobs payload modules at the other, and catches modules aimed at them. This keeps the momenum balanced.)

Tip Velocity and Material Strength

The maximum tip speed of all these systems is a function of the "launcher to payload mass ratio" of the tether system and the "characteristic velocity" of the material used. The characteristic velocity of the material in a tether is given by the square root of the ratio of the design tensile strength T of the tether to the density D of the tether material. u = (T_d/D)^1/2. In practice, the design tensile strength is usually chosen to be 50% of the measured strength for metals and 25% of the measured short-term individual fiber strength for other materials. Thus, using imperfect materials with reasonable safety margins, the characteristic velocity of most metals and fibers is around 1 km/s, with optimistic predictions for graphite and improved polymers reaching 3 km/s. With the development of a design for a high strength-to-weight tapered Hoytether, the design tensile strength can be safely chosen to be 60% of the measured strength of the individual fibers, allowing commercially available fibers to have characteristic velocities up to 4 km/s.


     "Just the general idea. It starts with the Spider again. Now it's spinning a different kind of web. Rockets are wrong. That's sitting there in your desk as we talk, but I didn't follow it far enough. I should have known you wouldn't stop with the beanstalk, that just gets us up and down from Earth. You wanted a way of moving materials around the whole System without using drives. And the Spider could give you that."...
     ..."Spin another cable," he went on. "Make it like the beanstalk, with superconducting cables and drive train attached to the load cable. This time, put the powersat at the center of the cable, with an equal length on each side of it. Fabricate it in space, but don't ever plan to fly it in and tether it. Leave it out near the orbit of Mars, or in the Belt, or in near Earth—key places in the System. Then start it rotating about its center, like a couple of spokes on a wheel. I assume that you began with just a couple of them, one in the Belt and one near Earth?"
     Regulo nodded calmly. He had finished fiddling with the control panel and now seemed oddly relaxed. "We started with two. That's just the beginning. The more you have, the better the efficiency of the whole operation. I've been thinking we'd build about five thousand of them through the Earth-Belt region."
     "You could handle that many?"
     "With Sycorax? Easily. We can track that number, and more—there are millions of orbits in the data banks already. This is just a few extra ones." Regulo's tone was that of a patient teacher. "I've told you before, Rob," he went on. "Think big. The System's a big place. You have to scale your thinking to match it."...
     ..."Just as you did. You have a rotating cable out in a free orbit—thousands of kilometers of it." He leaned forward, at the same time as Regulo moved his chair farther away from the desk.
     "Now suppose you want to move a space pod from the Belt to the Moon," Rob went on. "You make it rendezvous with the center of the cable, where the powersat sits. The center of mass of the cable would be moving in a free-fall orbit, travelling about the same speed as the pod, so you use hardly any reaction mass to make the rendezvous. You don't need much acceleration from the pod's drives, either, just a fraction of a gee will be enough. Once you have the pod at the middle of the cable, you let it move out along the drive train. As the pod moves from the center it feels a centripetal acceleration. You need to use the drive train on the cable to restrain it. When it reaches the end of the cable, you release it to move in free fall. You've given it a big velocity boost. But the trouble from the point of view of a human on the pod is the acceleration. Out at the end of the cable, it's huge. I looked at a couple of examples. A cable four thousand kilometers long, with end velocity of twenty-four kilometers a second, would give thirty gees at each end. That's what killed the Goblins."...
     ...He put the space pod to a cable rendezvous with a cargo Slingshot—one with high accelerations, never intended for people."
     "Do you have Slingshots for passengers?" Rob moved forward right up to the desk.
     "We built the first two, just a month ago. I could find out which cable your Goblins used easily enough, by checking the angular momentum of all of them. Each time we use a Slingshot we naturally increase or decrease its angular momentum." Regulo stood up, his back to the wall. "We lose angular momentum when we throw a cargo in toward the Sun, and pick it up when we catch something thrown in from Mars or the Belt. Provided we move the same mass of materials in and out, the whole system balances—just like the beanstalk back on Earth.

From THE WEB BETWEEN THE WORLDS by Charles Sheffield (1979)
     My post Orbital Momentum as a Commodity describes how a tether with a healthy anchor mass can catch and throw payloads. I tried to think of ways a tether might restore orbital momentum lost during a catch or throw. Two way traffic is one way to pay back borrowed momentum.

     Well, Mars' moon Phobos masses 1.066×1016 kg. With this huge momentum bank, catching and throwing payloads would have less effect than a gnat hitching a ride on a Mack truck. A Phobos anchored tether could catch and throw for millennia with little effect on Phobos' orbit.

     The tether illustrated above doesn't suffer the enormous stress of a full blown earth elevator or even a Mars elevator. It could be made from Kevlar with a taper ratio of about 11.

Access to Mars

     The tether foot pictured above moves about 0.6 km/s with regard to Mars surface. This is about 1/10 of the ~6 km/s the typical lander from earth needs to shed. Mars Entry Descent and Landing (EDL) would be vastly less difficult.

     Some have suggested Phobos 1.88 g/cm3 density indicates volatile ices. If so, the moon could also be used as a source of propellent. A Phobos propellent source would make EDL even less of a problem. However Phobos' low density might also be due to voids within a rubble pile.

     On page 2 of the Acceleration of the Human Exploration of The Solar System with Space Elevators Marshall Eubanks takes a look at how the foot of Phobos-Anchored Martian Space Elevator (PAMSE) might interact with Mars' atmosphere:
     The orbital eccentricity of Phobos amounts to 283 km, which is by coincidence comparable to the effective depth of the Martian atmosphere for satellite drag (typically ~ 170 km, but subject to variations due to atmospheric events such as dust storms). The average relative velocity between the lower tip and the surface of Mars is only 534 m/sec, roughly Mach 2 in the cold Martian atmosphere, and slow enough that it should not cause significant heating of the tip. This raises the interesting possibility that the PASME tip could dip down deep into the atmosphere to leave or recover payloads or perform reconnaissance, acting as a supersonic airplane for the period near periapse when it is near the surface.
     Eubanks' 534 m/sec is a little slower than the 0.6 km/s of my tether tip. This might be because I had placed my tether tip 300 km/s above Mars' surface thinking atmospheric friction would destroy a lower tether foot. Eubanks' analysis has changed my view.

     In the Facebook Asteroid Mining Group, Eubanks noted:
     The orbit of Phobos is equatorial, and there is a big mountain in the way, Pavonis Mons, the middle of the Tharsis volcanoes, straddling the equator and by far the highest obstacle in the path of the elevator tip. Maybe a railroad on top of the volcano could match speeds with the elevator tip, once every 3 days or so (when the orbit and volcano aligned). If so, you would have up to 3 minutes to shift cargo on and off. 
     as well as
     …the cool thing is that the tip can be something like a tethered airplane (with wings and flaps, etc.) and you should be able to use that to control oscillations. I was hoping to get money to begin actually "testing" this (i. e. in simulation), but, alas, not so far. 
     Remember, too, with the PAMSE the counterweight has ~ infinite mass, and so any oscillations have to end there. (of course, anchoring a PAMSE in Phobos is left as an exercise for the reader.)
     If Phobos is indeed a loose rubble pile, anchoring the elevator would be difficult. So while Eubanks eased my anxieties on oscillations and atmospheric friction, he calls my attention to a problem I hadn't thought of.

Access to Earth

     6155 km above Phobos the tether is moving faster than escape velocity with a Vinf of 2.65 km/s. This is sufficient to toss a payload down to a 1 A.U. perihelion. This could provide most of the delta V for Trans Earth Insertion.

     A ship coming from Earth would have a Vinf of 2.65 km/s and so rendezvous with this part of the tether might be accomplished with little propellent.

Access to the Main Belt

     7980 km above Phobos the elevator is moving with a Vinf of 3.27 km/s, enough to hurl payloads to a 2.77 A.U. aphelion. This part of the tether might send/receive payloads to/from the Main Belt. There are a lot of asteroids with healthy inclination, though. So there would be substantial plane change expense at times.

Possible Mars exports to the main belt

     One thing about the Main Belt, the pace is much more leisurely. Ceres moves about 1º every 5 days. In contrast earth moves about 1° a day and a satellite in low earth orbit moves about 4° a minute.

     So a month-long, low-thrust ion burn over there looks a lot more like an impulsive burn than it does in our neck of the woods. I believe high ISP ion engines are well suited for travel about the Main Belt.

     The inert gas argon can be used as reaction mass for ion thrusters. Mars' atmosphere is about 2% argon. It is also about 2% nitrogen and 96% carbon dioxide with traces of oxygen and water. Mars also has respectable slabs of water ice at the poles.

     Mars would be a good source of propellent for the entire belt as well as CHON for the volatile poor asteroids in the inner main belt.

     Ion engines don't have the thrust to weight ratio to soft land on the larger asteroids. But asteroids often have high angular velocity (in other words, they spin fast). High angular velocity combined with shallow gravity wells make asteroids amenable to elevators.

     For example the balance point for a Ceres elevator would only be 706 km above Ceres surface, that is the altitude of a Ceres-synchronous orbit. To provide enough tension to remain erect, the elevator would need to extend to an altitude of 2000 km. At 2000 km, the tether tip is moving about 0.46 km/s, a good fraction of the 2.82 km/s needed fro Trans Mars insertion. If this Ceres elevator is Kevlar, taper ratio would be about 1.02.

     If extended to an altitude of 14,500 km, the Ceres elevator top would be moving fast enough for Trans Mars insertion. This would require a taper ratio of around 5 for a Kevlar tether.

Incremental Development

     The tether pictured at the top of this post is ~14,000 km long with a taper ratio of 11 for Kevlar. While much smaller than a full blown Mars elevator, this elevator would still be a massive undertaking. But the whole thing doesn't need to be built overnight. Early stages of the elevator would still be useful.

     Pictured above a Deimos tether drops a payload to a Phobos tether.

     At apoapsis of the large ellipse, payload velocity matches the Deimos tether foot. At periapsis, the velocity matches the speed of the Phobos tether top. Thus payloads can be exchanged between these Martian moons using practically zero reaction mass.

     After descending the Phobos tether, the payload can be dropped to a Mars atmosphere grazing orbit.

     These tethers are a lot shorter than 14,000 km tether we were talking about and taper ratio is close to 1.

No Moons to Dodge

     A full blown Mars elevator capable of throwing payloads to the Main Belt or even earthward would have to dodge Deimos as well as Phobos.

     A Phobos elevator for flinging payloads to Ceres ends well below Deimos' orbit. And of course a Phobos anchored tether doesn't need to dodge Phobos.


     Tsiolkovsky's rocket equation and big delta V budgets are touted as show stoppers for routine travel to Mars' surface or the Main Belt.

     With judicious use of tethers and orbital momentum, rhinoceros sized delta V budgets are shrunk to hamster sized delta V budgets. No bucky tubes needed, ordinary materials like Kevlar can do the job.

Aldrin Cyclers

A trip to Mars is very expensive in terms of propellant. Rockets are very sensitive to mass. Remember that Every Gram Counts.

The Mars mission requires hydroponics for food and air for the astronauts, nine months worth. The habitat module. And worst of all, the massive anti-radiation storm cellar. All of this takes mass. Then you have to add the mass for the lander and the other equipment you'll need on Mars. Just think about the propellant bill.

Then if you have a second expedition, you have to pay for it all again. And for each subsequent expedition.

About this time, astronautics experts had the thought "what if we could re-use some of the required equipment?" More specifically, re-use the delta-V.

Take the habitat module, the hydroponics, and the storm cellar and make it into a space station. Spend enough propellant to delta-V it up into an orbit that passes by Mars and eventually returns to Earth. It will regularly pass by Earth and Mars for the rest of eternity, with a little mid-course correction now and then. So you now have a habitat module delta-Ved for a Mars mission that can be re-used. It is a Cycler.

For your next Mars mission, you have a transfer vehicle that will carry the crew and mission specific payload. It rendezvous with the cycler, more or less paying the same delta-V cost as the start of a Mars mission. Except it only pays the propellant cost for the crew and the mission payload, it does not have to pay for the habitat module. You will be re-using the delta-V for the hab module by using the cycler. When the cycler passes by Mars, the transfer vehicle leaves the cycler and burns enough propellant (or aerobrakes in the Martian atmosphere) to delta-V into Mars orbit. The cycler goes on its merry way, still full of delta-V, still available for re-use by a future expedition.

Keep in mind that you still need the propellant for the people and mission payload. But saving the propellant needed for the habitat module is a huge help.

Hop David has computed the orbits for Earth-Asteroid cyclers, discovering the existence of virtual "railroad towns".

Business Opportunities

RocketCat sez

I'm not sure if it is the third or fourth oldest profession, but salesman/con-artist/uses-car-dealer/grifter is one of the oldest.

It warms the liquid-hydrogen cooled cockles of my so-called heart to see you innocent naive simpletons who believe that humans will somehow become all noble and altruistic in the glorious space frontier. But that's not the way to bet. As long as there are space folk with money out there, others will be endlessly trying to figure out how to transfer those credit coins from the folk's pockets into theirs.

Since credit transferal by blatantly illegal means is covered elsewhere, here we will talk about the more legal means. The start is to discover a "hole in the market", that is, some desirable product or service that space citizens are willing to buy with their hard-earned credits.

If you can find one that is actually new, so much the better. Just be sure to cash in quick because scummy low-life copy-cats will rapidly try to make cheap knock-offs of your product. Or you might be returning the favor to some other company's lucrative monopoly (in which case you are obviously not a scummy low-life copy-cat, nay you are a virtuous monopoly-buster).

I compiled the list below simply by looking for clever solutions to major problems faced by space dwellers, then asking the question "how can I make a buck off of this?"

And never forget the attractiveness of a one-stop solution.

Example: A rock-rat asteroid miner delta-Vs to Billstown to shop. Packages of disposable space suit diapers might be over in the clothing section. Anti-fogging space helmet moist towelette packets are way over there in utility goods. Suit maintenance tools are in the hardware department. Emergency puncture repair patches are in the repair section.

Both you and I know that the rock-rat ain't a gonna waste their time bouncing around the entire freaking store looking for all this crap. They will probably only put one or two of the items in their shopping drone, which means Bill is not extracting the maximum amount of moola from the rock-rat's wallet.

But what if the rock-rat walked into Billstown, and saw by the entrance a stack of "Space-suit kits?" A nice shrink-wrapped canister containing a pack of diapers, a couple of boxes of anti-fogging towelettes, a modest suit maintenance tool set, and a stack of puncture repair patches. All in one box at a low-low price.

Bill has lowered the purchasing friction to a point where nine times out of ten the rock rat will buy the kit, thus buying all of those space suit products instead of just one or two. Bill is no longer leaving money on the table.

You may have encountered something like this at your local hardware store, say a kit of various cleaning products (a selection of soaps, detergents, sponges and brushes, all wrapped up in a cleaning bucket). The urge to purchase one is almost irresistible. A simple one-stop-shop item, a "kit" with all you need in a single package, just grab it and walk to the checkout line and you are done. I actually saw somebody look at one of those kits and say "I want to buy this, but I don't know why!"

That's the magic of a one-stop solution. "It's a Kit!"

In his novel Going Postal, Writer Terry Pratchett put it this way: “(The Postmaster) made a mental note: envelopes with a stamp already on, and a sheet of folded paper inside them: Instant Letter Kit, Just Add Ink! That was an important rule of any game: always make it easy for people to give you money.”

An example of a kit is "Beams-R-Us" below. If they just sold laser time that's will get them a bit of money. But if they also rented beam-rider spacecraft (just like a U-Haul truck) and had beam-riding cargo transports riding their own beams like a railroad train riding on its owner's railroad track, well, "It's a Kit!". Beams-R-Us has become one-stop shopping for all your interplanetary shipping needs. They might even branch out and offer spacecraft purchase financing, and cargo transport insurance. Why go to five different companies when you can get it all done at Beams-R-Us?

As I've mentioned so many times you must be sick of it, in the California Gold Rush of 1849, it was not the miners who grew rich, instead it was the merchants who sold supplies to the miners. Once people are traveling in space, there will arise numerous business opportunities to sell things to traveling people.

Please note that none of these are MacGuffinite, they are not economic motivation for the colonization and industrialization of space. But once there are people in space, they become potential customers.

Science fiction authors should note that the presence of these various spacegoing corporations can lead to a very colorful background for their novels. Indeed, the history of how a given corporation got started could be an interesting series of stories. Things are raw and cut-throat on the space frontier, especially when the people starting the company are novices learning the ropes the hard way. Hilarity ensues.

Laser Launch Services

Remember that once you get to orbit you are halfway to anywhere. So a company offering an affordable way to get your payload and crew into orbit will find their services in high demand. Freeman Dyson is of the opinion that a large country such as the United States should invest in such a service and offer it at a nominal fee, in order to promote interplanetary Prairie Schooners. See below.

For a grittier more ruthless-corporation view of the laser-launching business, do check out Jerry Pournelle's Laurie Jo Hansen stories, available in the collection Exile And Glory.

IKEA Space Habitat Modules
People living in space need a habitat module to live in (or they will rapidly stop living). So there is a build-in market. Flimsy cheap modules will do for orbital or asteroid locations. But sturdier modules will be needed if it has to be able to stand under its own weight on a planetary surface, or accelerated by a rocket engine if used as an impromptu spacecraft. In the real world Bigelow Aerospace is actively developing this, using NASA TransHab technology.
Wagon Train in Space

Jerry Pournelle foresees that with the availability of a laser launch service coupled with affordable habitat modules could lead to wagon train in space.

Mom and Pop pioneers/rock-rats/space-entrepreneurs just need the price of a hab module and laser boost fees for the overhead of space access. This gets them into LEO.

Then all Mom and Pop need (besides supplies for their business model) is transport. The Wagon Train Company would have orbital tugs for hire with regular service to haul hab modules to various interplanetary destinations. The tugs could probably haul long strings of hab modules at a time, especially if the tugs had a waterskiing thruster arrangement. Wagon train indeed!

The tug would probably also haul a company emergency module. If one of the hab modules springs a leak or otherwise has an emergency, the company module could rescue them. In exchange for a stiff fee, of course. In the wild west, wagon trains were mostly for mutual assistance, so the inhabitants of the various hab modules would probably want to try and help each other. Only if nobody offers any help would the unlucky Mom and Pop have to mortgage their souls to the company emergency module.

For a bit more money, travelers could upgrade from a rocketless habitat module to something with minimal rockets. Brian McConnell and Alex Tolley have a great concept called the Spacecoach that would be just perfect. But it would still make sense to travel in a wagon train led by a Wagon Train Company transport (even if you do not need their hauling services). Just in case you suddenly need the services of the company emergency module.

The Motel Aldrin

Entrepreneurs could sell habitat module services between Terra and Mars by making a space-going motel into an Aldrin Cycler. Space explorers on a budget would only need enough delta V to get themselves and their payload up to Mars transfer velocity, they could then rent a room and life-support services at Motel 6 km/s. This concept is quite similar to the Wagon Train in Space.

Convoy Services

Spacecraft going to a given destination, e.g., Mars, will tend to clump into convoys in order to take advantage of Hohmann transfer windows. Clever operators will have special ships in the group: not to travel to Mars but to do business with the other ships in the group (with an eye to making lots of money).

Things like being an interplanetary 7-Eleven all night convenience store, selling those vital little necessities (that you forgot to pack) at inflated prices.

A fancy restaurant spaceship for when you are truly fed up with eating those nasty freeze-dried rations.

A space-going showboat for outer space riverboat gambling.

An (expensive) health clinic, when you are not sure if that is merely a tummy-ache or actually full-blown appendicitis.

A flying bar with a wide variety of vacuum-distilled liquors (anybody for a Pan Galactic Gargle Blaster?).

Not to mention a orbital brothel.

Fans of TOS Battlestar Galactica will be reminded of the Rising Star, luxury liner and casino in space.

And the owners of an wagon train in space might want to add a couple of these company-owned modules, to sell stuff to the wagon train riders.


Orbital laser services might be just as lucrative as laser launching services. Owners of cheap laser thermal rockets could rent laser time from Beams-R-Us. Not to mention spacecoach owners. You could probably even rent the cheap laser thermal rockets for use with the laser time.

For that matter, Beams-R-Us would probably have their own cargo laser rockets for transport services, making them the interplanetary equivalent of the railroad (The Laser Horse). Even if there is no initial need for such services, a government might create it for political reasons. Even if it is eventually taken over by the military.

A laser railroad could easily become Wagon Train in Space.

See above for technical details on laser thrust services.

Orbital Propellant Depots

The multi-billion dollar Terran petroleum industry is a model for offering the services of orbital propellant depots. Since propellant is the sine qua non of rockets, owning a network of such depots and the supplying them by in situ resource utilization will be a license to print money.

There is also money to be made on the side by being the interplantary equivalent of a 7-Eleven convenience store attached to a gasoline station. With the same inflated prices.

Rob Davidoff and I worked up a science fiction background where the Martian moon Deimos becomes the water supplier for the entire solar system. We call it Cape Dread.

Momentum-energy Banks

These are giant spinning bola-like tether propulsion installations. A pod with engines not much stronger than attitude jets can attach itself to one and be precisely catapulted at a destination with many gravities of acceleration. At the destination the pod is caught by a similar installation. All for a fee, of course.

For an interplanetary Prairie Schooners owned by a Ma-and-Pa company, momentum-energy banks dovetail nicely with laser launch services. It doesn't matter that your tin-can habitat module has the same delta V as a can of underarm deodorant spray. The laser will boost it into orbit and the bola will sling it to the destination. The limits are [a] you can only travel between momentum-energy banks installations and [b] do you have enough money to pay for the bola services?

A "gold" strike in an asteroid belt or the establishment of a military base in a remote location may create a "boomtown". The sudden appearance of large numbers of asteroid miners or enlisted people is an economic opportunity to sell them whiskey, adult entertainment, and other hard to find luxuries at inflated prices. Not to mention supplies and tools. Civilian entrepreneurs may find it expedient to connect their ramshackle spacecraft together to make impromptu space stations. For an amusing look at the development and economy of a boomtown watch the movie Paint Your Wagon. But remember that boomtowns can become ghost towns quite rapidly, if mineral strike dries up or the military base is closed.
Camp Followers
Military units operating in a remote location will often attract "camp followers." These are civilian hangers-on who officially or unofficially see to needs of the troops. Official camp followers could be civilian contractors supplying official items like fuel, signal flares, and fragmentation grenades. Unofficial camp followers supply services like cooking, laundering, liquor, nursing, sexual services, and sutlery. For a price. Unofficial camp followers are notorious for after-battle scavenging and looting.
Sears, Robot & Co.
In the 1900's the Sears, Roebuck & Co. made good money doing mail-order catalog sales to rural inhabitants. The same model might be applied to asteroid dwellers. See below
Asteroid Mining Services
Asteroid miners have lots of needs that entrepreneurs can fulfil. From renting mobile refineries to purchasing ore. Although in reality the economies of scale seem to preclude individual mom-and-pop asteroid metal miners, volatile mining might be their only option.
New and Used Spacecraft Yards
Don't forget Dealer Dan, The Spaceship Man with his wide selection of new and slightly used rockets. "Now this little beauty was owned by a little old lady who only took it out on alternate synodic periods..."
Sears, Roebuck & Co.

Farmers did business in small rural towns. Before the Sears catalog, farmers typically bought supplies (often at high prices and on credit) from local general stores with narrow selections of goods. Prices were negotiated, and depended on the storekeeper's estimate of a customer's creditworthiness. Sears took advantage of this by publishing catalogs offering customers a wider selection of products at clearly stated prices. The business grew quickly. The first Sears catalog was published in 1888.

...By 1894, the Sears catalog had grown to 322 pages, featuring sewing machines, bicycles, sporting goods, automobiles and a host of other new items. By 1896, dolls, stoves and groceries had been added to the catalog.

... Rosenwald brought to the mail order firm a rational management philosophy and diversified product lines: dry goods, consumer durables, drugs, hardware, furniture, and nearly anything else a farm household could desire.

...In 1906, Sears opened its catalog plant and the Sears Merchandise Building Tower in Chicago. Also, by that time, the Sears catalog had become known in the industry as "the Consumers' Bible". In 1933, Sears issued the first of its famous Christmas catalogs known as the "Sears Wishbook", a catalog featuring toys and gifts, separate from the annual Christmas Catalog. The catalog also entered the language, particularly of rural dwellers, as a euphemism for toilet paper. From 1908 to 1940, the catalog even included ready-to-assemble kit houses.

Novelists and story writers often portrayed the importance of the catalog in the emotional lives of rural folk. For children and their parents, the catalog was a "wish book" that was eagerly flipped through. It was not a question of purchasing but of dreaming; they made up stories about the lives of the models on the pages. The catalog was a means of entertainment, though much of its magic wore off with the passing of childhood.

(ed note: now, in your mind, replace "rural" with "asteroid belt")

From the Wikipedia entry for Sears
Sears, Robot & Co.

Looking today at another article talking about the difficulties of infrastructure for space colonization with comparisons to the colonization of the West, I think there is one element in the latter that has been overlooked so far.

The Sears catalog. Kit homes included, and lengthy lead times on delivery also included.

Yes, I am picturing the future equivalent of Sears, Roebuck, & Co. having a big warehouse near Luna with giant mass driver attached, ready to lob e-catalog products at customers all over the System on demand.

For science! profit!

Also, IKEA inflatable habitats. Hopefully those two screws and the brackety-widgety-thing you had left over didn't do anything too important...

(ed note: and if your primary habitat O2 tank springs a leak, Sears Robot & Co will be happy to send a high-priority high-delta V shipment to save your life. After you use interplanetary internet public key encryption protocols to cybernetically sign in your own blood a mortgage on your soul.)


Mr. Blue:

Some station societies would form in a very organic fashion.

Let's say there's a big rush to mine (X) in the asteroid belt and a lot of independent prospectors head out to strike it rich.

Bill figures he can make a fortune selling space suits, mining tools and the like, so he loads up a freighter and sets up shop. Sally also had the idea of setting up a hydroponic farm/ yeast vat/ and restaurant, and also headed that way. As it's a pain for a miner to make two different stops, Bill and Sally decide to dock their freighters (man, there is no way to say that without sounding dirty) and maybe even set up an extra hab for a hotel...

Pretty soon, as word gets round, other enterprising individuals begin to connect. Bits and pieces are added — an empty fuel tanker as a bar, a repair yard, or even an official buyer for (X) — sure, he doesn't pay as much, but it's a lot better that flying it to Mars yourself. And other services begin to set up shop.

Then, Billstown becomes an interplanetary destination in it's own right. After all, where else on the 'Belt can one get their ship fixed, pick up some spare hands, have a good meal and a drink, and, um, visit the Seamstresses (hem hem).

Of course, once the mining runs out (or whatever else), the boomtown becomes a ghost town. Any spaceworthy ships will be flown off, everything else may be left behind, or salvaged.

But, if the location is good enough, this random jumble of habs, freighters, and other items can become something better...

(ed note: in Terry Pratchett's marvelous Diskworld series of satirical fantasy novels, the "Seamstresses" was an euphemism for the local brothel)

From comments to Transport Nexus
Gas (Giant) and Go!

(ed note: This is for the Traveller role playing game. In the game, starships usually refuel at a spaceport but can refuel by skimming gas giants in the wilderness. Some star-captains avoid spaceports in favor of gas giants because it saves money. Unfortunately there are no space stations around such gas giants for your journey weary crew's benefit. The government of the solar system may notice a business opportunity.)

Okay ships use wilderness refueling to save credits. However, their crews do have money to spend. While their captain won't want to head for the mainworld, which has no market for his cargo, the crew still wants some leave. Even a few hours. Smart captains will give a little. Forward thinking world governments will see a way to make some bucks off passing ships.

Presenting Last Chance Outposts. Also known as side ports, gas 'n goes and a variety of less wholesome names.

Many worlds with a C starport or worse establish a space station near the inner gas giant. Sometimes it's an orbiting base. Other worlds use one or more large insystem craft, the better to meet captains eager to make their schedule. The mobile outposts carry a variety of merchandise, spares, filters, vacc suits, ship's locker items and personal weapons.

A number of outposts have very basic repair services have basic repair stations and a large EVA crew to perform them for ships that have been damaged during refueling. Without exception such repairs always take at least a few hours allowing the ship's crew to partake of the other outpost services.

An outpost will have a restaurant of some type. They vary in quality though most at least serve fresh food. After all the crew can get microwaved packaged crap onboard for nothing. Other shops will sell local goods such as luxury items or handcrafts all at steep mark up.

There is usually a compartment or several reserved for various illicit activities. These red lit corridors have almost anything you could imagine for sale or rent though what's illicit varies wildly from world to world. You might wind up in a coffee bar or out of uniform. Note this section is not openly advertised and requires some Streetwise or Steward skill to learn about and enter (as well as credits).

Finally each outpost has a cargo hold filled with a variety of items for speculation. A lot of haggling happens here. A great many items are organic in nature. Dumping food cargos due to spoilage, mold or fungal infection is common. So common that no one really looks into it. Some dumped cargoes find their way to an outpost where they can be bartered for other organics leaving no paper trail for the revenue services to follow and tax.

Other cargos can find their way to the cargo hole depending on how believable a story the captain can come up with. You might get away with saying you dumped some pcs with viruses downloaded from the factory that weren't worth debugging for example or saying you got swindled on some goods and threw them out the airlock ("What the hell are 'Bollex' wrist chronometers?!")

Some outposts are owned outright by the mainworld governments. The mobile outposts are often franchise owners moving from system to system or in many cases squatters on the gas giants of worlds that haven't the means of chasing them off or assuring they get a cut of the profits.

Another lucrative role for these entrepreneurs is as camp followers, tagging along behind a large mercenary group or an invasion force catering to the military's whims. War can be a cash cow no matter who wins.

From Gas (Giant) and Go! by Rob Garitta (2015)

Laser Launching

Laser Launching is a remarkable inexpensive way to get payload into LEO (aka "Halfway to Anywhere"). Unfortunately it requires lots of money for creating the initial facillity.

Genius Freeman Dyson believes it would be a good investment for a country such as the United States to build a laser-launch site and charge a modest fee to anybody who wanted to boost a payload into orbit. Such as mom & pop asteroid mining businesses. This is similar to the political motivation behind the US transcontinental railroad mentioned here.

An affordable space-going version of a Prairie Schooner could be purchased by private individuals, boosted into orbit for a modest fee by laser launch, then another modest fee to an ion-drive tug to join the wagon train to Luna, Mars, or the Asteroid belt. LEO is halfway to anywhere, remember? This would also allow grizzled old asteroid miners to go prospecting in the belt.

For a possible space-going Prairie Schooner, take a look at the Spacecoach concept.

A Step Farther Out

That's the concept, and I think I was the first to use it in a science fiction story. Imagine my surprise, then, when at an AAAS meeting I heard Freeman Dyson of Princeton's Institute for Advanced Studies give a lecture on laser-launched systems as "highways to space."

Dyson is, of course, one of the geniuses of this culture. His Dyson spheres have been used by countless science fiction writers (Larry Niven cheerfully admits that he stole the Ringworld from Dyson). One should never be surprised by Freeman Dyson—perhaps I should rephrase that. One is always surprised by Freeman Dyson. It's just that you shouldn't be surprised to find you've been surprised, so to speak.

Dyson wants the U.S. to build a laser-launching system. It is, he says, far better than the shuttle, because it will give access to space—not merely for government and big corporations, but for a lot of people.

Dyson envisions a time when you can buy, for about the cost of a present-day house and car, a space capsule. The people collectively own the laser-launch system, and you pay a small fee to use it. Your capsule goes into orbit. Once you're in orbit you're halfway to anyplace in the solar system. Specifically, you're halfway to the L-5 points, if you want to go help build O'Neill colonies. You're halfway to the asteroid Belt if you'd like to try your hand at prospecting. You're halfway to Mars orbit if that's your desire.

America, Dyson points out, wasn't settled by big government projects. The Great Plains and California were settled by thousands of free people moving across the plains in their own wagons. There is absolutely no reason why space cannot be settled the same way. All that's required is access.

Dangerous? Of course. Many families will be killed. A lot of pioneers didn't survive the Oregon Trail, either. The Mormons' stirring song "Come Come Ye Saints" is explicit about it: the greatest rewards go to those who dare and whose way is hard.

That kind of Highway to Space would generate more true freedom than nearly anything else we could do; and if the historians who think one of the best features of America was our open frontiers, and that we've lost most of our freedom through loss of frontier—if they're right, we can in a stroke bring back a lot of what's right with the country.

Why don't we get at it?

Dyson envisions a time when individual families can buy a space capsule and, once Out There, do as they like: settle on the Moon, stay in orbit, go find an asteroid; whatever. It will be a while before we can build cheap, self-contained space capsules operable by the likes of you and me; but it may not be anywhere as long as you think.

The problem is the engines, of course; there's nothing else in the space home economy that couldn't, at teast in theory, be built for about the cost of a family home, car, and recreational vehicle. But then most land-based prefabricated homes don't have their own motive power either; they have to hire a truck for towing.

It could make quite a picture: a train of space capsules departing Earth orbit for Ceres and points outward, towed by a ship something like the one I described in "Tinker." Not quite Ward Bond in Wagon Train, but it still could make a good TV series. The capsules don't have to be totally self-sufficient, of course. It's easy enough to imagine way stations along the route, the space equivalent of filling stations in various orbits.

Dyson is fond of saying that the U.S. wasn't settled by a big government settlement program, but by individuals and families who often had little more than courage and determination when they started. Perhaps that dream of the ultimate in freedom is too visionary; but if so, it isn't because the technology won't exist.

However we build our Moonbase, it's a very short step from there to asteroid mines. Obviously the Moon is in Earth orbit: with the shallow Lunar gravity well it's no trick at all to get away from the Moon, and Earth's orbit is halfway to anywhere in the solar system. We don't know what minerals will be available on the Moon. Probably it will take a while before it gets too expensive to dig them up, but as soon as it does, the Lunatics themselves will want to go mine the asteroids.

There's probably more water ice in the Belt than there is on Luna, so for starters there will be water prospectors moving about among the asteroids. The same technology that sends water to Luna will send metals to Earth orbit.

Meanwhile, NERVA or the ion drive I described earlier will do the job. In fact, it's as simple to get refined metals from the Asteroid Belt to near-Earth orbit as it is to bring them down from the Lunar surface. It takes longer, but who cares? If I can promise GM steel at less than they're now paying, they'll be glad to sign a "futures" contract, payment on delivery.

It's going to be colorful out in the Belt, with huge mirrors boiling out chunks from mile-round rocks, big refinery ships moving from rock to rock; mining towns, boom-towns, and probably traveling entertainment vessels. Perhaps a few scenes from the wild west, or the Star Wars bar scene? "Claim jumpers! Grab your rifle—"

Thus from the first Moonbase we'll move rapidly, first to establish other Moon colonies (the Moon's a big place) and out to the Asteroid Belt. After that we'll have fundamental decisions to make. We can either build O'Neill colonies or stay with planets and Moons. I suspect we'll do both. While one group starts constructing flying city-states at the Earth-Moon Trojan points, another will decide to make do with Mars.

From A Step Farther Out by Jerry Pournelle (1979)

Orbital Tug

Early Days - economics of private space services

The reason an orbital tug is attractive is that rockets can launch much heavier payloads to a low orbit than they can to a high orbit. If the rocket does not have to launch hardware for moving the payload to a higher orbit then mass is saved, allowing the customer to use a cheaper launch vehicle or to launch a heavier payload for the same price.

An orbital transport provider would use a spacecraft, commonly called a tug or taxi, to deliver a payload to a different orbit. Ideally this vehicle would be reusable. This has been an area of active research since the 60's if not earlier, but I would argue that the ESPA ring and particularly the LCROSS mission represent a major step forward. The next step in this vein is probably the SSPS / Sherpa proposal from Spaceflight Inc for smaller payloads. Larger payloads could be handled by a Boeing ACES, Lockheed Martin Jupiter, ISRO PAM-G, RKK Energia Parom or Ad Astra concept vehicle. Of those, only Boeing and ISRO are known to be testing hardware. As far as I know, Boeing is the only contender investing heavily in microgravity cryogenic fluid management; this is a serious roadblock to in-flight refueling, which is a fundamental requirement for reusable tugs.

Ion-powered vehicles are popular concepts since they are so fuel-efficient. One drawback is that an ion-powered spiral from LEO to GEO exposes the payload to the Van Allen radiation belts. A possible solution is for the tug to provide radiation shielding for its payload during transit.

The Jupiter proposal is an example of a reusable tug with no depot. Tug fuel is included on the same launch vehicle as the payload. This is an efficient approach that minimizes risk in the near term. On the other hand, using a depot would allow the tug operator to purchase fuel at the lowest available launch cost and free up all available capacity on the customer's launch vehicle for their payload.

Satellite maintenance is in some ways an extension of an orbital tug. Either fuel or replacement parts are taken from LEO to the satellite's orbit. The craft is fueled, repaired or maintained in position while still operating. The largest market for this service is probably geosynchronous communication satellites, where receiving extra RCS fuel could extend their service lifetime by a decade or more. NASA has done in-space research on this subject under the Robotic Refueling Mission on ISS. Vivisat and MDA have both done work on commercial refueling services, with MDA's entry including a manipulator arm that could be used for ORU-style maintenance as well as refueling.

Adding the ability to swap out solar panels and transponders, a satellite bus could double its profitable lifespan. To take advantage of this the satellite needs to be designed for on-orbit maintenance from the beginning, similar to the way the ISS uses orbital replacement units.

An extension of this would be for a tug to retrieve a satellite and deliver it to a manned repair facility. Satellites with power or communication failures could be rescued or recovered this way, examined by human technicians, then possibly repaired and returned to their service orbit depending on the damage. Right now satellite operators are required to provide their own end-of-mission contingency; in most cases that means reserving a significant chunk of RCS fuel to either deorbit or move to GEO parking orbit. Having a service tug available might allow operators to eliminate that reserve, extending the useful life of satellites (potentially by several years) at the cost of a single tug mission.

In the longer term, most satellites at end of life are still structurally sound. If we start designing satellites with fully-replaceable parts then there is no reason why a GEO sat couldn't be retrieved, refueled, given new power hardware and upgraded navigation and outfitted with a new set of transponders before being placed back in GEO, all automated or remote-controlled. The basic structural bus might last many decades. Even for satellites currently in graveyard orbit, if a suitable crewed facility was available then the owners of those craft would gain considerable value from that mass by refitting or selling the bus to be refitted by someone else.


In 2010 Brian S. McConnell and Alex Tolley developed the Spacecoach concept and published it in a paper Reference Design for a Simple, Durable and Refuelable Interplanetary Spacecraft. This relatively low cost orbit-to-orbit spacecraft would be admirably suited for wagon trains in space. They could actually open up the solar system to pioneers if coupled with a low-cost surface-to-orbit transportation system such as a laser launcher. But McConnell and Tolley think the mass could be brought down enough to bring it within the boost capacity of, say a SpaceX Falcon 9 or Falcon 9 Heavy.

The basic premise of the spacecoach is to create a fully reusable orbit-to-orbit spacecraft that uses water and waste gases from crew consumables as its primary propellant.

So the design makes the consumables mass do double duty: first as life support for the crew, then as propellant. This drastically lowers the mass of the spacecraft, thus lowering the cost.

This also removes the incentive to install an expensive and cantankerous closed ecological life support system. Yes, supplies for a multiple year journey take up a lot of mass, but since it can be lumped under the heading of "propellant" it does not matter as much.

The water component of the consumables can do triple or quadruple duty. Before it is used as propellant, it can also serve as radiation shielding, supplemental debris shielding (as pykrete), and thermal regulation. In his simulation boardgame High Frontier developer Philip Eklund called water "the most valuable substance in the universe", and he was not kidding.

The spacecoach is also mostly constructed of water, in the form of pykrete. Very little metal is to be used.

The spacecoach will have sizable solar cell arrays used to power some species of electric rocket. There is some research underway to determine which of the many electric propulsion systems works best with water.

Ion drives, VASIMR, and helicon double layer rockets won't work because they are electricity hogs. They need to be fed by a nuclear reactor or equivalent, solar cells are too weak. Besides the insane price tag on a reactor and the ugly mass penalty, governments will be dubious about entrusting Ma and Pa Kettle with nuclear energy. They do have wonderful exhaust velocities, but the price is just too blasted high. Some won't even work with water as propellant.

Hall Effect Thrusters, Microwave Electrothermal Thruster (MET), and Electrodeless Lorentz Force Thruster (ELF) are much more suitable. They require much more modest amounts of electricity. Their exhaust velocities are weaker than the electricity hogs, but they are still much more potent than puny chemical rockets. These drives are also simpler to fabricate (i.e., cheaper, more reliable, lightweight, durable, and easily serviced). They can be clustered into arrays in order to increase the thrust. Electricity hog drives start interfering with each other if you cluster them.

The MET is especially simple. It isn't much more than a metal tube with a microwave magnetron attached. No moving parts either. It is sort of like a cross between a rocket engine and a microwave oven.

Current research shows a MET using water propellant can crank out a good 8,800 m/s exhaust velocity (Isp 900 sec) while an ELF can do about 16,700 m/s (Isp 1,700 sec). A Hall Effect thruster using water could theoretically do 29,000 m/s (3,000 sec) but researchers are still trying to figure out how to adapt them to water propellant.

For back-of-the-envelope calculations figure a spacecoach engine can do from 7,900 m/s to 20,000 m/s exhaust velocity (Isp 800 sec to 2000 sec). Compare this with chemical rocket's pathetic 4,400 m/s (450 sec).

20,000 m/s might not be quite enough to manage a trip to Ceres (10.593° inclination to ecliptic means a lot of delta V is needed), but the performance may be improved with more research.

The low thrust also minimizes the need for mass-expensive structural members.

McConnell and Tolley do have several design competitions open.

A Conestoga Wagon For The Solar System

In December 2010, the Journal of the British Interplanetary Society published our peer reviewed paper, "Reference Design For A Simple, Durable and Refuelable Interplanetary Spacecraft".

The paper describes a ship made mostly of water, powered by microwave engines, that will be capable of reaching destinations throughout the solar system, at just 1/10th to 1/100th the cost of conventional chemical rockets.

The system described in the paper is based entirely on existing technologies that have already been flight tested or are well under development, and is feasible with present day technology and Earth launch platforms to low orbit.

These ships, in addition to being cheaper to build, will be fully reusable, and will be mostly organic structures that will be far more comfortable than conventional capsule designs, and more like a scaled down version of Gerard K O'Neil's proposed space colonies than a metal ship.

We're coining the term spacecoach to describe these ships, a reference to the prairie schooners of the Old West.

We hope you enjoy this site and share it with your friends and colleagues.

Brian S McConnell
Alexander M Tolley
From the introduction at the Spacecoach website
Spaceward Ho!

The covered wagon or prairie schooner is one of the iconic images of the 19th century westward migration of the American pioneers. The wagon was simple in construction, very rugged, and repairable. They were powered most often by oxen that lived on the food and water found along the trail. The cost of a wagon, oxen and supplies was about 6 months of family wages.

In 2009 my colleague Brian McConnell and I were thinking about how to open up the exploration of space in an analogous way to the opening up of the American West during the 19th century pioneering era. We were looking for an approach that, like the covered wagon, was affordable, relatively low tech, provided safety in the case of emergencies and the space environment, could “live off the land” for propulsion like oxen, and preferably was reusable so that costs could be amortised over a number of flights.

What follows is a description of the “spacecoach” from the perspective of a new crew member making a first visit to the ship that will be on a Phobos return mission.

Our transfer vehicle docked gently with the Martian Queen airlock. On approach, the Martian Queen resolved into 4 fat sausages, linked end to end. On either side, from bow to stern, were solar PV arrays, partially unfurled. She looked like no spaceship seen since the dawn of the space age.. There was no gleaming metal hull, and she was devoid of all the encrustations of antennae and dishes of those earlier ships. Neither were there any signs of fuel tanks holding liquid cryofuels. Instead, the hull looked dull and somewhat like an old blimp, those non-rigid airships of the early 20th century. The only sign of exterior equipment were those solar PV panels. These were lightweight, moderate performance thin film arrays, extended out on booms to face the sun and drink her rays to power the ship. They looked more like square rigged sails as they fluttered every so gently in the tenuous atmosphere remaining at her orbit.

I knew from the briefing that the Martian Queen needed about 160KW of power, requiring about 800 m2 of arrays at Mars orbit. There was also talk of the next generation “spacecoaches” replacing the PV panels with lightweight rectennas, to convert microwave beams from the orbital transmitters. Most crews didn’t trust that idea yet, but adding a lightweight rectenna was considered a good idea to back up the PVs and also compensate for the lower intensity of sunlight as the newer ships were about to explore Jupiter space. So this was the Martian Queen, the “spacecoach” that would be my home, about to make her 2nd voyage to Phobos.

Following my crew mate Vicki, I passed through the airlock and entered a large space, nearly 60 m3 in volume, shaped like a large cylinder. The interior diameter was about 4.5 meters, about the same as the mothballed Orion I’d seen back at the Cape museum.. But with a length of 10 meters, the volume was 3x larger. The Martian Queen was composed of 4 modules, providing over 200 m3 of full sea level atmosphere pressurized volume, about 2/3rds that of the old Mir space station. Touching the inner skin of the hull it felt flexible, and slightly cool to the touch. A few light taps and the resonant sounds confirmed that there was liquid behind the skin.

Vicki answered my unspoken question about the liquid in the hull. Water was sandwiched between several layers of impermeable Kevlar in the hull. The primary, and ultimately end, use of all the water was for propellant. The spacoach had originally been folded for launch in a standard Falcon 9 fairing. Each module, without any propellant, weighed just 4 tonnes including payload. This was very little and reduced the deadweight mass of the ship. Once in orbit, the interior had been inflated and the hull filled with water. Most of that water had been launched by dumb, low cost boosters, but some was being supplied from extra-terrestrial resources. Supplies from the lunar south pole were becoming increasingly available as Chevron-Petrobras’ Shackleton base was building up mining production. Exploratory vessels were also initiating operations on asteroids, with 24 Themis looking promising with confirmed surface water. In a few decades, it was expected that all water would be supplied from extra-terrestrial sources.

“Why do you put all the water in the hull, rather than in separate tanks?” I asked.

Vicki explained that the water had a number of roles, not just as propellant. The primary reason was radiation protection. The water acted as a good radiation shield, with a halving of the radiation flux with every 18 cm (half value thickness of 18 cm). Starting with about 25 cm of water in the hull, the radiation level inside the module was just 40 percent of that striking the hull (0.5 ^ (25/18) = 0.38 = 40%). In the event of a major solar flare, the crew could also redirect the water to an interior tube to provide the best radiation shielding for the crew (storm cellar). It looked like that space could get very cozy for the crew, but better than suffering radiation burns.

But it didn’t end there. Micrometeoroids are a rare, but important hazard. The water acted as a shield, absorbing the energy of these grains and preventing penetration inside the hull. The tiny holes in the outer layers quickly heal too. The outer layers of water could be allowed to freeze, trapping a dense forest of fine fibers between the 2 outer fabric layers. This made a strong material, very much like pykrete [1] that offered a stiff outer hull to protect against larger impacts. At Earth’s 1 AU from the sun, reflective foils deployed over the hull allowed passive freezing of the outer layers providing both protection and a large heat sink for the engines.

A noticeable side effect of the hull architecture was the silence. There are no clicks and bangs from thermal heating stresses. Nor did the sunward side of the interior feel noticeably warmer. Thus the water was going to offer very good thermal control of the interior, with pumps in the hull circulating the water providing dynamic thermal control.

Vicki indicated that I should follow her forward to another module. This included the kitchen and dining space. There was a freezer of dried food packages that was being organized by Pieter. Enough for a long trip with a fair variety of meals.

“You seem to have ordered a lot of Boeuf Bourguignon”, joked Pieter.

I wondered when the taste of Boeuf Bourguignon would become rather tiresome after some months. Perhaps more spicy meals like curries would have been more appropriate. I noted that the water supply for rehydrating the food and drinks was connected to the hull too. Of course, I reminded myself, the hull was a huge reservoir of water, effectively inexhaustible are far as the crew was concerned, at least on the outward bound flight.

The facilities were oriented so that “down” was towards the end of the module. This was because during cruise the Martian Queen was going to be rotated, providing some artificial gravity(tumbling pigeon). This made the flight much more comfortable and familiar. We could even eat off regular plates.

(Spacecraft is 40 meters long, 20 meters spin radius. Nausea limit is 3 rotations per minute. At that rate of spin gravity at nose and tail will be 1/5 g, fading to zero g at spin center.)

Vicki quickly showed me the crew quarters and bathroom in the next module. The inner skin of the hull had been moulded into shapes that could contain water. The baths and showers were also connected to the hull’s water supply. The clean water input was connected to heaters and pumps to the various faucets and shower heads. The grey water from the drains was routed to the main purifier and returned to the hull. I inquired how frequently I could take a shower? Once, twice even three times a week?

“As much as you like”, said Vicki. “There is ample water supply for a single pass through the purifier for all the crew to shower once or twice a day. If the crew is particularly extravagant, even this can be increased with greater recycling. Hygiene is a huge morale booster on these trips.”

The toilet was apparently a composting type, although suitably modified for space. This made sense. The nitrogen and phosphorus was going to be needed for the plants growing in the interior, as well as the Phobos base agricultural areas. Nitrogen and phosphorus were still valuable elements with no rich, off-Earth supplies available. Ducking back into the kitchen space, it was clear that much of the interior was given over to growing plants. They provided the needed psychological connection with Earth, helped recycle the CO2, and freshened the air, removing unpleasant volatiles. The stale, locker room smell of most spaceships was almost absent. Some plants were also growing some fresh foods. I could just imagine the value of a fresh tomato after 6 months of spaceflight!

Pulling ourselves back through the leafy interior of the modules, I looked for the engine compartment in the last module. The engines were not obvious on docking, and I wondered where they were. At the rear of the last module, an airlock was currently open, showing an enclosed space beyond. Inside, Hans, the engineer was taking apart one of the engines. He was removing a metal liner from the engine and replacing it with a fresh one. He handed the old one to me and said “carbon deposits”.

I looked closely and saw what he was talking about. Carbon deposition from contaminants in the water supply could build up in the engines, reducing performance. The engines were not much more complex than microwave ovens, although they were fitted with electric grids to further accelerate the microwave heated water plasma.

The exhaust exited via the rear, when the bay doors were opened. Now they were closed, allowing the shirt sleeve repair of the engines. I asked how frequent engine repairs were. Hans informed me that an engine needed some rework after 3—6 hours of operation. The microwave electrothermal engine performance had an Isp of about 800s, although the secondary electric grids could double that by drawing on reserve energy from the solar arrays. Vicki thanked Hans and we drifted back to the main module.

I was a little surprised at the lack of windows, but pleased that there were many flat screens where windows should have been. I looked “out” and saw that I had missed the vernier and maneuvering jets on the hull.

“How are these powered?” I asked Vicki.

Hydrogen Peroxide, H2O2” she replied.

“Where’s the fuel?”.

“There isn’t any yet. It’s made during the flight. Some of the water in the hull is tapped off, run through that off-the-shelf, standard unit over there. We store the peroxide in hull pockets to wait for the next use. The peroxide engines aren’t very efficient, having an Isp of about 160s, but they provide higher thrust than the main engines and can be used to boost the ship for a faster departure, or land the ship on low gravity worlds with orbital delta-Vs of 0.5 km/s or less. The peroxide has other uses too. It can be decomposed to provide oxygen [3] more quickly than the main ESS electrolyzers, act as an energy store for emergency power [4] and finally as an excellent bactericide to keep the interior clean and remove the bacterial slimes and molds that grow on the inner skin, often in difficult to reach spaces. And before you ask, yes, we have rotating cleaning duties on the Martian Queen.”

So the water in the hull fulfilled a range of uses, before being finally consumed as propellant. Major uses included bathing, direct consumption, rehydrating food, growing plants and, of course, the main oxygen supply. It was converted to peroxide for the high thrust engines, for energy storage and for another emergency O2 supply.

“Vicki, a quick mental calculation seems to come up short on the water requirement for the flight. Is what I see all that is needed?”

Vicki smiled: “The impact of using water as propellant on performance is significant. The total water budget for the trip is about 4 times the total mass of the ship and payload, compared to about 14 times for a conventional liquid hydrogen and LOX chemical rocket, primarily because of the higher Isp of the electrothermal engines. But the low hull mass and reduced consumables payload reduces the main mass of the the Martian Queen allowing a much smaller, more efficient spaceship. She is also a lot roomier, more comfortable and much safer. An Apollo 13 type accident would not be survivable in a conventional ship, but we have very large reserves of consumables and oxygen for the crew to survive until a rescue or the return trajectory was complete. In addition, even without water supplies at Phobos, the baseline mission cost to Phobos and return is on the order of a $100m dollars. That is why your institution can afford to pay for your slot on this mission. Reusability of the Martian Queen for multiple missions, fresh water at Phobos, and better performing solar panels and electric engines will eventually reduce that cost perhaps another order of magnitude.

I pondered that for a moment. While not a cheap solution for interplanetary travel, it put the cost well within the realm of the super-rich and wealthy institutions. A mere decade earlier, a simple lunar flyby and return in an adapted Soyuz craft was priced at around $100m per passenger by Space Adventures. Spaceflight was definitely getting cheaper and safer.

If interplanetary travel is initially based around the design concepts of water propellant craft, then the economics and infrastructure requirements will be dependent on available supplies of water already in space at suitable locations for fuel dumps. Bodies that may harbor economically useful quantities of accessible water include the moon (shadowed polar regions), water rich asteroids and dead comets. A tantalizing possibility is Ceres, that Dawn is expected to rendezvous with this year (2015). Ceres is expected to have prodigious quantities of frozen water, possibly even a subsurface ocean. A mining operation to extract pure water from the brew of ice and chemicals might offer the opportunity to open up the inner solar solar system. Once at Jupiter, the icy moons offer an almost inexhaustible supply of water.


1. Pykrete

2. Bigelow Aerospace B330

3. 47kg O2/1000 kg H2O2 (10%)

4. ~2 MJ, kg.

5. J E Brandenburg, J Kline and D Sullivan, “The microwave electro-thermal (MET) thruster using water vapor propellant,” Plasma Science, IEEE Transactions on (Volume:33, Issue:2) pp 776-782 (2005).

6. E. Wernimont, M. Ventura, G. Garboden and P. Mullens. “Past and Present Uses of Rocket Grade Hydrogen Peroxide

From Spaceward Ho! by Alex Tolley (2015)

Interplanetary Internet

The Interplanetary Internet (based on IPN, also called InterPlaNet) is a conceived computer network in space, consisting of a set of network nodes which can communicate with each other. Communication would be greatly delayed by the great interplanetary distances, so the IPN needs a new set of protocols and technology that are tolerant to large delays and errors. While the Internet as it is known today tends to be a busy network of networks with high traffic, negligible delay and errors, and a wired backbone, the Interplanetary Internet is a store-and-forward network of internets that is often disconnected, has a wireless backbone fraught with error-prone links and delays ranging from tens of minutes to even hours, even when there is a connection.

From Interplanetary Internet entry in Wikipedia


Actually, given the great time lags in communications (and probable bandwidth issues), I would not expect interplanetary Tweets, phone calls or even emails.

Point to point communications would most likely resemble texting (including the incomprehensible abbreviations), but you would have anywhere from 1.4 seconds delay to the moon to many hours to Uranus.

This means another possible driver for high performance spacecraft would be mail delivery. (Consider a small car delivering 100 DVDs for Netflixx probably is carrying more information than you can access through your home internet connection in a day.) Contracts, magazines, movies, personal messages and anything else which needs more detail than a text message will all be loaded aboard mail servers on fast packets, and blasted to their destinations via the fastest means possible.

This of course leads to interesting scenarios where protecting and intercepting mail becomes important for intelligence agencies, business and criminals. Mail delivery will involve high levels of security and screening of the mail delivery personnel. I doubt anyone will hijack a mail packet in flight, but having a covert operative on board to hack the mail server and download the interesting information is a very real possibility.

Jim Baerg:

This sounds very implausible to me.

The light speed delays mean that all interplanetary communication will resemble emails with attachments more than phone calls.

The immense power required for torchship performance would make interplanetary communication lasers much more economical for sending even terabytes of data, much less an email greeting with a 1 MB photo.


Email in space — Should be no problem with this, even if the distances slow it down to telegraph speeds.

Text messaging in space — Will be restrained to within a few light-seconds, probably no more than 10 or so. Any longer than that and you might as well send a longer message.

Instant messaging — Will probably be restrained to 2-3 light-seconds. Like a phone call, any more delay defeats the whole purpose.

Physical packets — Documents that you don't want easily copied, high-density data storage for non-essential information (Movies, music, etc), items that can't be replicated at the destination (Due to lack of facilities), items that shouldn't be replicated at the destination (Gifts), and people (Diplomats, managers, mediators, etc).


To expand on Citizen Joe's point, would you like to receive "Male enhancement" emails with the olympusmon.mars address? How about "Dear Sir, I am the last surviving member of the Europan Resistance front and need your help to transfer $10 billion solars from the Bank of Callisto...."

On a more serious note, the high bandwidth links would probably be reserved for ship traffic, government and military communications and corporate communications (for companies with the financial clout to get in line for email). Certainly the Uranus Space Navy would not want the high bandwidth links clogged during their showdown with the Imperial Jovian Navy, nor would they want to risk malware or botnet attacks coming through those links; which suggests interplanetary comms would be tightly controlled and subscribers carefully vetted.


Since power and surface area aren't problems on the ground (and to a lesser extent, in orbit), communications would likely be predominantly TO ships while ship to shore (home base) comms would be limited to a confirmation of receipt. On Earth, we can afford to put up huge arrays to catch the smallest radio signal. Not so much in space. Likewise we can pump a lot of energy into the antenna to send back a longer message with a lot of bandwidth and strength even at stupendous ranges.

Now there are some tricks, like omnidirectional beacons and antenna that act as targets for the directional antennae. But you can only listen to data in the direction of the directional antenna. That might be limited to a single stream. Comm relays would likely have at least 4: Signal in, Signal out, Previous relay, Next Relay. By using multiple relays (at least 4 would get you around the sun) you wouldn't have black outs (except at ship orbit). And then there is the problem with the fragile gimbals needed for all the antennae.

In the end, yes, you can communicate via radio. No, it isn't broadband. No, it won't service a population comparable to the internet. It will likely be biased communication. It will still be expensive. There will be extreme needs that keep every carrier busy. So, although you COULD send a digital copy of Pluto Nash to Pluto, you would never get enough priority to use the carriers and thus it would be simpler to put it on a torch or fling it out the airlock.

Jean Remy:

What about relays at Lagrangian points?

Everyone knows where those are, and if someone needs to connect they can just link into the network. I don't even think lasers would even be needed. The relays would have high gain antennas to receive the data on broadband signals, and when a ship or colony needs to link in they can query the closest available platform with a much lower-gain antenna.

If we can be in contact with various probes (like Voyager probes) at interplanetary distances, on 1970s technology, then I hardly think you would need a giant technological leap to create a system-wide comm network.

Granted you won't have the bandwidth of fiberoptic cables, so no browsing for Earth-porn from Callisto, but I don't see communication as much of an impediment. The only real reason to use lasers (that I see) would be for private (read: military) communications that you don't want intercepted, but with a target area of 90 km in radius, it's not really very private anymore.


Surfing the interplanetary web would be a unique experience. Given the reply times measured in minutes or hours, getting a response for a search query would be more akin to making a request at the Library of Congress and then waiting for the attending librarian to go and bring you a copy of whatever they think you asked for (which may or may not be what you were actually looking for).

Since we survived the dark ages of dial-up modems, I think we could probably put up with the connection speed of the interplanetary net.


I think that interplanetary communications networks would be more like a cluster of 'webs'; one on Earth, one on Mars, one on Luna, ect. The different webs would send updates to each other on a regular schedule via dense-data/high-priority channels, and all other inquries/messages being sent via lower-priority channels. Most of your routine web activities would be with your local internet, but occationally you'd connect with another world's internet via the systen-wide web.

Jean Remy:

Interestingly enough, this is the way the "extranet" is postulated to work in the Mass Effect games. Essentially all colonies pack with them a web server full of the most needed and demanded data. If the information you are looking for is not on the server the system opens a communication link (FTL in the game) and hits the closest large colony server, and so on, until it finds the info, and it uploads it into the colony's server for easy retrieval later. In the game data storage is no longer an issue, but I assume if storage space is needed and a specific file hasn't been looked at for a while, it would be deleted.

However, since most early colonies will be science bases, I would assume large amounts of data will be passed back and forth as scientists on Callisto and on Earth look over the data, form theories and send them back and forth. It seems like a very fluid form of data exchange is needed even with local "nets". I also doubt early colonies will be very large, or widespread, and it is far more likely the Callisto colony terminals will be linked on a LAN to a single server rather than a network of servers in the first place.

Citizen Joe:

Viral propagation is another option. It doesn't guarantee speed or privacy. The idea would be that a message would be sent to any ship that is heading in the right direction that is within range. This could be a very long route. However, since there would likely be relatively few interplanetary vessels (compared to airplanes), Solar Space Traffic Controllers would have the full list of vessels and thus able to chart a route based on predicted paths. While the InterPlanetary Space ships would carry parcels, they would probably also serve as communication hubs for the viral network.


That sounds pretty close to how the modern internet functions, with data tracing geographically indirect paths as it goes from place to place. I like the efficiency of such a scheme: it would use the infrastructure that's already there to create an ad-hoc network backbone. On the other hand, you'd be trading out data security unless you've got some very good encryption (or just plain don't care who else reads your messages).

Jean Remy, I was thinking along those same lines. A lot of business/corporate/government entities would end up hosting proxies of their sites and databases on the far-flung colony servers, with periodic updates being beamed back and forth (ultra-secure data being handled differently).

With multiple proxies being hosted for a single database, with data exchange rates measured in minutes, how long do you think the system will last until Murphy's Law takes a server down through version conflicts?

Jean Remy:

Viral dissemination works on Earth because of thousands and thousands of privately owned servers.

However, even in the best-case scenario of a very developed interplanetary infrastructure, I don't see a lot of traffic in space. Say two cyclers between every major colonial epicenters (say 2 for Mars, 2 for the Jovian colonies, 2 for Saturn etc...) and a few "moon hopper" shuttles, but those would be so close to their giant primaries getting a Line of Sight on them would be an issue.

However the Comm relay platforms suggested are basically Voyager probes without the scientific instrumentation and a known stable orbit. Rather that throwing your message out omnidirectionally and hope that eventually it will reach your destination (because viral dissemination is kind of like shooting blind) you simply bounce the signal of a set number of known (and if want, secure) predetermined platforms. If your goal is to reach as many people as possible (the entire point of viral dissemination in the first place) then target the Cyclers. Chances are good the passengers en route back and forth have personal computers linked in to the ship's server, which keeps updated by linking in to the platforms.


The general outlines of communications in the plausible mid-future look a bit like the Victorian era. Fast and reliable close to home, a little slower if you want to contact the next 'city' over, slower again but still reliable if you want to contact another 'country', and best of luck to you if you want to contact someone in the backbeyond. In this case city, country, and backbeyond are defined by both linear distance and orbit.

You could even end up with a Pony Express situation. Someone sets up a Planet Express torchship delivery system to carry high information-density packages or mail that requires high-security delivery... And then nine months later someone else sets up a tightbeam relay network that can handle multiple high-bandwidth high-security messages... And suddenly you've got a lot of cheap ponies on the market.

Except in this case the ponies have 45 gW/30 milligee legs.

From On Torchships comments (2010)

Kessler Syndrome

This section has been moved here.

Landing Grid

This is very fringe science. I'm no expert, but the Richmond concept is probably more impractical than it is actually forbidden by the laws of science.

Nikola Tesla

Back in the early 1900's noted genius and mad scientist Nikola Tesla figured he could tap a conductive layer in Terra's upper atmosphere and used it to wirelessly broadcast electricity. The electricity would be held in standing waves around the entire globe, and could be tapped by machines in remote locations for electrical power. It would also make the entire upper atmosphere glow, making cities and shipping lanes happy while infuriating astronomers. Oh, and it would also work as a wireless telegraph.

While many of Tesla's devices were brilliant, this one was a total crack-pot idea. Telsa was suspicious of these new-fangled ideas about air-borne electromagnetic waves. Not to mention there was no way to send an electricity bill to the people using it.

Telsa managed to talk a bunch of investors into funding a pilot project, the Wardenclyffe Tower. The project was a disaster for various reasons and Telsa had a nervous breakdown.

Murray Leinster

About fifty years later science fiction writer Murray Leinster wrote a series of short stories featuring a huge device called a "landing grid." I have been unable to discover the source of Leinster's inspiration, but I suspect Telsa's Wardenclyffe Tower. As far as I have been able to determine the first of these stories was Sand Doom (1955), first of the Colonial Survey series.

Anyway a landing grid is a circular arrangement of steel girders and copper cables about half a mile high and one mile in diameter. It is set firmly into the planet's bedrock.

For a planetary colony, it supplies electrical power by tapping the electrical potential difference between the ground and the planet's ionosphere. The planet acts like a huge capacitor. One plate is the ground, the other plate is the ionosphere, and the insulating dielectric is the atmosphere in between.

Since the ionosphere is basically energized by the planet's sun it will supply electricity for as long as the sun shines. As to how much energy is available, the best I can say is "lots and lots." A certain Dr. Elizabeth Rauscher estimated that the ionosphere and magnetosphere had a potential energy of about 3 terawatts. No idea of how rapidly the energy would be replenished by the sun.

The second vital function a landing grid supplies a planetary colony is landing services. It can use technobabble tractor beams to grab a spacecraft at a range of tens of thousands of miles and gently lower it to land in the center of landing grid. Or gently lift a spacecraft from the grid up into space, releasing it several thousand miles altitude. The spacecraft does not have to spend horrific amounts of delta V to get halfway to anywhere. The inexhaustible supply of ionospheric electricity will do it for you.

The framework of girders requires about one foot of diameter for every ten miles of tractor beam range. They are typically one mile in diameter, giving the tractor beam a range of about 53,000 miles (about 6.7 Terran diameters).

When a new planetary colony is founded, the first construction crew lands in rocket-propelled vehicles (since there is no existing landing grid). Their priority is to quickly build a grid to get the colony started.

In theory, interplanetary and interstellar war was not possible in Leinster's novels. Naturally a planet would not be foolish enough to use their grid to land a hostile invasion force. And the grid was perfectly capable of attacking an enemy orbiting fleet with tractor-beam launched missiles, or even rocks for that matter. Without grid support, an invasion force trying to land troops would need lots of rockets with ugly mass ratios. The invading fleet can launch missiles and bombs, but they have limited supplies (limited to what they brought with them). The planet ain't going to run out of rocks.

And if the invaders destroy the landing grid, they will lose easy access to the surface. Worse, any invading forces actually on the planet will be stranded until a new grid can be constructed. So the invaders do not want to nuke the grid, but the grid can decimate their fleet with hypervelocity rocks.

The theory was exploded in Leinster's 1957 story The Grandfathers' War. Basically they built a space-going landing grid.

Conventional grids grab objects in space with a tractor beam and pulls it to the ground. This monster grabs the ground with a tractor beam and pushes the grid into space. Conveniently the FTL drive can operate the instant a ship (or space-going landing grid) is several planetary diameters away from the planet, so the grid does not even need any rockets. Directly into FTL drive it goes. The warlike grid travels under FTL drive then emerges into real space in orbit around the target planet. There it uses its tractor beam to land itself, instantly creating an invader-controlled grid on the surface of the hapless planet. The grid then lowers the hordes of invading troop carrier starships gently to the surface and the attack begins. The only question I have is can the space-going grid tap the target planet's ionosphere while in orbit?

Lucky for the peace of the galaxy, in Leinster's universe nobody ever copied the grid-ship idea, and it was forgotten. The idea was not used in subsequent novels.

Walt and Leigh Richmond

In 1962 Walter Richmond was doing research into atmospheric electricity and invented what he called the Solar Tap. It was a way to access the potential energy difference between the ionosphere and the ground, but it was rather hair-raising.

You build an insulator, a pyramid shaped pile of rock about 150 meters tall. Be sure you locate the insulator well away from the magnetic poles of the planet. From the peak is shot a powerful laser beam pulse to create a conducting ionized trail all the way to the ionosphere. A titanic bolt of lightning travels down the trail to hit the insulator. There equipment does its best to harvest as much of the lightning as it can, without destroying the equipment or too much of the surrounding landscape.

As an encore, distribute the energy world-wide by using some sort of technobabble Tesla style energy broadcasting technology.

Why is it so important to site this far away from the magnetic poles? Well, the lightning bolt will create a magnetic field cross-wise to the planet's natural magnetic field. The result is to pinch the bolt and stop it after a few microseconds. Then you shoot another laser blast to created the next lightning bolt. All nice and controlled.

If the insulator is at a magnetic pole, the lightning bolt's magnetic field will be parallel to the planet's field. The bold will not be pinched. It will be permanent until the ionosphere is depleted after a week or so (an "avalanche"). In other words about 3 terawatts of power will start evaporating the continent around the magnetic pole, split the tectonic plates and start the continents moving around, create nuclear winter, destroy all civilization and cause a global extinction event.

That would be bad.

In 1967 Walt and Leigh Richmond wrote The Lost Millennium aka Shiva. The idea behind the novel was that solar taps were not only possible, they had been invented about eight thousand years ago. The reason we were unaware of this is because the idiots back then had sited the main tap at the magnetic pole in the name of maximum power harvesting, and they resolved to be very very careful not to let an avalanche start. With predictable results. Pretty much erased their entire civilization, it did.

The reason the insulator for a solar tap is about the same size and shape as the Great Pyramid of Cheops is because the latter is an insulator for a solar tap. Apparently some survivors from Atlantis built Giza a couple of thousand years after the avalanche (the pyramid that caused the avalanche was pretty much obliterated). Well away from the magnetic pole you will note. The laser firing makes a noise that sounds like "SHEEEEE!" and the returning lightning bolt makes a sound like "OPS!". So the solar tap in operation sounds like SHEEE-Ops!, SHEEE-Ops!, SHEEE-Ops!. Which is where the Cheops pyramid got its name. Cute.

The novel includes all sorts of historical anomalies harvested from tales of Atlantis, ancient astronauts, and Chariots of the Gods? The reason archaeologists are not constantly stumbling over eight thousand year old automobiles and skyscraper girders is because the broadcast power system made large metal objects a dangerous idea.

Anyway the other item relevant to our interests is that the solar tap could also be used to boost and land spacecraft. The Richmonds are vague in the details but they maintain that a network of smaller pyramids can create a pattern of laser beams to craft a titanic Jacob's Ladder. The high-voltage traveling arc boosts or land spacecraft by electromagnetic induction. Somehow (the details are left as an exercise for the reader). In the novel, during boost mode the solar tap sounds like ANGOR-WATT! ANGOR-WATT! which is also cute.

In their later novel Gallagher's Glacier the Richmonds take up planetary liberation by solar tap. In the novel, all the poor planetary colonies are controlled by an evil corporation. The colonies are not allowed to have solar taps, because the corporation do not want the colonies to be anywhere near being self-sufficient.

Gallagher takes a tip from Leinster and mounts the solar tap on a spaceship. It is impossible for a colony to covertly build a solar tap over a couple of decades without the evil corporation goons noticing. But once Gallagher's space ship shows up, the colony instantly has a solar tap, and can use its energy to defeat the goons and kickstart building their own permanent solar tap.

Gallagher's Glacier

     The landing system was from what Gallagher called their solar tap. They were tapping the electrical potential that exists between a planet and its orbiting proton and electron belts—the belts of ionized particles caught in the planet's magnetic field.
     The landing system was part of a power system that produced, from this one site, enough electricity to power the entire continent on a broadcast basis.
     Broadcast power. It had been known on Earth since the days of Nicola Tesla—the system for putting power on the airwaves the way radio and TV are broadcast. Electric power that you could tune into, the way you tune in a radio.
     With broadcast power, you didn't have to have wires strung around the continent to plug in motors and appliances and furnaces and the like. You didn't have to carry your own fuel in! your ground car. You tuned in your motor to the power frequency, the way you tune in a radio to the frequency of the station you want to hear.
     Earth hadn't had broadcast power, though she'd known how to broadcast it, because the production of power was geared to installations that didn't have sufficient potential that you could waste it on the airwaves. But the power potential in the solar tap was so great you could throw it away on an inverse-square: basis and still be able to tune in at the coast lines, two thousand miles distant, and run anything you wanted to run, from a manufacturing complex to a skimmer.
     The power that exists between the ground potential on any planet and the orbiting proton and electron belts trapped in the magnetic field of any planet, is fed by the solar wind of the sun around which the planet orbits, and it is a practically limitless potential. Electrons from the solar wind make their way in through the magnetic poles of the planet, distribute themselves at its crust, and seep through the insulating atmosphere towards the strong positive potential of the inner proton belt.
     If you make a "short circuit" through the atmosphere by creating an ionized pathway with a laser beam that reaches to the ionosphere, the top of the insulating atmospheric layers, the electrons will jump across the short circuit, changing the groundside potential. When the groundside potential lowers, it makes it possible for more electrons to pour in from the solar wind to equalize the potential. The planet is effectively recharged, and you can short-circuit again.
     It's done in milliseconds, and it's done on a pulse-basis. You turn the laser-beam short circuit off and on in an alternating-current effect, and it's most efficient at a low sonic frequency, although it has radio-frequency overtones.
     There was a group of huge pyramidal structures that were the bases for the solar tap and landing system. A huge, central pyramid was the -tap itself; built of granite with a marble overlay, and of sufficient size to insulate the tremendous bursts of power flow from the ground. The laser installation was on a small platform at the peak of the pyramid, and the control systems were centered well inside where the X rays and other radiation from the flow would not harm the technicians.
     From this, central pyramid, the pulsed power was broadcast across the continent, and even from inside the canteen and at this distance you could hear the deep-throated roar of that power, pulsing through at a frequency within the audible range. Chee-ops, chee-ops, chee-ops, it seemed to say as it shorted in, was cut off, and pulsed in again.
     It was the landing system that used the smaller, satellite pyramids around the big one and that used other factors of the huge central pyramid as well.
     The landing system was a gigantic web of laser beams, angled upward and focused to create a huge electrical discharge spiral that used magnetic induction and repulsion to bring the meteors in. They could bring in any metallic ship as well on that huge spiral, even though the interstellar ships were comparatively fragile; for the gentle cradle of the magnetic induction-propulsion system could raise or lower the gigaton masses as evenly as a freight elevator might bring down a crate of delicate electronic equipment.
     The landing system. From the huge central pyramid, and from each of the smaller ones, two great alternating laser beams angled upward, aimed through tunnels internal to the pyramids and geometrically accurate to a hair. Those beams discharged their alternating spirals into a crisscrossed web of induction-repulsion that caught a ship and either stepped it up from rung to rung of the magnetic induction-propulsion ladder, or cradled it gently downward.

     "But where's the meteor we came down in, and what's your plan for it?" I asked. "That's a big plenty of steel."
     "Over there." He pointed to where I could see a glow in the sky at the center of the port complex. "We can use steel. We just use it with know-how."
     I stared at the glow in the sky. "Surely it couldn't have been that hot?"
     "That glow? That's not the meteor. That's the melting tap in operation. But the meteor did come in at a red heat, at least in its surface layers. You see, we land them direct into the furnace, "and as soon as everybody's clear, they change the frequency of the induction current and start melting them down. Saves quite a bit of time, and time's our most precious commodity. The energy we're not worried about—that we've got in plenty. But it takes time to reheat, and if the ejection mechanism doesn't work, it's a couple or three hours' setback to lose the heat that was built up during descent so that we can get the people out. And then we have to reheat the darned thing so we can melt it down."
     "Isn't that a rather expensive way to get steel?" I asked.
     He grinned. "You're just not used to the idea of really planetary power," he said. "Those meteors—asteroids, really—can be brought in, melted down, and ready to use for tool steel at a cost per ton of, say, a hundredth of a solar credit."

     The ridiculousness of shooting a planet with the ineffective sting of a fine-focused laser began to creep up on me. The focus on this device was so fine that it would probably make no more than a centimeter-diameter hole in whatever target it hit, and though that's plenty big to play utter havoc with a space vehicle, it would be less than the sting of a mosquito so far as a planet was concerned.
     "Set power pulse to three seconds."
     Gallagher's voice was slightly edged, but Cricket's came back in a singsong that showed no overtones of emotion.
     "Power pulse on three seconds by off point five seconds."
     "Initiate pulse."
     Cricket didn't have to respond to that one because the power machinery did it for her. There was a slow, rhythmic, mmm-pop, mum-pop from the power supply that went on and on and combined with the cheeee to form a now-familiar repetitive pattern; the song of power that I had heard on Betsy Ann: cheee-ops, cheee-ops.
     "I'll be damned," I yelled. "This thing's an upside-down solar tap!"
     There was a choke behind Gallagher's laugh, and his voice had a sweep and flow that spoke of tensions releasing.
     "We're way above the radiation belts," he said, "but the oscillating lens of our zoom focus makes an ionized path from Durango's ionosphere to its ground, and that's all you need for a tap. We didn't have time to build a pyramid down there, so we turned the tap upside-down."

From Gallagher's Glacier by Walt and Leigh Richmond (1970)

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