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?
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.
See the section on Laser Launching below.
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.
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.
Kuck Mosquito Propulsion H2-O2 Chemical Specific Impulse 450 s Exhaust Velocity 4,400 m/s Wet Mass 350,000 kg Dry Mass 100,000 kg Mass Ratio 3.5 ΔV 5,600 m/s Mass Flow 49 kg/s Thrust 220,000 newtons Initial Acceleration 0.06 g Payload 100,000 kg Length 12.4 m Diameter 12.4 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.
Outbound Inbound Body delta-V Surface to LEO (m/sec) time of flight (d) delta-V LEO to Surface (m/sec) time of flight (d) Phobos/Deimos 5600 270 1800 270 Moon 6000 3 3100 3 Mars 4800 270 5700 270
(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) Number Weight (grams) Ti Hammer DTH 210 16 233 3 699 No Under-reamer Guide 78 20 49.4 3 148.2 Yes 117 30 67.1 3 201.3 Yes Under-reamer 15 27 20 10 200 No 20 37 36.5 10 365 No Casing Shoe 21 24 16 10 160 No 26 35 29 10 290 No Tubing 2000 16 14 425 325 138125 Yes Casing 2000 22 20 595 100 59500 Yes 2000 32 30 1299 60 77940 Yes Collar Pipes 1000 43 40 1374 10 13740 Yes Total 291368.5
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.
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 (traveling to Mars)
- crewRe (returning to Terra)
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.
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 Medium.com magazine, about how self-driving trucks are going to decimate the economies of small towns in suddenly non-strategic locations.
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:
- 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.
- boom-towns spring up to relieve spacecraft crews of accumulated flight pay burning a hole in their pockets.
- The boom-towns grow into Star-Towns, maybe even becoming a full orbital colony. The gas stations on Route 66 have become small towns.
- 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).
- 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.
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.
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.
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.
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
- the chemical elements required from the disassembler for object currently being printed (does the local regiolith have all that is necessary?)
- the availability of blueprint files for the desired object (are the blueprints illegal?)
- the speed of printing the object (if it takes ten years to print, forget it)
- 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.
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.
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.
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.
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.
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.
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.
But we do not care about that, 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.
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!
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.
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.
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".
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.
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.
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.
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
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.
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.
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.
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?
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.
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.
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.
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.
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.