## Cheat Sheet

For some good general notes on designing spacecraft in general, read Rick Robinson's Rocketpunk Manifesto essay on Spaceship Design 101. Also worth reading are Rick's essays on constructing things in space and the price of a spaceship.

For some good general notes on making a fusion powered spacecraft, you might want to read Application of Recommended Design Practices for Conceptual Nuclear Fusion Space Propulsion Systems. There are also some nice examples on the Realistic Designs page.

For less scientifically accurate spacecraft design the Constant Variantions blog has a nice article on historical trends in science fiction spacecraft design.

Like any other living system, the internal operations of a spacecraft can be analyzed with Living Systems Theory, to discover sources of interesting plot complications.

## Strategies

Everything about fundamental spacecraft design revolves around the Tsiolkovsky rocket equation.

Δv = Ve * ln[R]

The variables are the velocity change required by the mission (Δv or delta-V), the propulsion system's exhaust velocity (Ve), and the spacecraft's mass ratio (R). Remember the mass ratio is the spacecraft's wet mass (mass fully loaded with propellant) divided by the dry mass (mass with empty propellant tanks).

The point is you want as high a delta-V as you can possibly get. The higher the delta-V, the more types of missions the spacecraft will be able to perform. If the delta-V is too low the spacecraft will not be able to perform any useful missions at all.

Looking at the equation, the two obvious ways of increasing the delta-V is to increase the exhaust velocity or increase the mass ratio. Or both. Turns out there are two more sneaky ways of dealing with the problem which we will get to in a moment.

Historically, the first approach has been increasing the exhaust velocity by inventing more and more powerful rocket engines. Unfortunately for the anti-nuclear people, chemical propulsion exhaust velocity has pretty much hit the theoretical maximum. The only way to increase exhaust velocity is by using rockets powered by nuclear energy or by power sources even more frightful and ecologically unsound. And you ain't gonna be able to run a large thrust ion-drive with solar cells.

The second approach is increasing the mass ratio by reducing the spacecraft's dry mass. This is the source of the rule below Every Gram Counts. Remember that the dry mass includes a spacecraft's structure, propellant tankage, lifesystem, crewmembers, consumables (food, water, and air), hydroponics tanks, cargo, atomic missiles, toilet paper, clothing, space suits, dental floss, kitty litter for the ship's cat, the ship's cat itself, and other ship systems. Everything that is not propellant, in other words. All of it will have to be trimmed.

To reduce dry mass: use lightweight titanium instead of heavy steel, shave all structural members as thin as possible while also using lightening holes, make the propellant tanks little more than foil balloons, use inflatable structures, make the floors open mesh gratings instead of solid sheets, hire short and skinny astronauts, use life support systems that recycle, impose draconian limits on the mass each crewperson is allowed for personal items, and so on. Other tricks include using Beamed Power so that the spacecraft does not carry the mass of an on-board power plant, and avoiding the mass of a habitat module by hitching a ride on an Aldrin Cycler. Finally the effective mass ratio can be increased by multi-staging but that should be reserved for when you are really desperate.

The third approach is trying to reduce the delta-V required by the mission. Use Hohmann minimum energy orbits. If the destination planet has an atmosphere, use aerobraking instead of delta-V. Get more delta-V for free by exploiting the Oberth Effect, that is, do your burns while very close to a planet. Instead of paying delta-V for shifting the spacecraft's trajectory or velocity, use gravitational slingshots. NASA uses all of these techniques heavily.

If your technology is high enough, use space tethers, launch catapults, and MagBeams.

The fourth and most extreme approach is to cheat the equation itself, to make the entire equation not relevant to the spacecraft. The equation assumes that the spacecraft is carrying all the propellant needed for the mission, this can be bent several ways. Use Sail Propulsion which does not use propellant at all. Use propellant depots and in-situ resource utilization to refuel in mid-mission. The extreme case of ISRU is the Bussard Ramjet which scoops up propellant from the thin interstellar medium, but that only works past the speed of 1% lightspeed or so.

In our Polaris example, given the mass ratio of 3, we know that the Polaris is 66% propellant and 33% everything else. Give the total mass of 1188.9 tons means 792.6 tons of propellant and 396.3 tons of everything else. Since each GC engine is 30 tons, that means 150 tons of engine and 246.3 of everything else.

## Every Gram Counts

The most fundamental constraint on designing a rocket-propelled vehicle is Every Gram Counts.

Why? Short answer: This is a consequence of the equation for delta-V.

Why? Slightly longer answer: As a general rule, a rocket with the highest delta-V capacity is going to need three kilograms of propellant for every kilogram of rocket+payload. The lower the total kilograms of rocket+payload, the lower the propellant mass required. This relates to the second strategy of rocket design mentioned above.

Say the mission needs 5 km/s of delta-V. Each kilogram of payload requires propellant to give it 5 km/s.

But that propellant has mass as well. The propellant needed for that original kilogram of payload will require a second slug of propellant so that it too can be delta-Ved to 5 km/s.

And the second slug of propellant has mass as well, so you'll need a third slug of propellant for the second slug of propellant — you see how it gets expensive fast. So you want to minimize the payload mass as much as possible or you will be paying through the nose with propellant.

This is called The Tyranny of the Rocket Equation.

Even worse, for a given propulsion system, the easiest way to increase the delta-V you can get out of that system is by increasing the mass ratio. It probably is not economical to push the mass ratio above 4.0, which translates into 3 kg of propellant for every 1 kg of rocket+payload. And it is nearly impossible to push the mass ratio above 20. Translation: spacecraft with a mass ratio of 20 or above are basically constructed out of gossamer and soap bubbles.

This is why rocket designers are always looking for ways to conserve mass.

Orion drive spacecraft and other torchships are not subject to this constraint, because they are unreasonably powerful.

It also does not apply to "stationary" items such as space stations and planetary bases, since they do not move under rocket propulsion. In fact, the added mass might be useful to stablize a space station's orbit, or as additional radiation shielding. Rocket vehicles might use aluminium, titanium, magnesium, or other lightweight metal as their structural material; but a space station would be better off using heavy iron or Invar.

The only consideration is if the station or base components have to be transported to the desired site by a rocket-propelled transport. Then it makes sense to make the components low mass, because then the station bits are payload. It makes even more sense to construct the space station or base on site using in-situ resources, so you don't have to eat the transport costs at all.

## Everything Is Connected

Like aircraft and sea-going warship design, one soon discovers that everything is connected to everything else. When the designer changes one aspect of the design this causes a series of related changes to ripple through the rest of the design.

For instance, if the designer reduces the propellant tank capacity by 5% this has implications for the spacecraft's mass ratio. If it is important for the spacecraft's delta V to stay the same, the payload will have to be reduced by the same amount. This might cut into the amount of life support consumables carried, which will reduce the number of days a mission can last. If the same amount of scientific observations have to be done in the reduced time, another crew member might have to be added. This will decrease the mass available for consumables even more. And so on.

The technical term is "cascading changes." The only thing worse is cascading failures.

As an example, I have some notes of graphing various space warship optimizations with examples of how various warship classes map onto the graph.

## Fundamental Design

As mentioned in Rick Robinson's Spaceship Design 101, all spacecraft are composed of two sections: the Propulsion Bus and the Payload Section.

The Propulsion Bus has the propulsion system, propellant tankage, fuel container (if any), power plant, power plant heat radiator (if any), anti-radiation shadow shield (if any), and a keel-structure to hold it all together. Sometimes the keel is reduced to just a thrust-frame on top of the engine, with the other components stacked on top.

The Payload Section is what the propulsion bus is pushing from planet to planet. It can include crew, flight control station, propulsion/power plant control station and maintenance center, astrogation station, detection and communication equipment, habitat module with life support equipment (including environmental heat radiators) and consumables (air, food, water), space taxis, space pods, and docking ports.

But most importantly, the payload section must contain the reason for the spacecraft's existence. This might be organized as a discrete mission module, or it might be several components mounted around the payload section.

### Rockets Are Not Hotels

If you look at most blueprints for the various iterations of the Starship Enterprise, you will notice that every single part of the spacecraft interior is pressurized, with doors, rooms, and toilets. The corridors are wide enough for five people to walk abreast on nice carpeted floors with indirect lighting.

This is ludicrously wrong. And it is not just Star Trek that does this, pretty much all of media science fiction has ships like this. TV Tropes calls this fallacy "Starship Luxurious".

This is an extension of the "Rockets are Boats" fallacy. Passenger aircraft and luxury liners have their entire interior pressurized because so is everything else at sea level on a planet with a breathable atmosphere. For free. So careless starship designers, without a thought, made the unconscious assumption that spacecraft would be totally pressurized as well.

Wrong. Tain't no air in space, and atmosphere is expensive when you have to cart it up out of Terra's gravity well. Not to mention the expensive pressurized hull that has to encase it.

And it is not just the cost of hauling it up the gravity well, the spacecraft's engine has to accelerate the mass of all that junk. Every Gram Counts, so every gram of carpeting, atmosphere, and pressure hull is one less gram of payload, i.e., the reason the spacecraft was created in the first place. Payload is what you are being paid to load, less payload means less pay. See The Tyranny of the Rocket Equation.

In the real world, spacecraft will be mostly tanks of propellant, propulsion system, payload bays, and a lacy lattice-work of support struts holding everything together. The part the people live in will be a tiny pressurized habitat module tucked away somewhere.

Ignorant starship designers have the unconscious assumption that the important part of a spacecraft is the crew, so they designed ships with their priorities reversed. Their ships were mostly gigantic habitat modules with a tiny engine stuck to the rear. Their ships are also ludicrously wrong. If the designers thought about it at all, they might grudgingly include a tiny fuel tank. Which is like the cherry on top of their big icecream sundae of Fail.

So quit drawing ship blueprints with every square inch pressurized and human-accessible. On a real spacecraft if the ship's engineer has to repair the propulsion system, heat radiators, power plant, propellant tanks, or anything like that, they will have to put on their space suit. They will not have the luxury enjoyed by Scotty the engineer, waltzing down a carpeted floor in a shirt-sleeve atmosphere.

The ships above are tail-sitters, so properly avoid the "wrong way is down" problem. But the artist made the second problem much worse. Apparently they figured the entire interior of the spacecraft was for habitable volume. Notice what they got wrong? Well, where the heck is the space for the rocket engines? I lay the blame for this at the artist, I know from experience that writer Jack Williamson knew better.

### Modular Construction

An attractive notion is the practice of constructing one's spacecraft out of mix-and-match replaceable components. So if your spacecraft needs to do a planetary landing you can swap the low thrust ion drive for a high thrust chemical rocket. In Charles Sheffield's The MacAndrews Chronicles, the protagonist just calls her ship "the assembly", customized out of whatever modules it needs for the current mission contract.

For detailed examples, see the Boeing Space Tug, NASA Space Tug, JPL Modular Hab System, Minimal Volume Spacecraft Cabin, and the Flyaway Engine.

This will also make ships basically immortal. It will also make it really easy for space pirates to fence their captured prize ships. All they have to do is get the prize ship to the spacecraft equivalent to an automobile chop-shop. There the ship vanishes as an entity, becoming an inventory of laundered easily sold anonymous ship modules with the serial numbers filed off.

One can also imagine junker spacecraft, lashed together out of salvaged and/or junk-heap spacecraft modules by stone-broke would-be ship captains down on their luck.

Or mechanically inclined teenagers who want a ship. This would be much like teens in the United States back in the 1960's used to assemble automobiles out of parts scavenged from the junkyard, since they could not afford to purchase a new or used car. Such teens would gain incredible practical skills as spacecraft mechanics. I wonder if this is how Kaylee from Firefly learned her trade.

Yet another scenario is Our Hero stranded in the interplanetary Sargasso Sea of lost spacecraft, trying to scavenge enough working modules from three broken spacecraft in order to make one working spacecraft.

Rick Robinson notes that attractive as the concept is, there are some practical drawbacks to extreme modularity:

I thought of a problem with modular designs, based on the ancient Ship of Theseus paradox.

This is my Grandfather's ax.
This is my Grandfather's ax.
My Father replaced the handle.
This is my Grandfather's ax.

Is it really still Grandfather's ax or not?

Plutarch first wrote about the paradox in 75 CE. But it was that 17th-century smart-ass Thomas Hobbes who slipped the exploding cigar into the box. He asked the question: what if somebody saves the original discarded handle and ax-head, then assembled them into a second ax. Which one of the two axes is Grandfather's ax? Both, neither, the new one, the old one?

This sounds academic, until you apply it to modular spacecraft.

For purposes of insurance, liability, national registration, contract penalties, mortgages, and a host of other expensive issues; it is crucially important to know the identity of the spacecraft in question. Which ship exactly is being referred to in all those legal documents?

But what if the SS SkyTrash's modules are replaced and the old modules used to make a new ship? Legally which one is the SkyTrash? For that matter, intentionally making a stolen ship vanish by passing it through a spaceship chop-shop can make another set of legal headaches.

The problem of spacecraft identity has got to be legally nailed down.

Don't look to the Theseus Paradox for a solution. The problem was stated almost two thousands years ago and they are still arguing about it

Off-hand I'm not sure what a fool-proof solution would be. My first thought was to attach the identity of the spacecraft to some sine qua non "must-have" ship module. Unfortunately there does not seem to be any. Not all ships are manned, so the habitat module won't work. The only must-have module I see is the propulsion bus (otherwise you have a space station, not a spacecraft). However Captain Affenpinscher might find it strange that the identity of her ship has changed just because she swapped out the propulsion module.

I had a discussion on Google Plus with some of my brain-trust:

### Specialized Ship Types

This section has been moved here

## Spacecraft Parameters

For an given type of automobile, there are parameters that tell you what kind of performance you can expect. Things like miles per gallon, acceleration, weight, and so on.

Spacecraft have parameters too, it is just that they are odd measures that you have not encountered before. I am going to list the more important ones here, but they will be fully explained on other pages. Refer back to this list if you run across an unfamiliar term.

Habitat Module
The pressurized part of the spaceraft where people live. Included in Payload Section. Remember that Rockets Are Not Hotels. Unlike the Starship Enterprise a real spacecraft is a huge expanse of airless machinery with a tiny pressurized habitat module tucked away in a corner where people can walk around without spacesuits.
The part of the spacecraft that is its reason for existance. For a satellite booster, the payload is the satellite it is lifting into orbit. For a transport ship: habitat module, passengers, ship controls. For a warship: habitat module, crew, weapons, defenses, ship controls. For a robot freighter: robot controls and cargo. Some payload like cargo and crew are removable from the spacecraft. Some payload like weapons and habitat modules are fixed parts of the spacecraft. Included in Payload Section.
Engine or Thruster
The rocket engine that moves the spacecraft, and the empty propellant tanks. Included in Propulsion Bus.
Power Plant
Part that generates electricity. Included in Propulsion Bus.
Struture
Struture is the skeleton and skin of the spacecraft. Included in both Propulsion Bus and Payload Section.
Propellant and Fuel
Propellant or Reaction mass (remass) is what the thruster fires out the exhaust nozzle to create thrust. Fuel is the source of energy used to propel the propellant. Remember that Fuel Is Not Propellant. In chemical rockets, the chemicals are both propellant and fuel. In nuclear rockets the liquid hydrogen is the propellant and the uranium is the fuel. Included in Propulsion Bus.

Mass of all the payload. For NASA vessels this is typically 26.7% of Dry Mass. Note that for many spacecraft there is no specific set maximum payload mass. You can strap as much payload to the ship's nose as you want. Understanding that the price will be reducing the spacecraft's delta-V due to the increase in payload degrading the spacecraft's mass ratio.
Payload mass as percentage of wet mass. Mpl / M
Structural Mass (Mst)
Mass of all the struture. For NASA vessels this is typically 21.7% of Dry Mass.
Propellant Mass (Mpt)
The mass of all the propellant in the spacecraft's propellant tanks. Does not include fuel that is retained after it is burnt, e.g., uranium fissioned inside a solid core reactor. For some calculations, you will use instead the mass of propellant that will be expended in a given maneuver.
Power Plant Mass (Mpp)
The mass of the electrical generation system. Includes any heat radiators. For NASA vessels this is typically 28% + 3.4% of Dry Mass
Thruster System Mass (Mts)
The mass of the rocket engines, including the empty propellant/fuel tanks. For NASA vessels this is typically 3.7% of Dry Mass
Propulsion System Mass (Mps)
Thruster System Mass + Power Plant Mass.
Inert Mass (Mi)
Mass of spacecraft with no propellant and no payload. Propulsion System Mass + Structural Mass.
Inert Mass Fraction (δ)
Inert mass as percentage of wet mass. Mi / M
Dry (Empty, Burnout) Mass (Me)
Mass of spacecraft with no propellant but with payload. Propulsion System Mass + Structural Mass + Payload Mass.
Wet (Total, Ignition) Mass (M)
Total mass of spacecraft. Propellant Mass + Propulsion System Mass + Structural Mass + Payload Mass.
Mass Ratio (R)
Ratio of wet mass to dry mass. Wet Mass / Dry Mass.
Parametric Mass Ratio (r)
λ + δ.
Propellant Fraction (Pf, PMF, or ζ)
Percentage of wet mass that is propellant. 1 - ( 1 / MassRatio )

Propellant Mass Flow (mDot or )

How quickly does the Thruster System drain the propellant tanks? Rated in kilograms per second.

mDot constrains the amount of thrust the propulsion system can produce. Changing the propellant mass flow is a way to make a spacecraft engine shift gears.

Exhaust-Velocity (Ve)

How fast does the propellant shoot out the exhaust nozzle of the Thruster System? Rated in meters per second. Exhaust velocity (and delta V) is of primary importance for space travel. For liftoff, landing, and dodging hostile weapons fire, thrust is more important.

Broadly exhaust velocity is a measure of the spacecraft's "fuel" efficiency (actually propellant efficiency). The higher the Ve, the better the "fuel economy".

Generally if a propulsion system has a high Ve it has a low thrust and vice versa. The only systems where both are high are torch drives. Some spacecraft engines can shift gears by trading exhaust velocity for thrust.

For a more in-depth look at exhaust velocity look here

Specific Impulse (Isp)
Another way of stating exhaust velocity. Exhaust Velocity / 9.81 where 9.81 = acceleration due to gravity on Terra in meters per second. Specific Impulse is rated in seconds. It is also a broad measure of the spacecraft's "fuel" efficiency.
Delta V or Δv

Spacecraft's total change in velocity capability. This determines which missions the spacecraft can perform. Arguably this is the most important of all the spacecraft parameters. Rated in meters per second.

This can be thought of as how much "fuel" is in the tanks of the spacecraft (though it is actually a bit more complicated than that).

Velocity Ratio
Δv / Ve
Thrust (F)

Thrust produced by Thruster System. Rated in Newtons. Thrust is constrained by Propellant Mass Flow. Thrust (and acceleration) is of primary importance in liftoff, landing, and dodging hostile weapons fire. For space travel exhaust velocity (and delta V) is more important.

Generally if a propulsion system has a high Ve it has a low thrust and vice versa. The only systems where both are high are torch drives. Some spacecraft engines can shift gears by trading exhaust velocity for thrust.

Acceleration (A)

Spacecraft's current acceleration. Current total mass / Thrust. Rated in meters per second per second. Divide by 9.81 to get g's of acceleration.

In space, a spacecraft with higher acceleration will generally not travel to a destination any faster than a low acceleration ship. But a high acceleration ship will have wider launch windows for a given trajectory.

Note that as propellant is expended, current total mass goes down and acceleration goes up. If you want a constant level of acceleration you have to constantly throttle back the thrust.

5 milligee (0.05 m/s2) : General rule practical minimum for ion drive, laser sail or other low thrust / long duration drive. Otherwise the poor spacecraft will take years to change orbits. Unfortunately pure solar sails are lucky to do 3 milligees.

0.6 gee (5.88 m/s2) : General rule average for high thrust / short duration drive. Useful for Hohmann transfer orbits, or crossing the Van Allen radiation belts before they fry the astronauts.

3.0 gee (29.43 m/s2) : General rule minimum to lift off from Terra's surface into LEO.

For a more in-depth look at minimum accelerations look here.

Thrust Power (Fp)
Power produced by Thruster System. ( Thrust × Exhaust Velocity ) / 2. Rated in watts.
Specific Power (Fsp)
Power density of spacecraft. Thrust Power / Dry Mass. Rated in watts per kilograms.
Specific Mass
Alpha of Thruster System. Thruster System Mass / Thrust Power. Rated in kilograms per watt.

## Structure

Typically the percentage of spacecraft dry mass that is structure is 21.7% for NASA vessels.

What is the structure of the ship going to be composed of? The strongest yet least massive of elements. This means Titanium, Magnesium, Aluminum, and those fancy composite materials. And all the interior girders are going to have a series of circular holes in them to reduce mass (the technical term is "lightening holes").

### Spacecraft Spine

Many (but not all) spacecraft designs have the propulsion system at the "bottom", exerting thrust into a strong structural member called the ship's spine. The other components of the spacecraft are attached to the spine. The spine is also called a keel or a thrust frame. In all spacecraft the thrust frame is the network of girders on top of the engines that the thrust is applied to. But only in some spacecraft is the thrust frame elongated into a spine, in others the ship components are attached to a shell, generally cylindrical.

If you leave out the spine or thrust frame, engine ignition will send the propulsion system careening through the core of the ship, gutting it. Spacecraft engineers treat tiny cracks in the thrust frame with deep concern.

OK, forget what I just said. On top of the engine will be the thrust frame or thrust structure. On top will be the primary structure or spaceframe. The thrust frame transmits the thrust into the spaceframe, and prevents the propulsion system careening through the core of the ship.

The spaceframe can be:

• A long spine/keel with the propellant tanks and payload section bits attached in various places.
• A large pressurized vessel, either propellant tank or habitat module. Other propellant tanks and payload section bits are attached to main tank or perched on top.
• Something else.

The engineers are using a pressurized tank in lieu of a spine in a desperate attempt to reduce the spacecraft's mass. But this can be risky if you use the propellant tank. The original 1957 Convair Atlas rocket used "balloon tanks" for the propellant instead of conventional isogrid tanks. This means that the structural rigidity comes from the pressurization of the propellant. This also means if the pressure is lost in the tank the entire rocket collapses under its own weight. Blasted thing needed 35 kPa of nitrogen even when the rocket was not fueled.

As Rob Davidoff points out, keel-less ship designs using a pressurized tank for a spine is more for marginal ships that cannot afford any excess mass whatsoever. Such as ships that have to lift off and land in delta-V gobbling planetary gravity wells while using one-lung propulsion systems (*cough* chemical rockets *cough*).

This classification means that parts of the propulsion bus and payload section are intertwined with each other, but nobody said rocket science was going to be easy.

### Ship Spine Example

This is the von Braun Round the Moon Ship

1. At the bottom are the four rocket motors. During a burn, the rocket thrust they create pushes upward.

2. The rocket thrust pushes upward on the thrust frame (dark blue), which is right above the motors.

3. Built on top of the thrust frame is the spaceframe (light blue), the same way that the skeleton of a skyscraper is built atop the ground. The spaceframe is pushed upward by the thrust frame.

4. All the other spacecraft components: personnel sphere, hydrazine tank, nitric acid tank, solar mirrors, radar antennae, and everything else is hung from the spaceframe. As the spaceframe is pushed upwards, it drags along all the spacecraft components.

### Lighten That Spaceframe!

Getting back to the spine/spaceframe. Remember that every gram counts. Spacecraft designers want a spine that is the strongest yet lowest mass structural member possible. The genius R. Buckminster Fuller and his science of "Synergetics" had the answer in his "octet truss" (which he called an "isotrophic vector matrix", and which had been independently discovered about 50 years earlier by Alexander Graham Bell). You remember Fuller, right? The fellow who invented the geodesic dome?

Each of the struts composing the octet truss are the same length. Geometrically it is an array of tetrahedrons and octahedrons (in terms of Dungeons and Dragons polyhedral dice it uses d4's and d8's).

Sometimes instead of an octet truss designers will opt for a weaker but easier to construct space frame. The truss of the International Space Station apparently falls into this category.

A bit more simplistic is a simple stack of octahedrons (Dungeons and Dragons d8 polyhedral dice). This was used for the spine of the Valley Forge from the movie Silent Running (1972), later reused as the agro ship from original Battlestar Galactica.

Spacecraft spines are generally down the center of the spacecraft following the ship's thrust axis (the line the engine's thrust is applied along, usually from the center of the engine's exhaust through the ship's center of gravity).

This can be a pain to spacecraft designers if they have anything that needs to be jettisoned. Such items will have to be in pairs on opposite sides of the spine, and jettisoned in pairs as well. Otherwise the spacecraft's center of gravity will shift off the thrust axis, and the next time the engines are fired up it's pinwheel time.

In a NASA study TM-1998-208834-REV1 they invent a clever way to avoid this: the Saddle Truss.

The truss is a hollow framework cylinder with a big enough diameter to accommodate standard propellant tanks, consumables storage pods, and auxiliary spacecraft. One side of the cylinder frame is missing. The thrust axis is cocked a fraction of a degree off-center to allow for the uneven mass distribution of the framework.

The point is that tanks and other jettison-able items no longer have to be in pairs if you use a saddle truss. When it is empty you just kick it out through the missing side of the saddle truss. No muss, no fuss, and no having to have double the amount of propellant plumbing and related items.

Examples of the saddle truss can be found in the Bimodal NTR and the SNRE Spacecraft.

#### Waterskiing Spacecraft

This is a quite radical method to drastically reduce the structural mass of a spacecraft, allowing a handsome increase in valuable payload mass. It also dramatically increase the separation between a dangerously radioactive propulsion system and the crew, allowing a drastic decrease in the radiation shadow shield mass. This allows yet more handsome increases in valuable payload mass. As the cherry on top of the cake, it allows using the tumbling pigeon method of spin gravity without the direction of gravity inverting.

Please note this has never actually been used in a serious nuclear spacecraft design due to its unorthodox nature.

And warships with such a design would have their manoeuvring critically handicapped (or it's "crack-the-whip" time and the cable breaks).

The concept comes from the observation that for a given amount of structural strength, a compression member (such as a girder) generally has a higher mass that a corresponding tension member (such as a cable). And we know that every gram counts.

Charles Pellegrino and Dr. Jim Powell put it this way: current spacecraft designs using compression members are guilty of "putting the cart before the horse". At the bottom is the engines, on top of that is the thrust frame, and on top of that is rest of the spacecraft held together with girders (compression members) like a skyscraper. But what if you put the engine at the top and have it drag the rest of the spacecraft on a long cable (tension member). You'll instantly cut the structural mass by an order of magnitude or more!

And if the engines are radioactive, remember that crew radiation exposure can be cut by time, shielding, or distance. The advantage of distance is it takes far less mass than a shield composed of lead or something else massive. The break-even point is where the mass of the boom or cable is equal to the mass of the shadow shield. But the mass of a shadow shield is equal to the mass of a incredibly long cable. The HELIOS cable was about 300 to 1000 meters, the Valkyrie was ten kilometers.

But keep in mind that this design has no maneuverability at all. Agile it ain't. If you turn the ship too fast it will try to "crack the whip" and probably snap the cable. This probably makes the design unsuitable for warships, who have to jink a lot or be hit by enemy weapons fire.

Examples include HELIOS, the Valkyrie Antimatter Starship, the ramrobots from Larry Niven's A Gift From Earth and the ISV Venture Star from the movie Avatar.

Certain propulsion systems incorporate the waterskiing concept in spacecraft that use the propulsion. The main one is the Medusa, which sets off nuclear explosions inside a huge parachute-shaped sail. The sail accelerates, and drags along the payload on a long cable. Long because the payload does not want to be any closer to a series of nuclear explosions than it has to be.

The various types of sail propulsion drag the payload with a long cable as well. But for them, the long cable is not because the sail is radioactive, just that it is typically several kilometers in radius.

Cosine Thrust Loss

If the exhaust is radioactive or otherwise dangerous to hose the rest of the spacecraft with, you can have two or more engines angled so the plumes miss the ship.

Angled engines do reduce the effective thrust by an amount proportional to the cosine of the angle but for small angles it is acceptable. The delta V of the spacecraft is also reduced by the same proportion.

Note in the HELIOS design Krafft Ehricke figured that the 300 meter separation was enough to render the exhaust harmless so it does not angle the engine at all. Krafft has a single engine blasting straight at the habitat module. The only concession to the exhaust is mounting the cables on outriggers, so the cables do not pass through the zillion degree nuclear fireball exhaust plume. It would be most embarassing if the cables melted.

##### Pendulum Fallacy

Now those waterskiiing spacecraft designs look much like Robert Goddard's first liquid-fueled rocket "Nell " (i.e, engine on top). Don't be fooled, it is just a coincidence.

The waterskiing spacecraft designs are trying to subsitute almost mass-less engine standoff distance for ultra-penalty-mass radiation shield. Because on the one hand: Every Gram Counts, but on the other: nuclear radiation kills crewmembers dead.

Goddard's rocket was designed for totally different reasons (which you should have been tipped off by the fact it had no nuclear engine).

Goddard reasoned that if you put the rocket engine at the bottom and build the rest of the rocket on top of that, it would be as unstable as a waiter carrying a tall tippy bottle of wine on a tray held overhead by one hand. One minor shake of the hand and the wine goes crashing to the ground.

But if you put the rocket engine at the top and had it dragging the rest of the rocket, it would be as inherently stable as holding a pendulum by its string. If the engine tips over from its upward flight, the weight of the rest of the rocket will un-tip the engine. Right?

Nowadays rocket designers call this the Pendulum Rocket Fallacy. Meaning it looks good on paper, but it just doesn't work. Having the engines at the top is no more stable than at the bottom. A top-engine design superficially resembles a pendulum, but the system of forces acting on it are totally different.

Goddard discovered this the hard way with Nell's test flight. It rose barely 41 feet, tipped over, flew 184 feet horizontally, then augered into a cabbage field. All of his subsequent designs had the now-standard engine on the bottom arrangement.

Real spacecraft achieve stability by controlling some type of attitude actuator via some type of inertial measurement unit.

#### Space Trains and Truckers

This section has been moved here

### Fire

There are some hazards to worry about with these space-age materials. Titanium and magnesium are extremely flammable (in an atmosphere containing oxygen). And when I say "extremely" I am not kidding.

Do not try to put out a magnesium fire by throwing water on it. Blasted burning magnesium will suck the oxygen atoms right out of the water molecules, leaving hydrogen gas (aka what the Hindenburg was full of). A carbon-dioxide fire extinguisher won't work either, same result as water except you get a cloud of carbon instead of hydrogen. Instead use a Class D dry chemical fire extinguisher or a lot of sand to cut off the oxygen supply. Oh, did I mention that burning magnesium emits enough ultraviolet light to permanently damage the retinas of the eyes?

The same goes for burning titanium. Except there is no ultraviolet light, but there is a chance of ignition if titanium is in contact with liquid oxygen and the titanium is struck by a hard object. It seems that the strike might create a fresh non-oxidized stretch of titanium surface, which ignites the fire even though the liquid oxygen is at something like minus 200° centigrade. This may mean that using titanium tanks for your rocket's liquid oxygen storage is a very bad idea.

An emergency crew at a spaceport, who has to deal with a crashed rocket, will need the equipment to deal with this.

And if the titanium, magnesium, or aluminum becomes powdered, you have to stop talking in terms of "fire" and start talking in terms of "explosion."

### Corrosion

As an interesting side note, rockets constructed of aluminum are extremely vulnerable to splashes of metallic mercury or dustings of mercury salts. On aluminum, mercury is an "oxidizing catalyst", which means the blasted stuff can corrode through an aluminum beam in a matter of hours (in an atmosphere containing oxygen, of course). This is why mercury thermometers are forbidden on commercial aircraft.

Why? Ordinarily aluminum would corrode much faster than iron. However, iron oxide, i.e., "rust", flakes off, exposing more iron to be attacked. But aluminum oxide, i.e., "sapphire", sticks tight, protecting the remaining aluminum with a gem-hard barrier. Except mercury washes the protective layer away, allowing the aluminum to be consumed by galloping rust.

Alkalis will have a similar effect on aluminum, and acids have a similar effect on magnesium (you can dissolve magnesium with vinegar). As far as I know nothing really touches titanium, its corrosion-resistance is second only to platinum.

### Protective Paint

If you want a World War II flavor for your rocket, any interior spaces that are exposed to rain and other corrosive planetary weather should be painted with a zinc chromate primer. Depending on what is mixed into the paint, this will give a paint color ranging from yellowish-green to greenish-yellow. In WWII aircraft it is found in wheel-wells and the interior of bomb bays. In your rocket it might be found on landing jacks and inside airlock doors.

Naturally this does not apply to strict orbit-to-orbit rockets, or rockets that only land on airless moons and planets. Well, now that I think about it, some of the lunar dust is like clouds of microscopic razor blades so they are dangerously abrasive.

### Rocket Tumble

The basic idea is that the Axis of Thrust from the engines had better pass through the the spacecraft's center of gravity (CG) or everybody is going to die. In addition, if the spacecraft is currently passing through a planet's atmosphere the axis of thrust had better be parallel to the aerodynamic axis or the same thing will happen.

Specifically, "everybody is going to die" means the spacecraft is going to loop-the-loop or tumble like a cheap Fourth-of-July skyrocket (Heinlein calls this a rocket "falling off its tail"). If this happens during lift-off the ship will auger into the ground like a nuclear-powered Dinosaur-Killer asteroid and make a titanic crater. If it happens in deep space, the rocket will spin like a pinwheel firework spraying atomic flame everywhere. This will waste precious propellant, give the spacecraft a random vector, and severely injure the crew with unexpected spin gravity. If they are lucky the crew's broken bones will heal about the same time that they run out of oxygen.

The axis of thrust is a line starting at the center of the exhaust nozzle's throat, and traveling in the exact opposite direction of the hot propellant. It is the direction that the thrust is pushing the rocket. As long as the axis of thrust passes through the CG, the spacecraft will be accelerated in that direction. If the axis of thrust is not passing through the CG, the spacecraft will start to spin around the CG. When done on purpose this is called a yaw or pitch maneuver. When this is done by accident, it is called OMG WE'RE ALL GOING TO DIE!

Some engines can be gimbaled, rotating their axis of thrust off-center by a few degrees. This is intended for yaw and pitch, but it can be used in emergencies to cope with accidental changes in the center of gravity (e.g., the cargo shifts).

When laying out the floor plan, you want the spacecraft to balance. This boils down to ensuring that the ship's center of gravity is on the central axis, which generally is the same as the axis of thrust. There are exceptions. The Grumman Space Tug has its center of gravity shift wildly when it jettisons a drop tank. To compensate, the engine can gimbal by a whopping ±20°.

Balancing also means that each deck should be "radially symmetric". That's a fancy way of saying that if you have something massive in the north-west corner of "D" deck, you'd better have something equally massive in the south-east corner. Otherwise the center of gravity won't be centered.

For a cargo ship, the Loadmaster has to ensure that the cargo is stored in a radially symmetric balance.

This is another reason to strap down the crew during a burn. Walking around could upset the ship's balance, resulting in the dreaded rocket tumble. This will be more of a problem with tiny ships than with huge cruisers, of course. The same goes for the cargo. The load-master better be blasted sure all the tons of cargo are nailed down so they don't shift. And be sure the cargo is evenly balanced around the ship's axis to keep the center of gravity in the center.

Small ships might have "trim tanks", small tanks into which water can be pumped in order to adjust the balance. The ship will also have heavy gyroscopes that will help prevent the ship from falling off its tail, but there is a limit to how much imbalance that they can compensate for.

### Propellent Tankage

A cursory look at the rocket's mass ratio will reveal that most of the rocket's mass is going to be propellant tanks.

For anything but a torchship, the spacecraft's mass ratio is going to be greater than 2 (i.e., 50% or more of the total mass is going to be propellant). Presumably the propellant is inside a propellant tank (unless you are pulling a Martian Way gag and freezing the fuel into a solid block). Remember, RockCat said all rockets are giant propellant tanks with an engine on the bottom and the pilot's chair at the top.

If you have huge structure budget, you have a classic looking rocket-style rocket with propellant tanks inside. If you have a medium structure budget, you have a spine with propellant tanks attached. If you have a small structure budget, you'll have an isogrid propellant tank for a spine, with the rest of the rocket parts attached.

And if you are stuck with a microscopic structure budget, you'll have a foil-thin propellant tank stiffened by the pressure of the propellant, with the rest of the rocket parts attached. But the latter tends to collapse when the propellant is expended and the pressure is gone. This was used in the old 1957 Convair Atlas rocket, but not so much nowadays. You cannot really reuse them.

Our running example Polaris spacecraft has a gas core nuclear thermal rocket engine.

The fuel is uranium 235. It will probably be less than 1% of the total propellant load so we will focus on just the propellant for now.

Nuclear thermal rockets generally use hydrogen since you want propellant with the lowest molecular mass. Liquid hydrogen has a density of 0.07 grams per cubic centimeter.

The Polaris has 792.6 metric tons of hydrogen propellant. 792.6 tons of propellant = 792,600,000 grams / 0.07 = 11,323,000,000 cubic centimeters = 11,323 cubic meters . The volume of a sphere is 4/3πr3 so you can fit 11,323 cubic meters in a sphere about 14 meters in radius . Almost 92 feet in diameter, egad! It is a pity hydrogen isn't a bit denser.

If this offends your aesthetic sense, you'll have to go back and change a few parameters. Maybe a 2nd generation GC rocket, and a mission from Terra to Mars but not back. Maybe use methane instead of hydrogen. It only has an exhaust velocity of 6318 m/s instead of hydrogen's superior 8800 m/s, but it has a density of 0.42 g/cm3, which would only require a 1.7 meter radius tank. (Methane has a higher exhaust velocity than one would expect from its molecular weight, due to the fact that the GC engine is hot enough to turn methane into carbon and hydrogen. Note that in a NERVA style engine the reactor might become clogged with carbon deposits.)

Propellant Tank Mass

Robert Zubrin says that as a general rule, the mass of a fuel tank loaded with liquid hydrogen will be about 87% hydrogen and 13% tank. In other words, multiply the mass of the liquid hydrogen by 0.15 to get the mass of the empty tank (0.13 / 0.87 = 0.15).

So the Polaris' 792.6 tons of hydrogen will need a tank that masses 792.6 * 0.15 = 119 tons.

87% propellant and 13% tank is for a rocket designed to land on a planet or that is capable of high acceleration. An orbit-to-orbit rocket could get by with more hydrogen and less tank. This is because the tanks can be more flimsy since they will not have to endure the stress of landing (A landing-capable rocket that uses a propellant denser than hydrogen can also get away with a smaller tank percentage). Zubrin gives the following ballpark estimates of the tank percentage:

PropellentEngineTank %
ArgonIon rocket4
WaterNuclear salt water rocket4
HydrogenNTR / GCR10
LOX/HydrogenChemical6

But if you want to do this the hard way, you'd better warm up your slide rule.

The total tank volume (Vtot) of a tank is the sum of four components:

1. Usable Propellant Volume (Vpu): the volume holding the propellant that can actually be used.
2. Ullage Volume (Vull): the volume left unfilled to accomodate expansion of the propellant or contraction of the tank structure. Typically 1% to 3% of total tank volume.
3. Boil-off Volume (Vbo): For cryogenic propellants only. The volume left unfilled to allow for the propellant that boils from liquid to gas due to external heat.
4. Trapped Volume (Vtrap): the volume of unusable propellant left in all the feed lines, valves, and other components after the tank is drained. Typically the volume of the feed system.

Vtot = Vpu + Vull + Vbo + Vtrap

No, I do not know how to estimate the Boil-off Volume. A recent study estimated that in space cryogenic tanks suffered an absolutely unacceptable 0.1% boiloff/day, and suggested this had to be reduced by an order of magnitude or more. When the boil-off volume is full, a pressure relief valve lets the gaseous propellant vent into space, instead of exploding the tank.

Tanks come in two shapes: spherical and cylindrical. Spherical are better, they have the most volume for the least surface area, so are the lightest. But many spacecraft have a limit to their maximum diameter, especially launch vehicles. In this case cylindrical has a lower mass than a series of spherical tanks.

The internal pressure of the propellant has the greatest effect on the tank's structural requirements. Not as important but still significant are acceleration, vibration, and handling loads. Unfortunately I can only find equations for the effects of internal pressure. Acceleration means that tanks which are in high-acceleration spacecraft or in spacecraft that take-off and land from planets will have a higher mass than tanks for low-acceleration orbit-to-orbit ships. My source did say that figuring in acceleration, vibration, and handling would make the tank mass 2.0 to 2.5 times as large as what is calculated with the simplified equations below.

In the Space Shuttle external tank, the LOX tank was pressurized to 150,000 Pa and the LH2 tank was pressurized to 230,000 Pa.

The design burst pressure of a tank is:

Pb = fs * MEOP

where:

Pb = design burst pressure (Pa)
fs = safety factor (typically 2.0)
MEOP = Maximum Expected Operating Pressure of the tank (Pa)

Tank Materials
Material

Density
ρ
kg/m3
Allowable Strength
Ftu
GPa
Efficency
Ftu/(ρg0)
km
Mass Factor
φtank
m
2219 - Aluminum2,8000.413
0.214 welded
15.042,500
Titanium4,4601.2328.812,500
4130 - Steel7,8300.86211.232,500
Graphite Fiber
Composite
1,5500.89558.8810,000

Spherical Tanks

You have to make Vs so it is equal to Vtot, or at least equal to Vtot - Vtrap.

Vs = 4/3 * π * rs3

As = 4 * π * rs2

ts = (Pb * rs) / (2 * Ftu)

Ms = As * ts * ρ

where:

rs = radius of sphere (m)
As = surface area of sphere (m2)
Vs = volume of sphere (m3)
ts = wall thickness of sphere (m)
Pb = design burst pressure (Pa)
Ftu = allowable material strength (Pa) from tank materials table
Ms = mass of spherical tank (kg)
ρ = density of tank structure material (kg/m3 from tank materials table

Cylindrical Tanks

Cylindrical tanks are cylinders where each end is capped with either hemispheres (where radius and height are equal) or hemiellipses (where radius and height are not equal). As it turns out cylindrical tanks with hemiellipses on the ends are always more massive than hemispherical cylindrical tanks. So we won't bother with the equations for hemielliptical tanks. In the real world rocket designers sometimes use hemielliptical tanks in order to reduce tank length.

What you do is calculate the mass of the cylindrical section of the tank Mc using the equations below. Then you calculate the mass of the two hemispherical endcaps (that is, the mass of a single sphere) Ms using the value of the cylindrical section's radius for the radius of the sphere in the spherical tank equations above. The mass of the cylindrical tank is Mc + Ms.

Vc = π * rc2 * lc

Ac = 2 * π * rc2 * lc

tc = (Pb * rc) / Ftu

Mc = Ac * tc * ρ

where:

rc = radius of cylindrical section (m)
lc = length of cylindrical section (m)
Ac = surface area of cylindrical section (m2)
Vc = volume of cylindrical section (m3)
Pb = design burst pressure (Pa)
Ftu = allowable material strength (Pa) from tank materials table
ρ = density of tank structure material (kg/m3 from tank materials table
tc = wall thickness of cylindrical section (m)
Mc = mass of cylindrical tank section (kg)

Ullage

When the rocket is sitting on the launch pad, the planet's gravity pulls the propellant down so that the pumps at the aft end of the tank can move it to the engine. When the rocket is under acceleration, the thrust pulls the propellant down to the pumps. Once the engines cut off and the rocket is in free fall, well, the remaining pooled at the bottom turns into zillions of blobs and starts floating everywhere. See the video:

This isn't a problem, up until the point where you want to start the engine up again. Trouble is, the propellant isn't at the aft pump, it is flying all over the place. What's worse, some of the liquid propellant might have turned into bubbles of gas, which could wreck the engine if they are sucked into the pump. Vapor lock in a rocket engine is an ugly thing.

In 1960 Soviet engineers invented the solution: Ullage Motors. These are tiny rocket engines that only have to accelerate the rocket by about 0.001g (0.01 m/s). That's enough to pull the propellant down to the pump, and to form a boundary between the liquid and gas portions. In some cases, the spacecraft's reaction control system (attitude jets) can operate as ullage motors.

In the Apollo service module, they use a "retention reservoir" instead of an ullage burn (but they have to burn anyway if the amount of fuel and oxidizer drops below 56.4%).

Liquid oxygen in the oxidizer storage tank flows into the oxidizer sump tank. During an engine burn, oxygen flows to the bottom of the sump tank, through an umbrella shaped screen, into the retention reservoir, then into a pipe at the bottom leading to the engine. The same system is used in the fuel tanks.

When the burn is terminated and the oxygen breaks up into a zillion blobs and starts floating everywhere, the oxygen under the screen umbrella cannot escape. Surface tension prevents it from escaping through the screen holes. The oxygen is trapped under the umbrella, inside the retention reservoir.

When the engines are restarted there is oxygen right at the pipe to feed into the engine, instead of a void with random floating blobs. The engine thrust then settles the oxygen in the sump tank for normal operation.

As near as I can figure, the 56.4% ullage limit happens when the storage tank is empty, so the sump tank is only partially full. But I'm not sure.

### Heat Shield

Aerobraking is used to get rid of a portion of a spacecraft's velocity without using a rocket engine and reaction mass. Or as NASA thinks of it: "For Free!" This can be used for landing, for planetary capture, for circulating spacecraft's orbit, or other purposes.

Robert Zubrin says mass of the heat shield and thermal structure will be about 15% of the total mass being braked.

The general rule is that aerobraking can kill a velocity approximately equal to the escape velocity of the planet where the aerobraking is performed (10 km/s for Venus, 11 km/s for Terra, 5 km/s for Mars, 60 km/s for Jupiter).

This will mostly be used for our purposes designing a emergency re-entry life pod, not a Solar Guard patrol ship. With a sufficiently advanced engine it is more effective just to carry more fuel, so our atomic cruiser will not need to waste mass on such a primitive device.

NASA on the other hand uses aerobraking every chance it gets, since they do not have the luxury of using atomic engines. Many of the Mars probes use aerobraking for Mars capture and to circularize their orbit. Some use their solar panels as aerobraking drage chutes in order to make a given piece of payload mass do double duty. Some of the Space Tug designs listed in the Realistic Design section economize on reaction mass by using a ballute when returning to Terra orbit.

In the movie 2010, the good ship Leonov had a one-lung propulsion system, so they needed an aerobraking ballute to slow them into Jovian orbit. If you are thinking about aerobraking, keep in mind that many worlds in the Solar System do not have atmospheres.

You can find a more in-depth look at heat shields here.

## Propulsion

Typically the percentage of spacecraft dry mass that is propulsion is 3.7% for NASA vessels.

For a list of various spacecraft propulsion systems, go to the engine list.

### Penalty Weight

As you are beginning to discover, mass is limited on a spacecraft. Many Heinlein novels have passengers given strict limits on their combined body+luggage mass. Officials would look disapprovingly at the passenger's waistlines and wonder out loud how they can stand to carry around all that "penalty weight". There are quite a few scenes in various Heinlein novels of the agony of packing for a rocket flight, throwing away stuff left and right in a desperate attempt to get the mass of your luggage below your mass allowance.

Keep in mind that every gram of equipment or supplies takes several grams of propellant. Try to make every gram do double duty.

### Miniaturization

In Frank Herbert's DUNE, spacemen had books the size of a thumb-tip, with a tiny magnifying glass.

### Ruthless Optimization

Other innovations are possible. Perhaps boxes of food where the boxes are edible as well. The corridor floors will probably be metal gratings to save mass (This is the second reason why cadet shipboard uniforms will not have skirts or kilts. Looking up at the ceiling grating will give you a peekaboo up-skirt glimpse of whoever is in the next deck up. No panchira allowed. The first reason is the impossibility of keeping a skirt or kilt in a modest position while in free-fall.) In Lester Del Rey's Step to the Stars all documents, blueprints, and mail are printed on stuff about as thick as tissue paper (have you ever tried to lift a box full of books?).

With regards to low mass floors, the lady known as Akima had an interesting idea:

David Chiasson expands upon Akima's idea. There is an outfit called Metal Textiles which produces knitted wire mesh.

Michael Garrels begs to differ:

### Stowaways

If you are dealing with a conventional spacecraft ruled by the iron law of Every Gram Counts, a stowaway is a disaster. If they had not jettisoned a payload mass equal to their mass, there will not be enough propellant to perform the vital maneuvers. The ship will run out, and go sailing off into the Big Dark and a lonely death for everybody on board.

Even if the stowaway jettisions enough mass, there probably won't be enough breathing mix and food aboard for the additional person. Everybody will suffocate and/or starve.

As Dr. Feynman observed about the Challenger disaster, "Nature cannot be fooled." If the equations say that your spacecraft does not have enough fuel, they don't mean "maybe."

For survival's sake, the crew will have little choice but to immediately throw the stowaway out the nearest airlock.

This was highlighted in a famous story called The Cold Equations by Tom Godwin. The story is chilling abet scientifically accurate, but it still caused an uproar when it first came out.

But if the ship is a torchship or uber-powerful faster-than-light starship, things are a little less tense. Since they are not actually threatening the lives of the crew, stowaways will be treated more like their terrestrial counterparts if discovered on a sea-going vessel.

## Power Generation

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### Energy Harvesting

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### Fuel Cells

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### Solar Thermal Power

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### Solar Photovoltaic Power

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### Nuclear Fission Reactors

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#### Bimodal NTR

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#### Dusty Plasma Fission Reactors

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#### Nuclear MHD

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### Fusion Reactors

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#### Lattice Confinement Fusion

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### Exotic power sources

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#### Beamed Power

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#### Antimatter Power

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#### Vacuum energy

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#### Mass Converters

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### Shorepower

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#### Ship to Shore

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## Power Storage

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### Energy Transport Mechanism

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### Batteries

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### Flywheels

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### Regenerative Fuel Cells

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### Superconducting magnetic energy storage

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### Kerr-Newman black hole

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## Habitat Module

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### TransHab

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## Atomic Rockets notices

This week's featured addition is SPIN POLARIZATION FOR FUSION PROPULSION

This week's featured addition is INsTAR

This week's featured addition is NTR ALTERNATIVES TO LIQUID HYDROGEN