SF Writer in need of assistance - SPACESHIP FUEL

  • #1
Hello all - once again!
I am an aspiring SF writer currently in the process of writing a book. I am looking for ideas (go nuts!) for different types of spaceship fuels.

The idea is that the fuel has to be something that exists in abundance (preferably naturally occurring), and that it's harvesting is not through exploitative methods (i.e. mining).

I thank you for your ideas and continued support!

C
 

Answers and Replies

  • #2
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The idea is that the fuel has to be something that exists in abundance (preferably naturally occurring), and that it's harvesting is not through exploitative methods (i.e. mining).
The last is a bit fuzzily defined...what's "exploitative"? You're also going to have to mine stuff to build the spaceship with...depending on its purpose, requirements, and technology, maybe more stuff than you'd need to mine to fuel it.

Anyway, the obvious is hydrogen/helium. Most common elements in the universe, and useful as fusion fuel. You'll need to mine them, though...whether it's by scooping them out of a gas giant's atmosphere, digging up ice on a moon, or drilling deep into terrestrial planets to find geological structures that trap helium produced by radioactive decay. And unless you have some new technology that forces protons together, you'll want specific isotopes, mainly deuterium, and He-3 if you use some reactions...you'll need to go through a fairly large amount of hydrogen/helium to collect the stuff useful as fuel.

Some form of stabilized metallic hydrogen is another semi-plausible high-tech rocket fuel. In this case, the hydrogen is just reaction mass and an energy storage medium...you need another source of energy to make it from plain hydrogen.

And of course, you can just turn water into hydrogen and oxygen, a good chemical fuel though difficult to handle in atmosphere (due mainly to the need to insulate the hydrogen from said atmosphere), and requiring huge fuel tanks (less of a problem if the tanks don't need to be insulated against an outside atmosphere).

You haven't given any idea of the technologies these ships would be using. You might get more relevant replies if you gave some more details.
 
  • #3
Lots of great considerations to work on from my end. I'm still very much in the development phase of the book, so other technology is still forthcoming.

Thanks for the great feedback!
 
  • #4
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cjameshuff covered most of the spectrum of non-exotic possibilities. (Although he missed mining hydrogen from moons like Titan that are covered in hydrocarbons.)

What counts as exotic? For chemistry "single-H" stabilized metallic hydrogen is about as exotic as you can get. For fission? Shrug. The best thing to do with fission reactors in space is to generate power for plasma thrusters. If you can accumulate thrust over a month or so, you end up distinguishing between power generation and the exhaust mass that gives you thrust. If you need to take off from planets that you don't particularly mind polluting, Orion (throwing A-bombs under a thrust plate with big shock absorbers) gets you to orbit fast.

With fusion, it does make sense to throw some of the fuel out the back as reaction mass if you use a magnetic pinch reactor. We could build straight-line systems with today's engineering know-how, but only if built in space. Otherwise, 99% of the reactor mass is devoted to keeping air out and radiation in. Remember though that D-T fusion is incredibly dirty, even if you don't use neutron multipliers to breed more tritium. B11-H often written B11-p is aneuronic, but requires much higher temperatures than d-t or He3-d fusion.

To go real exotic, of course, use antimatter. Great fuel, easy to use, but really hard to make. And also should not be stored on inhabited planets, in greater than microgram quantities.
 
  • #5
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I note that there appears to be a surplus of unused Hope & Change lying around. Maybe your characters will find something useful to do with it.
 
  • #6
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How about a p-B11 fusion fuel? See current research here:
http://www.lawrencevilleplasmaphysics.com/
They expect the 'exhaust' products, which are only He4, to be spit out
in a single direction, which is ideal for high thrust efficiency...
And, with very few neutrons, it's much safer than a standard D-T cycle.
 
  • #7
LURCH
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Of course, the most efficient fuel you can hope for is antimatter. This is produced in significant quatities by solar flares, if your sci-fi scenario allows for a way to harvest it.
 
  • #8
pervect
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What sort of space-ship is being considered? If it's not within the solar system, i.e. an interstellar spaceship, more specifically an interstellar rocket, you'll probably need to go to anti-matter for a plausible fuel. This would probably have to be manufactured (though the occurence in solar flares as suggested by Lurch is interesting and might provide an alternative).

I'd say you'd need a civilization with a Kardashev level http://en.wikipedia.org/wiki/Kardashev_scale approaching 2 to have the necessary technology to manipulate the required energies for commercial production of anti-matter. This may or may not fit within the framework of your story, you can solve a lot of problems by throwing enough energy at them.

So if a Karadashev-2 civilization is not the sort of backdrop required for your plot, but you still want interstellar travel, you're probably going to wind up fudging the physics a bit.
 
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  • #9
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http://en.wikipedia.org/wiki/Relativistic_rocket

This may be helpful. Also, if you care to stick with fusion, you can imagine an optimized cycle, where the temperature is so hot, the final exhaust products are largely Fe. Since the p-B11 cycle takes over 2 billion degrees, we'd need to get much much hotter than this (but I can't quantify it). The fuel density would also need to be so high that the intermediate fusion products could not escape, until the reaction ends and mostly Fe remains. You would not want anything heavier than Fe, as that would cost you net energy.
 
  • #10
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If the starship is fully electrical powered (not needing fuel to fly around), we could have an extremely high capacitance capacitor as its energy storage. It would be recharged at the docking port using solar power.

This high energy capacitor will be using molecules itself as its capacitor plates or simply, 'atom-thin' plate/dielectric so you could store vast amounts of energy in a small space.

The huge advantage of using capacitors as electrical storage is they can be fully recharged very quickly and could survive quite many charge/discharge cycles.

When the ship is flying at relativistic speeds, the diffuse interstellar gas will be utilized to ionize the outer hull of the ship to help supplement the electrical energy consumed by the propulsion system - this shouldn't result to violation of conservation of energy since, interaction with diffuse interstellar gas at relativistic speeds could cause a lot of drag. We are just extracting some energy from this interaction so energy efficiency is improved.
 
  • #11
sylas
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If you don't mind something that sounds superficially plausible and hard-sciencey, but is probably physically impossible, you could have a method able to extract large amounts of energy from the vacuum. Vacuum energy density really does exist, it seems. What is likely to be impossible is extracting it in a usable form.

Magnitudes of the vacuum energy density are a bit of a puzzle. Consideration of cosmology suggests something like 10-9 J/m3, while estimates from quantum physics typically get values more than 120 orders of magnitude larger; a whopping 10113 J/m3.

You can find lots of websites discussing this stuff... both crank and legitimate. For the purpose of a story you could propose various kinds of advance; perhaps a fuel involving a false vacuum state with very high energy density which can be extracted as it decays to the normal vacuum.

Cheers -- sylas
 
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  • #12
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If you don't mind something that sounds superficially plausible and hard-sciencey, but is probably physically impossible, you could have a method able to extract large amounts of energy from the vacuum. Vacuum energy density really does exist, it seems. What is likely to be impossible is extracting it in a usable form.
It's actually quite common in SF literature. For example, in Star Trek, they have managed to weaponize the know-how of vacuum energy into the 'quantum torpedo'. Also in Star Trek, the Romulan race, uses miniature but stabilized black holes held by a certain field to power their starships. These mini black holes could be used to harness vacuum energy(Hawking Radiation).
 
  • #13
davenn
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I'm suprised no one has mentioned the good old Sci Fi way of fuelling a spacecraft
by using a ram-scoop....

short quote from part of the wikipedia entry.....

The Bussard ramjet is a theoretical method of spacecraft propulsion proposed in 1960 by the physicist Robert W. Bussard, popularized by Larry Niven in his Known Space series of books, and referred to by Carl Sagan in the television series and book Cosmos.

Bussard proposed a ramjet variant of a fusion rocket capable of fast interstellar spaceflight, using enormous electro-magnetic fields (ranging from kilometers to many thousands of kilometers in diameter) as a ram scoop to collect and compress hydrogen from the interstellar medium. High speed forces the reactive mass into a progressively constricted magnetic field, compressing it until thermonuclear fusion occurs. The magnetic field then directs the energy as rocket exhaust opposite to the intended direction of travel, thereby accelerating the vessel.
 
  • #14
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This high energy capacitor will be using molecules itself as its capacitor plates or simply, 'atom-thin' plate/dielectric so you could store vast amounts of energy in a small space.

The huge advantage of using capacitors as electrical storage is they can be fully recharged very quickly and could survive quite many charge/discharge cycles.
Such a capacitor wouldn't be able to store any more energy per kg than chemical fuels (fuel cell, chemical battery, etc), and would likely store much less. Capacitors in general are very low energy density, their advantages over batteries are in charge and discharge rates and ability to charge and discharge many times without wearing out. Even double-layer supercapacitors (which already use molecule-thick dielectrics) have energy densities far lower than common batteries. (a 5 V 10 F capacitor stores about 7 mA-h of energy, compared to 500-1000 mA-h for a typical AAA cell)

If you're optimizing simply for energy per kg, you scale in the opposite direction...thicker dielectric, lower capacitance, higher operating voltage. Supercapacitors go for massive capacitance values largely because they're mainly used in low voltage electronics, where their long lifetime gives them an advantage over coin cells, and situations where brief but frequent surges of high current at low voltage are needed. Even ultra-high-voltage large-gap vacuum capacitors seem unlikely to run a starship, though.

Some hand-wavy vacuum energy gadget that produces vast amounts of power out of nowhere is really rather appealing, despite its implausibility. It's about the only way you can pull off things like photon rockets and relativistic spaceflight...otherwise you end needing huge amounts of antimatter. Getting a ship moving at 0.9c takes a *lot* of energy, and you then have to stop at the destination...and that's not even fast enough for really strong time dilation effects (at 0.9c, the ship experiences roughly half the time of its origin and destination). Getting interstellar travel fast enough for a person to make multiple trips pretty much requires either a magic FTL gadget or a magic infinite energy gadget.

A completely different approach is possible. Build huge arrays of lasers, and use them to push a craft using a photon sail. This sidesteps a lot of issues...the massive powerplants, lasers, and other equipment never moves, the ship doesn't have to carry massive amounts of fuel or equipment to push it between stars. It does require either a similar facility at the destination to allow you to brake, or a really long range beam and some fancy work with discarding parts of the ship to act as a reflector to allow the rest of the ship to brake (look up Robert Forward's Rocheworld for an example of this approach).
 
  • #15
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I'm suprised no one has mentioned the good old Sci Fi way of fuelling a spacecraft
by using a ram-scoop....
They seem to have gone out of style. Better data and analysis gave them a rather disappointingly low maximum velocity...probably better for braking than for accelerating.


Of course, the most efficient fuel you can hope for is antimatter. This is produced in significant quatities by solar flares, if your sci-fi scenario allows for a way to harvest it.
Antimatter's actually not very efficient, half the energy escapes as neutrinos. It's certainly dense, though. Gas giant radiation belts might be a more predictable and reliable source of naturally occurring antimatter than flares.
 
  • #16
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i'm no professional cosmologist but if you can accelerate to an initial velocity relatively close to the speed of light wouldn't you be colliding with a measurably large amount of blue shifted light which you could collect with say some kind of advanced type of solar collectors thereby providing yourself with enough energy to collect and accelerate interstellar hydrogen to a high enough exhaust velocity to propell yourself to a much higher velocity close to the speed of light? it seems that the faster you go the more fuel energy you would have available to you. maybe it wouldn't be all you need but it could cut down on your required fuel supply, couldn't it?
 
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  • #17
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Just use good ol' dark energy. If it is good enough to increase the rate of expansion of the universe, it should be good enough to fuel a spaceship. It currently accounts for 73% of the total mass-energy of the universe, so it's abundant. ????
 
  • #18
D H
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i'm no professional cosmologist but if you can accelerate to an initial velocity relatively close to the speed of light wouldn't you be colliding with a measurably large amount of blue shifted light which you could collect with say some kind of advanced type of solar collectors thereby providing yourself with enough energy to collect and accelerate interstellar hydrogen to a high enough exhaust velocity to propell yourself to a much higher velocity close to the speed of light? it seems that the faster you go the more fuel energy you would have available to you. maybe it wouldn't be all you need but it could cut down on your required fuel supply, couldn't it?
No, for a bunch of reasons.

1. Collecting that blue-shifted light is going to exert an effective force on your vehicle. It's called radiation pressure. This is the principle behind solar sails.

2. Unless you are near a star this is not a problem because your "measurably large amount of blue shifted light" is calculably very small. With that, there goes your idea ...

3. Collecting the interstellar hydrogen is going to exert an effective force on your vehicle. It's called drag. This is the principle behind parachutes.


You are essentially talking about a Bussard ramjet. The top speed of a Bussard ramjet is very high compared to chemical propulsion, but it is still only about 1/4 of the speed of light relative to the interstellar medium.
 
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  • #19
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how about if you accelerate your reaction mass so high that it's gamma factor is say millions of times higher than the gamma factor of your spacecraft so that the reaction mass is small but highly effective. i'm just a humble sci-fi writer myself and may not be aware of all the physical restrictions; i'm just trying to help out. maybe if you could combine this effect with a ramscoop and a conversion reactor that optimizes on the theory of proton decay at one times ten to the -29 cm. the fuel cost would be lower than with fusion or even antimatter. of course the fuel would be mostly interstellar hydrogen combined with a small onboard tank.
 
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  • #20
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Hmm. I just came up with a different idea that I need to go do the math on. Let's assume that we have a much larger version of the LHC. (Building it in space reduces the cost a lot.) Moreover, have different speeds for the particles rotating in the two rings, or two different masses, your choice.

When a collision occurs route the resulting relativistic black hole into an iron rod end on. (You can use lead, but you will see why iron in a minute.) Do it all correctly, and you create a black hole that will eat some of the iron rod before coming out the other end at very low velocity. Put a big pusher plate there, and convert the Hawking radiation into thrust. (Some of the Hawking radiation will be positrons and antiprotons, etc., so some of the thrust will come from eating the thrust plate.)

Using such a system for a star drive is interesting. You can extract energy from the (extremely) hot thrust plate to power the system. You have to carry all your reaction mass with you. You do get a nice efficiency for converting fuel to relativistic particles though.

However, let's just put one in (high) Earth orbit, and instead of a pusher plate use an electromagnetic system to extract more energy from the particles than just a pusher plate, and perhaps some non-thermal system for extracting energy from the gamma rays.

Have we reversed entropy? Gets to be an interesting question. If you want to imagine a star with a black hole in the center in equilibrium--I don't think such a system can be made stable--then iron is not the ultimate form of matter, low energy photons are, and we can keep the universe going a lot longer than previously thought.

I'd like to put my name on this. Unfortunately the name that will stick is probably black hole drive.
 
  • #21
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how about if you open up a stargate like wormhole in the heart of a star and have the other end firing out the back of your ship. i'm sorry i'm getting silly now, if you really want to focus on the story just make up a fuel like maybe neutronium or something, give it a couple of rules like it doesen't work too close to gravity but it carries you faster than light when you get outside the solar system give it some arbitrary speed like a light year every couple of hours and say you use thrusters in the star systems and always follow those same rules without fail and get on with your story(which is of course the important part).
 
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  • #22
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I am a big Science Fiction fan, and have read and watched a great deal of what is available. Science Fiction at its' best deals with the same major issues other great fiction does: Human suffering, loss, struggle, triumph, love, hate, revenge, prejudice, oppression, society, government, deception, honesty, and above all integrity, to name a few.

The primary literary device that separates Science Fiction from other Fiction is 'setting'. That is, the 'setting' is some semi-plausible future where scientific advancements have made some fundamental changes in familiar objects and (typically) meliorated some types of struggle and suffering. (For instance, hunger and illness may be removed).

This device in many cases allows the author to focus on specific flaws and strengths in characters without societal norms, prejudices and preoccupations of the period.

I love Science Fiction filled with Battle-stars, X-Wing fighters and FTL, but the plausibility of the science behind these stories is ALWAYS lacking. A "real dog-fight" in space would be VERY anticlimactic in comparison to anything on the big screen. But the true excitement of the "space battles" lies more in the audience's empathy with the characters and plot than the plausibility of the spacecraft.

In the end, any science fiction book or cinema that involves space travel is going to have to deal with "artificial gravity" because it is just awkward and darn inconvenient to write about or film people in constant free-fall. So, if you as a writer are going to "write-in" artificial gravity, then how you power your ship is a fairly trivial afterthought from a scientific plausibility point-of-view.

Why not reference the "discovery of the 'graviton'" and use gravity as your fuel? Your "graviton engine" allows you to align 'gravitons' into "a bi-polar orientation" so that the star you are leaving "pushes you away", and the star you are traveling to, "pulls you toward it", meanwhile, you can use control over 'gravitons' to be a plausible solution to gravity aboard your ship. It is neat, clean and concise (of course, scientifically absurd) and it will allow you plenty of ink to develop interesting characters in a well developed plot.

Fish
 
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  • #23
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speaking of spaceship fuel, have you ever in main stream science fiction seen the ship run out of fuel? isn't it funny that i should think of it but i think i have a valid point; maybe this is off the subject a little. anyways about the ramscoop idea, i have some space maps that show that an area around our sun, large area the density of interstellar hydrogen is low because of supernovae have occured within the general area of our solar system; of course otherwise how did the earth get its heavy elements but in some areas there are dense hydrogen clouds that could provide fuel. if you had a ramscoop and a large hydrogen tank you could feed off of the tank untill you found rich clouds to feed off of, that's of course if you did not want to penetrate any starsystems looking for jovian planets to scoop up hydrogen from.
 
  • #24
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i've got another strange idea that i had thought of in high school years ago. a friend was telling me about a book he had read in which a sea vessel was surrounded by electromagnetic fields in order to cloak it which worked however the ship travelled from the east coast to the west coast in impossible time. the theory was that the electromagnetic fields compressed space-time around the vessel increasing the speed matter travells through it allowing it to do that. you could have a huge battery powering space-time compression allowing your ship to speed ahead so that it will arrive at its destination quickly. your "fuel" would be a battery that adds energy to particles that split as energy is added, likely matter/antimatter with a small bleed-off that fuels the containment field. the more you use the batteries the easier they can contain themselves and the "charge" fuels your space-time compressor and simple propulsion system. you "fuel up" with solar cells in any star system.
 
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  • #25
FtlIsAwesome
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I know this thread is 5 weeks old, but I'd like to point this out:

http://en.wikipedia.org/wiki/Alcubierre_drive" [Broken]

It is often described as a warp drive.
It uses negative mass (something we haven't discovered yet) to bend space around a craft.
This allows sublight and translight travel without any acceleration or time dilation for the passengers.
You'll need some explanation for acquiring negative mass.
There are some bugs with the idea. For example you may not be able to steer it, you'd have to set your destination at depature. And the required level of negative mass is very high.
 
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