# Feasibility of anti-matter as a fuel

Now, taking out the cost to produce/collect it, assume somehow we perfected a formula or find a natural source (because that is currently very prohibitive), how feasible would be to use antimatter as a fuel source primarily for space-travel/exploration? Along with that, how much would you need to power a star ship - say, a FireFly class?

Could it be safely stored in any great quantity? It's not like if you get a little leak you can just go patch it quickly.

From Wikipedia:

The reaction of 1 kg of antimatter with 1 kg of matter would produce 1.8$\times$1017 J (180 petajoules) of energy (by the mass-energy equivalence formula, E = mc2), or the rough equivalent of 43 megatons of TNT – slightly less than the yield of the 27,000 kg Tsar Bomb, the largest thermonuclear weapon ever detonated.

The main problem with antimatter would be containment. You cannot simply put it into a normal container, because the normal container would be made of matter, and the antimatter would annihilate with it. So you need to find a way to keep the antimatter safely away from any matter in your ship. At the same time, you also need to allow it to safely be transported to the reaction place where a controlled annihilation with matter would happen.

The only way to contain and manipulate antimatter would be using fields. Assuming you don't have a special force field a la star trek, that would mean electromagnetic fields. Probably the antimatter would be held magnetically as a plasma, quite similarly to the hydrogen in a fusion reactor (the hot hydrogen gas in the fusion reactor also has to be kept away from the walls, although there it's because of its high temperature).

The yearly world energy consumption is somewhere between 100 and 200 Petawatt-hours. Using your quoted number (A petawatt-hour is 3600 petajoules), to produce that energy, one would need about 4 to 8 metric tons of antimatter to fulfil the current world energy needs for a whole year. How much energy a ship would need of course depends on how fast the ship needs to go, how often it needs to accelerate/decelerate (non-accelerated flight is free), how efficient its engines are, and how often it can be refueled, but I think it is safe to assume that it will be significantly less than the current yearly world energy production. Thus I think even a single gram of antimatter should be more than enough; probably it would need just a few milligrams.

• You wouldn't want to hold the antimatter as plasma - even though containment is good enough for fusion it still leaks some neutral particles which then annihilate with the physical container, and probably produce way to much heat. Keeping a solid in position electromagnetically in a vacuum chamber would be easier. But even the vacuum needs to be quite good. – Andreas Krey Sep 30 '14 at 12:47
• Well, fortunately the one thing that's easy to get in space is a very good vacuum. I don't know how easy/hard it is to keep a solid in position electromagnetically (well, it probably depends on the solid; I'd expect generated antimatter to be anti-hydrogen, which probably isn't the best thing to control electromagnetically), but even if you manage that, I think it will be hard to remove just a little bit from it for operating your drive. – celtschk Sep 30 '14 at 20:54
• Main storage should have fuel in the form of a simple liquid, in a tank made of solid antimatter (so as not to annihilate with the antimatter fuel). That tank is your solid to more easily hold in suspension. then you need worry about the fiddly bits only for the fuel currently being handled for use; the main tank can be fairly stable even against things like loss of power, at least at low acceleration, with permanent magnets backing up the electromagnets. – Matthew Najmon Oct 1 '14 at 16:56
• @MatthewNajmon: OK, that's a possibility. However it would not just need an antimatter source, it would need the availability or ability to create a whole set of antimatter materials, which is several of magnitudes harder than just generating some antimatter (as I already wrote, I'd expect generated antimatter to be anti-hydrogen). Indeed, I think you'd encounter all the problems you try to solve that way in the creation of the materials (plus a few more since you'd essentially need to have an antimatter fusion reactor in order to produce heavier antimatter atoms). – celtschk Oct 1 '14 at 18:58
• Encountering those problems at the factory facility where the fuel tanks are produced, which may well be a planetside or orbital facility, seems much less prohibitive than facing those same problems onboard a starship, where space, power, manpower, hotlab-like facilities, and every other conceivably relevant resource would be much harder to come by. As for the antimatter fusion reactor to produce heavier atoms, the need for that is entirely dependent on on the antimatter source. Harvested sources are almost entirely speculative, so there's no real way to assess how likely certain types are. – Matthew Najmon Oct 1 '14 at 22:20

I'll address storage of antimatter, because that is the one thing in your question humans have done successfully so far. While we may someday build an antimatter-based propulsion device, it's a ways off. Storing antimatter is another story.

Currently, the best way to store antimatter is a Penning trap. It uses a magnetic field and an electric field to store charged particles (so this would not work for neutral particles unless they were "attached" to charged particles, perhaps like neutrons are bound together with protons in a nucleus). A magnetic field (or an electric field) on its own could not keep a particle in a stable position because of Earnshaw's theorem; using a Penning trap provides a loophole.

Now, a Penning trap is generally used for keeping a particle in a desired position, i.e. in a static state. There is a chance you could refine one to move some of the antimatter, but it would be difficult. That said, any civilization that can build a starship probably has pretty sophisticated technology. . .

Okay, I might as well try to address one more problem that is . . . well, a big problem. When you bring the antimatter into contact with matter, you can't simply have it in the storage area. If it's in a small storage area, the energy released may destroy the Penning trap (or whatever else you're using). If it's in a large storage area, the explosion probably won't be near whichever end of the craft you designate the rear. Either way, the explosion won't be directed rearwards, as with a typical rocket.

The solution like this might be to accelerate the antimatter and matter out the end of the spaceship. Particle accelerators do this via superconducting magnets. The problem is, these accelerators are incredibly large - the Large Hadron Collider is 27 kilometers in circumference! Perhaps that would be tough to do on a small spaceship. To solve that issue, I would suggest using a small ion engine: to accelerate the matter and antimatter. Have them accelerated perpendicular to each other and away from the ship, and you could direct the explosion to the rear. Again, the particles have to be charged, but it's a small price to pay for a powerful spacecraft.

This is my first activity on the Worldbuilding site; I hope my answer suits it.

• Yes! A very nice, clean answer. And welcome! – CAgrippa Oct 4 '14 at 21:59
• Robert L Forward described solid-state antimatter traps Camelot 30K. Details of antimatter propulsion can be read in The Starflight Handbook. – JDługosz Dec 20 '14 at 22:41
• Cutting-edge research on replacing microwaves with optical frequency in a silicon chip would reduce the size of the accelerator by orders of magnitude, as does plazma wakefield acceleration. – JDługosz Dec 20 '14 at 22:48

Annihilation often produces light high energy particles (gamma quants, electrons, positrons, and neutrinos) that may not be very trivial to use. If you want to propel a spacecraft, they must be directed all the same way towards exhaust. If you want to cook your dinner, these high energy particles must pass they energy to the surrounding atoms somehow rather than just flying away.

This may work with some specially designed device, but may not be easy and some energy would probably be lost during conversion.

Imagine a ring where particles fly at high speed in circles, being contained magnetically, just like a particle acelerator... but with three modes: accelerating/stable/off.

Particles run continously in a rotation. When you need to use energy, you divert a single particle or more via a door towards the engine where it hits a target made of ordinary matter... This will generate photons that heat up a rankine cycle engine... Simple and effective...

• Not that simple. As the antimatter leaves the accellerator, it will react instantaneously due it will find matter in that very moment. But you probably want the antimatter to hit specifific matter, not the first on its way. So basicly you need another accellerator (which is way simpler because it doesn't have to keep a field up when not needet). Both accellerators have to shot their particles (the matter and the antimatter) simultaniousely towards each other in a vacuum at its best. – Sempie Jan 11 '16 at 9:39
• If you don't do this, you'll have two problems: #1: The Energygain might not be at it's optimum. #2: The Antimatter will "eat" your engine over time, because it just reacts with the very first particle it mets which could be a part of your engine. – Sempie Jan 11 '16 at 9:41

The potential of the storage of antimatter is only just beyond our grasp, due to the fact that scientists at CERN have discovered an electromagnetic 'trap' to contain antimatter, however as said in previous comments it would be hard to propel a ship of any kind using it.

This is because Einstens theory (E=mc^) states that the energy of matter antimatter annihilation would be released two ways with photons, and so some energy would hit the ship, potentially doing damage and the rest of the energy being inneficient. However if you could manipulate the antimatter to send the energy in concentrated blasts into the ship using some kind of deflector shield then it could possibly propel the ship.

There is also the possibility of designing a 100% efficient hadron collider that directs the end product of antimatter towards the rear of the ship- therefore solving the question of storing it as a fuel. You never know- in the early 1900's no one thought it would be possible to go to the moon, and they did due to technological advancements in 1969.

There is also the possibility of using antimatter to replace fossil fuels as in 2008 only 368kg of antimatter was needed to fuel the world to to the fact that when it annihilates it releases 1.8x10^17j of energy and so it could potentially replace the worlds energy problem, if of course you build a 100% efficient collider and then no electricity would be wasted on the process as it is very costly; also if larger amounts of antimatter could be produced in the particle collision. I hope my answer was to standard and detailed!

• Hi, Ben, welcome to Worldbuilding! You may want to break this up; the wall of text doesn't make for easy reading. – HDE 226868 Jan 10 '16 at 16:01
• Thank you very much for your feedback, a was worried about the chunk of text being too big and also far too detailed! – Ben Jan 12 '16 at 16:05