Feasibility of anti-matter as a fuel

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.

posted about 10 years ago

celtschk‭

341 reputation 24 102 42 10

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.

posted about 10 years ago

HDE 226868‭

601 reputation 61 463 80 49