seanDNRC

KSP disallowed Mechjeb when I upgraded to 1.0.2. I shall patiently await the update :-) Love mechjeb, I would suck so much without it.

That's theoretically true. But a good engineer, and Dr. Zubrin certainly is one, will tell you that a practical spacecraft can be engineered to achieve a speed about twice that of its engine's exhaust velocity. in a D-He3 fusion rocket that is about .05C, which means the spaceship could get up to about 10% of C. (Entering Space, Robert Zubrin 1999) In Kerbal things are different of course.

that last part was hyperbole, somewhat. But you're right, at the moment it'd cost in the trillions to fuel an interstellar mission. Even a 1,000x increase in efficiency would still make antimatter 10,000x as expensive as equivalent fusion fuel, but fusion will never get you beyond 10% of lightspeed. Using water as the fuel of our AM rocket would get expensive rather quickly. a single ounce of antimatter annihilating an once of matter has a destructive force of 1.22 megatons. You'll need a lot of water, like an iceberg a second.

That's exactly how Robert Zubrin's photon rocket works. Instead of doing all the tricky work of bringing equal amounts of matter and antimatter together in a controlled reaction you just blast anti-protons against a block of tungsten or graphite. Heating it immensely and sending photons the other way out a mirrored nozzle. Simple and gets you up to 50% of light-speed with little trouble. Much simpler than a plasma drive. And when then annihilation block is exhausted you just replace it. You don't need to replace the whole engine. But you still have to burn a solar system's worth of energy to make the antimatter.