chasonreddit t1_j0vebyu wrote on December 19, 2022 at 6:33 PM

Reply to comment by BlueSkyToday in Nuclear fusion breakthrough: What does it mean for space exploration? by Gari_305

Well SI per lb of fuel is quite a bit higher for fission, but I understand what you are saying. Since we don't have a fusion reactor, it's hard to say what that might be.

Now I've always been fascinated by the concept of the Bussard ramjet, but that's a whole different animal and fictional as well.

BlueSkyToday t1_j0wk7ye wrote on December 19, 2022 at 11:13 PM

I suspect that the mass of the fuel is a very small portion of the mass of the engine.

chasonreddit t1_j0wnkve wrote on December 19, 2022 at 11:38 PM

Really depends on the distance and expected acceleration. You would be surprised. With Hohmann orbits, well those are designed to use minimal reaction mass. It's still a huge proportion. To really get around even the solar system you really want constant acceleration and ultimately 1 G acceleration. Even at high ejection velocities that's a lot of reaction mass.

I won't vouch for the math, but I remember reading that even with a 100% mass conversion drive (the ultimate) a ship would use approximately half of it's mass to make a round trip to nearer stars at 1G.