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BlueSkyToday t1_j0vdfzd wrote

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

Yup, heat-is-heat, but I think that there's about as much overlap between a laser fusion or a tokamak, and a fission plant as there is between a coal fired plant and a fission plant.

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chasonreddit t1_j0vebyu wrote

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.

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BlueSkyToday t1_j0wk7ye wrote

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

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chasonreddit t1_j0wnkve wrote

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.

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