[buildsjets]

If you are fantasizing the implementation of an imaginary future technology, why not fusion power for SPACE ships?

[simne]

Because nobody predict so large grow of space industry, which could make fusion profitable.

Second problem, for space weight is so expensive, that it made fission viable, and solve proliferation problem (very little risk, somebody will steal materials from Moon or beyond).

[nancyminusone]

You still need somewhere for the heat to go, and that's a lot easier if you're on top of water instead of nothing.

Although, a good radiator on a spacecraft still seems trivially easy compared to having a working fusion reactor in the first place.

[oldgradstudent]

Controlled by a quantum computer, obviously.