There is very little justification for human involvement in space combat. We are very fragile, and space is a harsh mistress. Not only is aviation headed toward

There is very little justification for human involvement in space combat. We are very fragile, and space is a harsh mistress. Not only is aviation headed towards automation, every extra-terran spacecraft that has been built has also been automated. Even if the life support systems were entirely costless, having to keep acceleration under certain limits (i.e. below the point where people turn into paste) seems like it would be disadvantageous. To me the question of propulsion is most interesting, and specifically I wonder how feasible it would be to solve the problem of engine design by using two different engines. Nuclear propulsion looks good on paper, but a ready supply of fissile material is likely to be difficult to obtain. Lastly we might consider whether or not space combat will happen at all. Spacecraft are very expensive, and the conditions which give rise to warfare on Earth seem unlikely. When your political entities are light-years away from each other, it's hard to have resource conflicts. Or, in a universe with FTL, it's probably hard to have conflicts when you don't have causality.