Comment Re:Wrong Focus (Score 1) 132
Note that it's technically possible to have something like this with a slow reactor; you could for example use steam as a moderator, which will transmit a reasonable proportion of near infrared through it (the hotter you can run your fuel particles, the better transmission you'll get). But not only will you lose some light, but just the simple act of neutron moderation is a very heat-intensive process, meaning big radiators if you want big power (not to mention that the moderator itself for such a slow reactor is also far heavier than the core). The whole point of my variant is to avoid the moderator and avoid the ship having to ever capture anything but incident heat lost due to generation, transmission, reflection, etc losses.
One possibility for a slow reactor, albeit only directly applicable to the rocket mode above, is to have your propellant be your moderator, absorbing both IR and moderating fast neutrons. The fact that it's heating then becomes irrelevant (actually an advantage), since you're dumping it out the nozzle for thrust. If one wanted mission flexibility in such a scenario you could have such a moderator-ejecting rocket mode used to get to orbit, and then switch to retaining the moderator once in orbit and cooling it instead in order to make use of the fission fragment operating mode.
But a fast reactor would obviously be highly preferable so you don't have to worry about a moderator at all.