All the recent work on compact reactors has been on modular ones that don’t care about weight. I think there have been studies about nuclear rockets but no active development programs.
Fission rockets are useless for launching to space because the thrust is too low, or the weight is too high. They could be useful in space because their higher exhaust velocity. But high exhaust velocity means low thrust.
Fission rockets are useless for launching to space because the thrust is too low, or the weight is too high. They could be useful in space because their higher exhaust velocity. But high exhaust velocity means low thrust.