you're asking the wrong drg, my funny flying machine nerdy knowledge ends at the kármán line - I'm really more of a winged, air-intaking sorta critter. But uh. Project Orion remains the funniest shit, fissile material is a "fuel mix" if you think about it
tell the class about the nuclear thermal jet bombers both the US and USSR tried at some scale
Unfortunately neither of the two ever actually were powered by their reactors, they were mostly testbeds for the general idea of "can we safely operate a reactor on a bomber"/"can we make shielding etc light and effective enough"
Both of them were supposed to have a second prototype model/design that would be at least partly powered by the reactor, but both were canceled cuz of cost and "oh god if these crash or get shot down that'll be very fucking bad" reasons
fascinating example of both sides of the iron curtain trying the same thing and arriving at basically the same conclusion