(I'm not sure I put this thread in the right sub-forum) If we need to operate a nuclear-powered heat engine in space to run a generator, meaning it can only be cooled by radiation, what kind of system should we go for, if we want the power per unit mass ratio to be as high as possible? I've "researched" this on my own, and found a few things: #1 Due to the Stefan-Boltzmann law being a fourth grade equation radiator temperature being high is very important. #2 The reactor experiments that were part of the NERVA-program were by far the "hottest" reactor cores ever operated, at an exhaust temperature of 2370K. #3 The mechanical strength of all known metals and alloys seems to drop so much as to become almost useless at 1500K or so. #4 Graphite is apparently strong even at extremely high temperatures. But graphite being graphite, I can't imagine it being very shock-resistant or able to resist "grinding". Could a ceramic/graphite stirling engine be built? How would heat be carried from the "cold sink" to the radiator? What would the ratio of the cold to hot sink temperatures ideally be?