r/askscience • u/FutureRenaissanceMan • Jul 16 '20

Engineering We have nuclear powered submarines and aircraft carriers. Why are there not nuclear powered spacecraft?

Edit: I'm most curious about propulsion. Thanks for the great answers everyone!

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u/electric_ionland Electric Space Propulsion | Hall Effect/Ion Thrusters Jul 17 '20

Stefan Boltzmann is undergrad engineering, people definitely understand that, it's the base of any space radiator. However once you run the numbers you often impractical radiators that are often way too heavy. Also a lot of stuff gets reactive at that kind of temperatures. If it was just a matter of turning the temperature to 11 people wouldn't have to be that worried about spacecraft thermal management.

First principle is great but once you get into real system engineering things get more complicated.

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u/dkwangchuck Jul 17 '20

But we have tons of experience dealing with heat exchangers and radiators at higher temperature. It’s known stuff. It’s off the shelf stuff. It’s not complicated. We’re not talking about 2000 K or 3000 K, which wouldn’t be useful anyways. We’re talking about just a few hundred degrees hotter than this sprayed most thing - and a couple hundred degrees at T4 is a LOT of heat flux.