Why do people use rocket fuel instead of nuclear power for spacecraft?
In: Technology
Nuclear reactors make heat. Heat isn’t particularly useful in and of itself. Heat can be turned into electricity through a number of types of cycles, that’s how spacecraft use it, as well as the nuclear plant down the street. Electricity isn’t that useful in propulsion, as electrons have very small mass.
To move a rocket, you shoot **stuff** out the nozzle at high speed. There is a relationship between the mass of the stuff and the speed of the stuff that determines the thrust of the rocket.
To make a nuclear powered rocket, you need the nuclear reactor **plus** stuff to shoot out. With a chemical rocket, the combusted fuel used to make the energy **is the stuff** shot out. there is no energy transfer (or 100% efficient energy transfer if you prefer) which gives very high efficiency. The nuclear solution has to transfer the energy to the stuff, which is less efficient.
TL;DR: High weight (for safety) and low efficiency makes nuclear energy a bad rocket choice.
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