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gaunt79 t1_j6ooewc wrote

Reply to comment by ShedDoor2020 in NASA and DARPA to partner on nuclear thermal propulsion demonstration by returnofjuju

Liquid hydrogen takes the place of water in a terrestrial reactor. The hydrogen is pumped into the reactor core (cooling the nozzle and reactor casing on its way) where it is superheated. It then passes to the nozzle, where it expands and is focused into the thrust plume that propels the spacecraft.

This diagram may make more sense.

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ShedDoor2020 t1_j6p362x wrote

Thank you for the explanation. So, do you have to replenish/refuel the hydrogen periodically? Or is it a closed system like a car radiator?

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gaunt79 t1_j6p5hdo wrote

It would need to be replentished, but it would theoretically be easier/safer to refill only hydrogen propellant than to refill both a fuel and an oxidizer. I don't think that refueling is in DRACO's mission parameters, though. Future NTP spacecraft may be reusable in that manner.

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