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moral_luck t1_j7hy8f5 wrote

Does anyone know what the total mass of the exhaust* (momentum generator) would be in a nuclear rocket versus a chemical one?

And what would that exhaust* be?

*I'm not sure what the correct term is, maybe propellant?


Backlit_keys t1_j7iungd wrote

The propellant mass of nuclear thermal rockets would vary based on the fuel chosen (ideally, hydrogen) and the specific mission requirements but generally an equivalent NTR will have twice the efficiency of a chemical rocket. So twice your delta-v for the same propellant and mission payload.


littlebitsofspider t1_j7j6g2y wrote

Isp is the term you want, it's a measure of fuel efficiency for generated thrust. For example, Ultra Safe Nuclear generated a reference design for NASA for a small, 25MWth NTR with an Isp of 900 seconds. Traditional chemical rockets (like the Raptor engines from SpaceX) are ~325-360 seconds depending on altitude.