Which is the range of thrust (minimum and maximum) that a nuclear thermal rocket is estimated to produce?

Knowing these values, which thrust to weight ratio would be able to produce?


1 Answer 1


The American NERVA program developed a design expected to produce up to 333kN (75klbf) of thrust in a 6.8 ton package, for a thrust to weight ratio of about 5:1. It was never completed or flown. NERVA 2 was supposed to produce 867kN (195klbf) from 11.9 tons, a thrust to weight ratio of 7.5:1. Those are figures for thrust in vacuum.

The Russian RD-0410 was similar in concept, but smaller, producing 35kN and weighing 2 tons, a 1.8:1 TWR.

Those TWRs are for the engine itself, not including any fuel tankage. Generally these engines weren't considered for first-stage launch from Earth's surface, both because of environmental concerns and because their TWR is fairly low; many such engines would need to be clustered to achieve 1.2 TWR off the pad with any substantial fuel tankage.

I believe nuclear thermal rockets are simpler to throttle than bipropellant chemical rockets. I don't know how far down they can throttle but I would guess they can go to quite low thrust values with good specific impulse across their whole range.

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    $\begingroup$ Also, their thrust can be improved at cost of ISp through use of denser propellants. Probably an engine capable of handling both hydrogen and zinc could switch between two quite different thrust profiles. $\endgroup$
    – SF.
    Apr 14, 2016 at 3:03

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