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Methane, ammonia and water are sometimes suggested as alternatives to hydrogen for a nuclear thermal rocket.

While they have a lower specific impulse, they offer much better density, thrust, and handling characteristics.

How does hydrazine $N_2 H_4$ compare to ammonia $NH_3$ in terms of specific impulse? Its density is significantly better (1.021 g/cm³, compared to 0.682 g/cm³), and the hydrogen content isn't too much lower. The performance here depends heavily on the dissociation of these molecules at high temperatures, and I haven't found good numbers on how the $H_2$-$NH_3$-$N_2$ ratios work out.

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I ran across this chart on Twitter. I do not know its provenance so take with a large dose of hydrazine salts.

If the chart is correct, hydrazine is somewhat superior to ammonia, especially at low reactor temperatures.

enter image description here

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  • $\begingroup$ Someone, at some point, has done a performance calculation, using an unknown methodology. Better than nothing, I guess. $\endgroup$ Mar 10, 2023 at 6:36

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