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In "Ignition! An Informal History of Liquid Rocket Propellants", John D. Clark in one of the chapters gives an overview of the then current state of hydrazine and hydrazine derivatives.

The main components of such fuels were hydrazine, monomethyl hydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH), in all kinds of mixing ratios.

I know for a fact that these combinations are still perfectly relevant.

He goes on to list several commonly used additives, including diethylene triamine for better density, acetonitrile for viscosity reduction and hydrazine nitrate. He also list some potentially useful future candidates like ethylene di-hydrazine and tetramethyl tetrazene which may have some uses.

Have hydrazine-derived fuels progressed any further in the 50+ years since Clark wrote the book? Are any new additives or major components in common use?

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The problems with fancy fuels and additives is that they tend to increase costs and complex chemical mixtures may potentially create serious stability issues (see sections on RFNA and chlorine trifluoride in the same book - storage handling and stability are all important. Things can go bang in strange ways - see section on ozone) . So unless the gains are particularly good it is less likely that they would be used. I don't know for sure but suggest that mixtures in use today are probably simple variants like aerozine 50. If any are used they are likely in very specialist applications.

The advent of Starship with its projected very low costs (when it becomes operational) my change the calculus as well especially if means are perfected for the long term storage of methalox in space.

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