Common Hypergolic Propellant Combinations
- Aerozine 50 + nitrogen tetroxide (NTO) - widely used in historical American rockets, including the Titan 2; all engines in the Apollo Lunar Module; and the Service Propulsion System in the Apollo Service Module
- Aerozine 50 is a mixture of 50% UDMH and 50% straight hydrazine (N2H4).
- Unsymmetrical dimethylhydrazine (UDMH) + nitrogen tetroxide (NTO) - frequently used by the Russians, such as in the Proton rocket and supplied by them to France for the Ariane 1 first and second stages (replaced with UH 25); ISRO PSLV second stage.
- UH 25 is a mixture of 25% hydrazine hydrate and 75% UDMH.
- Monomethylhydrazine (MMH) + nitrogen tetroxide (NTO) - smaller engines and reaction control thrusters: Apollo Command Module reaction control system; Space Shuttle OMS and RCS; Ariane 5 EPS; Draco thrusters used by the SpaceX Dragon spacecraft.
The trend among western space launch agencies is away from large hypergolic rocket engines and toward hydrogen/oxygen engines with higher performance. Ariane 1 through 4, with their hypergolic first and second stages (and optional hypergolic boosters on the Ariane 3 and 4) have been retired and replaced with the Ariane 5, which uses a first stage fueled by liquid hydrogen and liquid oxygen. The Titan II, III and IV, with their hypergolic first and second stages, have also been retired. Hypergolic rockets are still widely used in upper stages when multiple burn-coast periods are required.
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