MMH (monomethyl hydrazine)
MMH (monomethyl hydrazine) is a clear, colorless, hygroscopic liquid, with the chemical formula CH3NHNH2, that is derived from hydrazine. It is used as a hypergolic liquid rocket fuel, with nitrogen tetroxide as an oxidizer, in the orbital maneuvering system (OMS) and reaction control system (RCS) of the Space Shuttle Orbiter. The specific impulse of the MMH/N2O4 combination in the Space Shuttle orbiter ranges from 260–280 seconds in the RCS, to 313 seconds in the OMS. The higher efficiency of the OMS system is attributed to higher expansion ratios in the nozzles and higher pressures in the combustion chambers.