Encyclopedia Astronautica

Monomethylhydrazine (CH3NHNH2) is a storable liquid fuel that found favour in the United States for use in orbital spacecraft engines. Its advantages in comparison to UDMH are higher density and slightly higher performance.

Monomethylhydrazine (MMH) is 95+ per cent pure, while the normally expected impurities are methylamine and water. MMH is a clear, water-white hygroscopic liquid which tends to turn yellow upon exposure to air. MMH is a toxic, volatile liquid which will react with carbon dioxide and oxygen. MMH has the typical sharp ammoniacal or fishy odour of amines. It is completely miscible in all proportions with hydrazine, water, and low molecular-weight alcohols. MMH is not sensitive to impact or friction; it is more stable than hydrazine on mild heating and similar to hydrazine in sensitivity to catalytic oxidation.

Monomethylhydrazine may be produced by a modified Raschig process; methylamine is substituted for ammonia in the reaction with chloramine. In general, substituted hydrazines may be prepared by the reaction of an alkylsulfate or halide with hydrazine. In 1959 the price for MMH was $ 15 per kg. It was projected that this would be reduced to $ 2.00 per kg in mass production. By 1990 NASA was actually paying $ 17.00 per kg due to stringent environmental protection regulations. By 2006 this had skyrocketed to $170.00 per kg.

Mixed oxides of nitrogen / monomethylhydrazine.

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