Aerozine 50

Aerozine 50 is a 50/50 mix of hydrazine and unsymmetrical dimethylhydrazine (UDMH). Originally developed in the late 1950s by Aerojet-General Corporation as a storable, high-energy, hypergolic fuel for the Titan ICBM rocket engines, Aerozine continues in wide use as a rocket fuel, typically with dinitrogen tetroxide as the oxidizer, with which it is hypergolic (ignites on contact). Aerozine 50 is more stable than hydrazine alone, but has a higher density and boiling point than UDMH alone.

This type of fuel is mainly used for interplanetary probes and spacecraft propulsion systems, because rockets and spacecraft using it can stay fueled indefinitely. This is not true with most rockets. In some cases, it is used in ground launched rockets, such as the entire Titan rocket, or as part of a rocket upper stage, such as the Delta II and Delta III rocket (the Delta IV rocket, on the other hand, uses a cryogenic upper stage). In addition to the Titan rocket family (Titan II, Titan III, and Titan IV), it was also used by both components of the Apollo Spacecraft (the Apollo Lunar Module and Apollo CSM), and some interplanetary probes (such as Voyager 1 and Voyager 2).