Hypergolic propellant

Hypergolität is a property of certain rocket propellants, the components react with each other spontaneously, when they are brought into contact or are mixed. The term comes from the hypergolic German Wolfgang Carl Noeggerath (1908-1973) who, like the Me 163B used this designation for self-igniting fuel mixtures, for example, for the first time.

The components of hypergolic propellants are usually strong oxidizing and reducing agents, which upon contact instantly, partly explosively ignite. Since the fuel reacts after injection into the combustion chamber and burns immediately, with too much fuel in the combustion chamber can never accumulate before the engine is ignited. Ignition is definitely what is essential for weapons systems such as intercontinental ballistic missiles and upper stages of launchers.

The components of hypergolic propellants are usually toxic, unstable and often difficult to store. For larger weapons systems, one is therefore transferred to solid boosters and used hypergolic fuels only for ignition.

Hydrazine derivatives with dinitrogen tetroxide are today the only hypergolic fuels that are still used. Although they are poisonous, but because they can be stored without refrigeration problems for a long time, they of satellites and space probes are used for their engines. Also in some space rockets (mainly upper stages ) they are used. Manned spacecrafts (eg Space Shuttle ) they also use mostly for their thrusters.

Examples of hypergolic fuels are:

• Dimethylhydrazine and nitrogen tetroxide ( the most widely used Hypergol, for example, in the proton (rocket) used )
• Dinitrogen tetroxide and monomethyl hydrazine (eg in the EPS upper stage of the Ariane 5 uses )
• Dimethylhydrazine and nitric acid
• Hydrazine and nitric acid
• Aniline and nitric acid
• Hydrogen peroxide and a mixture of hydrazine hydrate, methanol and 13% water
• Highly concentrated hydrogen peroxide and kerosene