UH 25

UH 25 is a fuel mixture for rockets. It was developed for the European Ariane 2-4 launch vehicles.

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UH 25 was developed after a disaster during flight 2 of the Ariane 1 rocket. During launch, one of the four Viking engines on the first stage developed a combustion instability which lead to an engine fire, subsequent explosion and destruction of the vehicle. Following this event and starting with Ariane 2, the fuel was changed from pure UDMH to the mixture UH 25.

UH 25 fuel mixture was used in Ariane rocket versions 2 through 4 and is used today in Indian PSLV and GSLV rockets. The Indian rockets uses in India in license build Viking engines.

UH 25 is a mixture of 75% UDMH und 25% hydrazine. Together with the oxidizer, dinitrogen tetroxide, it gives a hypergolic, toxic and corrosive rocket fuel combination, storable at normal temperatures.

Danger

UH 25 is, like hydrazine and UMDH, toxic and acidic. The constituent UDMH is carcinogenic, as is hydrazine.

Safety labels

T toxic	F easily flammable