UH 25 is a fuel mixture for rockets. It was developed for the EuropeanAriane 2–4 launch vehicles.

UH 25 was developed after a disaster during flight 2 of theAriane 1 rocket. During launch, one of the fourViking engines on the first stage developed a combustion instability which led to an engine fire, subsequent explosion and destruction of the vehicle. Following this event and starting withAriane 2, the fuel was changed from pure UDMH to the mixture UH 25.^[1]

UH 25 was used in Ariane rocket versions 2 through 4, and in the IndianGSLV Mk III.

UH 25 is a mixture of75%UDMH and25%hydrazine hydrate.^[2] It ishypergolic withdinitrogen tetroxide as oxidizer, and both can be stored as liquids at room temperature.

Like its components, UH 25 is flammable, toxic (carcinogenic) and corrosive.

T Toxic	F Easily flammable

• Aerozine 50 - a 50:50 mix of hydrazine and UDMH
• C-Stoff, the mix of hydrazine and methanol fuel used for theHWK 109-509 German rocket motor series

• Schmidt, Eckart W. (2022). "Properties of UDMH/N₂H₅OH Mixtures".Dimethylhydrazines.Encyclopedia of Liquid Fuels. De Gruyter. pp. 1547–1549.doi:10.1515/9783110750287-017.ISBN 978-3-11-075028-7.

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