Unsymmetrical dimethylhydrazine in the context of "Viking (rocket engine)"

The Viking rocket engines were members of a series of bipropellant engines for the first and second stages of the Ariane 1 through Ariane 4 commercial launch vehicles, using storable, hypergolic propellants: dinitrogen tetroxide and UH 25, a mixture of 75% UDMH and 25% hydrazine (originally UDMH).

The earliest versions, developed in 1965, had a sea-level thrust of about 190 kN. By 1971, the thrust had improved to 540 kN, with resulting engine named Viking 1 and adopted for the Ariane program. The engine first flown on the Ariane 1 rocket in 1979 was Viking 2, with thrust further improved to 611 kN.