Question: Which chemical archaically called diamidogen was used in the Viking rocket engines?
Sentence (from "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, N2O4/UH 25 (mixture 75% UDMH and 25% Hydrazine.)
Relevant evidence: Yes