Rockets using liquid propellants power most spacecraft and some launch vehicles. The liquid propellants currently use dinitrogen tetroxide (N2O4) as an oxidizer, and fuel mixtures containing hydrazine (N2H4), monomethyl hydrazine (MMH), and unsymmetrical dimethyl hydrazine (UDMH). For convenience, N2H4, HDH, MMH, UDMH, Aerozine-50, and N2O4 together are referred to as