UDMH (unsymmetrical dimethylhydrazine) is a hypergolic liquid rocket fuel derived from hydrazine. It has the chemical formula N(CH3)2NH2. UDMH is often used instead of, or in mixtures with, hydrazine because it improves stability, especially at higher temperatures. UDMH is employed by many Russian, European, and Chinese rockets. The Titan family of launch vehicles and the second stage of the Delta use a fuel called Aerozine 50, which is a mixture of 50% UDMH and 50% hydrazine.