UDMH (Unsymmetrical Dimethylhydrazine) ((CH₃)₂NNH₂) is a hypergolic fuel propellant used as a fuel. Storable for years at ambient temperature. Typical ISP: 280–310 s (with NTO) seconds.
UDMH, short for unsymmetrical dimethylhydrazine, is a powerful liquid rocket fuel prized for one rare quality: it can be stored for long periods at room temperature and fired at a moment’s notice. That convenience has made it a mainstay of many rockets and spacecraft, even though it is dangerously toxic to handle.
Quick facts
- Type: a liquid rocket fuel, usually paired with the oxidizer nitrogen tetroxide.
- Family: a hydrazine-based chemical, derived from ammonia.
- Key trait: hypergolic, meaning it bursts into flame the instant it touches its oxidizer, with no spark needed.
- Storable: stays liquid at normal temperatures, so tanks can be loaded and kept ready for long periods.
- Used in: the Proton and Long March rockets, the Titan family, and many satellite and spacecraft engines.
How it works
Most rockets need an ignition system, but hypergolic propellants like UDMH light themselves. When UDMH meets nitrogen tetroxide, the two chemicals react and ignite on contact, which makes engines simpler and very reliable to restart, an important quality for steering thrusters and upper stages that must fire again and again in space. Because neither chemical needs to be kept super-cold, a fueled rocket can sit ready for launch for days or longer, which is why military missiles and deep-space probes have favored them.
Why it matters, and its downside
UDMH made dependable, restartable, long-storage rockets possible, and it powered some of the most-used launchers in history. But it comes at a cost. UDMH and its oxidizer are extremely toxic, corrosive, and harmful to people and the environment, requiring crews in full protective suits and creating contamination where spent stages fall. For these reasons, newer rockets increasingly favor cleaner fuels like kerosene, methane, and hydrogen, though UDMH remains in wide use where its self-igniting, storable nature is hard to beat.
Developed in the 1950s for storable missile propellants. Used extensively in Proton, Kosmos, Long March 2/3/4, and PSLV/GSLV vehicles.
Storable, hypergolic, good low-temperature performance, stable in storage
Highly toxic and carcinogenic, lower Isp than cryogenic propellants, environmental hazard
