Hypergolic propellant
（重定向自Hypergol）
![The hypergolic fuel hydrazine being loaded onto the MESSENGER space probe. Note the safety suit the technician is wearing.](/Images/godic/202501/19/Hypergolic_Fuel_for_MESSENGER2632.jpg")
![The first hypergolic-propellant rocket engine used for human flight, the Walter 109-509A of 1942–45.](/Images/godic/202501/19/Walter_Triebwerk_HWK109-509_A_Luftwaffenmuseum_Berlin-Gatow_Denis_Apel2632.JPG")
![Hypergolic propellant tanks of the Orbital Maneuvering System of Space Shuttle Endeavour](/Images/godic/202501/19/OMS_Pod_removal2633.png")
A hypergolic propellant combination used in a rocket engine is one whose components spontaneously ignite when they come into contact with each other.
The two propellant components usually consist of a fuel and an oxidizer. Although commonly used hypergolic propellants are difficult to handle because of their extreme toxicity and/or corrosiveness, they can be stored as liquids at room temperature and hypergolic engines are easy to ignite reliably and repeatedly.