Cryogenic rocket engine

A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel and oxidizer; that is, both its fuel and oxidizer are gases which have been liquefied and are stored at very low temperatures.^[1] These highly efficient engines were first flown on the US Atlas-Centaur and were one of the main factors of NASA's success in reaching the Moon by the Saturn V rocket.^[1]

Rocket engines burning cryogenic propellants remain in use today on high performance upper stages and boosters. Upper stages are numerous. Boosters include ESA's Ariane 5, JAXA's H-II, ISRO's GSLV, LVM3, United States Delta IV and Space Launch System. The United States, Russia, Japan, India, France and China are the only countries that have operational cryogenic rocket engines.