Centaur (rocket stage)

The Centaur is a family of rocket-propelled upper stages that has been in use since 1962. It is currently produced by United Launch Alliance (ULA) in two main versions. The 3.05 m (10 ft) diameter Centaur III (also known as the Common Centaur) serves as the second stage of the retiring Atlas V rocket, and the 5.4 m (17.7 ft) diameter Centaur V is used as the second stage of the Vulcan Centaur rocket. Centaur was the first rocket stage to use hydrolox propellant—liquid hydrogen (LH2) and liquid oxygen (LOX)—a high-energy combination well suited for upper stages but difficult to handle because both propellants must be stored at extremely low cryogenic temperatures. Centaur stages are built around stainless steel pressure-stabilized balloon propellant tanks with 0.51 mm (0.020 in) thick walls. It can lift payloads of up to 19,000 kg (42,000 lb). The thin tank walls minimize mass, maximizing overall stage performance. A common bulkhead separates the LOX and LH2 tanks, further reducing weight. The bulkhead consists of two stainless steel skins separated by a fiberglass honeycomb, which limits heat transfer between the extremely cold LH2 and the comparatively warmer LOX. The main propulsion system consists of one or two RL10 engines made by Aerojet Rocketdyne.