Centaur is a rocket stage designed for use as the upper stage of space launch vehicles. Centaur boosts its satellite payload to geosynchronous orbit or, in the case of an interplanetary space probe, to or near to escape velocity. Centaur was the world's first high-energy upper stage, burning liquid hydrogen (LH2) and liquid oxygen (LOX).
A new version, the Centaur-G, was developed for use with the Space Shuttle. It was optimized for installation in the Orbiter payload bay by increasing the hydrogen tank diameter to 14 feet while retaining the 10-foot-diameter (3.0 m) oxygen tank. Its initial mission was to boost the Galileo scientific probe to Jupiter.
The Centaur, as carried in the Shuttle payload bay, required an extremely complex airborne support system, which was integrated into the Centaur Integrated Support System, the CISS. In addition to controlling Centaur pressurization in flight, the CISS had to be able to dump propellants overboard quickly in the event of a Return To Launch Site Abort, a capability needed to permit the Orbiter to land safely. After the Challenger accident, NASA realized that it was far too risky to fly the Centaur on the Shuttle.
