[Illustration: 52. RL-10 engines used to power Centaur launch
vehicle.]
The RL-10 is an upper stage propulsion system that can be stopped and
restarted in space. It is a regeneratively cooled engine which burns
liquid hydrogen and liquid oxygen to produce 6800 kilograms (15,000
pounds) of thrust. RL-10s pioneered the use of liquid hydrogen as a
rocket fuel. They powered the Centaur launch vehicles that boosted such
craft as Surveyor and Viking into space. A six-engine cluster of RL-10s
was also used to propel the S4 stage of the Saturn 1.
The RL-10 was developed by Pratt & Whitney Aircraft division of the
United Aircraft Corporation.
The RL-10 engine is from the National Aeronautics and Space
Administration.