The
Aerojet Rocketdyne RS-25, otherwise known as the
Space Shuttle Main Engine (
SSME), is a
liquid-fuel cryogenic rocket engine that was used on
NASA's
Space Shuttle and is planned to be used on its successor, the
Space Launch System. Built in the
United States by
Rocketdyne, the RS-25 burns
cryogenic liquid hydrogen and
liquid oxygen propellants, with each engine producing of
thrust at liftoff. Although the RS-25 can trace its heritage back to the 1960s, concerted development of the engine began in the 1970s, with the first flight,
STS-1, occurring on April 12, 1981. The RS-25 has undergone several upgrades over its operational history to improve the engine's reliability, safety and maintenance load.