The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated for 30 years by the U.S. National Aeronautics and Space Administration or just NASA as part of the Space Shuttle program. Its components include the Orbiter Vehicle with three clustered Rocketdyne RS-25 main engines, a pair of recoverable solid rocket boosters, and the expendable external tank with liquid hydrogen and liquid oxygen in our fanart Space Shuttle cursor.