Each Space Shuttle was a reusable launch system composed of three main assemblies:
- the reusable orbiter vehicle,
- the expendable external tank,
- and the two reusable solid rocket boosters.
Shortly after the tank and boosters are jettisoned, the orbiter vehicle enters orbit alone. At the conclusion of the mission, the orbiter fires its orbital maneuvering system to de-orbit and re-enter the atmosphere.