 NASA's Space Shuttle, officially called the Space Transportation System (STS), is the United States government's most recent manned launch vehicle. A total of five usable orbiters were built, of which three were in use until the program's retirement in 2011. The winged shuttle Orbiter is launched vertically, usually carrying five to seven astronauts (although eight have been carried and eleven could be accommodated in an emergency) along with up to 50,000 pounds (23,000 kg) of payload into low earth orbit. When its mission is complete, it fires its manoeuvring thrusters to drop out of orbit and re-enters the Earth's atmosphere. During the descent and landing, the shuttle Orbiter acts as a glider and makes a completely unpowered landing.
