Space Shuttle Atlantis (Orbiter Vehicle Designation: OV-104) is one of the three currently operational orbiters in the Space Shuttle fleet of NASA, the space agency of the United States. (The other two are Discovery and Endeavour.) Atlantis was the fourth operational shuttle built. In early 2008, NASA officials decided to keep Atlantis flying until 2010, the projected end of the Shuttle program. This reversed a previous decision to retire Atlantis in 2008.