Space Shuttle Orbiter Atlantis is one of the fleet of space shuttles belonging to the U.S. National Aeronautics and Space Administration (NASA). It was the fourth operational shuttle built. Following the destruction of Columbia, it is one of the three fully operational shuttles remaining in the fleet. The other two are Discovery and Endeavour. After it completes STS-125, the final Hubble Space Telescope service mission, Atlantis is scheduled to be the first shuttle retired from the fleet.