Which space shuttle flew the most missions?

Space Shuttle Discovery (Orbiter Vehicle Designation: OV-103) is one of the orbiters from NASA's Space Shuttle program and the third of five fully operational orbiters to be built. Its first mission, STS-41-D, flew from August 30 to September 5, 1984. Over 27 years of service it launched and landed 39 times, gathering more spaceflights than any other spacecraft.

Discovery became the third operational orbiter to enter service, preceded by Columbia and Challenger. It embarked on its last mission, STS-133, on February 24, 2011 and touched down for the final time at Kennedy Space Center on March 9, having spent a cumulative total of almost a full year in space. Discovery performed both research and International Space Station (ISS) assembly missions. It also carried the Hubble Space Telescope into orbit. Discovery was the first operational shuttle to be retired, followed by Endeavour and then Atlantis.