Space Shuttle Discovery Prepares for its Final Return to Earth

In a frame grab made from NASA TV, space shuttle Discovery leaves the International Space Station for the last time Monday, March 7, 2011. Discovery is due back on Earth on Wednesday. It's being retired after touchdown and sent to the Smithsonian Instit

The U.S. space shuttle Discovery has completed its work at the International Space Station on its 39th and final mission, and is preparing for Wednesday's scheduled landing at the Kennedy Space Center in Florida.

The shuttle successfully undocked from the space station early Monday at 1200 UTC. After completing its 13-day mission,Discovery will be retired as the oldest and longest-serving space shuttle in the 30-year-old NASA program.

The shuttle and its crew of five men and one woman spent nearly nine days docked at the space station, after NASA added two days to its mission. In addition to ferrying essential supplies for the orbiting outpost, theDiscovery astronauts installed a new pressurized multipurpose storage module on the Earth-facing side of the space station. They also delivered a new humanoid robot, called Robonaut 2. NASA hopes Robonaut 2 eventually will be upgraded to function as the space station's official astronaut helper.

The space shuttle crew Monday morning received a special wake-up greeting modified for Discovery from the opening theme of the original 1960'sStar Trek television series. The surprise salutation was a recording by the show's star, William Shatner, who played the iconic Captain James T. Kirk of the 23rd-century star ship, Enterprise.

Shuttle flight managers later hinted that the Discovery astronauts might receive another unique wake-up experience on Tuesday.

NASA's other two remaining space shuttles, Endeavour and Atlantis, will join Discovery in retirement after they complete their final missions in April and June.