An orbital sunrise brightens this view of space shuttle Discovery's vertical stabilizer,..

The International Space Station is seen in this view from the space shuttle Discovery after the undocking of the two spacecraft in this photo provided by NASA and taken March 7, 2011. Astronauts aboard the space shuttle Discovery prepared on Tuesday to bring NASA's most-traveled spacecraft back to Earth, wrapping up its 39th and final mission



Space shuttle Discovery mission specialist Alvin Drew works on the aft flight deck in this photo provided by NASA and taken March 7, 2011. Astronauts aboard the space shuttle Discovery prepared on Tuesday to bring NASA's most-traveled spacecraft back to Earth, wrapping up its 39th and final mission

An orbital sunrise brightens this view of space shuttle Discovery's vertical stabilizer, orbital maneuvering system (OMS) pods, docking mechanism, remote manipulator system/orbiter boom sensor system (RMS/OBSS) and payload bay in this photo provided by NASA and taken March 7, 2011. Astronauts aboard the space shuttle Discovery prepared on Tuesday to bring NASA's most-traveled spacecraft back to Earth, wrapping up its 39th and final mission

NASA astronaut Michael Barratt watches a water bubble float freely near him on the middeck of space shuttle Discovery in this photo provided by NASA and taken March 7, 2011. Astronauts aboard the space shuttle Discovery prepared on Tuesday to bring NASA's most-traveled spacecraft back to Earth, wrapping up its 39th and final mission.

Space shuttle Discovery's vertical stabilizer, orbital maneuvering system (OMS) pods, remote manipulator system/orbiter boom sensor system (RMS/OBSS) and payload bay are featured in this photo provided by NASA and taken March 7, 2011. Astronauts aboard the space shuttle Discovery prepared on Tuesday to bring NASA's most-traveled spacecraft back to Earth, wrapping up its 39th and final mission.

Space Shuttle Discovery Pilot Eric Boe (L), Commander Steve Lindsey and mission specialist Alvin Drew (R) work on the aft flight deck of the shuttle in this photo provided by NASA and taken March 7, 2011. Astronauts aboard the space shuttle Discovery prepared on Tuesday to bring NASA's most-traveled spacecraft back to Earth, wrapping up its 39th and final mission

Space Shuttle Discovery pilot Eric Boe works the controls for the remote manipulator system (RMS) on the aft flight deck of the shuttle in this photo provided by NASA and taken March 7, 2011. Astronauts aboard the space shuttle Discovery prepared on Tuesday to bring NASA's most-traveled spacecraft back to Earth, wrapping up its 39th and final mission