<b>Pictures:</b> Space Shuttle Discovery on STS-133

Backdropped by the thin line of Earth’s atmosphere and the blackness of space, a docked Russian Soyuz spacecraft (R), a portion of the International Space Station’s Quest airlock and solar array panels are featured in this March 1, 2011 NASA handout image photographed by an STS-133 crew member while space shuttle Discovery remains docked with the station.   (HO, AFP/Getty Images)

Expedition 26 and STS-133 crew members pose for a photo in the newly-attached Permanent Multipurpose Module (PMM) of the International Space Station while space shuttle Discovery remains docked with the station in this March 1, 2011 NASA handout image. Clockwise from lower left are: NASA astronauts Scott Kelly, Expedition 26 commander; Alvin Drew, Steve Bowen, Nicole Stott, all STS-133 mission specialists; Russian cosmonauts Oleg Skripochka and Alexander Kaleri, NASA astronaut Cady Coleman, Russian cosmonaut Dmitry Kondratyev, all Expedition 26 flight engineers; NASA astronaut Steve Lindsey, STS-133 commander; European Space Agency astronaut Paolo Nespoli, Expedition 26 flight engineer; NASA astronauts Eric Boe, STS-133 pilot; and Michael Barratt, STS-133 mission specialist.   (HO, AFP/Getty Images)

This NASA March 1, 2011 handout image the newly-attached Permanent Multipurpose Module (PMM), docked space shuttle Discovery (STS-133) and the Canadian-built Dextre, also known as the Special Purpose Dextrous Manipulator (SPDM), photographed by an Expedition 26 crew member on the International Space Station. The blackness of space and Earth’s horizon provide the backdrop for the scene.   (HO, AFP/Getty Images)

This NASA TV framegrab shows Discovery shuttle astronaut Steve Bowen takes some photographs during the second spacewalk March 2, 2011 outside of the International Space Station (ISS). Steve Bowen and Alvin Drew embarked on their second spacewalk together at 10:42 Eastern time (1542 GMT) to complete work on a failed ammonia pump, remove installation on the Tranquility module and install spare parts on the Canadian robot Dextre.   (HO, AFP/Getty Images)

This NASA TV framegrab shows Discovery shuttle astronaut Steve Bowen’s view as he takes some photographs during the second spacewalk March 2, 2011 outside of the International Space Station (ISS). Steve Bowen and Alvin Drew embarked on their second spacewalk together at 10:42 Eastern time (1542 GMT) to complete work on a failed ammonia pump, remove installation on the Tranquility module and install spare parts on the Canadian robot Dextre.   (HO, AFP/Getty Images)

This NASA TV framegrab shows Discovery shuttle astronaut Steve Bowen(C top) during the second spacewalk March 2, 2011 outside of the International Space Station (ISS). Steve Bowen and Alvin Drew embarked on their second spacewalk together at 10:42 Eastern time (1542 GMT) to complete work on a failed ammonia pump, remove installation on the Tranquility module and install spare parts on the Canadian robot Dextre.   (HO, AFP/Getty Images)

The space shuttle Discovery lifts off February 24, 2011 from Kennedy Space Center in Florida on a mission to the International Space Station. This will be the 39th and final flight for Discovery.   (STAN HONDA, AFP/Getty Images)

The space shuttle Discovery lifts off February 24, 2011 from Kennedy Space Center in Florida on a mission to the International Space Station. This will be the 39th and final flight for Discovery.   (STAN HONDA, AFP/Getty Images)