The International Space Station is seen in this view from the space shuttle Discovery with the earth's horizon in the background after the undocking of the two spacecraft in this photo provided by NASA and taken March 7, 2011. [Photo/Agencies]

The space shuttle Discovery lands at the Kennedy Space Center in Cape Canaveral, Florida, March 9, 2011. The space shuttle Discovery capped a successful 13-day spaceflight with a smooth landing in Florida on Wednesday, ending a 27-year flying career for NASA's most-traveled spaceship as the agency prepares for an uncertain future. [Photo/Agencies]