May 28, 2008, file photo: Space shuttle Discovery commander Mark Kelly, right, gestures as he walks with his twin brother astronaut Scott Kelly, left, and mission specialist Ron Garan, after arrival at Kennedy Space Center in Cape Canaveral, Fla. Terry Renna/AP hide caption

itoggle caption Terry Renna/AP

The space shuttle Atlantis docked to the International Space Station in May 2010. NASA has announced that Atlantis will fly one last mission in June 2011 before retirement. NASA/Getty Images hide caption

itoggle caption NASA/Getty Images