In this Thursday, March 17, 2010 picture, Expedition 26 Commander Scott Kelly, left, is reunited with his twin brother, Mark Kelly following a flight back to Ellington Field in Houston from Kustanai, Kazakhstan. Scott Kelly landed in Kazakhstan on March 16 with his Russian crewmates in the Soyuz TMA-01M spacecraft after 159 days in space, 157 days on the International Space Station. Mark Kelly is in the final weeks of training as Commander of the final flight of Endeavour, STS-134, that will spend more than a week docked to the ISS. Endeavour is targeted for launch on April 19, 2011. (AP Photo/NASA, Rob Navias)

Photo by: Rob Navias

In this Thursday, March 17, 2010 picture, Expedition 26 Commander Scott Kelly, left, is reunited with his twin brother, Mark Kelly following a flight back to Ellington Field in Houston from Kustanai, Kazakhstan. Scott Kelly landed in Kazakhstan on March 16 with his Russian crewmates in the Soyuz TMA-01M spacecraft after 159 days in space, 157 days on the International Space Station. Mark Kelly is in the final weeks of training as Commander of the final flight of Endeavour, STS-134, that will spend more than a week docked to the ISS. Endeavour is targeted for launch on April 19, 2011. (AP Photo/NASA, Rob Navias)