FILE - In this 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. Scott and his twin Mark are taking part in an unprecedented study of identical twins looking into the effects of prolonged weightlessness. Mark will undergo tests on Earth while Scott will embark on a one-year space station stint. (AP Photo/Terry Renna, File)
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