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ZHEZKAZGAN, KAZAKHSTAN - MARCH 2: In this handout provided by NASA, The Soyuz TMA-18M spacecraft is seen as it lands with Expedition 46 Commander Scott Kelly of NASA and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos on March 2, 2016 near the town of Zhezkazgan, Kazakhstan. Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. (Photo by Bill Ingalls/NASA via Getty Images)

ZHEZKAZGAN, KAZAKHSTAN - MARCH 2: In this handout provided by NASA, The Soyuz TMA-18M spacecraft is seen as it lands with Expedition 46 Commander Scott Kelly of NASA and Russian cosmonauts Mikhail Kornienko and Sergey Volkov of Roscosmos on March 2, 2016 near the town of Zhezkazgan, Kazakhstan. Kelly and Kornienko completed an International Space Station record year-long mission to collect valuable data on the effect of long duration weightlessness on the human body that will be used to formulate a human mission to Mars. Volkov returned after spending six months on the station. (Photo by Bill Ingalls/NASA via Getty Images)