U.S. astronaut Scott Kelly (left) and Russian cosmonaut Mikhail Kornienko will spend an entire year aboard the International Space Station beginning in 2015. The extended mission will provide a medical foundation for future missions around the moon, as well as far-flung trips to asteroids and Mars. (AP Photo/Gagarin Cosmonaut Training Center via NASA)

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U.S. astronaut Scott Kelly (left) and Russian cosmonaut Mikhail Kornienko will spend an entire year aboard the International Space Station beginning in 2015. The extended mission will provide a medical foundation for future missions around the moon, as well as far-flung trips to asteroids and Mars. (AP Photo/Gagarin Cosmonaut Training Center via NASA)