The U.S. and Russia named the two men on Monday who will spend a year aboard the International Space Station to gather more data on the impact of outer space on humans to help prepare for future interplanetary missions.
NASA's Scott Kelly and Mikhail Kornienko of Russia's space agency Roscosmo will take part in the mission set to start in spring 2015. A key goal is to help reduce health risks for planned NASA missions around the moon, an asteroid and ultimately Mars.
William Gerstenmaier, NASA's associate administrator, said the year spent on the Space Station "will increase our knowledge regarding the effects of microgravity on humans as we prepare for future missions beyond low-Earth orbit."
Kelly, a veteran of several space missions who has logged more than 180 days in space, and Kornienko, who traveled to the station in 2010, will start training for the mission early next year.
Kelly's twin brother, Mark Kelly is the husband of former Arizona congresswoman Gabrielle Giffords who was targeted in a 2011 assassination attempt and he was the skipper of Space Shuttle Endeavour on its last mission in 2011. He then retired.
International crews so far have done only six-month stints on the International Space Station, although many Russian cosmonauts spent longer stints on the Soviet-built Mir space station before it was discarded in 2001. Russian cosmonaut Valery Polyakov holds the world's record for the longest ever single space mission, having spent 437 days in space in 1994-1995.
Boris Morukov, the head of the Moscow-based Institute for Medical and Biological Problems, Russia's main space medicine research center, said on Interfax news agency that the forthcoming mission by Kelly and Kornienko may include tighter controls of their food rations and the limiting of communications to simulate an interplanetary travel, among other things.