An American astronaut and a Russian cosmonaut are moving into the International Space Station this week and staying for an entire year.
After more than two years of training, Scott Kelly and Mikhail Kornienko are eager to get going. It will be the longest space mission ever for NASA, and the longest in almost two decades for the Russian Space Agency, which holds the record at 14 months.
Their Soyuz rocket is scheduled to blast off from Kazakhstan on Friday afternoon in the U.S. (early Saturday morning in Kazakhstan.)
The world's space agencies want to know how the body adapts to an entire year of weightlessness before committing to even longer Mars expeditions. The typical stint at the space station is six months.