Friday, NASA astronaut Scott Kelly will blast into space, where he will spend an entire year at the International Space Station - that's the longest space mission ever for NASA.
His identical twin brother, retired astronaut Mark Kelly, will remain on earth, and as a result, NASA plans to conduct a study comparing the two. The study will focus on how space affects different human organs, decision making, organisms in the gut, and how genes react.
More year-long missions are planned, as space agencies need to learn how the body adapts to an entire year before committing to even longer mars expeditions.
And what's one thing Scott Kelly made sure to pack before lift off? His belt. The astronaut says he got tired of his shirttails flying out of his pants on his first mission at the space station.