Astronaut Scott Kelly to return to space for one year

On Friday, 51-year-old astronaut Scott Kelly, who has flown three previous space missions, will return to the International Space Station where he will remain for a year. A whole year.

Joining him on the long mission will be Russian cosmonaut Mikhail Kornienko.

Long-term space travel can do a number on the human body, causing muscle atrophy, bone loss and changes to the eyes. The space travelers’ sleep patterns, behavior, cognitive function, gut microbes and vision will be closely monitored during this time. From NASA:

“Functional studies will examine crew member performance during and after the 12-month span. Behavioral studies will monitor sleep patterns and exercise routines. Visual impairment will be studied by measuring changes in pressure inside the human skull. Metabolic investigations will examine the immune system and effects of stress. Physical performance will be monitored through exercise examinations. Researchers will also monitor microbial changes in the crew, as well as the human factors associated with how the crew interacts aboard the station.”

Meanwhile, Kelly’s twin brother, Mark Kelly, a retired NASA astronaut, will undergo a number of comparative tests on the ground.

Both Kelly and Kornienko told the Washington Post that they’d miss nature the most:

“Kornienko expects to miss flowing water — stuff he can swim in, not the floating globs he’ll deal with in space — and Kelly will miss the outdoors of his Houston home. “