Each additional day in orbit is part of Kelly’s one-year mission  with cosmonaut Mikhail Kornienko to study the effects of long-duration spaceflight on humans. The pair arrived at the space station in March 2015 and are participating in studies during their 342 days in space that provide new insights into how the human body adjusts to weightlessness, isolation, radiation and stress of long-duration spaceflight. Kelly’s twin brother, former astronaut Mark Kelly, will participate in parallel twin studies on Earth to help scientists compare the effects on the body and mind in space.

Breaking such a record for time in space is important because every additional day helps us better understand how long-duration spaceflight affects bodies and minds, which NASA scientists say is critical to advancing the space agency’s future missions to Mars. The investigations in progress on the space station will help scientists better understand how to protect astronauts as they travel into deep space and eventually on missions to the Red Planet.

Kelly is scheduled to return to Earth on March 3, 2016, by which time he will have compiled 522 total days living in space during four missions.