Three International Space Station crew members said goodbye Wednesday as the ISS prepares for a new Expedition team.

NASA Cmdr. Barry Wilmore and his two Russian colleagues left the station and are scheduled to returned to Earth on a Russian Soyuz capsule shortly after 10 p.m.

The remaining crew members are now preparing for the arrival of some new colleagues. In less than three weeks, the new crew will head to the ISS. Among them is Scott Kelly, an ISS veteran. Kelly will spend a whole year in space as part of a study on the effects of long-term missions on the human body.

Kelly is uniquely suited for this study. While he is in space, NASA will study his twin brother, former astronaut Mark Kelly, to compare the results.