Astronauts Suni Williams and Butch Wilmore, who have been stranded at the International Space Station for nine months, closed the hatch to the SpaceX Dragon capsule Monday night to begin their journey back to Earth.

Two astronauts are one step closer to returning to Earth. A SpaceX Dragon carrying a crew of four will dock at the International Space Station later tonight. The crew will replace Butch Wilmore and Suni Williams, who have been in space for more than nine months.

That’s how long Boeing Starliner’s mission — its first flight test with crew aboard — was supposed to last. But this mission has been singular in almost every way, and astronauts Butch Wilmore and Suni Williams have instead spent the past nine and a half months aboard the International Space Station.