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.

Butch Wilmore and Suni Williams, two NASA astronauts who have been stuck on the International Space Station for nine months, are scheduled to begin their return to Earth early Tuesday morning on a long-awaited flight home to cap an unusual mission.