Butch Wilmore and Suni Williams originally planned to go to space for just eight days but got stuck on the station after their Boeing Starliner spacecraft experienced problems.

A SpaceX capsule delivered four astronauts to the International Space Station early on Sunday in a NASA crew-swap mission that will allow a pair of stuck astronauts, Butch Wilmore and Suni Williams, to return home after nine months on the orbiting lab.

Butch Wilmore and Suni Williams are due to return home after nine months in space. A SpaceX crew capsule arrived at the International Space Station on Sunday, delivering the replacements for NASA’s two stuck astronauts.

Reaching orbit from NASA’s Kennedy Space Center, the newest crew includes NASA’s Anne McClain and Nichole Ayers, both military pilots; and Japan’s Takuya Onishi and Russia’s Kirill Peskov, both former airline pilots. They will spend the next six months at the space station, considered the normal stint, after springing Wilmore and Williams free.

The crew-swap mission will enable NASA’s Butch Wilmore and Suni Williams to return to Earth from the International Space Station.