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

SpaceX scrubbed the launch of a relief crew on Wednesday night, delaying the handoff for NASA astronauts who have been awaiting a return trip to Earth.

The replacements for NASA’s two stuck astronauts launched to the International Space Station on Friday night, paving the way for the pair’s return after nine long months. Butch Wilmore and Suni Williams need SpaceX to get this relief team to the space station before they can check out.