After their weeklong journey turned into a monthslong stay on the International Space Station, two Boeing Starliner astronauts will soon be united with the spacecraft that will eventually bring them home.

SpaceX launched the rescue mission on Saturday with a downsized crew of two astronauts and two empty seats reserved for Butch Wilmore and Suni Williams, who will return next year. The Dragon capsule docked in darkness as the two craft soared 265 miles (426 kilometers) above Botswana.