NASA astronauts Butch Wilmore and Suni Williams set out for a weeklong mission at the International Space Station last year. After nine months, they are coming home.

The Boeing Starliner they took to the space station almost didn't make it. Soon after liftoff in June, helium leaked and thrusters malfunctioned. NASA and Boeing spent the summer trying to figure out what went wrong and whether the problems would repeat on the flight back.

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