Astronauts Suni Williams and Butch Wilmore, who have been stranded at the International Space Station for nine months, will finally return to Earth on Tuesday, one day earlier than expected.

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.