SpaceX has launched a rocket carrying a new crew to the International Space Station (ISS) as part of a plan to bring astronauts Butch Wilmore and Suni Williams home.
The pair were due to be on the ISS for only eight days, but because of technical issues with the experimental spacecraft they came on, they have been there for more than nine months.
The astronauts are due to begin their journey back to Earth two days after the new crew arrives. Steve Stich, manager of Nasa's commercial crew programme said he was delighted at the prospect.
"Butch and Suni have done a great job and we are excited to bring them back," he said.
The astronauts, along with their ISS workmates, Nasa's Nick Hague and Roscosmos cosmonaut Aleksandr Gorbunov, will be relieved by four astronauts, from Russia, Japan and two from the US.
There will be a two-day handover after which the old crew are due to begin their journey back to Earth. But there could be a small further delay, as they wait for conditions on Earth to be right for a safe re-entry of the returning capsule, according to Dana Weigel, manager, of the ISS programme.
"Weather always has to cooperate, so we'll take our time over that if it is not favourable," she told reporters.
Ms Weigel explained that the astronauts had begun getting ready for the handover last week.
"Butch rang a ceremonial bell as Suni handed over command to cosmonaut Alexei Ovchinin," she said.
