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.

The astronauts have consistently said that they have been happy to be on board the space station, with Suni Williams describing it as her “happy place”. But Dr Simeon Barber, of the Open University, told BBC News that there would likely have been a personal cost.

“When you are sent on a work trip that is supposed to last a week, you are not expecting it to take the best part of a year,” he said.

“This extended stay in space will have disrupted family life, things will have happened back home that they will have missed out on, so there will have been a period of upheaval.”

Butch and Suni arrived at the ISS at the beginning of June 2024 to test an experimental spacecraft called Starliner, which was built by the aerospace firm Boeing, a rival to SpaceX.

The mission had been delayed by several years because of technical issues in the spacecraft’s development, and there were problems during its launch and docking on to the ISS. This included issues with some of Starliner’s thrusters, which would be needed to slow the spacecraft for re-entry into the Earth’s atmosphere, and leaks of helium gas in the propulsion system.

Nasa decided that it would not take even a small risk in bringing back Butch and Suni on Starliner, when they had the option of returning them on SpaceX’s Dragon capsule. Nasa decided the best option was to do this during a scheduled crew rotation, even though it would mean keeping the astronauts on the space station for several months.

Boeing has consistently argued that it would have been safe to bring Butch and Suni back on Starliner, and were unhappy about the decision to use a rival’s capsule instead, which will be “embarrassing” for Boeing, according to Dr Barber.

“It’s not a good look for Boeing to see astronauts they took into space come back in a competitor’s craft.”

Both President Trump and SpaceX CEO Elon Musk have said that Butch and Suni could have been brought home sooner, most recently in a joint interview with Fox News in February.

President Trump states: “They got left in space.”

When the interviewer, Sean Hannity, elaborates, saying “They were supposed to be there eight days. They’re there almost 300,” Mr Trump responds with one word: “Biden.” Mr Musk follows up asserting: “They were left up there for political reasons.”

The assertion is denied by Nasa’s Steve Stitch.

“We looked at a wide range of options and worked hand-in-hand with SpaceX to look at what was the best thing to do overall and when we laid all that out the best option was to have the one we are embarking upon,” he said.

That decision was supported by Dr Libby Jackson, who is head of space at the Science Museum in London and worked at Europe’s control centre for the ISS.

“Butch and Suni’s wellbeing would always have been at the very forefront of everybody’s minds as the decisions were being made for how best to deal with the circumstances that they were presented,” she said.

“Nasa made those decisions based on good technical reasons, on programmatic reasons, and found the right solution that has kept Butch and Suni safe.

“I really look forward to seeing them return to Earth, safe and sound, along with the rest of their crewmates.”