Starliner astronauts Sunita Williams and Butch Wilmore's return to Earth delayed again

They cannot leave until a handover crew arrives at the International Space Station in late March

Astronauts Suni Williams and Butch Wilmore have seen an eight-day mission on the International Space Station stretch to 10 months. AP

Two astronauts who arrived at the International Space Station in early June aboard a Boeing Starliner capsule for what was intended to be an eight-day mission are now facing another delay in their return.

Sunita Williams and Butch Wilmore travelled to the ISS on Starliner's first crewed test flight, in a drive to ensure that Nasa can start launching its astronauts in a number of operators' spacecraft.

But after technical issues made their Starliner craft unreliable, Nasa in September dispatched a SpaceX Crew Dragon to bring them back. This has two spaces to take the stranded astronauts back to Earth at the end of its mission, initially scheduled for next February. But that return date now been pushed back until a new set of astronauts arrives on the station for a handover.

Nasa said on Tuesday it had adjusted launch date of the SpaceX/Nasa Crew-10 mission with the handover crew to “no earlier than late March” – almost 10 months after Ms Williams and Mr Wilmore arrived at the ISS.

The Starliner spacecraft docked with the International Space Station in June. AP

“The change gives Nasa and SpaceX teams time to complete processing on a new Dragon spacecraft for the mission,” the agency said. “The new spacecraft is set to arrive to the company’s processing facility in Florida in early January.”

The agency’s SpaceX Crew-9 mission, with Ms Williams, Mr Wilmore, fellow Nasa astronaut Nick Hague and Russian cosmonaut Aleksandr Gorbunov, will return to Earth following the arrival of Crew-10 at the ISS.

Space agencies consider the handover an important step to ensure a smooth transition on the space station. It allows the departing crew to brief the incoming astronauts on continuing experiments and station maintenance before taking over full responsibilities.

The Starliner faced technical issues with its propulsion system and navigation sensors, which compromised its ability to safely return the astronauts to Earth. These problems prompted Nasa to bring back the craft empty and arrange September's rescue using a SpaceX Crew Dragon.

This situation has been particularly embarrassing for Boeing, as the technical issues with Starliner forced Nasa to rely on its competitor SpaceX. It also raises questions about when Boeing will be able to begin long-promised commercial Starliner operations.