(NEW YORK) – The two astronauts who flew to the International Space Station (ISS) on Boeing’s Starliner will have to return home on another spacecraft, NASA officials announced Saturday.

Astronauts Barry “Butch” Wilmore and Sunita “Suni” Williams, who conducted the first manned test flight of the Starliner, will return with Space-X Crew 9 in February 2025, according to NASA.

The Boeing Starliner will return in a separate, unmanned flight, NASA said.

“The decision to keep Butch and Suni onboard the International Space Station and bring the Boeing Starliner home unmanned is the result of a commitment to safety,” NASA Administrator Bill Nelson said at a press conference.

When Wilmore and Williams launched on June 5, they were originally scheduled to stay on the ISS for only one week and return on June 14. Since then, however, their return has been postponed several times.

As the couple integrated into the Expedition 71 crew aboard the ISS, assisting with research and other tasks, NASA officials said Wilmore and Williams were using up more supplies intended for the ISS crew.

Steve Stich, program manager for NASA’s Commercial Crew Program, said NASA teams spent the summer reviewing data on Starliner and concluded there was too much risk with the vehicle’s engines.

“The risk was too great for the crew,” he said.

A Boeing spokesman said in a statement that the company “continues to focus primarily on crew and spacecraft safety.”

“We are executing the mission as defined by NASA and preparing the spacecraft for a safe and successful unmanned return,” Boeing said.

NASA officials said Wilmore and Williams would assist with scientific experiments, maintenance and possibly some spacewalks during their extended stay on the ISS.

Stich said during a press conference earlier this month that NASA was considering sending SpaceX’s Dragon Crew-9, scheduled to launch in September, to the ISS with only two of the four assigned astronauts.

The spacecraft would carry additional spacesuits for Wilmore and Williams. However, the two would remain on the ISS until February 2025, when Crew-9 is scheduled to return to Earth. Stich said at the time that the proposed plan had not yet been officially approved.

Stich added that Starliner is currently unable to undock autonomously from the ISS. This would require Starliner’s software to be updated and Boeing’s flight control team to undergo additional training.

Starliner is part of NASA’s larger Commercial Crew Program, which tested whether Boeing’s spacecraft could be certified for routine missions to and from the ISS.

Starliner was already struggling with problems before launch. The flight test was originally scheduled for May 6, but was canceled after a problem with an oxygen valve on a rocket made by United Launch Alliance (ULA), which makes and operates the rockets that put spacecraft into orbit.

The new launch date had been set for May 25, but a small helium leak was discovered in the service module, which contains support systems and instruments for operating a spacecraft.

Helium leaks and an engine problem then threatened to delay the Starliner’s docking. Five days after docking with the ISS, NASA and Boeing announced that the spacecraft had five “small” helium leaks and that there was still enough helium left at that time for the return mission.

Last month, teams at NASA’s White Sands Test Facility in New Mexico conducted ground tests of the Starliner’s engine, subjecting it to similar conditions the spacecraft faced on its way to the ISS to see how it would respond during undocking.

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