Stranded astronauts will remain on the space station until February, according to NASA

Two NASA astronauts who flew to the International Space Station in June aboard Boeing’s defective Starliner spacecraft will have to return to Earth early next year on a SpaceX vehicle, NASA said on Saturday, deeming problems with the Starliner’s propulsion system too risky to bring the first crew home.

NASA’s decision to entrust Boeing’s biggest space rival with the astronaut return is one of NASA’s most consequential decisions in years. Boeing had hoped the test mission would save the Starliner program after years of development problems and budget overruns of more than $1.6 billion since 2016.

Boeing is also struggling with quality problems in the production of its most important products, commercial aircraft.

Veteran NASA astronauts Butch Wilmore and Suni Williams, both former military test pilots, were the first crew members of the Starliner on June 5 when they launched to the ISS for what is expected to be an eight-day test mission.

But within the first 24 hours of the flight to the ISS, Starliner’s propulsion system experienced a series of malfunctions that caused months of delays. Five of the 28 engines failed and there were several leaks of helium, which is used to pressurize the engines.

In a rare shakeup of NASA’s astronaut operations, the two astronauts are now expected to return in February 2025 aboard a SpaceX Crew Dragon spacecraft scheduled to launch next month as part of a routine astronaut rotation mission. Two of the Crew Dragon’s four astronaut seats will remain open for Wilmore and Williams.

Starliner will undock from the ISS without a crew and attempt to return to Earth as it would have done with astronauts on board.

Boeing struggled for years to develop Starliner, a gummy bear-shaped capsule designed to compete alongside Crew Dragon as the U.S.’s second option for transporting astronaut crews to and from Earth orbit.

Starliner failed in an uncrewed test launch to the ISS in 2019, but was largely successful in a repeat attempt in 2022, again with some engine issues. A crewed mission was required before NASA would certify the capsule for routine flights, but now Starliner’s certification path has been turned on its head.

Since Starliner docked with the ISS in June, Boeing has been busy trying to investigate the cause of the engine malfunctions and helium leaks. The company has been running tests and simulations on Earth to collect data it will use to try to convince NASA officials that Starliner is safe to fly the crew home.

But the results of those tests raised more difficult technical questions and ultimately failed to allay NASA officials’ concerns about whether Starliner would be suitable for the manned return flight – the most difficult and complex part of the test mission.

NASA’s decision and the Starliner’s now uncertain path to certification will exacerbate a crisis for new Boeing CEO Kelly Ortberg, who took office this month with the goal of restoring the company’s reputation after a door panel on a 737 MAX passenger plane dramatically blew off in mid-air in January.