Boeing will return its Starliner capsule from the International Space Station without the NASA astronauts that it delivered to orbit in early June, the agency announced on Saturday.

With Starliner coming back to Earth empty, NASA will now have astronauts Butch Wilmore and Suni Williams return via SpaceX’s Dragon spacecraft, which is expected to launch its ninth regular mission to the ISS for the agency on Sept. 24.

Ultimately, Wilmore and Williams will stay at the ISS for about six more months before flying home in February on SpaceX’s Crew-9 vehicle. The test flight was originally intended to last about nine days.

The decision to bring Starliner back from the ISS empty marks a dramatic about-face for NASA and Boeing, as the organizations were previously adamant that the capsule was the primary choice for returning the crew.

But Starliner’s crew flight test, which had been seen as the final major milestone in the spacecraft’s development, faced problems — most notably with its propulsion system.

“Boeing has worked very hard with NASA to get the necessary data to make this decision,” NASA Administrator Bill Nelson said during a press conference with top NASA officials at Johnson Space Center in Houston on Saturday. “We want to further understand the root causes and understand the design improvements so that the Boeing Starliner will serve as an important part of our assured crew access to the ISS.”

He reiterated that test flights are “neither safe, nor routine,” and that the decision was the “result of a commitment to safety.”

NASA will now conduct another phase of its Flight Readiness Review to determine when to bring the empty Starliner home.

Boeing officials had been adamant in press briefings that Starliner was safe for the astronauts to fly home in the event of an emergency, despite delaying the return multiple times. NASA said there was a “technical disagreement” between the agency and the aerospace company, and said it evaluated risk differently than Boeing for returning its crew.

Nonetheless, NASA officials repeatedly expressed support for Boeing, and Nelson said he was “100% certain” that Starliner would be able to launch with a crew again someday.

“We continue to focus, first and foremost, on the safety of the crew and spacecraft,” Boeing said in a statement posted on X on Saturday. “We are executing the mission as determined by NASA, and we are preparing the spacecraft for a safe and successful uncrewed return.”

Ken Bowersox, NASA associate administrator, said NASA officials were unanimous in their decision to choose SpaceX to bring the crew home.

Meanwhile, SpaceX will bring two astronauts along on its Crew-9 vehicle — instead of four who were originally planned to go — to make room for Wilmore and Williams.

“SpaceX stands ready to support @NASA however we can,” President and COO Gwynne Shotwell responded in a social media post on X.

Boeing’s Starliner capsule “Calypso” has been at the International Space Station since early June on a mission that NASA extended indefinitely as the agency and company tried to identify why multiple of the spacecraft’s thrusters failed during docking.

Those thrusters, part of the spacecraft’s propulsion system, are key to Starliner’s safe return from the ISS. NASA cited the thrusters on Saturday as an ongoing problem.

The Starliner crew flight test was supposed to be a final box checked for Boeing and a key asset gained for NASA. The agency was hoping to fulfill its dream of having two competing companies — Boeing and Elon Musk’s SpaceX — flying alternating missions to the ISS.

Instead, the flight test is further setting back Boeing’s progress in NASA’s Commercial Crew program and, with over $1.5 billion in losses absorbed already, threatens the company’s future involvement with it.