It was a blow to Boeing, adding to the safety concerns plaguing the company on its aeroplane side. Boeing had counted on Starliner’s first crew trip to revive the troubled spacecraft program after years of delays and ballooning costs. The company had insisted Starliner was safe, based on all the recent thruster tests both in space and on the ground.

Boeing did not participate in the news conference by NASA, but released a statement: “Boeing continues to focus, first and foremost, on the safety of the crew and spacecraft.” The company said it is preparing the spacecraft “for a safe and successful return”.

Wilmore, 61, and Williams, 58, are both retired Navy captains with previous long-duration spaceflight experience. Before their June 5 launch from Cape Canaveral, Wilmore and Williams said their families bought into the uncertainty and stress of their professional careers decades ago.

During their lone orbital news conference last month, the astronauts said they had trust in the thruster testing being conducted. They had no complaints, they added, and enjoyed pitching in with space station work.

Wilmore’s wife, Deanna, was equally stoic in an interview earlier this month with WVLT-TV in Knoxville, Tennessee, their home state. She was already bracing for a delay: “You just sort of have to roll with it.”

Flight operations director Norm Knight said he talked to the astronauts and they fully support the decision to postpone their return. There were few options.

The SpaceX capsule currently parked at the space station is reserved for the four residents who have been there since March. They will return in late September, their routine six-month stay extended a month by the Starliner dilemma. NASA said it would be unsafe to squeeze two more into the capsule, except in an emergency.

The docked Russian Soyuz capsule is even tighter, capable of flying only three — two of whom are Russians wrapping up a year-long stint.

So Wilmore and Williams will wait for SpaceX’s next taxi flight. It’s due to launch in late September with two astronauts instead of the usual four. NASA is yanking two to make room for Wilmore and Williams on the return flight in late February.

NASA said no serious consideration was given to asking SpaceX for a quick stand-alone rescue. Last year, the Russian Space Agency had to rush up a replacement Soyuz capsule for three men whose original craft was damaged by space junk. The switch pushed their six-month mission to just over a year.

Former Canadian astronaut Chris Hadfield, applauded the decision via X: “Good to err on the side of caution for astronaut lives.” He said long missions are “what astronauts work their entire career for. I’d take it in a heartbeat!”

Starliner’s woes began long before its latest flight.

Bad software fouled the first test flight without a crew in 2019, prompting a do-over in 2022. Then parachute and other issues cropped up, including a helium leak in the capsule’s propellant system that nixed a launch attempt in May. The leak was eventually deemed to be isolated and small enough to pose no concern. But more leaks sprouted following liftoff, and five thrusters also failed.

All but one of those small thrusters restarted in flight, but engineers were perplexed by ground testing that showed a thruster seal swelling and obstructing a propellant line. They theorised that the seals in orbit may have expanded, then reverted to their normal size. Officials said the results marked the turning point, as their concerns grew.

With all the uncertainty about how the thrusters might perform, “there was too much risk for the crew,” Steve Stich, NASA’s commercial crew program manager, told reporters.

These 28 thrusters are vital. Besides being needed for space station rendezvous, they keep the capsule pointed in the right direction at the flight’s end as bigger engines steer the craft out of orbit. Coming in crooked could result in catastrophe.

With the Columbia disaster still fresh in many minds — the shuttle broke apart during reentry in 2003, killing all seven aboard — NASA made an extra effort to embrace open debate over Starliner’s return capability.

Despite Saturday’s decision, NASA isn’t giving up on Boeing. Nelson said he is “100 per cent” certain that Starliner will fly again.

NASA went into its commercial crew program a decade ago, wanting two competing US companies ferrying astronauts in the post-shuttle era. Boeing won the bigger contract: more than $4 billion, compared with SpaceX’s $2.6 billion.

With station supply runs already under its belt, SpaceX aced its first of nine astronaut flights in 2020, while Boeing got bogged down in design flaws that set the company back more than $1 billion.

NASA officials still hold out hope that Starliner’s problems can be corrected in time for another crew flight in another year or so.

AP

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