NASA is considering keeping two astronauts on the International Space Station until February, after their Starliner spaceship encountered issues mid-flight.
The agency said it is still evaluating options to bring NASA astronauts Butch Wilmore and Suni Williams back to Earth safely, and no plan has been made yet.
But officials acknowledged they may decide to use a SpaceX capsule to reach them.
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“Our prime option is to return Butch and Suni on Starliner,” NASA Commercial Crew Program manager Steve Stich said.
“However, we have done the requisite planning to make sure we have other options open and so we have been working with SpaceX to ensure that they’re ready to respond.”
Wilmore and Williams arrived at the space station on June 6 on the first crewed test flight of Boeing’s Starliner capsule.
The initial plan was for them to stay in space for about a week, but problems with five of Starliner’s thrusters and helium leaking from the capsule’s propulsion system have stranded the astronauts there for more than two months.
Engineers on the ground are gathering data about the issues and attempting to troubleshoot their spacecraft.
The mission was designed to be the final step before the agency could certify Boeing to conduct routine crewed flights to and from the ISS.
The fate of that process is now up in the air.
NASA did not offer any potential timeline as to when the astronauts might return if they travel back on Boeing’s capsule, but Stich said that a final decision likely needs to be made by mid-August.
NASA Space Operations Mission Directorate associate administrator Ken Bowersox said there have been disagreements over how to bring the astronauts home safely.
“I have to admit that sometimes when we get disagreement, it’s not fun,” Bowersox said.
“It can be painful having those discussions, but it’s what makes us a good organisation, and it’s what will get us to a good decision as we approach that point here in the future. And I don’t think we’re too far away from making that call.”
In the event Wilmore and Williams fly home on a different vehicle, mission managers could make software adjustments to the Starliner and have it undock from the space station and return to Earth without a crew.
Boeing officials said: “We still believe in Starliner’s capability and its flight rationale. If NASA decides to change the mission, we will take the actions necessary to configure Starliner for an uncrewed return.”
What happened?
The thruster issues cropped up as Starliner was nearing the space station in June, forcing delays during the docking process.
The helium leaks, meanwhile, were already on mission managers’ radar before liftoff.
They said at the time the leaks were unlikely to affect the mission or the astronauts’ safety.
Engineers from NASA and Boeing have been trying to replicate conditions in orbit on a test engine at the agency’s White Sands Test Facility in New Mexico.
Stich said Wednesday that tests have revealed a tiny Teflon seal appears to swell under high temperatures and may be partly to blame for the thruster problems.
When the seal expands, it likely blocks the flow of propellant into the thrusters, he said.
More testing is needed to understand the potential blockages and why they were not detected during the most recent hot fire test.
Last week, NASA reported the thrusters, which are used to manoeuvre the spacecraft around in orbit and guide it into position before plunging through Earth’s atmosphere, appeared stable.
“That gives us a lot of confidence in the thrusters, but we can’t totally prove with certainty what we’re seeing on orbit is exactly what’s been replicated on the ground,” Stich said.
The recent Starliner saga has been a blow for Boeing, particularly since the program was already years behind schedule and more than $1.5 billion over budget before the astronauts launched.