NASA is wrestling with how and when to bring back two astronauts from the International Space Station (ISS) after repeatedly delaying their return aboard the trouble-plagued Boeing space capsule.
Barry "Butch" Wilmore and Sunita "Suni" Williams have been up there since June 5, recently passing the two-month mark on what was supposed to be an eight-day mission.
The pair launched into orbit on the first crewed mission of Boeing's Starliner space capsule, which encountered technical difficulties during the journey up.
Testing is still being carried out on the capsule, with Boeing expressing confidence in its spacecraft but NASA experts remaining divided.
Do they take a chance and send them home soon in Starliner? Or wait and bring them back in February 2025 aboard Elon Musk's SpaceX Dragon rocket?
A decision is expected to be made next week.
What's wrong with the spacecraft?
This is Boeing's first time launching astronauts, after flying a pair of empty Starliners that suffered from software issues and other problems.
Even before Mr Wilmore and Ms Williams blasted off in June, their capsule sprang a leak in propulsion-related plumbing.
Boeing and NASA judged the small helium leak to be stable and isolated, and proceeded with the test flight, but as Starliner approached the space station the next day, four more leaks erupted. Five thrusters also failed.
The capsule managed to dock safely, and four of the thrusters ultimately worked. But engineers scrambled to identify the problem, conducting thruster test-firings on the ground and in space.
After two months, the root cause of the thruster malfunctions is still unknown. All but one of the 28 thrusters seem functional, but the fear is that if too many break down again, the crew's safety could be jeopardised.
Thrusters are critical in maintaining the right position of the capsule during its deorbit.
Are the two astronauts stranded?
NASA bristles at any suggestions that the pair is stranded or stuck.
The agency has stressed from the get-go that in an emergency at the space station, like a fire or decompression, Starliner could still be used as a lifeboat to leave.
Former NASA executive Scott Hubbard on Thursday said the astronauts were "kind of stuck", although certainly not stranded, adding they had plenty of supplies and still had lots of work to do.
If NASA decides to go with a SpaceX return, the pair would not simply board the Dragon currently docked with the ISS — a move which would leave other astronauts stranded without a lifeboat.
Instead, Starliner would be cut loose to open up the other one of the two docking spots reserved for US capsules, and SpaceX would then launch another Dragon to fill that slot.
Why might they have to wait until 2025?
Like Boeing's Starliner, SpaceX's Dragon is meant to carry four astronauts.
To make room for Mr Wilmore and Ms Williams, NASA said it could bump two of the four astronauts due to launch to the space station next month with SpaceX.
The empty seats would be reserved for the pair, but they would have to wait until February for their return when the remaining crew completes their mandatory minimum station mission of six months.
Some missions have lasted a year.
There's no thought given to ordering up a special SpaceX express, and the Dragon at the station now is the ride home next month for four residents.
This isn't the first time a US astronaut has had their stay extended.
NASA astronaut Frank Rubio and his two Russian crewmates ended up spending just over a year in space after their docked Soyuz capsule was hit by space junk and leaked all its coolant. An empty Russian capsule was sent up to bring them back last September.
What do the astronauts think about this?
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Both Mr Wilmore, 61, and Ms Williams, 58, are retired Navy captains and longtime NASA astronauts who have previous space station missions behind them.
They previously said going into this test flight they expected to learn a lot about Starliner and how it operates.
During a news conference from space in July, they assured reporters they were keeping busy, helping with repairs and research, and expressed confidence in the Starliner testing going on behind the scenes.
There's been no public word from them yet on the prospects of an eight-month stay.
Are there enough supplies?
The astronauts' suitcases were removed from Starliner before lift-off to make room for equipment urgently needed for the space station's urine-into-drinking-water recycling system.
They have since made do with spare clothes already up there.
A supply ship finally arrived this week with their clothes, along with extra food and science experiments for the entire nine-person crew.
More supplies are due in a few months.
As for air, the space station has its own oxygen-generating systems.
But despite the reserves, NASA would like to get back to normal as soon as possible.
Besides Mr Wilmore and Ms Williams, there are four other Americans and three Russians on board.
Why is NASA sticking with Starliner?
NASA deliberately hired two companies to get its crews to and from the space station, just as it did for delivering cargo.
The space agency considered it an insurance policy of sorts — if one crew or cargo provider was grounded, the other could carry the load.
"You want to have another alternative, both for cost reasons and for safety reasons and options," said Scott Hubbard, who served on the Columbia Accident Investigation Board in 2003.
"NASA needs Boeing to be successful."
Even with the latest setbacks, NASA insists it wants to keep using Boeing Starliners for astronaut rides.
The goal is to send up one Dragon and one Starliner every year with crews, six months apart, until the station is retired in 2030. SpaceX has been at it since 2020.
What does Boeing say?
The aerospace company insists its capsule could still safely bring the astronauts home, however, it says it will take the steps necessary to bring the capsule back empty if NASA decides to do so.
Last week Boeing posted a list of all the tests that have been conducted on the thrusters since lift-off.
"We still believe in Starliner's capability and its flight rationale," it said.
A longtime space contractor, Boeing has had to overcome multiple Starliner problems over the years.
The company had to launch an empty spacecraft twice before committing to a crew, repeating the initial flight test because of bad software and other issues. The delays have cost the company about $US1.6 billion ($2.4 billion) since 2016.
Mr Hubbard questioned whether NASA and Boeing should have launched the crew with the original helium leak, which cascaded into further issues.
"Whatever happens with the Starliner, they need to find out what the problem was and fix it," he said.
"And give everybody confidence they are still in the aerospace business in a major way."
AP
