They were meant to return on June 14.
Earlier this month, after years of delays, Boeing finally launched its new spacecraft, designed to deliver astronauts and cargo to and from the International Space Station (ISS).
Despite a known helium leak, the launch went ahead on June 5, launching veteran Nasa astronauts Barry ‘Butch’ Wilmore and Sunita ‘Suni’ Williams into orbit.
The mission was meant to last eight days, but almost three weeks later, the pair are still on the space station – and no one knows when they’ll come home.
Multiple helium leaks, five dead manoeuvering thrusters and a propellant valve fail means crews in space and on the ground in Houston are racing to fix the craft.
So far, Nasa has rescheduled the six-hour return journey three times. There is currently no official scheduled return, although sources inside Nasa suggested the target is July 6.
But the team cannot wait indefinitely.
Starliner can stay docked at the ISS for up to 45 days, according to comments by Nasa’s commercial crew manager Steve Stich, because the Harmony module that it is attached to has limited fuel.
This means a cut-off of July 21 – the craft arrived at the ISS on June 6, a day after lift-off.
If absolutely necessary, such as if more problems arise that mission officials cannot fix in time, it could stay docked for up to 72 days, relying on various backup systems, according to a person familiar with flight planning. This would be August 17.
To set off back to Earth, Starliner’s propulsion system will need to be fixed, which is needed to back the capsule away from the ISS and position it to dive through Earth’s atmosphere. Many of Starliner’s thrusters have overheated when fired, and the leaks of helium – used to pressurise the thrusters – appear to be connected to how frequently they are used, according to Mr Stich.
He said recent test-firings of the thrusters while Starliner remains docked gave mission teams confidence in a safe return, though tests and reviews are ongoing.
The mission management team, made up of Nasa and Boeing personnel, is scrutinising data on the propulsion issues, running simulations in Houston and considering how to fix them, such as by updating software or changing how the hardware is used.
Once Nasa officials give the team a go-ahead for a return, Starliner’s thrusters would be used to undock the capsule from the ISS and begin a roughly six-hour journey home, gradually tightening its orbit before plunging into Earth’s atmosphere for a landing, assisted by parachutes and airbags, at one of several potential locations in the southwestern US.
Even with the propulsion system issues, Nasa has said Starliner still would be capable of returning the astronauts to Earth if absolutely necessary – that is, if the capsule had to serve as an escape pod from the ISS in an emergency, or if any of Starliner’s perishable items, such as its solar panels, show signs of expiring earlier than planned.
But if Starliner were to be deemed incapable of safely returning Captain Wilmore and Captain Williams to Earth, one option would be to send a SpaceX Crew Dragon capsule to pick them up, which ferried four astronauts to the station in March and is able to fit more people in an emergency.
That scenario, considered unlikely, would undoubtedly be embarrassing for Boeing. But Nasa and Boeing officials, as well as engineers familiar with the programme, told Reuters nothing about Starliner’s current problems indicates this would be needed.
Metro.co.uk has contacted SpaceX for comment but no response has been received.
In such a scenario, Starliner’s fate would depend on various factors including the extent of its technical issues.
The last time a Nasa astronaut needed an alternative ride home came in 2022, when Russia’s Soyuz capsule sprang a coolant leak after delivering to the station two cosmonauts and American astronaut Frank Rubio.
Nasa had considered Crew Dragon as an alternative ride home for Colonel Rubio but he eventually used an empty Soyuz capsule that Russia launched as a rescue craft. His mission was extended from six months to a bit more than a year – 371 days – a record-breaking duration for an American in space.
