Nasa astronauts Butch Wilmore and Suni Williams are still stuck on board the International Space Station – and plans for their journey back down are becoming increasingly complicated.
The pair had left on board Boeing’s troubled Starliner in June, for what was supposed to be an eight day test mission. But the spacecraft – which had been delayed and hit by issues even before it took off – ran into some issues during its flight, which led engineers to delay the mission to work them out.
Now Nasa has said that it is not yet sure that the Starliner would be able to return the crew safely as planned. They might instead have to come home in February, hitching a ride on a SpaceX spacecraft.
Why are the astronauts stuck?
It all relates to questions over whether Boeing’s Starliner is safe to bring them back home. They had been scheduled to come back in eight days, but the safety fears have repeatedly delayed that, and they have now been there for more than two months.
Nasa has stressed that the astronauts are not strictly stuck – in the event of an emergency on board the space station, they would be able to come back home, for instance.
What are the problems with the Starliner?
The main problem relates to thruster failures that were noted as the Starliner arrived to dock with the space station in June. Engineers are also concerned about leaks of helium, which are used to pressurise the thrusters.
Boeing has been testing the spacecraft remotely to try and understand the problems and find fixes for them, with the hope that it can reassure Nasa that it is safe to bring its astronauts home. But that testing has revealed yet more problems, leading Nasa to say that the return is in doubt.
How are the astronauts going to get home?
Boeing still hopes that the concerns with Starliner will be be sorted out. “We still believe in Starliner‘s capability and its flight rationale,” the company said.
And Nasa has been clear that it is still working with the company “to evaluate the spacecraft’s readiness, and no decisions have been made regarding Starliner‘s return”. That decision might not be made until August.
If that falls in Boeing’s favour, then the astronauts will come home as planned, though on a different schedule.
However, if engineers’ concerns remain, then the two astronauts will instead make their way home on a SpaceX flight. That mission is scheduled for late September, and at the moment is planned to take four astronauts – but if necessary, two will be left behind, and those seats will instead be taken by the Starliner’s test crew.
That team are due to come back in February. So the two test pilots would return with them, early next year.
Is that a problem?
Most of the current concerns have been about Starliner’s safety if left for that long, and fear that it would run out of resources with too long a delay. Starliner is rated for a 90 day stay, and has been at the Space Station for 63 days, so time is running out.
Nasa has been able to send extra supplies in the meantime to ensure that the astronauts are comfortable. This week, a SpaceX rocket carried a supply capsule made by Northrop Grumman which held food and supplies, including more food as well as clothes for the two Starliner test pilots.
The space station is able to serve as a home for a long time – Nasa astronaut Frank Rubio holds the record, at 371 days, much longer than the Starliner’s crew will have to stay – and the space agency’s officials seem confident that a longer stay will be safe.
What will happen to the Starliner if the astronauts come down another way?
Boeing has said that, if the astronauts have to come home on a different flight, then it will “take the actions necessary to configure Starliner for an uncrewed return”. That will include reconfiguring the software so that the Starliner is able to bring itself back to Earth without a crew.
It will have to do so because it needs to free up the docking port that will be used by the incoming SpaceX craft.
That will likely mean that at least most of the craft will burn up on its entry to Earth. That has always been the plan, and is one of the reasons behind the delay: engineers will lose most of the spacecraft on its journey through the atmosphere, so want more time with it intact to better understand what might have gone wrong with it.
Has this affected any other missions?
Yes, it has already – even if more are not needed in the future.
Another set of four astronauts should have been setting off this month, but will instead go next month, Nasa said this week. There are only two docking ports for US capsules on the space station, and both are currently occupied, given that the Starliner has been there for longer than expected.
It also means that the SpaceX crew of four that arrived in March will be staying for longer than they had planned.
