Image source, Reuters
That wraps up our live coverage. You can find out more about Boeing's Starliner test mission here:
Today's live page was edited by Brandon Livesay and Emily McGarvey, and the writers were Nadine Yousif and Georgina Rannard.
Pallab Ghosh
Science correspondent, BBC News
In the meantime, the tests and analysis of the propulsion system will continue before Nasa and Boeing make their call.
A return on their arch-rival’s spacecraft and the astronauts wearing SpaceX suits would be deeply embarrassing for Boeing, but it would not be the end of the line for Starliner, especially if it makes it back to Earth safely in an uncrewed landing.
Nasa has repeatedly said that it is committed to developing two independent means to take crew and cargo into space.
It is likely that the Space Agency will give Boeing every chance to do that.
Pallab Ghosh
Science correspondent, BBC News
Time and again Nasa officials were asked what they might learn that would reassure them that they would have a safe return despite the problems with the thruster system.
Each time they did not have an answer to that question.
Dr Simeon Barber, a space scientist at the Open University believes that there won’t be a new piece of information that will reassure those at the space agency who have concerns.
“It seems that there are decision makers at Nasa who are unconvinced that a safe return can be guaranteed, which is why they have brought in experts to look through the data to try and diagnose the fault in a small component in a complex propulsion system that is in space.
“It is hard to see how that will be possible, so it feels to me that we are heading inexorably towards a return on SpaceX’s Dragon Spacecraft”.
That is not a view shared by Boeing, who have repeatedly said they have full confidence in Starliner to bring Butch and Suni home safely.
Mike Wendling
US reporter
One potential option being considered by Nasa to get the astronauts home is to attach them to a mission that’s scheduled to launch in September, and return them to earth with that mission in February 2025.
That flight to the space station will be made by a SpaceX Crew Dragon craft.
The initial plan was for four crew members to be aboard, but two of the seats could be left empty if needed.
That plan would mean the astronauts would spend more than eight months – rather than eight days – aboard the International Space Station (ISS).
If the Crew Dragon is used, the Starliner craft would be returned to Earth without any crew, under computer control.
Using a SpaceX craft to return the astronauts would be a blow to Boeing, which has for years tried to compete with the company and its more experienced Crew Dragon.
Nasa has just wrapped up its press conference on Sunita Williams and Barry 'Butch' Wilmore, the two astronauts who are currently stuck on the International Space Station (ISS).
Here's a summary of what was said:
Joel Montalbano, Nasa's deputy associate administrator, finishes the briefing.
He says a supply vehicle will dock with the International Space Station (ISS) this Saturday. Nasa has said there are no issues with supplies with the extra astronauts at the space station.
That's it from Nasa's update, but stick with us. We have some more updates and analysis on the way.
A reporter asks how astronauts Butch and Suni are doing, given that they went out to the International Space Station (ISS) expecting to be there for eight days, but instead have been there for two months and counting.
Acaba says that because it is a test flight into space, there is always an expectation that it could go on longer than anticipated.
He adds that he has spoken to them in the last day and they are "doing fine".
"In my office, right now I can watch them working on the ISS," adding that they have fully integrated into the station's crew.
"But we are human," he says. "And this is hard on crew members and their families, and we take that into account. But again, as professional astronauts, they are prepared for this. They are doing great."
Bowersox says he has "tremendous respect" for Boeing, and "that respect has grown through this process".
"We've had very honest discussions with each other, and I am not surprised the Boeing team are 100% behind their vehicle," he says.
"But I can also tell you that they want to work with us in a partnership. What the Nasa team thinks is important, and when we get to a decision, we will work through it together," he adds.
Georgina Rannard
Science reporter
A bit more on those space suits. Returning on SpaceX's Crew Dragon Crew 8, which would leave the ISS in the autumn, would bring additional risks to the two astronauts because they would be travelling without a space suit.
Some returns to Earth require astronauts to wear a space suit, so without that protection, Butch and Suni could face additional danger.
They also face risks from extra radiation by staying in space longer on the ISS.
These issues highlight again that this is not just a question of swapping one craft for another.
Georgina Rannard
Science reporter
Image source, EPA
Butch Wilmore and Sunita Williams pictured ahead of the launch in June
An important question is how easy it would be for the astronauts to simply switch to coming home in a different spacecraft.
Officials say the space suits they travelled in to the International Space Station (ISS) on Starliner would not be suitable on the SpaceX craft, if it's used to take them home.
"They would come unsuited in the Crew Dragon," says Joel Montalbano, Nasa's deputy associate administrator, referring to the SpaceX machine.
Remember these space suits are incredibly complex pieces of engineering designed to protect and support the astronauts.
Officials say their major concern is ensuring a "successful deorbit burn", referring to the process of removing a spacecraft from orbit, using its retrorockets to re-enter the atmosphere.
"That's why we're looking so closely at the thruster jets and even thinking about how the larger thrusters work," they say.
A reporter asks: What does Nasa deem as an acceptable risk for a space flight mission, and how can they make a call on how to bring the astronauts home when they don't know for certain what the outcome will be?
Nasa officials say they begin with an understanding of the "baseline risk" and then balance that with the risk of whatever new plan they might have to pivot to.
And then they focus on getting as much information as possible. "The best way to make risk decisions is with the best information," Bowersox says.
Image source, EPA
Starliner docked in Florida before its launch in June
He adds that the entire team is consulted in order to get to a consensus on what to do.
"That doesn't mean that we have to have consensus to make the call," he notes. "Sometimes you just have to make a decision and you don't have time to bring everyone to agreement."
Bowersox adds that the challenge here is there are risks with both the baseline plan and the alternative plan.
"And we always knew that a test flight was potentially higher risk versus a return with a vehicle that has a lot of flights under it," he says.
Georgina Rannard
Science reporter
Nasa reiterates that it has "a lot of confidence" in Starliner.
The officials add that the fact that the astronauts can spend weeks on board the International Space Station means that they have time to try to get to the bottom of the technical issues with the craft.
A reporter asks if Starliner is still safe for the astronauts to travel back home on, in case of an emergency.
Bowersox answers by saying that Starliner is still the contingency vehicle for the two.
"We think the risk is reasonable to put Butch and Suni on that vehicle in a contingency," he says.
Georgina Rannard
Science reporter
A journalists asks about the shifting deadlines for Nasa to decide when they will bring the astronauts home.
It was originally promised to be mid-August but now Nasa are saying it will be the last week of the month.
But there's "no sharp cut-off", officials say.
Image source, Reuters
Butch Wilmore and Sunita Williams have been in space for more than two months
A reporter asks: If Starliner returns successfully but without a crew on board, would the mission be classified as a "mishap"?
Russ DeLoach, chief of Nasa's Office of Safety and Mission Assurance, says in that case, the astronauts would still ride back home to earth on another aircraft.
"If we, Nasa, intervene and make the call to change the mission - that the crew would ride home on something other than Starliner - we wouldn't necessarily need to classify that as a massive mishap," he says.
Joe Acaba, Nasa’s chief astronaut, says astronauts like Sunita Williams and Butch Wilmore "embark on missions fully aware of the various scenarios and outcomes that may become our realities".
He says astronauts undergo rigorous training to make sure they are mentally and physically prepared for the challenges that may arise in any given mission.
"This mission was a test flight... they knew this mission might not be perfect," he says.
"Human space flight is inherently risky, and as astronauts, we accept that as part of the job."
Image source, Reuters
Boeing's Starliner test flight launch on 5 June
Georgina Rannard
Science reporter
We've known for while now that the astronauts could be on the International Space Station (ISS) until after Christmas if they cannot return on Starliner.
Officials have just said if they don't return on the craft, they could be in orbit for eight months - that's because they will have to wait for a SpaceX flight instead.
Georgina Rannard
Science reporter
As expected, Nasa officials are saying it's a major decision whether the two astronauts return on the Starliner craft.
They will meet next week, and will review the flight readiness next week or the following week.
Bowersox says that astronauts Sunita Williams and Barry 'Butch' Wilmore are "well engaged" on the International Space Station.
"I know if I was in their position I'd be really happy to be there," he says. "I'd be happy to have the extra time."
They are enjoying the environment, "eating that great space food", and being able to look out the window, he adds.
"I know that they're making the best of this time, but I'm sure they're eager for a decision just like the rest of us."
Image source, Reuters
Williams and Wilmore before pictured before they went into space on Starliner