Inside the daring rescue mission to save two NASA astronauts stranded in space for almost a year

Two NASA astronauts trapped on the International Space Station (ISS) since June have been dealt another blow as their rescue mission is delayed once again.

Veteran astronauts Suni Williams and Butch Wilmore arrived at the ISS aboard Boeing's doomed Starliner capsule with plans to stay for just eight days.

An initial delay saw the pair told they would head home alongside two other astronauts in February.

However, they have now learned they will be stuck in space until March at the very earliest - 10 months after they first left home.

With the Starliner capsule having returned to Earth empty in September, the pair have no choice but to wait for more help to arrive from SpaceX. 

The latest delay will give SpaceX extra time to prepare its brand-new capsule for lift-off.

Steve Stich, manager of NASA’s Commercial Crew Program, says: 'Fabrication, assembly, testing, and final integration of a new spacecraft is a painstaking endeavor that requires great attention to detail.'

Here's how the daring rescue mission will work.

Mission commander Williams and flight engineer Wilmore took off from Cape Canaveral Space Force Station in Florida on June 5 for a test flight of Boeing's new Starliner capsule.

The plan was to ride Starliner out of the atmosphere, perform a few test manoeuvres, and dock with the ISS for an eight-day stay before returning to Earth in the same capsule.

However, things almost immediately began to go wrong for the problem-plagued capsule as the craft experienced thruster failures and a helium leak.

While Williams and Wilmore were safely delivered to the ISS, by the time Starliner arrived it had sprung more helium leaks and five of its 28 thrusters had failed.

After weeks of tests, NASA made the decision that it was not safe for the astronauts to return aboard Starliner as originally planned.

In September, Starliner was sent back to Earth empty, touching down in New Mexico after slowing its descent with parachutes.

That choice left the Boeing test crew stuck aboard the ISS without their vehicle until someone could be sent to get them.

In a humiliating blow for Boeing NASA contracted the firm's arch-rival, Elon Musk's SpaceX, to provide the rescue effort.

In September, shortly after Starliner's return, NASA's Crew 9 mission launched from Florida aboard a SpaceX Dragon crew capsule.

Two of the mission's original crew were left back on Earth, freeing up a seat each for Williams and Wilmore.

Crew 9 made it safely to the ISS, but Boeing's stranded astronauts still can't leave the station until a replacement crew arrives.

Under the original plan, NASA would send the four astronauts of Crew 10 to the ISS on a brand-new SpaceX Dragon capsule in February next year.

After a 'handover period' to help Crew 10 get up and running, Williams, Wilmore, and the members of Crew 9 would then return to Earth in their original capsule at the end of the month.

However, NASA has now revealed that the new SpaceX capsule isn't going to be ready in time to hit that deadline.

The capsule isn't expected to arrive at the company’s processing facility in Florida until early January and will still need more than a month of testing before it is ready.

NASA is now targeting no earlier than late March 2025 to launch the rescue crew, meaning Williams and Wilmore might not get back to Earth until April.

Mr Stich says: 'We appreciate the hard work by the SpaceX team to expand the Dragon fleet in support of our missions and the flexibility of the station program and expedition crews as we work together to complete the new capsule’s readiness for flight.'

NASA says that it considered a number of alternative options including using another Dragon spacecraft but concluded that this would be the best option.

The space agency maintains that the ISS is well-stocked with everything the crew needs, including food, water, clothing, and oxygen, adding that a recent resupply even brought some 'special items' to help celebrate the holidays.

But with Williams and Wilmore now set for a 10-month stay in space, there are growing concerns about the possible health impacts.

Last month images of mission commander Williams looking gaunt sparked concerns that she might be suffering from excessive weight loss or malnutrition.

Dr David Shaker, an internist at Holy Name Physicians in Hackensack, New Jersey, previously told MailOnline: 'This, to me, strikes me as low nutrition - low-calorie intake.'

While in microgravity, astronauts are at high risk of muscular deterioration as their bodies no longer need to strain against the force of gravity.

This means that the ISS crew are required to spend at least two hours per day exercising on specially designed 'weightlifting' machines, treadmills, and exercise bikes to maintain their muscles.

After all that work an astronaut can burn as much as 3,500 calories per day while living on the station.

However, the physiological and psychological effects of life in space often lead to a reduced appetite that can make it hard for astronauts to eat enough.

An unnamed NASA employee told the New York Post that Williams has been struggling to keep up with the high-caloric diets that astronauts must eat.

Despite these claims, Ms Williams says that her unusually thin appearance is due to 'fluid shift' within the body caused by microgravity.

In space the distribution of liquids in the body changes, which can make astronauts' faces puffy and give them an unusual appearance.

Mission commander recently Williams hit back at the suggestions of malnutrition and even says that she has gained weight since arriving on the station.

'My thighs are a little bit bigger, my butt is a little bit bigger,' she said in a video.

But with at least three more months aboard the ISS ahead of them, NASA will be watching very carefully to ensure that Williams and Willmore remain healthy until they can finally return home.