Why returning to Earth is so dangerous as NASA's 'stranded' astronauts come home
Getting home from space is far from easy – both for spacecraft and the human body
NASA astronauts Suni Williams and Butch Wilmore are finally on their way back to Earth after their week-long voyage to the International Space Station (ISS) turned into a nine-month-long mission.
The pair launched into space on a Boeing Starliner's first astronaut flight in June 2024, but problems with the spacecraft meant it had to return to Earth with no crew, leaving Butch and Suni 'stranded' on the space station.
The astronauts departed the station on Tuesday morning (March 18) alongside NASA's Nick Hague and Russia’s Alexander Gorbunov. The crew are currently hurtling back to Earth on a SpaceX Dragon capsule, which is due to splashdown later today.
The 'stranded' astronauts are likely itching to get home to friends and family, but experts warn the transition won't be easy.
'Dangerous' re-entry
As the SpaceX Dragon capsule makes its rapid re-entry through the Earth's atmosphere, a heatshield will protect the astronaut from scorching 1,600C temperatures. Once the spacecraft hits the atmosphere, the astronauts will begin to feel gravity again – four times of that on Earth.
"They'll pull 4g – and when you speak to astronauts, this is the most fun part of it," explains Professor Damian Bailey, Editor-in-Chief of Experimental Physiology and Professor of Physiology and Biochemistry at the University of South Wales.
"They love re-entry, despite the fact it's the most dangerous part of the mission, that and the docking. It's like a rollercoaster ride," he added.
Re-entry is particularly dangerous to astronauts because of the extreme heat and extreme speeds, which cause the spacecraft to encounter huge amounts of atmospheric friction. What's more, the capsule has to hit the atmosphere at exactly the right angle to ensure it hits the correct landing point – and the astronauts return safely to Earth.
But beyond the incomprehensible technical challenges, life back on Earth can be particularly hard for the human body.
'Space brain' and 'space legs'
The NASA astronauts, Butch and Suni, will be carried away on stretchers after they return to Earth. "The reason for that is because they've had nine months in zero gravity so their muscles and bones are not very strong," explains Prof Bailey, who says astronauts will have "wobbly legs" when they first try to walk on Earth.
"The biggest risk is astronauts falling over and banging their heads, so they're carried out," he adds.
They also get what's called gravity sickness, which Prof Bailey likens to "spinning around on a chair keeping your eyes closed." Because the brain is getting conflicting sensory input, the astronauts will likely feel sick and dizzy, in a phenomenon known as 'space brain'.
A more concerning risk is the possibility of a "space clot". According to Prof Bailey, experts have recorded two astronaut cases of a venous thromboembolism in the left carotid artery, which supplies blood and oxygen to the brain.
"We think the reason for that relates to the impaired draining of blood from the brain. Also they're in a chronic state of inflammatory stress [in space]," explains Prof Bailey. Astronauts are therefore checked over by medical professionals at sea level.
Returning to life on Earth
It takes astronauts around two days for sensory input to the brain to normalise, but things don't begin to feel "normal" again for at least a month, according to Prof Bailey.
"The first two days are the worst in terms of sensory input to the brain. They might make a cup of coffee and forget they can't let go of the cup, so there's lots of broken china and bumping into things," he explains.
Since the astronauts are battling with muscle atrophy and bone density loss due to their long stint in a microgravity oven, they are put on an intense rehabilitation program.
"They've been spending two hours a day exercising in the space station, but exercise is just not enough. You cannot curb the changes that occur, you can only offset them slightly," explains Prof Bailey. Rehabilitation will include physiotherapy and strength and conditioning so that astronauts can gain muscle back.
The astronauts will also be more prone to infection for their first few weeks back on Earth because they will be "surrounded by a whole host of pathogens," according to Prof Bailey.
Experts in rehabilitation say Butch and Suni have a long road of recovery ahead. "As a general rule of thumb – and it's not the same for everybody – for every one day you spend in space, we'd expect you to spend one day recovering on Earth. Instead of a quick one or two week recovery, they've got lots of recovery ahead of them now," explains Dr Kirsty Lindsay, Assistant Professor in Rehabilitation Sciences at Northumbria University, who specialises in space physiology.