As Barry Wilmore and Suni Williams prepare to come home after their unexpected nine-month ISS stay, here is what they may experience

Gravity may seem like a drag, but spending long periods of time without its grounding force can wreak havoc on your body. On Friday, Nasa and SpaceX will launch the space agency’s Crew-10 mission to the  to retrieve astronauts Barry “Butch” Wilmore and Suni Williams, after what was meant to be an eight-day stay turned into nine months.

While it is not the most time a human has spent as an extraterrestrial – Oleg Kononenko and Nikolai Chub hold the record, with 374 days – most long space missions are a maximum of six months.

So what happens to a person’s body – and mind – back on earth?

## Gravity

The lack of gravity causes significant, and irreparable, bone density loss. It also causes muscles to waste in your arms, legs, trunk and elsewhere, including your heart, which, because it doesn’t have to pump blood against gravity, has to work much less hard.

Your blood volume shrinks, and the way your blood flows changes – it slows in some areas, which can lead to clots. Fluids also don’t come down, or drain, as easily.

In space, explained Alan Duffy, an astrophysicist at Swinburne University: “Fluids build up in their heads, to they feel like they have a constant cold.” Olfactory senses are also diminished, “which is probably a good thing, by the way, because it reeks up there,” he said, of an aircraft after two decades of visitors and no windows thrown open.

On the plus side, when they return, they will likely feel like they have finally kicked a nine-month cold. They’ll also struggle to walk, get dizzy easily, and have bad eyesight.

The build up of fluid also changes the shape of their eyeballs, and weakens their vision, he said. This is why often you see astronauts wearing spectacles on board, though they’ve started with perfect vision. This tends to mostly go back to normal, though they may need glasses for the rest of their lives, said Duffy.

“The brain becomes waterlogged,” said Meng Law, professor and director of radiology, neuroscience at Monash University. The Russian cosmonauts had a device, a bit like a wetsuit, that would suck the fluid and blood away from the brain, he said.

Today,  X and Nasa are working on centrifuges that astronauts could sleep in, which would spin fluid out of their heads, said Law.

When they return, their reconditioning is similar to the intense physiotherapy that anyone who has come out of a coma will have been put through, said Duffy.

It is also very tiring, said Brad Tucker, an astrophysicist at Australian National University, which can contribute to the psychological impacts of returning. So the team of doctors has to strike a balance between strengthening the astronauts and not tiring them out.

Their return “is itself a research project”, said Duffy. It can help inform how to treat patients on earth who suffer from conditions that involve long stays in hospital –living without gravity has many of the same impacts as being bedridden. Because most research so far is based on six-month stays, Wilmore and Williams will be especially interesting to their team of doctors and scientists.

One more really surprising challenge, Duffy said, was that because clothing floats off your skin, your skin gets “almost baby-like sensitivity”. Back on earth, some astronauts feel like their clothing is sandpaper.

## Radiation

Perhaps the most dangerous impact of extended stays in space is being exposed to radiation, which can increase the risk of cancers and rare cancers. Earth’s atmosphere and magnetic field shield us from high levels of radiation, but in space, people don’t have that protection.

“Not only will astronauts be exposed to more radiation in space than on Earth,” according to , “but the radiation they are exposed to could pose increased risks.”

According to Nasa, astronauts are exposed to three sources of radiation. These include particles trapped in the earth’s magnetic field, solar energetic particles from the sun, and finally galactic cosmic rays. The National Oceanic And Atmospheric Administration Space Weather Prediction Center describes these as: “the slowly varying, highly energetic background source of energetic particles that constantly bombard Earth” from outside our solar system, “likely formed by explosive events such as supernova”.

How to protect people against space radiation is one of the problems that scientists are trying to solve as we prepare to send people to Mars or the Moon for longer periods.

Because astronauts tend not to have an obligation to participate in studies once they retire, little is known about how this radiation might impact them later in life, said Tucker. So Williams and Wilmore, who are at the end of their careers, might also offer useful research in this area.

## ‘The overview effect’

“For anyone who’s been stranded in the wrong airport for a day or two, wanting to get home – imagine you’ve been able to see home that entire time,” Duffy said. Then consider that lasting for nine months. “These people are truly astonishing in terms of their resilience,” he said.

But on returning, anxiety – the result of having been in extreme conditions for so long – and depression are common, said Tucker.

The pair may also experience something called “the overview effect”. Seeing the curvature of the earth, and seeing it from above – as its own kind of space ship, said Duffy – has led some astronauts to report an incredible connection to humanity, an immediate sense of its fragility.

“Some people call it a feeling of inspiration. Some people call it feelings of inadequacy in terms of just how big the world is,” said Tucker.

And then they have to come back down to earth, both literally and figuratively. “They have to make breakfast and they have to drive to work,” said Tucker. “It is a huge transition from living in a very inspiring environment.”
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