Former astronaut shares challenges NASA astronauts will face when returning to Earth after nine months

After eight days turned into nine months, NASA astronauts Barry 'Butch' Wilmore and Sunita 'Suni' Williams are now making their highly anticipated return to Earth.

The pair blasted off in June last year as the test pilots for Boeing's Starliner capsule. However a series of technical malfunctions meant the pair would go on to have an extended stay onboard the International Space Station and achieved worldwide recognition as the so-called 'stranded' astronauts.

However Butch and Suni's time in space is now coming to an end, with the pair currently expected to splash down off the coast of Florida later today (18 March) — an astonishing 286 days after they initially left Earth.

Given the fact that the human body has spent millions of years evolving and adapting to life on Earth; jetting off into the cosmos has a rather large toll on astronauts' physical well-being, with returning crew members being greeted by muscle atrophy, and bone density loss.

It's been over eight months, but Butch Wilmore and Suni Williams are now on their way home (NASA)

So what are the impacts of spending an extended period of time in space?

Here to explain the experience is retired astronaut turned author Chris Hadfield, who successfully completed three missions and was the first Canadian national to serve as Commander of the ISS.

"It's a really interesting, fun and somewhat physically harrowing process to return home," he explained to LADbible, revealing that an astronaut's body has to readjust to a number of things while returning to Earth.

"When they first land, it'll be quite dizzy. It's almost oppressive, the unfair weight of gravity, crushing you, grinding you back down into the dirt of the Earth," he continued.

Walking will feel a little different this time around, but it's nothing the pair aren't trained for (Joe Raedle/Getty Images)

Although the changes to the body caused by being in space are all reversible, the experience of coming home from the ISS does appear to be a little daunting.

According to Chris, it takes on average one week before a returning astronaut can walk properly again, a couple of weeks before you're able to drive a car once more and a month until you're able to pilot a plane.

When it comes to bone density, the former astronaut predicts it could take around 24 months for Butch and Suni's to return to normal, after spending three months in space.

"I could run after a week, but I felt like I was a badly built puppet," he added.

Retired astronaut and now author Chris Hadfield described returning to Earth as 'interesting' and 'physically harrowing' (Ian Tuttle/Getty Images for Breakthrough Prize)

The toll of returning to Earth doesn't start at the moment an astronaut exits the capsule either, as astronauts will experience 'two, three or even four times the force of gravity' while re-entering the atmosphere.

"So [it's] especially unfair to have not only your own weight, but the weight of three other people lying on top of you," Chris added.

"It feels unfair. You've been so joyously weightless for so long, and now this invisible force is crushing you into your seat and pushing down your arms and pushing the skin back on your face."

The whole process may sound pretty harrowing for you or I, but Chris was keen to stress this is something which both Butch and Suni will be trained to deal with.

"It's just part of the deal as a professional astronaut."

Chris Hadfield's latest novel, Final Orbit, will be released in October and is available to pre-order here.