TRANSCRIPT
The dragon spacecraft making its way home back to earth.
Astronauts Butch Wilmore and Suni Williams re-enter Earth's atmosphere after nine months in orbit.
The footage of their descent may look calm but inside the spacecraft, it's far from it.
British astronaut Tim Peak describing what the pair likely experienced.
"It's about 1600 Celsius outside the spacecraft. You can see the plasma enveloping the whole spacecraft out the windows. So it gets very warm inside."
Another former astronaut - American Scott Kelly - once described the return of gravity as slow at first, and then it hits "with a vengeance."
Breathing becomes difficult, he said, as "G Forces clamp down on the trachea..."
"There we have it, some thumbs up, some waves and some smiles."
Relief as the astronauts disembarked the spacecraft.
But experts say the pair have a long and intense recovery ahead because of how space travel impacts the body - and mind.
Dr Rebecca Allen is the co-director of the Space Technology and Industry Institute at Swinburne University of Technology.
"Our most important muscle, our heart, pumps blood differently in space because fluids don't flow, of course, without gravity there. Our immune system function, our gut microbiome, even our very DNA changes."
The fluids in the body shift upward in space and that can put pressure on the eyes and cause vision problems.
There is lower nutrient absorption and increased exposure to radiation can damage our DNA and increase cancer risk.
On the space station, astronauts routinely exercise using specialised devices to run, cycle and lift weights
Even still, Allen says, without constant tug of gravity muscle mass deteriorates and the bones breakdown.
"Our muscles get strong because they're used to holding us up against gravity. When you take that away, they no longer have that resistance to really build up strength, and so they very quickly deteriorate. But also the bones that they're attached to, they don't have that continuous pull of the muscles on them, so our bones also start to break down."
The good news is that most of the changes - though not all - are temporary. Intense physical and psychological rehabilitation is now required.
Long-duration space missions require astronauts to live in confined and isolated environments with limited social interaction.
"The whole world has kind of been watching these astronauts seemingly left in space and stuck there for a prolonged mission. Now they have to wake up, make breakfast and get stuck in traffic going to work. It is a transition that is hard for some astronauts. And then kind of catching up with the personal life that they have missed for nine months. They were only planning maybe two weeks away, but they've missed birthdays and other scenarios, and you know, life logistics, life admin that they now have to catch up on."
The pair don't hold the record for the longest time in space. I-S-S missions typically last six months, though some astronauts stay in orbit for up to a year.
And with ambitions to reach Mars - they'll have to stay in space far longer
A round trip is expected to take three years.
"I think this is the untold part of space travel … how do we make humans survive the trip? How do we solve all of the health issues, the psychological issues, the food supplies? We can't send a resupplied mission to Mars."
Extended trips to space, like Wilmore and Williams', will be the key to understanding such questions.
