In preparation for his second mission to the International Space Station, ESA astronaut Thomas Pesquet is training for possible spacewalks at NASA’s Johnson Space Center. His second six-month mission is called Alpha and will see Thomas launch as part Crew-2 on the SpaceX Dragon spacecraft with NASA astronaut Megan Behnken and Shane Kimbrough and Japanese astronaut Aki Hoshide.

Watch this underwater spacewalk training session in 4K with audio from the astronauts and “mission control” recorded on 2 December 2020. Thomas is moved into position on a functional mockup of the International Space Station’s robotic arm to install hardware.

Astronauts practice spacewalks in NASA’s Neutral Buoyancy Laboratory. The training pool is the largest indoor swimming pool in the world, holding over 23 million litres of water, but it is still not large enough to hold the complete Space Station. Instead, specific parts of the Station structure are used as needed for training.

Training underwater is as close as it gets to experiencing weightlessness on Earth so spending time in a full spacesuit is used to practise techniques for spacewalks and neutral buoyancy is substituted for microgravity. Support and training divers are on hand to guide the astronauts during their tasks. In space, the astronauts are aided by mission control and colleague astronauts on the Station.

Extra Vehicular Activities (known as EVAs or spacewalks) are the most challenging tasks for an astronaut. When venturing from their spacecraft in a self-contained spacesuit to carry out repairs or install new equipment outside the International Space Station safety and efficiency are vital.

It might be relaxing and soothing to watch this underwater spacewalk at home, but spacewalks are marathons that require concentration and physical exertion for six hours at a time, with no food or bathroom breaks.

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