Tim training for the PADI Rescue Diver certificate at Esa’s astronaut training centre in Cologne, Germany. “The better diver you are, the better you will be at spacewalks,” explains Hervé Stevenin, head of the Astronaut Training Unit preparing Esa astronauts for spacewalks. “Scuba diving is as close as it gets to experiencing weightlessness on Earth for long periods of time.”

Photograph: Dr. H. Rüb/ESA