On the way back, he pondered what he would do if the water reached his mouth. The only idea he came up with, he said, was to open the safety valve on his helmet and let out some of the water.

“But making a ‘hole’ in my spacesuit really would be a last resort,” he wrote.

Mr Parmitano said it seemed like an eternity – not just a few minutes – until he peered through “the curtain of water before my eyes” and spotted the hatch. Mr Cassidy was close behind. The astronauts inside quickly began repressurising the air lock, to get to the spacewalkers.