Space controllers are taking no chances after an incident in 2013 when Italian astronaut Luca Parmitano discovered his helmet was starting to fill with water during a spacewalk.

His ventilation system had sprung a leak. Liquid doesn't flow under microgravity, so the water sat in his helmet, forcing him to cut short his spacewalk.

"I started going back to the airlock and the water kept trickling," Parmitano has said.

"It completely covered my eyes and my nose. It was really hard to see. I couldn't hear anything. It was really hard to communicate.

"I couldn't breathe through my nose - I felt isolated and when I tried to tell ground that I was having trouble finding my way, they couldn't hear me, and I couldn't hear them either.

"Instead of focussing on the problem - which was I may drown with the next gulp of air - I started thinking about solutions."

Parmitano gradually felt his way back to the airlock and made it safely back inside.