An Italian astronaut who nearly drowned in his helmet during a spacewalk last month has shared details about the terrifying experience and how he devised a plan to save himself.

Writing in his online blog Luca Parmitano described how the water sloshed around inside his helmet outside the International Space Station (ISS) and gradually rose to cover his nose and eyes.

The former test pilot wrote: “By now, the upper part of the helmet is full of water and I can’t even be sure that the next time I breathe I will fill my lungs with air and not liquid.”

Mr Parmitano, 36, a major in the Italian Air Force making just his second spacewalk, wasn’t sure which direction to head to reach the station’s hatch.

He tried to contact his spacewalking partner, American Christopher Cassidy, and Mission Control. Their voices grew faint, and no one could hear him.

“I’m alone. I frantically think of a plan. It’s vital that I get inside as quickly as possible,” he wrote.

Mr Parmitano had water in his ears and nose

Mr Parmitano realised Mr Cassidy – making his way back to the air lock by a different route – could come and get him. “But how much time do I have? It’s impossible to know,” he said.

That is when Mr Parmitano remembered his safety cable. He used the cable recoil mechanism, and its force, to “pull” him back to the hatch.

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.

“The water is now inside my ears and I’m completely cut off,” he said.

The International Space Station
The International Space Station

He recalled how he tried to stay as still as possible to keep the water from moving inside his helmet. He knew that because of the repressurisation, he could always open his helmet if the water overwhelmed him.

“I’ll probably lose consciousness, but in any case, that would be better than drowning inside the helmet,” he wrote.

“Finally, with an unexpected wave of relief,” Mr Parmitano saw the internal door open, and the crew pulled him out and his helmet off.

He remembers thanking his crewmates “without hearing their words because my ears and nose will still be full of water for a few minutes more”.

Nasa has traced the problem to his spacesuit backpack which is full of life-support equipment.

But the precise cause is still unknown as the investigation continues into quite possibly the closest call ever during an American-led spacewalk. Nasa has suspended all US spacewalks until the problem is resolved.

“Space is a harsh, inhospitable frontier and we are explorers, not colonisers,” Mr Parmitano wrote.

“The skills of our engineers and the technology surrounding us make things appear simple when they are not, and perhaps we forget this sometimes.

“Better not to forget.”