An Italian astronaut who nearly drowned during a July 16 spacewalk outside the International Space Station used his blog to describe the terrifying ordeal.

"At this exact moment... I 'feel' that something is wrong," Luca Parmitano, an astronaut with the European Space Agency, wrote in a blog post. "The unexpected sensation of water at the back of my neck surprises me -- and I'm in a place where I'd rather not be surprised."

Last month, Parmitano and NASA astronaut Chris Cassidy were working (to prepare the space station for the addition of a Russian multipurpose laboratory module. They were scheduled to replace a video camera, move wireless television camera equipment and reconfigure thermal insulation over a failed electronics box.

However, they were just an hour into what should have been a six-and-a-half-hour spacewalk, when water began leaking into Parmitano's helmet, forcing NASA to cancel the spacewalk and bring both astronauts back inside as quickly as possible.

Most of the work set to be done that day was rescheduled into future spacewalks.

NASA has noted that the trouble began around 9 a.m., when Parmitano reported that there was water floating behind his head inside his helmet, caused by a leak in his helmet.

The space agency reported at the time that the leak didn't pose an immediate hazard to the astronaut. However, it was a harrowing experience for Parmitano.

At first, the two astronauts thought the water was coming from his drinking flask, but Parmitano wrote that he quickly realized that couldn't be the problem because the water level in his flask was not going down.

When NASA terminated the spacewalk, Cassidy and Parmitano had to separate and take different routes around the space station to get back to the airlock and inside where Parmitano could safely take off his helmet. But when they separated, Parmitano was alone in dark space as the water continued to fill his helmet, creeping up over his ears, moving into his nose and making it impossible for him to see where he needed to go.

"The water has also almost completely covered the front of my visor, sticking to it and obscuring my vision," he wrote. "I realize that to get over one of the antennae on my route I will have to move my body into a vertical position... as I turn 'upside-down', two things happen: the Sun sets, and my ability to see -- already compromised by the water -- completely vanishes, making my eyes useless; but worse than that, the water covers my nose -- a really awful sensation that I make worse by my vain attempts to move the water by shaking my head."

Now Parmitano's helmet is filling and he can't see.

"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," he wrote. "To make matters worse, I realize that I can't even understand which direction I should head in to get back to the airlock. I can't see more than a few centimeters in front of me, not even enough to make out the handles we use to move around the station."

And now Parmitano loses communications. He can barely here NASA and his fellow astronauts and they can't hear him.

"I'm alone," he said. "It's vital that I get inside as quickly as possible. I know that if I stay where I am, Chris will come and get me, but how much time do I have? It's impossible to know."

Then Parmitano remembers his safety cable. He grabs it and follows it back to the airlock.

"I force myself to stay calm and, patiently locating the handles by touch, I start to move, all the while thinking about how to eliminate the water if it were to reach my mouth," he wrote. "The only idea I can think of is to open the safety valve by my left ear: if I create controlled depressurization, I should manage to let out some of the water, at least until it freezes through sublimation, which would stop the flow. But making a 'hole' in my spacesuit really would be a last resort."

When Parmitano and Cassidy get inside the airlock, Parmitano can't even hear the hatch close. He only senses it by vibration.

"The water is now inside my ears and I'm completely cut off," he wrote. "Now that we are repressurizing, I know that if the water does overwhelm me, I can always open the helmet. I'll probably lose consciousness, but in any case that would be better than drowning inside the helmet."

Once the area is repressurized, the inside door opens and the other astronauts are there to pull his helmet off as quickly as possible.

"Space is a harsh, inhospitable frontier and we are explorers, not colonizers," 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," he writes.

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin, on Google+ or subscribe to Sharon's RSS feed . Her email address is sgaudin@computerworld.com.

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