And this was not a small problem. Recall that an astronaut's spacesuit is a spaceship for one, an astronaut's only lifeline back to the Station and, with it, the Earth. Recall as well that, in microgravity, liquid doesn't pool -- it floats. It clings. At one point, per one account, "there was so much water inside Parmitano's ears and around his face that he couldn't hear or speak to communicate with the other astronauts."

"Squeeze my hand if you're fine," Cassidy said to Parmitano.

There was no squeeze. NASA abruptly aborted the spacewalk, and the crew pulled Parmitano back into the Station, freeing him from his suit. The first order of business: toweling off his face and head. "He looks miserable, but is OK," the crew told Mission Control after they'd dried him off, balls of water flying away as they did so.

The crew, and Mission Control, are still trying to determine the cause of the liquid incursion. Cassidy, for his part, suspects it was water seeping from Parmitano's drink bag. He said it looked like a half-liter -- about 2 cups -- of water had leaked out into Parmitano's helmet.

ISS Astronauts had to scramble to get Luca Parmitano out of his spacesuit after a leakage malfunction aborted his spacewalk. (NASA TV via Universe Today)

Parmitano, it turns out, is only the latest astronaut to experience the waking nightmare that is the liquid-filled helmet. As early as 1966, during the second-ever U.S. EVA, astronaut Gene Cernan experienced a similar problem. Space-walking was new back then, and NASA, it seems, had underestimated exactly how much work -- "work" in the sense of "manual labor" -- would be required of the astronaut doing the space walk. "Lord, I was tired," Cernan would later recall of that early EVA. "My heart was motoring at about 155 beats per minute, I was sweating like a pig, the pickle was a pest, and I had yet to begin any real work." At one point, as the walk progressed, Cernan's heart rate shot up to 195 beats per minute -- and flight surgeons began fearing that he would pass out from the exertion.

Cernan, ultimately, didn't lose consciousness; he did, however, lose some of his sight. The space-walker's body heat and the sweat it generated fogged up the helmet of his suit. Suddenly, Cernan was seeing the spaceship before him as if through a frosted window. And he had no means of fading the fog. NASA aborted the EVA -- and, as a result of Cernan's experience, began applying anti-fogging chemicals to the interior surfaces of the spacesuit helmets that would follow.

Anti-fogging chemicals, however, don't do much to prevent liquid from seeping into helmets from elsewhere in the suit -- as seems to have happened to Parmitano. In 2004, halfway through a standard spacewalk, the cosmonaut Alexander Kaleri startled Mission Control in Moscow with an announcement: "It's amazing. I have rain inside the helmet," he said. The "full condensation" he was experiencing was accompanied, alarmingly, by a rise in Kaleri's suit temperature -- which would not prove to be hazardous, but which would offer immediate evidence of a suit malfunction. Ground Control aborted the spacewalk -- though it had to repeat the decision multiple times before Kaleri and his fellow spacewalker, the American Mike Foale, acquiesced: both had planned to retire after the mission, and were reluctant to bring their final spacewalking experiences to premature ends.