CAPE CANAVERAL, Fla. — In one of the most harrowing spacewalks in decades, an astronaut had to rush back into the International Space Station on Tuesday after a mysterious water leak inside his helmet robbed him of the ability to speak or hear and could have caused him to choke or even drown.
Luca Parmitano, an Italian, was reported to be fine after the dangerous episode, which might have been caused by a leak in the cooling system of his suit. His spacewalking partner, Christopher Cassidy, an American, had to help him inside after NASA quickly aborted the spacewalk.
No one — neither the astronauts in orbit nor flight controllers in Houston — breathed easier until Parmitano was back inside and his helmet was yanked off.
‘‘He looks miserable. But OK,’’ Cassidy assured everyone.
It was the first time in years that a spacewalk came to such an abrupt halt and the first time since NASA’s Gemini program in the mid-1960s that a spacewalker became so incapacitated. Spacewalking always carries high risk; a puncture by a micrometeorite or sharp edge, if big enough, could result in instant death.
In a late-afternoon news conference, NASA acknowledged the perilous situation that Parmitano had found himself in, and space station operations manager Kenneth Todd promised to ‘‘turn over every rock’’ to make sure it never happens again.
Spacewalking is dangerous already, noted flight director David Korth. Then on top of that, ‘‘go stick your head in a fishbowl and try to walk around. That’s not anything that you take lightly,’’ he said. ‘‘He did a great job of just keeping calm and cool’’ as the amount of water ominously increased.
‘‘Grace under pressure,’’ Korth said.
The two astronauts were outside barely an hour, performing routine cable work on their second spacewalk in eight days, when Parmitano reported the leak. It progressively worsened as the minutes ticked by, drenching the back of his head, then his eyes, nose and, finally, mouth. He could have choked or drowned on the floating globs of water, NASA officials acknowledged.
Between 1 and 1½ liters of water leaked into his helmet and suit, NASA estimated.
The source of the leak was not immediately known, but the main culprit appeared to be water that is piped through the long underwear worn under a spacesuit, for cooling. The system holds nearly 4 liters, or 1 gallon. Less likely was the 32-ounce drink bag that astronauts sip from during lengthy spacewalks; Parmitano reported the leaking water tasted odd.