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 at times and could have caused him to choke or even drown.

Italian Luca Parmitano was reported to be fine after the dangerous episode, which might have been caused by an unprecedented leak in the cooling system of his suit. His spacewalking partner, American Christopher Cassidy, had to help him head 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 by the time he was in the air lock, the pressure chamber. He could have choked or drowned on the floating globs of water, NASA officials said.

Between 1 and 1½ liters of water leaked into his helmet and suit, NASA estimated.

The source of the leak wasn’t immediately known, but the main culprit appeared to be iodine-laced 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 (about 1 liter) drink bag that astronauts sip from during lengthy spacewalks; Parmitano reported the leaking water tasted odd.

At first, Parmitano, 36, a former test pilot and Italy’s first spacewalker, thought it was sweat accumulating on the back of his bald head. But he was repeatedly assured it was not sweat. He agreed. “How much can I sweat?” he wondered aloud.

It was only his second spacewalk; his first was last Tuesday, six weeks after moving into the space station.

The water eventually got into Parmitano’s eyes. That’s when NASA ordered the two men back inside. Then the water drenched his nose and mouth, and he had trouble hearing on the radio lines.

Cassidy quickly cleaned up the work site, then joined Parmitano in the air lock.

The three Russians and one American who anxiously monitored the drama from inside hustled to remove Parmitano’s helmet. They clustered around him, eight hands pulling off his helmet and using towels to mop his head. Balls of water floated away.

Parmitano blinked hard several times but otherwise looked fine as he gestured with his hands to show his crewmates where the water had crept around his head.

Cassidy told Mission Control: “To him, the water clearly did not taste like our normal drinking water.” A smiling Parmitano then chimed in: “Just so you know, I’m alive and I can answer those questions, too.”

He later tweeted: “Thanks for all the positive thoughts!”

Mission Control praised the crew for its fast effort and hooked them up with flight surgeons on the ground.

Parmitano used the same suit during last week’s spacewalk without any problems. Before the gush of water made its way into his helmet, the astronaut reported a bad sensor for measuring carbon dioxide in his suit. NASA managers concluded the sensor likely failed due to all the water.

Spare spacesuits and equipment are on board for future NASA spacewalks.

The four remaining spacewalks planned for this year involve Russian astronauts wearing Russian suits, different than the U.S. models. They’re preparing for the arrival later this year of a new Russian lab. The year’s previous four spacewalks encountered no major snags. This was the 171st spacewalk in the 15-year history of the orbiting outpost.

There was no immediate word on when Tuesday’s undone tasks might be attempted again. None of the chores was urgent, simply things that had piled up over the past couple years.

It was the fastest end to a spacewalk since 2004 when Russian and American spacewalkers were ordered back in by Mission Control outside Moscow because of spacesuit trouble. That spacewalk lasted a mere 14 minutes. Tuesday’s spacewalk lasted one hour and 32 minutes.

During NASA’s old shuttle program, spacewalks occasionally were stymied by stuck hatches and ripped gloves. By coincidence, Cassidy had to end a 2009 station-building spacewalk early because of a potentially dangerous buildup of carbon dioxide in his suit. This marked the sixth spacewalk for the 43-year-old former Navy SEAL, who’s midway through a half-year station stint.

In 1966, two Gemini flights ended up with aborted spacewalks. Gemini 11 spacewalker Richard Gordon, was blinded by sweat. Gemini 9 spacewalker Gene Cernan breathed so heavily and sweated so much that fog collected inside his helmet visor and froze.

On the Russian side, the world’s first spacewalker, Soviet cosmonaut Alexei Leonov, could barely get back into his spacecraft in 1965. He had to vent precious oxygen from his suit in order to fit through the hatch. Decades passed before his peril came to light.

“Today was certainly a very serious issue,” said Karina Eversley, lead spacewalk officer. The goal, each time, is to get the crew back inside “before things get too serious,” she added.

In that respect, Tuesday was a success, Todd noted. “Today the team did a great job.”

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