CAPE CANAVERAL, Fla. -- In one of the most harrowing spacewalks in years, 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.
Italian Luca Parmitano seemed fine after the dangerous episode, which might have been caused by a leaky drinking bag. His spacewalking partner, American Christopher Cassidy, had to help him inside after NASA quickly aborted the spacewalk.
No one -- neither the astronauts in orbit nor flight controllers in Houston -- breathed easily 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.
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 on the floating drops of water.
The source of the leak wasn't immediately known but a potential culprit was the 32-ounce drink bag that astronauts sip from during lengthy spacewalks, although Parmitano later reported the leaking water tasted odd. Water also is piped through the long underwear worn under a spacesuit, for cooling.
His last words before becoming mum were: "It's a lot of water."
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.
Cassidy suggested it might be water from his drink bag; it looked like half had leaked out.
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 once Parmitano was back in the air lock, then followed him in.
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. Engineers, meanwhile, scrambled to determine the source of the leak.
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.
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.
This was the second spacewalk for Parmitano, a major with the Italian Air Force. He became the first Italian to conduct a spacewalk last Tuesday, six weeks after moving into the space station.
Cassidy, 43, a former Navy SEAL, is a six-time spacewalker. He's midway through a half-year station stint.