HOUSTON — NASA is promising an aggressive investigation of a spacesuit leak that allowed dangerous blobs of water to gather on the eyes, nose and mouth of European Space Agency astronaut Luca Parmitano during a July 16 spacewalk outside the International Space Station with his NASA colleague Chris Cassidy.

The incident was unprecedented and could have caused the 36-year-old Italian test pilot to choke or even drown as an estimated 1-1.5 liters of water leaked from his NASA spacesuit, most of it into his helmet, before the planned 6- to 7-hr. excursion was halted after 92 min., says Karina Eversley, lead spacewalk officer at NASA’s Mission Control (Aerospace DAILY, July 17).

Though none of the tasks left unfinished were considered urgent, the pace of the inquiry could determine if and how quickly astronauts occupying the station’s U.S. segment could be called upon to respond to any of a dozen or so serious external issues, including problems with the critical solar power and thermal control systems. Initial troubleshooting seemed to point to the suit’s water-circulating cooling system as a potential leak source.

“Clearly, we have a problem we don’t quite understand,” ISS Mission Management Team Chair Kenny Todd told a Johnson Space Center news briefing late July 16. “We will take the next day or two to sort through it, probably do a little bit of troubleshooting on orbit and the [engineering] team will be working through a fault tree to get a better understanding of what’s going on.”

As the 13-year assembly of the station’s U.S. segment drew to a close in mid-2011, NASA shifted the operational focus of the six-person orbiting lab to scientific research. External maintenance items are permitted to accumulate, unless safe operations are jeopardized, until a spacewalk is warranted.

The spacesuit’s primary sources of water are a 32-oz. (0.95-liter) drink bag for astronaut hydration, a 1-gal. (3.8-liter) cooling system that circulates water from a reservoir through narrow tubes in an astronaut’s undergarment, and astronaut perspiration.

All that worked well during a successful July 9 spacewalk in which Parmitano and Cassidy were outfitted in the same suits, making the July 16 incident all the more puzzling.

Less than an hour into their task list, Parmitano noted an erratic CO2 sensor, a device that warns of an unwanted buildup of poisonous carbon dioxide in the oxygen-rich spacesuits. That was followed by a wet sensation on the back of his head beneath the communications cap that fits snugly under the helmet.

Parmitano continued to work as NASA’s flight control team monitored his activities through medical sensors on his body and occasional voice checks. Then the water began to increase, forming blobs in the weightlessness. There is little material in the suit to absorb moisture.

Cassidy left his nearby ISS work site to check on his colleague. He found water gathering around Parmitano’s nose and mouth, and suggested that Parmitano taste the water to see if it was coming from his internal drink bag. After several minutes of deliberation, Mission Control ordered the two men back to the safety of the station’s airlock.

The moisture in Parmitano’s helmet continued to increase as he made his way to the airlock, while his ability to see, speak and breathe degraded.

An early finding seemed to absolve the drink bag. “I would say the likelihood the leak is coming from the drink bag is pretty low given what the crew has told us,” Eversley said. “Our whole spacewalk community will be working through a fault tree and checking off every possibility.”