NASA is looking into a possible cooling system leak after water seeped into the helmet of spacewalking European Space Agency astronaut Luca Parmitano on July 16, prompting an early end to a two-man excursion that was to advance preparations for the arrival of Russia’s Multipurpose Laboratory Module (MLM) later this year.

Neither Parmitano nor lead U.S. spacewalker Chris Cassidy faced imminent danger, and all of the missed tasks can be rescheduled without urgency, according to NASA’s Mission Control.

The incident was the most serious to confront ISS spacewalkers since June 24, 2004, when NASA’s Mike Fincke and cosmonaut Gennady Padalka retreated after 14 min. when Fincke’s Russian space suit experienced an oxygen leak. The July 16 issue involved the NASA space shuttle era suits worn by Canadian, Japanese and European as well as American astronauts for work outside the station’s U.S. segment.

Cassidy and Parmitano embarked at 7:57 a.m. EDT on the scheduled 6 1⁄4 hr. spacewalk to work their way through a series of tasks started during a successful July 9 excursion. The outing was over with Parmitano and Cassidy safely inside the station’s airlock 92 min. later.

At 8:43 a.m., Parmitano reported water at the back of his head and seeping inside the communications cap that fits tightly against his head under the helmet.

The ESA astronaut was wedged between two modules as he began to extend Ethernet cabling from the U.S. to the Russian segments as a future data link for the MLM.

“It feels like a lot of water. I don’t know where it’s coming from,” Parmitano reported, as Cassidy began to move to his partner’s aide.

Parmitano reported he was sipping at the water to diminish the buildup.

“It’s a lot of water,” Cassidy observed. “It’s in his eyes as well as his nose and mouth.”

After several minutes of deliberation, NASA’s Mission Control ordered Parmitano to return to the airlock and directed Cassidy to end his activities as well by gathering tools and equipment.

At that point, it appeared water might be leaking from Parmitano’s internal space suit drink bag. That assessment changed as the two astronauts conferred in the airlock and began to remove their protective space suits

“Clearly the water did not taste like the normal drink water,” relayed Cassidy to Mission Control. The water tasted of iodine, a chemical placed in the water that circulates through tubing as a coolant in the undergarments worn by spacewalkers. The iodine inhibits microbial growth.

Cassidy also reported possible damage in the “belly button” portion of Parmitano’s space suit and moisture around a cooling vent in the back of his colleague’s helmet.

The leak was unparalled in ISS spacewalk operations, said Karina Eversley, who served as the lead spacewalk officer in NASA’s Mission Control. “Choking or drowning were definitely possiblities,” Eversley told a news July 16 news briefing.

Evidence gathered in the aftermath, including photos and comments from Cassidy and Parmatano, indicated the 32-oz. drink bag in his suit was not the leak source, said Eversley and David Korth, the NASA flight director during the excursion. Parmitano wore the same space suit during his July 9 spacewalk.

Though their outing was greatly abbreviated, Cassidy managed to complete external power cable reconfigurations he began July 9. The changes provide a second source of electricity to an assortment of critical systems, including control moment gyros, thermal control and Ku-band communications links, in response to external electrical or cooling system failures.

The alteration will enable astronauts to reroute power to critical systems from inside the station rather than interrupt other activities to prepare for a spacewalk.

Meanwhile, Parmitano extended U.S. power and data utility cables to a power and data grapple fixture installed on the Russian segment. The grapple fixture serves as one of several anchor points for the station’s Canadian robot arm. The 58-ft. robot arm often serves as a mobile work platform for spacewalking astronauts.

A U.S. solar power cable was extended to the Russian segment for the MLM during the July 9 spacewalk. Once it is joined by Ethernet cabling, spacewalking cosmonauts plan to extend both power and Ethernet cabling to the berthing port for the MLM.

The near 44,000-lb. combination Russian lab, airlock and docking module, also known as Nauka, is currently scheduled for a December launching.