U.S. astronauts aboard the International Space Station area readying their NASA spacesuits, including the protective garment that leaked water into a helmet during a July 16 excursion, for a series of spacewalks intended to repair a crippled external cooling system.

Veteran NASA astronaut Rick Mastracchio and Mike Hopkins, a first-time flyer, will tackle the repairs intended to address a faulty flow control valve in a refrigerator-sized pump control module over three spacewalks. The tasks for each spacewalk are as follows:

Dec. 21: Deactivate and loosen fasteners on the Loop A cooling system pump; de-mate ammonia coolant lines and electrical connectors on the pump.

Dec. 23: Remove and replace the 780-lb. pump module. A spare is stowed near the work site along the onboard section of the station’s right-side solar power truss. Temporarily stow the failed pump module at the work site.

Dec. 25: If not accomplished previously, re-stow the failed pump module; clean up the work site; and put away tools. Engineers believe the old pump module could be equipped with a new flow control valve in the future and perhaps installed again.

Each of the 6- to 7-hr. excursions is scheduled to start at 7:10 a.m. EST. The schedule may change, but NASA would like to complete the repairs by Dec. 30, when Sun angles on the station’s orbital plane exceed thermal limits for external activities through Jan. 9.

Hopkins will don the spacesuit worn by Italian astronaut Luca Parmitano on July 16, when 1 to 1 1⁄2 liters of water flowed into his helmet during an excursion with NASA astronaut Chris Cassidy. Though the root cause is still under investigation, engineers believe the fan pump separator in his personal life support system (PLSS) backpack became blocked.

The fan pump separator in Hopkins’ suit was replaced, as well as internal water lines. Both suits have also been equipped with makeshift internal snorkels fabricated from plastic tubing and wrapped in Velcro to secure them in place. If water began to leak again, an astronaut can place his mouth over one end of the tube. The far end extends to an air pocket in the midsection of the suit.

In addition, the spacewalkers will place pads atop their heads fashioned from off-the-shelf water absorbency pads, wrapped in T-shirt cotton and topped with additional absorbency material. The pads can absorb 600-800 milliliters of water, according to ground tests.

“We think we are taking out two clean suits to the best of our knowledge,” said Dina Contella, who will be the NASA ISS flight director during the spacewalks. “(But) we can’t rule out that we would have water in the suits again.”

Mastracchio and Hopkins regularly conduct “feel” tests for water in their helmets as part of a change in procedures.

The cooling system difficulties surfaced Dec. 11, when a flow control valve in Loop A of the station’s dual loop external cooling system faltered. Loop A and B circulate ammonia coolant through external radiators to remove heat from the station’s electronics, including those associated with life support and research hardware.

The loss of thermal control prompted the shutdown of noncritical systems in the station’s European and Japanese research modules as well as the U.S. Harmony node.

Earlier this week, NASA flight control teams achieved limited success in restoring a backup Loop A cooling capability using an isolation valve and software patches.

The difficulties also forced NASA to reschedule the launch of Orbital Science Corp.’s ORB-1 resupply mission to the ISS from Dec. 19 to no earlier than Jan. 13. The launch of the Antares rocket and Cygnus cargo capsule from Virginia’s Eastern Shore will mark the first under an eight-flight, $1.9 billion Commercial Resupply Services contract between Orbital and NASA.

The flow control valve is located within the pump module. Three spare pump modules are stowed outside the ISS, with the replacement cradled on the starboard truss in the External Stowage Platform 3.

Mastracchio, 53, is a three-flight, six-spacewalk veteran who was selected by NASA for astronaut training in 1996. Hopkins, 44, is a U.S. Air Force colonel who is flying for the first time, following his selection by NASA for astronaut training in 2009. Mastracchio and Hopkins reached the ISS for six-month assignments on Nov. 6 and Sept. 25 respectively.

Japanese astronaut Koichi Wakata, 50, a three-flight veteran, will serve as the operator of the Canadian robot arm during the spacewalks. The 58-ft.-long robot arm will allow the spacewalkers to be moved around outside the station. cherry picker style. Selected for astronaut training in 1992, he arrived at the station on Nov. 6.

Parmitano and Cassidy aborted their planned 6- to 7-hr. spacewalk as water invaded Parmitano’s helmet through an air vent and massed around his eyes, ears and nose.

On Nov. 10, Parmitano descended to Earth with U.S. and Russian crewmates and the suspect fan pump separator and contaminants that were extracted from his spacesuit’s PLSS on Oct. 24. Most of the small water release ports in the small centrifuge were blocked by contaminants, whose source is still being traced, according to Mike Suffredini, NASA’s ISS program manager.

 The backpack houses life support systems that supply and clean the breathing air of the pressurized garment and circulate cooling water.

NASA initiated an engineering investigation into the cause of the leak and convened a mishap investigation board to assess the cause, identify contributing factors and recommend changes in procedures as warranted. 

In addition to the NASA spacewalks, ISS cosmonauts Oleg Kotov and Sergey Ryazanskiy are preparing for an unrelated Dec. 27 spacewalk to install two external Earth observing cameras and service external experiments.