Saturday Spacewalk Kicks Off Addition of Commercial Crew Docking Ports to ISS

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Spacewalking NASA astronauts Barry "Butch" Wilmore and Terry Virts initiated the installation of the first of two planned International Space Station docking ports for future U.S. commercial crew transportation vehicles on Saturday by extending external power, data and thermal control cabling along the orbiting science lab's Harmony and Destiny laboratory modules.

The near seven hour excursion unfolded without difficulties from either of the fan pump separators in the two space suits, a safety concern that emerged in December and January and persisted up to the start of Saturday's spacewalk. Virts experienced a slight buildup of carbon dioxide in his suit from all of the exertion.

NASA's Barry "Butch" Wilmore, left, and Terry Virts install power, data and heater cables near future ISS docking port for commercial crew vehicles. NASA photo

The two men started 30 minutes late but surged ahead of schedule, accomplishing some of the work assigned to the second in a series of three excursions over the next nine days.

The fan pump separators are part of the space suit life support system that circulates air and cooling water. The devices originally assigned to Saturday’s excursion failed to spin up during late 2014/early 2015 checkouts inside the station's airlock.

The steady performance of the fan pump separators on Saturday was a welcome development.

NASA plans a second and third spacewalk by the two men on Wednesday and Mar. 1 to complete the power, data and thermal control cable task. They also intend two antenna installations and communications cable extensions before Wilmore's scheduled return to Earth. He departs late Mar. 11 with two Russian cosmonauts to conclude 167 days aboard the orbiting science lab.

The primary work site for Saturday's outing was the 16-year-old Pressurized Mating Adapter-2 on the forward end of Harmony, which served as the docking port for NASA's space shuttle fleet until the winged orbiters were retired in mid-2011. Wilmore, the station's current commander, and Virts made five power, data and thermal control connections under two orbital debris shields on either side of PMA-2 and three additional cable connections, including two linkups that were originally scheduled for the second spacewalk.

"I worked up a lather on that one," quipped Wilmore as he marched through the first set of PMA-2 cable connections.

"You guys have done just a superb job,” Mission Control told the two men as they entered the home stretch of Saturday’s activities.

In all, Wilmore and Virts are to install 10 cables totaling 364 feet over the first two spacewalks to prepare PMA-2 for outfitting with the first of new NASA and Boeing developed International Docking Adapters. The IDAs will serve as the actual mechanical links between the station and future commercial crew vehicles operated by Boeing and SpaceX under NASA contracts.

As Saturday’s spacewalk drew to a close at 2:26 p.m., EST.

NASA's goal is to achieve the first commercial crew vehicle docking with astronauts by the end of 2017.

SpaceX is to deliver the first of the IDAs aboard the company's seventh commercial re-supply mission in June. The initial IDA would be installed on PMA-2 during a NASA spacewalk currently planned for July.

This year, NASA also plans to move the identical PMA-3 from the station's Tranquility module to the space facing circumference of Harmony. A second IDA is manifested for delivery aboard another SpaceX resupply mission planned for late this year.

During Wednesday's spacewalk, Wilmore and Virts are to complete the PMA-2 cabling and lubricate the grappling mechanism on the station's Canadian-furnished robot arm. The 58-foot-long mechanical limb will be used to relocate PMA-3 as well as move the station's Leonardo Permanent Multipurpose Module from the Earth facing side of the station's Unity module to the forward end of Tranquility. That move will ensure sufficient clearances for a pair of commercial cargo berthing ports as well as the two commercial crew parking spots.

During the March 1 spacewalk, Wilmore and Virts are to install two communications antennas and string another 400 feet of cabling along the station's port and starboard solar power trusses to support the transmission of navigational data for automated commercial crew rendezvous and dockings.

The source of the balky space suit fan pump separator issue that surfaced in December and January  was traced to a corrosion buildup on internal bearings. The corrosion was blamed on water intrusion. Those initial suspicions were confirmed after the two fan pump separators that failed to activate were removed from the space suits and returned to Earth earlier this month aboard the fifth SpaceX Dragon resupply mission. The devices were turned over to United Technologies Corp., the space suit contractor, for evaluation.

The fan pump separators have been activated between spacewalks at an accelerated pace during check outs of cooling system water quality, which has increased the opportunity for exposure of the bearings to water, according to NASA.

The unwanted presence of silica particles in the cooling water was blamed for a July 2013 incident in which water flowed into the space suit helmet worn by European Space Agency astronaut Luca Parmitano. Parmitano retreated to the airlock as water invaded an airflow vent, massing around his eyes, nose and ears. Engineers found small water ports in the pump blocked by silica particles that migrated from water filters. The blockage diverted cooling water into the helmet air flow vent.

The U. S. chaired ISS mission management team cleared Saturday's spacewalk on Thursday after determining any corrosion in the fan pump separators in suits worn by Wilmore and Virts was minimal.

However, NASA's Mission Control refined the governing rules for the excursion by stipulating that work would be halted without further troubleshooting if there were signs of problems with the air and water circulation devices.

In the meantime, NASA has also changed its space suit cooling water quality checkouts to include additional air flow over the bearings as a dry out measure.

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