Expedition 45 Spacewalkers Set to Restore Troublesome P-6 Cooling System to ‘Default Setting’

Barely a week since their first career spacewalk together, Expedition 45 astronauts Kjell Lindgren and Scott Kelly will venture outside the Quest airlock of the International Space Station (ISS) at approximately 7:15 a.m. EST tomorrow (Friday, 6 November) for around 6.5 hours to restore the cooling system of the P-6 segment—the furthest-outboard port-side element of the vast, 356-foot-long (108.5-meter) Integrated Truss Structure (ITS)—to its original configuration, following several years of efforts to isolate ammonia leakages and replace suspect hardware components. Known as P-6 Return to Original Configuration (RTOC), the spacewalk (designated “U.S. EVA-33”) will see Lindgren designated “EV1,” with red stripes on the legs of his space suit, and Kelly as “EV2,” clad in a pure-white suit. This alternates their respective roles following last week’s EVA. According to Lead EVA-33 Officer Art Thomason, speaking at a media briefing at the Johnson Space Center (JSC) in Houston, Texas, on 22 October, the decision will ensure that both Kelly and Lindgren gain experience in the EV1 lead-spacewalker role. A similar expertise-gathering exercise was seen during EVA-30 on 25 February and EVA-31 on 1 March, when Expedition 42 spacewalkers Barry “Butch” Wilmore and Terry Virts alternated roles.

Supporting the spacewalkers will be Capcom Megan Behnken, who will serve as “Ground Intravehicular (IV)”—having previously supported EVA preparations during her role as a member of the STS-125 crew, the final Hubble Space Telescope (HST) servicing mission, back in May 2009—and Expedition 45’s Japanese member, Kimiya Yui, who will act as “Suit IV,” assisting Kelly and Lindgren into their bulky Extravehicular Mobility Unit (EMU) space suits and transferring them and their gear from Quest’s inner “equipment lock” to its outer “crew lock.” The Flight Director for U.S. EVA-33 is Scott Stover. Only a week since they first savored the opportunity to work outside the confines of their spacecraft, it seems that both Kelly and Lindgren are buzzing about the experience; a buzz which very quickly found its way onto Twitter. “Still trying to wrap my head around why we call it #spacewalk, not #spacework,” Kelly told his 587,000-strong audience after the completion of 28 October’s EVA-32. Sharing his own image taken from the 14,800-pound (6,700-kg) Alpha Magnetic Spectrometer (AMS) on the Upper Inboard Payload Attach Site on the S-3 truss, Lindgren added “The view was spectacular during my #spacewalk.”

During the course of the last week, the six-man Expedition 45—which, in addition to the U.S. Orbital Segment (USOS) crew, also includes Russian Orbital Segment (ROS) cosmonauts Mikhail Kornienko, Oleg Kononenko, and Sergei Volkov—have brought eerie Halloween greetings and a poignant bagpipes performance by Lindgren in honor of the recent passing of Wyle Labs’ research scientist and astronaut instructor Victor Hurst IV. Last weekend, Lindgren and Yui also celebrated 100 days in orbit since their 22 July launch aboard Soyuz TMA-17M, and, on Monday, 2 November, the ISS Program observed 15 years of continuous habitation of the multi-national orbiting outpost. In among these activities, and ongoing science and maintenance of the station, Kelly, Lindgren, and Yui have worked on preparing their suits and equipment for Friday’s EVA-33.

The spacewalk will be the 33rd U.S. “Stage” EVA, executed out of the Quest airlock, in U.S.-built EMUs and performed without a space shuttle being present. As noted in a previous AmericaSpace article, the first of these excursions (“U.S. EVA-1”) was performed by Expedition 4 astronauts Carl Walz and Dan Bursch on 20 February 2002—the 40th anniversary of John Glenn’s pioneering orbital mission—and subsequent spacewalks have prepared the ISS for future expansion, removed and replaced a failed ammonia pump module and a failed Main Bus Switching Unit (MBSU) and tended to other urgent issues, including ammonia leakages and the deterioration of several key pieces of hardware. More than two years ago, in July 2013, the unforgiving nature of the near-vacuum environment was experienced first-hand by U.S. EVA-22 spacewalker Luca Parmitano, who suffered life-threatening water intrusion into the helmet of his suit and was forced to return promptly to the airlock. Much of the training for these EVAs has been completed with the astronauts already in orbit, reliant upon their pre-flight “EVA Skills” work in the Neutral Buoyancy Laboratory (NBL) at JSC and checklists, presentations, tools, and suited run-through tasks aboard Quest itself.

Early tomorrow morning, assisted by Yui and Volkov, the two spacewalkers will undertake 60 minutes of “pre-breathing” on masks, during which time the inner “equipment lock” of Quest will be depressed from its ambient 14.7 psi to 10.2 psi. Upon completion of this well-trodden, pre-EVA protocol, Lindgren and Kelly will don and purge their EMUs and the airlock’s atmosphere will be repressurized back up to 14.7 psi. This will allow the men to enter a nominal pre-breathing regime, lasting 50 minutes, followed by a further 50 minutes of In-Suit Light Exercise (ISLE). The latter was first trialed during the third EVA of the STS-134 shuttle mission in May 2011—which, coincidentally, was commanded by Kelly’s identical twin brother, Mark—and serves to rapidly remove nitrogen from the spacewalkers’ bloodstreams, thereby avoiding a potentially fatal attack of the “bends” and skirting the need for the EVA crew to “camp out” overnight in Quest.

At length, Yui and Volkov will transfer the fully-suited astronauts and their equipment, including the Simplified Aid for EVA Rescue (SAFER) units, affixed to the lower segment of their life-sustaining backpacks, from the equipment lock into the outer “crew lock.” Hatches between the locks will be closed and depressurization will begin. When it reaches 5 psi, it will briefly halt for pressure and leak checks, then resume until the crew lock achieves a condition of near-vacuum. U.S. EVA-33 is scheduled to officially get underway at about 7:15 a.m. EST, when Lindgren and Kelly transfer their suits’ life-support utilities from ISS power over to internal batteries. As the lead spacewalker, Lindgren will emerge first, followed by Kelly, who will be carrying a Crew Lock Bag with tools. The pair will perform customary “buddy checks” of each other’s suits and tethers, before Lindgren collects a Vent Tool Bag from the zenith face of the crew lock and the pair set about their respective tasks.

According to Lead EVA-33 Officer Art Thomason, the principal goal of tomorrow’s spacewalk is to “restore the P-6 cooling system back to its original configuration,” and Lindgren and Kelly will be based at this truss segment for most of their time outside. The P-6 truss—which is equipped with two electricity-generating Solar Array Wings (SAWs), as well as the Photovoltaic Thermal Control System (PVTCS) and Photovoltaic Radiator (PVR)—was delivered and installed by the STS-97 shuttle crew on 3 December 2000, where it provided early power-producing capability, before being moved to its final location at the furthest-outboard port-side of the ITS on 30 October 2007, during STS-120.

Eight years on, tomorrow’s core task for Lindgren and Kelly can trace its heritage back to U.S. EVA-20 on 1 November 2012, when Expedition 33 spacewalkers Suni Williams and Aki Hoshide attempted to isolate an ammonia leak in P-6’s cooling system. It was speculated at the time that the leak possibly arose following a Micrometeoroid Orbital Debris (MMOD) strike to its PVR or possibly resulted from age-induced cracking, but by mid-2012 the leak had increased to 5.2 pounds (2.4 kg) per year. This represented about ten percent of P-6’s original load of ammonia coolant and, in turn, raised the alarming risk that its critical “2B” power channel—which carries major electrical loads across the entirety of the space station—could have been forced to shut down before the end of 2012.

Williams and Hoshide’s EVA isolated the 2B coolant loop and deployed the accordion-like Trailing Thermal Control Radiator (TTCR) for subsequent cooling, allowing engineers to pinpoint the exact location of the ammonia leak. However, six months later, in May 2013—shortly before the return to Earth of the Expedition 35 crew—ammonia “snow” was seen emanating from the 2B power channel, which necessitated the contingency U.S. EVA-21 by spacewalkers Chris Cassidy and Tom Marshburn. The pair were unable to locate the source of the leak, but removed, replaced and tested a suspect Pump Flow Control Subassembly (PFCS), which was expected to yield additional clues for investigators in their search for a solution. Almost 30 months later, Lindgren and Kelly will set out to restore the P-6 cooling system to its original state, prior to U.S. EVA-20.

According to Mr. Thomason, tomorrow’s activity at the P-6 worksite will be divided into four categories. Firstly, the astronauts will re-integrate the Channel 2B PVR and admit ammonia into the radiator to cool its electronics, after which they will isolate the PVTCS and the Early External Thermal Control System (EETCS), which are currently linked together. “By isolating them,” Mr. Thomason explained, “it does put us in a better posture in case we did get another leak, as the systems are no longer tied together.” With the normal radiator returned to service, Lindgren and Kelly will retract the TTCR (nicknamed “the ticker”), cinch it down and install a protective thermal cover, in case it is needed in the future. Lastly, they will top off both ammonia systems.

“We do have enough ammonia in the systems to run now,” said Mr. Thomason at the 22 October media briefing, “but we want to have that extra margin in case we ever need it in the future. In order to do that, we have a pipeline that runs from the P-1 Ammonia Tank Assembly (ATA), all the way out to P-6. Most of that pipeline is already in place, but there is a section that’s about 20 feet (6.6 meters) long, over the Solar Alpha Rotary Joint (SARJ).” The latter is one of two alpha joints—one at the P-3/P-4 junction, the other on the starboard side of the truss, at the S-3/S-4 junction—which rotate the U.S.-built arrays and allow them to continuously track the Sun. “We can’t really have that in place,” said Mr. Thomason of the pipeline, “and still rotate the joint, so that’s stowed on the P-4 bulkhead,” requiring the spacewalkers to install a jumper, whose ends are both fitted with Fluid Quick Disconnects. The latter have proven “finicky from time to time,” notably during the EVA efforts by Expedition 24 spacewalkers Doug Wheelock and Tracy Caldwell-Dyson to remove and replaced a failed ammonia pump module on the S-1 truss in August 2010.

According to NASA’s Rob Navias, U.S. EVA-33 has required about six months of planning on the ground to get to the refined details, although he told AmericaSpace that this particular spacewalk was trained for by Kelly and Lindgren in the NBL prior to their respective launches aboard Soyuz TMA-16M in March and Soyuz TMA-17M in July. After leaving the Quest airlock, Lindgren will move via handholds along the port-side of the truss to the P-6 worksite, setting up a “slingshot” to gain the maximum length out of his tether. During this translation, he will stow the Vent Tool Bag at the TTCR, for use later in the EVA, before heading over to the Fluid Quick Disconnect Coupler. Joined by Kelly, the pair will remove and cover and drive a bolt to open a valve and permit ammonia flow into the PVR. As Lindgren breaks the connection and closes the valves which link the PVTCS and EETCS, Kelly will move to the P-3/P-4 junction to install a jumper across the SARJ to complete the ammonia-fill pipeline. Reaching the ATA, Kelly will reposition a jumper, in order to route ammonia from the tank into the fill line, as Lindgren sets up the Vent Tool and Vent Tool Extender in order to properly vent the fill line and thus avoid the risk of overpressurization.

After a brief leak check, Lindgren will mate the P-5/P-6 jumper over to P-6 and begin to fill the EETCS, before returning to the Early Ammonia Servicer (EAS) jumpers and initiating the filling of the PVTCS. With the ammonia loading process expected to require about 20 minutes, he will set to work with a Pistol Grip Tool (PGT) and, with about 50 turns, will drive a bolt and retract the TTCR, accordion-like, into its stowed configuration. Following the completion of ammonia filling, Lindgren will head back to the EAS jumpers, close the connection between the two systems and place them into a safe configuration to leave them isolated. He will then move to the P-5/P-6 jumper, break the connection in the fill line and route it to the Vent Tool and Vent Tool Extender. For the next 17 minutes, Lindgren will vent the fill line—following a virtually identical procedure as done by STS-134 spacewalker Drew Feustel in May 2011—and watch as ammonia is cleared from the system.

Later, both spacewalkers will head back to the SARJ. “We’ve had some vibrations in the data that we got down to the ground,” explained Mr. Thomason in the 22 October briefing, “and we think that’s because there’s a strut that’s loose.” To resolve this issue, Lindgren and Kelly will drive a bolt on two different struts, with no more than a fraction of a PGT turn expected to be necessary. Kelly will then remove the P-3/P-4 jumper across the SARJ and stow it, allowing for the resumption of movement of the alpha joint. Cleaning up their respective tools, the two men will reunite at the now-stowed TTCR and work together to install six cinches to compress the radiator, secure it in place, and prevent it from becoming damaged. During U.S. EVA-7 in February 2007, Expedition 14 Commander Mike Lopez-Alegria—whose record for the longest single U.S. space mission was last week broken by Kelly—installed a similar cinch, which required him to expend about ten pounds (4.5 kg) of force to push down the trailing radiator.

Lindgren and Kelly will then fit a thermal cover onto the TTCR, which is a two-person job, with one of them positioned on the space-facing (or “zenith”) side and the other at the Earth-facing (or “nadir”) side of the radiator. With this final major task complete, Kelly will return to the airlock, stowing the Vent Tool Extender bag, as Lindgren reconfigures the jumper at the ATA, moving it to the “vent” position, in case a future overpressurization of the system occurs. He will then pick up Kelly’s tether at the slingshot location and return back to Quest after approximately 6.5 hours.

Assuming that U.S. EVA-33 runs to the timeline, and when one takes into account the seven hours and 16 minutes which they both spent outside during last week’s U.S. EVA-32, Kelly and Lindgren can expect to accrue just shy of 14 hours of total spacewalking experience. According to Mr. Navias, no “get-ahead” tasks are scheduled for tomorrow’s spacewalk. One task deferred from U.S. EVA-32 was the removal of a cover and the installation of a Non-Propulsive Vent (NPV) onto the Tranquility node—previously removed during U.S. EVA-30 in February to provide adequate clearance for May’s relocation of the Leonardo Permanent Multipurpose Module (PMM)—and this will be performed at a later date.

 

 

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