From the moment she transferred her critical life-support utilities from International Space Station (ISS) power to the internal batteries aboard her space suit, it was clear that Expedition 50 Flight Engineer Peggy Whitson was set to break records. At 7:29 a.m. EDT today (Thursday, 30 March), she became the first woman in history to record as many as eight discrete periods of Extravehicular Activity (EVA). Previously, Whitson’s career tally of seven EVAs was tied with fellow astronaut Sunita Williams. A little over four hours into today’s seven-hour and four-minute spacewalk, Whitson also exceeded Williams’ record for the greatest number of EVA hours by a woman; a record she is expected to advance yet further on Friday, 7 April. Both achievements come less than two weeks after Whitson became the first woman to log a cumulative 500 days in space.
Designated “U.S. EVA-41”, today’s spacewalk was the 41st excursion performed by crew members in U.S.-built Extravehicular Mobility Unit (EMU) suits from the station’s Quest airlock, in the absence of the Space Shuttle. Unlike last week’s EVA-40, in which Expedition 50 Commander Shane Kimbrough and Flight Engineer Thomas Pesquet worked independently for virtually all of their time outside, today’s spacewalk required Kimbrough and Whitson to work closely together. Their core goal was to reconnect cables between Pressurized Mating Adapter (PMA)-3 at the space-facing (or “zenith”) Common Berthing Mechanism (CBM) of the Harmony node and attach Micrometeoroid Orbital Debris (MMOD) shielding. This will provide protection at PMA-3’s permanent location at the forward-facing end of the station’s U.S. Orbital Segment (USOS).
As outlined previously by AmericaSpace, PMA-3 is one of the oldest components aboard the ISS. Launched in October 2000, it served as a docking port for two shuttle missions, before being relocated several times in the first decade of the 21st century, as new pressurized modules arrived. In February 2010, it wound up installed on the port side of the newly-arrived Tranquility node—partly for storage, partly for MMOD protection of the node’s port-facing CBM—where it remained for more than seven years.
PMA-3 subsequently received a new lease of life as a secondary docking port for the Commercial Crew Program, which will see it potentially greet incoming Boeing CST-100 Starliners and SpaceX Crew Dragons from mid-2018 onwards. This required its relocation to the Harmony-zenith interface, because Tranquility-port would have created clearance issues with the station’s expansive Solar Array Wings (SAWs) and radiators. During EVA-40, Kimbrough disconnected cables from PMA-3, preparatory to its relocation. Last Sunday (26 March), ground-based controllers moved PMA-3 with the 57.7-foot-long (17.6-meter) Canadarm2. In an approximately 3.5-hour operation, the adapter was translated away from the port-facing end of Tranquility and swung delicately into position atop Harmony. This set the scene for one of today’s critical EVA-41 tasks.
Yesterday (Wednesday), the astronauts completed final in-depth briefings and reviews of documentation, as well as configuring tools, installing batteries into EMUs #3008 (Kimbrough) and #3006 (Whitson) and checking suit systems for integrity. Early Thursday morning, they awoke early, with Pesquet and fellow Expedition 50 crewmate Oleg Novitsky overseeing the EVA preparations inside the Quest airlock. “Today is @astro_kimbrough and @astroPeggy’s turn to go out,” Pesquet tweeted at 3:50 a.m. EDT. “I will be in charge of the @Space_Station while they are on their #spacewalk.” However, unlike EVA-40, no Canadarm2 support will be required for the crew, allowing Pesquet to devote his time to monitoring the progress of his colleagues outside.
Kimbrough and Whitson marched smoothly through 60 minutes of pre-breathing on masks, during which time the inner “equipment lock” of Quest was depressed from its ambient 14.7 psi to 10.2 psi. The EMUs were purged and the airlock’s atmosphere was repressurized back up to 14.7 psi to allow the spacewalkers to head into a nominal pre-breathing regimen of about 50 minutes. Soon after 6 a.m. EDT, Kimbrough and Whitson began 50 minutes of In-Suit Light Exercise (ISLE) to rapidly remove nitrogen from their bloodstreams—and avoid a potentially fatal attack of the “bends”—and the fully-suited duo were manhandled from the equipment lock into Quest’s outer “crew lock” by Pesquet and Novitsky shortly after 6:30 a.m.
Monitoring these steps were the “Orbit 2 Team” in the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas. Leading the team was Flight Director Emily Nelson, who observes ten years as a qualified flight director in 2017 and had been handed responsibility to oversee EVA-41 by fellow Flight Director Greg Whitney. By the time the EVA started, a pair of Capcoms were on-console: veteran spacewalker Steve Bowen as “ISS Capcom” and “rookie” astronaut Ann McClain as “EVA Capcom”. Also on hand to oversee today’s events was EVA-41 Spacewalk Officer John Mularski.
Hatches between the two locks were closed by Pesquet a little before 6:50 a.m., allowing for the depressurization of the crew lock to commence. This process paused briefly at 5 psi around 7:05 a.m. and at 2 psi a few minutes thereafter, for standard leak checks, before decreasing down to a condition of near-vacuum, hitting 0.5 psi a little after 7:20 a.m. In the final moments, the spacewalkers were told that they would emerge into orbital darkness when the EVA began and advised to switch on their helmet lights. At 7:29 a.m., Kimbrough and Whitson transferred their suits to battery power, officially kicking off EVA-41 and setting the first of several records for the world’s No. 1 female spacefarer.
Fittingly, perhaps, it was Whitson who was first to depart the airlock, followed in short order by Kimbrough. “Beneath” them, the two spacewalkers beheld the expansive grandeur of the Pacific Ocean, 255 miles (410 km) beneath their boots. The pair performed customary “buddy checks” of their suits and tethers, before proceeding to their initial work sites. Kimbrough headed along the airlock “spur”, towards the S-0 truss, where he was tasked with removing the second of two External Multiplexer-Demultiplexers (EXT/MDMs) and replacing it with an upgraded Enhanced Processor & Integrated Communications (EPIC) MDM. As outlined in AmericaSpace’s EVA-40 article, Kimbrough performed a similar procedure on the other MDM at the same location last Friday.
Although neither EXT/MDM is exhibiting any faults, they are being replaced with the EPIC MDMs, which privide greater data bandwidth and ethernet capability for payload services. By 8 a.m., Kimbrough was already hard at work with a Pistol Grip Tool (PGT) to extract the EXT/MDM box. Despite experiencing difficulties with the requisite number of PGT turns, he had removed the EXT/MDM by 8:15 a.m. and set to work inspecting the EPIC MDM, prior to installing it.
As Kimbrough tackled the MDM task, Whitson threaded her way around the airlock to reach External Stowage Platform (ESP)-2. She then proceeded along the “top” of the U.S. Destiny lab and Harmony node, to reach the newly relocated PMA-3 around 8 a.m. Whitson’s first major objective on EVA-41 was to hook up a pair of heater cables, which will allow the adapter to pressurize and allow for stowage to be put back inside. She then set to work on her second task, to remove the MMOD cover from the end of PMA-3.
The cover had previously protected PMA-3’s docking port whilst at the Tranquility port location, but in view of its upcoming use for Commercial Crew operations it had to be removed. This will enable an International Docking Adapter (IDA) to be installed onto the end of PMA-3 early in 2018, thereby reconfiguring it from the shuttle-era Androgynous Peripheral Attach System (APAS)-95 to Boeing’s new Soft Impact Mating and Attenuation Concept (SIMAC) for future CST-100 Starliner and Crew Dragon visitors.
By 8:30 a.m., Whitson had successfully removed the MMOD cover and about 15 minutes thereafter she had begun bagging it up for return to the airlock. At about the same time, Kimbrough wrapped up the installation of the EPIC MDM and bagged up the old EXT/MDM, before joining Whitson to finish bagging up the MMOD cover. Returning to Quest, their next task was to collect a set of Axial Shields for installation onto Tranquility’s port-side CBM. The axial ports on the USOS do not possess CBM “petals” and the removal of PMA-3 has left an area of the hatch exposed to potential MMOD damage.
No further use of Tranquility’s port-side CBM is expected for another two years. It will eventually become the home of NanoRacks’ commercial airlock module, which is scheduled for launch in 2019. This was officially announced last year as a partnership between NanoRacks and Boeing with NASA, via a Space Act Agreement, to install the first-ever private airlock aboard the space station. Boeing will fabricate a passive CBM for the new airlock, which is expected to see CubeSats and other deployable scientific payloads in the coming years. More recently, in February 2017, NASA announced that it had formally accepted NanoRacks’ proposal to develop the airlock.
As a result, Tranquility’s port-side CBM risked exposure to MMOD damage for a highly undesirable two years. Kimbrough and Whitson set to work transporting a pair of Axial Shields from their stowage location outside Quest to the installation site. They translated from the airlock, over the top of the Unity node, then below the junction between Tranquility and the Bigelow Expandable Activity Module (BEAM), before finally arriving at the far-port end of their destination. In addition, two other Axial Shields had been stowed outside Tranquility during EVA-38 in January, making a total of four shields to provide protection of each of the four “quadrants” of the port-side CBM.
Then, shortly after they began to work, one of the shields apparently slipped from Kimbrough’s gloved fingers a few minutes after 10 a.m.
“Wait, I don’t have the shield,” he said with concern.
“Where is it?” queried Whitson.
“I don’t know. Can’t see it.”
Mission Control quickly confirmed that it was floating away, passing one of the station’s external radiators. The inadvertent loss brought back unpleasant reminders of spacewalker Heidemarie Stefanyshyn-Piper losing a Crew Lock Bag (CLB)—laden with a pair of grease guns, scrapers, wipers and tool caddies—during her first EVA on the STS-126 shuttle mission, way back in November 2008. By unfortunate coincidence, Kimbrough was one of Stefanyshyn-Piper’s crewmates on that mission.
As a result of today’s incident, three Axial Shields were fitted to three of the four “quadrants” around Tranquility’s port-side CBM, with the fourth left exposed. NASA noted that one quadrant remained “exposed to the elements” for the present time, with an expectation that the lost shield would offer no “recontact” risk with the ISS and should burn up harmlessly in the atmosphere in a few days. Meanwhile, an undeterred Kimbrough and Whitson proceeded to close the flap over the Centerline Berthing Camera System (CBCS) in the middle of the port-side CBM.
Amid the disappointing loss of the Axial Shield was a moment of triumph at 11:51 a.m. EDT, when Whitson surpassed Sunita Williams’ record of 50 hours and 40 minutes, becoming the world’s most experienced female spacewalker, in addition to her already-secured records for the greatest number of EVAs by a woman. She is also the oldest woman ever to perform a spacewalk, aged 57. At around the same time, the astronauts received the welcome news that the heaters aboard PMA-3 had been brought successfully back online. However, they were called back to the airlock, as discussions proceeded on the ground about what to do about the missing Axial Shield. At length, Capcom Ann McClain advised them that the recently removed MMOD cover from PMA-3 would be utilized as a stop-gap Axial Shield for the exposed fourth quadrant on Tranquility.
By 12:20 p.m., the impromptu repair was completed, with the former MMOD cover secured and tacked into place, protecting the node from the risk of debris or micrometeoroid impacts. The disappointment steadily began to lift, as McClain advised them to press ahead with an already-scheduled task of installing additional MMOD shielding—nicknamed “cummerbunds”, on account of their appearance—around the “waist” of PMA-3. The need for these cummerbunds arose because of PMA-3’s offset-conical shape, which creates a “slanting” configuration in its new position atop Harmony zenith. This configuration exposes areas at the base of the docking adapter to potential MMOD damage.
The cummerbund installation was completed as EVA-41 approached the six-hour mark, with McClain asking Kimbrough to translate to Harmony’s Earth-facing (or “nadir”) port to perform a photographic inspection of the CBM. “Documenting a build-up of contamination on the sealing surface of the Node 2 Nadir CBM,” NASA noted, “& using a scraper to clean it up.” This particular port is one of two interfaces—the other being at Unity nadir—set aside for unpiloted Visiting Vehicles, including Japan’s H-II Transfer Vehicle (HTV), Orbital ATK’s Cygnus and SpaceX’s Dragon. Most recently, it hosted the CRS-10 Dragon in February-March 2017.
According to NASA TV, the official end of EVA-41 occurred at 2:33 p.m. EDT, after seven hours and four minutes. Kimbrough and Whitson can reflect upon a job well done after an excursion likened to Apollo 13 in terms of responding to unexpected challenges. Wrapping up her record-breaking eighth excursion—and having extended her own record, set in January, for the world’s oldest female spacewalker—Whitson has secured a personal career tally of 53 hours and 22 minutes, surpassing NASA astronaut Rick Mastracchio to enter fifth place on the world EVA list. If her next 6.5-hour spacewalk, next Friday, runs to timeline, she will surpass both John Grunsfeld and Jerry Ross to enter third place, behind Mike Lopez-Alegria and the current world record-holder, Anatoli Solovyov. Not to be left outdone, Kimbrough concluded his sixth career spacewalk, and his fourth EVA of Expedition 50, with a total of 39 hours exactly. This establishes him within the Top 40 most experienced spacewalkers of all time.