On a day which spelled calamity for SpaceX—as its Upgraded Falcon 9 booster, laden with Israel’s Amos-6 communications satellite, suffered a catastrophic failure during fueling at Cape Canaveral Air Force Station, Fla.—a pair of astronauts sailed smoothly through a lengthy Extravehicular Activity (EVA) outside the International Space Station (ISS). Expedition 48 spacewalkers Jeff Williams (EV1) and Kate Rubins (EV2) spent six hours and 48 minutes in the near-total vacuum of space, retracting and securing the Trailing Thermal Control Radiator (TTCR) and tending to several other important tasks. Their EVA comes only days before Williams and his Russian crewmates Alexei Ovchinin and Oleg Skripochka are due to return to Earth, aboard Soyuz TMA-20M.
Designated “U.S. EVA-37,” today’s spacewalk represented the 37th excursion in U.S.-built Extravehicular Mobility Units (EMUs) and conducted from the space station’s Quest airlock, without the presence of a space shuttle, since February 2002. It followed hard on the heels of the highly successful U.S. EVA-36 on 19 August, during which Williams and Rubins installed the International Docking Adapter (IDA)-2 onto Pressurized Mating Adapter (PMA)-2 on the forward face of the Harmony node. A subsequent EVA was timelined, but was brought forward following delays to Orbital ATK’s OA-5 Cygnus cargo ship—whose launch aboard the first Antares 230 rocket is now expected to occur no sooner than 13 October—and to Japan’s H-II Transfer Vehicle (HTV)-6, whose own target launch date of 1 October has been postponed, following the discovery of leaking pipework. This opened up a “window” of time in the Expedition 48 crew’s schedule to support a second EVA and thus put a number of important ISS maintenance tasks behind them.
Perhaps the most important was the retraction of the accordion-like TTCR. As outlined in AmericaSpace’s U.S. EVA-37 preview, this originally formed part of the Early External Active Thermal Control System (EEATCS) on the P-6 element of the Integrated Truss Structure (ITS). After installation in late 2000, it provided early ammonia cooling capabilities, before being retracted in early 2007, shortly before P-6 itself was relocated from the Z-1 truss to its permanent perch at the furthest-port “end” of the ITS. However, a very slow ammonia leak from late 2006 onward got progressively worse and necessitated the redeployment of the TTCR in November 2012 to provide interim cooling as engineers explored a suspected problem with the main Photovoltaic Radiator (PVR). At length, a failed Pump Flow Control Subassembly (PFCS) was identified as the root cause and replaced, allowing plans to be set in motion to once again retract the TTCR.
Despite its age, the value of the old radiator—nicknamed “the ticker”—as a high-priority spare makes it desirable to retract and cover it, thereby keeping it protected and in good condition, in the event that it is ever needed again. Last November, spacewalkers Kjell Lindgren and Scott Kelly successfully retracted the TTCR, but a combination of factors prevented them from fully cinching it down and closing its Micrometeoroid Orbital Debris (MMOD) shroud. As a result, it was redeployed, with the intention that its retraction would be tackled by another EVA crew in the fall of 2016. Delays to both OA-5 and HTV-6 have allowed that EVA task to be correspondingly brought forward.
In readiness for U.S. EVA-37, Williams and Rubins have spent the last several days collecting tools and reviewing timelines. Early Thursday, joined by their Expedition 48 crewmates Takuya Onishi of Japan and Anatoli Ivanishin of Russia, they spent about 60 minutes pre-breathing on masks in the station’s Quest airlock. The inner “equipment lock” was depressed from its ambient 14.7 psi to 10.2 psi, allowing them to check and purge their suits. The airlock was then repressurized back up to 14.7 psi, allowing Williams and Rubins to undertake a nominal pre-breathing regime on masks, followed by about 50 minutes of In-Suit Light Exercise (ISLE). Shortly afterwards, Onishi and Ivanishin transferred the fully suited pair from the equipment lock into Quest’s outer “crew lock” and closed the connecting hatches. Depressurization of the crew lock got underway shortly after 7 a.m. EDT.
With a scheduled EVA start time of 8:05 a.m., the crew and Mission Control worked ahead of the timeline and the spacewalkers transferred their suits’ life-support utilities to battery power and U.S. EVA-37 began at 7:53 a.m. Embarking on his fifth career spacewalk, Williams—identified by the presence of red stripes on his suit—was first to leave the airlock, followed in short order by Rubins, who became one of only seven women in history to have performed more than one EVA. As is customary immediately after egress, the duo set to work on “buddy checks” of each other’s suits, tethers, tools, gloves, and Helmet Absorption Pads (HAPs). Williams then headed along the airlock “spur” to the ITS, where he set tethers for himself and Rubins on the P-1 truss, before translating along the port side of the ITS to reach P-6 at the far end.
By 8:30 a.m., a little more than a half-hour into the EVA, both spacewalkers had reached the TTCR worksite, slightly ahead of the timeline. Williams positioned himself at the Earth-facing (or “nadir”) side of the truss, with Rubins at the space-facing (or “zenith”), and the pair conducted visual inspections to ensure that no debris blocked the retraction. Williams then set to work with a Pistol Grip Tool (PGT) and, within about 12 minutes, the TTCR had retracted into its stowed configuration. Rubins noted some possible MMOD damage to the old radiator, which was photographed, and a little after 9 a.m. the spacewalkers completed the installation of four cinches to secure the TTCR in place. Next, they removed wire ties and covered the radiator with its MMOD shroud, a task which was wrapped up by 10 a.m.
With the primary objective of U.S. EVA-37 thus behind them, Williams and Rubins pressed on with their secondary tasks. Williams collected an Articulating Portable Foot Restraint (APFR), which he mounted onto the 57.7-foot-long (17.6-meter) Canadarm2 mechanical arm, deftly manipulated by Takuya Onishi. Meanwhile, Rubins returned to the airlock to collect Orbital Replacement Unit (ORU) bags, containing a replacement light for the Camera Group (CG)-9 location on the P-1 truss and the External High Definition Camera Assembly (EHDCA). After ingressing the APFR, Williams was moved to the P-1 worksite, where he made short work of removing an old, burned-out light and fitting and securing its replacement. Three hours into the EVA, a little after 11 a.m., the new light was in place and confirmed to be fully functional, as Williams successfully installed the EHDCA.
Controlled from the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas, the EHDCA forms part of the ISS Communications and Tracking System and is designed “to provide an external high-definition video capability to view Earth and ISS.” Four locations at the Camera Port (CP)-3, 8, 9 and 13 sites on the ITS will provide a home for the modified Nikon D4 DSLR cameras, with 28-300 mm lenses. In addition to Earth observations, these cameras will provide high-definition imagery of visiting vehicles, specifically piloted Soyuz craft.
As Williams labored on replacing the CG-9 light and installing the EHDCA camera, Rubins returned along the port-side truss to the Solar Alpha Rotary Joint (SARJ). This is one of a pair of massive joints, each weighing around 2,500 pounds (1,130 kg), which rotate the space station’s port-side and starboard-side solar array groups to continuously track the Sun. Her primary task was to tighten three struts on the SARJ and perform a visual inspection, after which the spacewalkers wrapped up their work with a Multi-Layered Insulation (MLI) task and a check of the brakes on the Crew and Equipment Translation Aid (CETA) cart. Hopes to inspect and photograph the status of the Alpha Magnetic Spectrometer (AMS) were called off as the EVA closed in on the six-hour mark, and Williams and Rubins cleaned up their respective worksites and headed back to Quest.
U.S. EVA-37 ended at 2:41 p.m. EDT, after six hours and 48 minutes. This pushes Williams’ career total up to 31 hours and 54 minutes across five EVAs, making him the 43rd most experienced spacewalker in the world. In total, 216 men and women from Russia, the United States, France, Germany, Japan, Switzerland, Canada, Sweden, China, Italy, and the United Kingdom have performed spacewalks since Alexei Leonov’s pioneering excursion into vacuum, way back in March 1965. As for Rubins, she becomes only the seventh woman—after Kathy Thornton, Linda Godwin, Peggy Whitson, Heidemarie Stefanyshyn-Piper, Sunita Williams, and Tracy Caldwell-Dyson—to complete more than one EVA. As such, with a cumulative 12 hours and 45 minutes across her two EVAs from Expedition 48, she is now the world’s sixth most seasoned female spacewalker.