Expedition 46 astronauts Tim Kopra of NASA and Britain’s Tim Peake have completed a somewhat truncated four-hour and 43-minute spacewalk outside the International Space Station (ISS), successfully replacing a failed Sequential Shunt Unit (SSU) and tending to a number of “get-ahead” tasks, including power and data cable installation, ahead of the expected debut of Commercial Crew vehicles by mid-2017. The duo also supported the re-installation of a Non-Propulsive Valve (NPV) onto the Tranquility node, but the completion of the cabling work and a couple of other activities were called off and U.S. EVA-35 terminated early when water was spotted inside Kopra’s helmet. This brought back unpleasant memories of a water-intrusion incident in Italian astronaut Luca Parmitano’s suit, back in July 2013, and it was prudent for the EVA to be curtailed in the interests of safety. Wrapping up his third career EVA, Kopra now has a total of 13 hours and 31 minutes of spacewalking time under his belt, whilst Peake—who last month became Britain’s first “official” astronaut, formally sponsored by the UK Government—was embarking on his first excursion into vacuum.
As outlined in AmericaSpace’s U.S. EVA-35 preview article, today’s spacewalk represents the 35th time that astronauts have departed the station’s Quest airlock, clad in U.S.-built Extravehicular Mobility Unit (EMU) suits, and without a space shuttle being present, since U.S. EVA-1 in February 2002. The anticipation in the UK for the EVA was not lost on the Expedition 46 crew, which currently consists of Commander Scott Kelly of NASA and his Russian crewmates Mikhail Kornienko, Sergei Volkov, and Yuri Malenchenko, together with Kopra and Peake. Tweeting a spectacular night-time view of a sleeping Northern Europe on Thursday, Kelly noted that it was the 293rd day of his (almost) year-long mission with Kornienko and added: “#Spacewalk on a new dawn & #UK will have a new star out there!” For Peake, who completed the final On-Orbit Fit Verification (OFV) checks of his suit on Monday, the eagerness to get outside for the first EVA of his career was palpable. “Popping outside for a walk tomorrow,” he tweeted to his 322,000 followers, late Thursday, but added: “Exhilarated—but no time to dwell on emotions.”
His comments were greeted with well-wishes from several other astronauts, including British-born Nick Patrick, who performed three spacewalks during the STS-130 shuttle mission to install the Tranquility node and multi-windowed cupola onto the space station, way back in February 2010. “Good luck @astro_timpeake!” Patrick tweeted Thursday. “Enjoy the view during your #ISS spacewalk.” Although several UK-born astronauts have performed EVAs previously—including Patrick himself, together with Mike Foale, who has four spacewalks to his credit, and Piers Sellers, who has six—they have done so in their capacity as dual-citizenship holders with U.S. nationality. All three wore the Stars and Stripes on the arm of their respective EMUs, whereas Peake wore the Union Jack. This marked the first time in history that the national flag of the UK has graced the space suit of a British national during an EVA.
Kicking off today’s activities, Kopra (designated “EV1,” with red stripes on the legs of his suit for identification) and Peake (“EV2,” clad in a pure white ensemble) undertook 60 minutes of “pre-breathing” on masks, during which time the inner “equipment lock” of the station’s Quest airlock was depressed from its ambient 14.7 psi to 10.2 psi. Assisted by Scott Kelly, who served as the Intravehicular (IV) crew member, they donned and purged their EMUs and the airlock’s atmosphere was repressurized back up to 14.7 psi. This allowed Kopra and Peake to begin a nominal pre-breathing regime at about 5:20 a.m. EST, lasting 50 minutes, followed by an additional 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 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. Assisted by cosmonaut Sergei Volkov, Kelly oversaw the transfer of Kopra, Peake, and their equipment from the equipment lock into the outer “crew lock” by about 7:10 a.m.
Depressurization of the crew lock commenced, pausing briefly at 5 psi for pressure and leak checks, before resuming until it achieves a condition of near-vacuum. U.S. EVA-35 officially began at 7:48 a.m., about seven minutes ahead of the timeline. With the primary objective of U.S. EVA-35 being the removal and replacement of a failed Sequential Shunt Unit (SSU) on Power Channel 1B—which serves to regulate electrical power output from one of the space station’s eight massive Solar Array Wings (SAWs)—Kopra brought out tools and Peake carried the replacement SSU.
“It looks great to see that Union Jack going outside,” opined Kelly from inside the airlock. “It’s explored all over the world; now it’s explored space.”
“Thank you, Scott, it’s great to be wearing it,” replied Peake, who became the 215th person in the history of the space program to perform an EVA, stretching back to Soviet cosmonaut Alexei Leonov in March 1965. “A huge privilege, proud moment.”
The duo performed customary “buddy checks” of each other’s suits, before Kopra led the way to the Starboard Crew and Equipment Translation Aid (CETA) cart to retrieve an Articulating Portable Foot Restraint (APFR), which he would need to stabilize himself at the SSU worksite. Connecting safety tether anchors for both himself and Peake at a handrail on the S-1 segment—which lies close to the center of the station’s 356-foot-long (108.5-meter) Integrated Truss Structure (ITS)—he then began the intricate process of translating along the truss toward its extreme starboard end. By 8:45 a.m., a little less than an hour into U.S. EVA-35, Kopra reached the worksite at the S-6 truss, which boasts a pair of SAWs and supports a pair of power channels, including the failed and isolated Power Channel 1B. A few minutes later, he was joined by Peake, who positioned himself to provide good visuals of the Removal & Replacement (R&R) task and pass tools to Kopra.
Due to the intricate nature of the work, and handling hardware components which could produce electrical output, the replacement task was timed to occur during the 45-minute “night” period of the station’s 90-minute orbit. “This time pressure,” explained Lead U.S. EVA-35 Spacewalk Officer Paul Dum, “means that it’s critical that the crew is ready to step into contingency procedures quickly, if necessary.”
After waiting until the onset of orbital darkness, the failed SSU was released by Kopra by 9:40 a.m. and presented to Peake for inspection, to ascertain any internal damage. Within about 20 minutes, the replacement SSU had been installed and secured into place, but it was at this point that a shadow fell over U.S. EVA-35. At first, it manifested itself in a possible “bad” carbon dioxide (CO2) sensor in Kopra’s suit, although the spacewalk was allowed to continue. Checks of both spacewalkers’ suits—including gloves and Helmet Absorption Pads (HAPs)—proved nominal and, working ahead of the timeline by a few minutes, Kopra and Peake headed into their second respective tasks.
First, Peake brought the failed SSU back to Quest and stowed it inside the crew lock at around 10:30 a.m. His next activity encompassed completing the installation of power and data cables, preparatory to the arrival of two International Docking Adapters (IDAs) for future use by Boeing and SpaceX Commercial Crew vehicles. First, he translated to the Earth-facing (or “nadir”) side of the U.S. Destiny laboratory, where he began routing cables, with one “leg” heading aft, towards the Unity node. Meanwhile, another leg of cables—supporting the Enhanced Processor & Integration Communications (EPIC) Multiplexer-Demultiplexer (MDM)—headed over the space-facing (or “zenith”) side of the lab and then in a portward direction.
“One of the key challenges EV2 Tim Peake will face during this portion of the EVA,” said Mr. Dum in a recent U.S. EVA-35 briefing, “will be the tightness of the translation path and the number of other cables that present snag hazards for him as he goes.” This was particularly apparent at the so-called “Rat’s Nest,” a closely packed area of cables at the central S-0 truss, which Peake was required to negotiate. Elsewhere, Tim Kopra had made short work of his second task, which called for the installation of a Non-Propulsive Valve (NPV) onto the port end-cone of the Tranquility node. The valve was removed by Expedition 42 Commander Barry “Butch” Wilmore during U.S. EVA-30 back in February 2015, in order to provide better clearance for the Leonardo Permanent Multipurpose Module (PMM) relocation in May. After several months stored inside the station, the installation of the NPV was to be performed by Kjell Lindgren during U.S. EVA-32 in October 2015, but deferred, and only now is it being returned to its original location. Kopra remove a cover plate, installed by Wilmore, then secured the NPV back into position with four bolts. By 11:45 a.m. EST, about four hours into U.S. EVA-35, he was able to declare success.
Having sustained a possible “bad” carbon dioxide sensor, earlier in the spacewalk, Kopra had pressed through subsequent glove and HAP checks, without incident. Then, shortly before midday EST, he reported the presence of water in his helmet, about 3 inches (7 cm) from his head. Instantly, this brought back unpleasant memories of the experience of Italian spacewalker Luca Parmitano, who suffered significant water intrusion into his helmet during U.S. EVA-23 in July 2013—after which a formal NASA investigation highlighted its potentially life-threatening implications—and it was not long before efforts to terminate U.S. EVA-35, as a precautionary measure, entered high gear.
As the two astronauts wrapped up their respective tasks and returned to the airlock, Peake noted that the water bubble in Kopra’s helmet was smaller than a golf ball. The decision was taken to allow Kopra to enter the airlock first, with Peake closing the hatch, and EV1 was back inside Quest by about 12:15 p.m. Britain’s first official spacewalker re-entered the station a few minutes later and sealed the outer hatch, with U.S. EVA-35 classified as successful in having accomplished its primary objective. All told, the EVA had run for four hours and 43 minutes, pushing Kopra up the experience table from his previous place as the 158th most experienced spacewalker to his current position at No. 118. Kopra now has 13 hours and 31 minutes of spacewalking time, across three EVAs. Meanwhile, Peake became the 215th person in history to perform a spacewalk and, by experience, is now the 189th most experienced spacewalker. Tweeting earlier this evening, Peake exulted that “Today’s exhilarating #spacewalk will be etched in my memory forever—quite an incredible feeling!”
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