Expedition 46 spacewalkers Scott Kelly and Tim Kopra today performed an “Unplanned EVA”, lasting three hours and 16 minutes, to successfully oversee the movement and latching-down of the stalled Mobile Transporter (MT) to Worksite 4 on the central S-0 truss of the International Space Station (ISS), ahead of the arrival of Russia’s Progress-MS cargo ship on Wednesday. The stall—which occurred last week, as outlined in an AmericaSpace article on Saturday—was apparently caused by one of the handles on the attached Crew and Equipment Translation Aid (CETA) cart being improperly positioned.
Assisted by the Robotics Officer (ROBO) and Capcom Mike Hopkins in the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas, the two spacewalkers completed the principal task of U.S. EVA-34 within a half-hour of leaving the Quest airlock and were directed to undertake a number of “get-ahead” tasks, associated with cable routing for the Commercial Crew-related International Docking Adapters (IDAs) and for Russia’s long-delayed Nauka (“Science”) Multipurpose Laboratory Module (MLM). “What a great day!” tweeted Expedition 46’s Tim Peake after the conclusion of the EVA. “Hard work getting @astro_tim and @StationCDRKelly safely out & back but they were awesome.”
Described as an “Unplanned EVA”—to differentiate from a “Contingency EVA” associated with one of the “Big 12” spacewalk tasks, required to tend to critical electrical, thermal control and other systems failures, which could potentially place the ISS into an unacceptable “Zero-Fault-Tolerant” state—the operation performed by Kelly and Kopra was significant and needed to be performed in relatively short order. As explained by ISS Operations and Integration Manager Kenny Todd last Friday, the MT had been in the process being robotically moved from Worksite 4, near the U.S. Destiny laboratory, out to Worksite 2, which resides midway along the starboard side of the 356-foot-long (108.5-meter) Integrated Truss Structure (ITS). It was being moved in support of ongoing Robotic Refueling Mission (RRM) payload operations, but stalled 6-8 inches (15-20 cm) “short” of Worksite 4.
Movement of the station’s Canadian-built Canadarm2 robotic arm and its Mobile Base System (MBS) is conducted by means of the 1,950-pound (885 kg) MT, which runs along the length of the ITS. Described as “the first railroad in space” at the time of its launch in April 2002, the MT—which measures about 9 feet (2.7 meters) wide and long, by about 38 inches (97 cm) in height—was installed during shuttle Atlantis’ STS-110 mission and travels on rails to enable Canadarm2 to reach various worksites along the length of the truss. It also supports the Crew and Equipment Translation Aid (CETA) hardware, which is utilized by spacewalking astronauts to move along the ITS.
The station’s robotic assets are required to be securely latched-down ahead of any dynamic events, such as maneuvers or the undocking and docking of Visiting Vehicles (VVs). The robotics team on the ground managed to move the MT within 4 inches (10 cm) back of Worksite 4, in the hope that it could be latched-down in readiness for the Progress M-28M departure on Saturday and the Progress-MS arrival on Wednesday, but according to Mr. Todd this was not enough. Although the team reviewed loads analyses and became comfortable with predicted perturbations across the ISS during efforts to maneuver the station into the proper Progress undocking/docking attitude, it was imperative that the MT was latched down in short order.
An EVA plan was finalized over the weekend and formally given the go-ahead on Sunday afternoon, whilst Expedition 46’s U.S. Orbital Segment (USOS) crew—consisting of Commander Scott Kelly and new arrivals Tim Kopra and Tim Peake—worked to prepare their Extravehicular Mobility Unit (EMU) space suits and tools. “Working weekend @space_station for likely #spacewalk,” tweeted Kelly on Saturday. “No easy job. Decision tmrw.” Added his British crewmate Tim Peake on Sunday: “Busy day on #ISS today preparing possible EVA for @astro_tim & @StationCDRKelly tomorrow. My job is to help them get out and back safely.”
Today’s spacewalk has become known as “U.S. EVA-34” and represents the 34th excursion performed in U.S.-built suits, conducted from the station’s Quest airlock, and performed in the absence of the Space Shuttle, since the inaugural U.S. EVA-1 by Expedition 4 astronauts Carl Walz and Dan Bursch, way back on 20 February 2002. Assisted by Peake, who served as the “Suit Intravehicular” (IV) crew member, and Russian cosmonaut Sergei Volkov—himself a veteran of three EVAs, totaling 18.5 hours—the spacewalkers undertook 60 minutes of “pre-breathing” on masks, during which time the inner “equipment lock” of Quest was depressed from its ambient 14.7 psi down to 10.2 psi.
Upon completion of this well-trodden, pre-EVA protocol, Kelly and Kopra donned and began the process of purging their EMUs at about 4:30 a.m. EST and the airlock’s atmosphere was repressurized back up to 14.7 psi. This enabled them to follow a nominal pre-breathing regime, 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—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, working about 45 minutes ahead of the timeline, Peake and Volkov transferred the fully-suited Kelly and Kopra and their gear from the equipment lock into the outermost “crew lock”.
Hatches between the two locks were closed just after 7 a.m., more than an hour ahead of the planned 8:10 a.m. start time, and the astronauts and cosmonauts stepped smartly through depressurization, halting briefly a 5 psi for pressure and leak checks, before resuming until the crew lock reached a condition of near-vacuum. U.S. EVA-34 officially began at 7:45 a.m. EST, about 25 minutes ahead of schedule, when Kelly and Kopra transferred their suits’ critical life-support utilities from ISS power onto internal batteries. Leading today’s spacewalk as “EV1”, with red stripes on the legs of his suit for identification, Kelly was first outside, followed by Kopra, designated “EV2” and clad in a pure white EMU. As soon as the spacewalk began, its choreography was assumed by Capcom Mike Hopkins in Mission Control, who is himself a veteran of two unplanned EVAs in December 2013.
Kelly and Kopra undertook customary “buddy checks” of each other’s suits and tethers, before starting out towards Worksite 4 and the stalled MT. And thus began one of the smoothest EVAs to date, as they positioned themselves close to the CETA cart—which was suspected to be at the root of last week’s stall, perhaps due to a stuck brake handle—in order to assist in a series of ROBO operations. In short order, ROBO was able to move the MT about 4.7 inches (12 cm) in a portward direction and by about 8:20 a.m. it had been successfully centered on Worksite 4. It was subsequently noted that an engaged brake was indeed the primary factor in the stall.
As ROBO set to work locking-down the MT at Worksite 4, Kelly and Kopra prepared for a number of “get-ahead” tasks. In his remarks on Friday, Kenny Todd explained that the penalty paid for preparing to go EVA leads to an inherent desire to get as much “additional” work done as possible and he directed his team “to look at those things that are out there in that general area that we might be able to do”. Those things turned out to the completion of International Docking Adapter (IDA) cable routing along the exterior of the Destiny and Harmony modules by Kelly, in anticipation of the arrival of two International Docking Adapters (IDAs) for Commercial Crew operations, and an Ethernet cable by Kopra in support of Russia’s long-delayed Nauka laboratory.
As the spacewalkers worked, the MT was successfully latched-down by 8:40 a.m., less than an hour into U.S. EVA-34. It had been expected that the excursion would last in the region of 3.5 hours and shortly after 10 a.m. EST Kelly and Kopra were beginning the process of wrapping up their tasks and heading back to Quest. The hatch was closed and locked and the spacewalk officially ended at 11:01 a.m., after three hours and 16 minutes, whereupon Capcom Mike Hopkins handed communications back over to Tim Peake to oversee the repressurization of the airlock. Returning inside the station at the end of his third career spacewalk—following U.S. EVAs-32 and 33 in October-November—Kelly has now accrued 18 hours and 20 minutes, whilst Kopra has concluded his second EVA, with a combined total of 8 hours and 48 minutes.
At least three more U.S. spacewalks are planned during the Expedition 46/47 increment, with the now-renumbered “U.S. EVA-35” anticipated between 15-19 January to remove and replace the failed Sequential Shunt Unit (SSU), belonging to Power Channel 1B on the station’s S-6 truss segment. Depending upon SpaceX’s Dragon launch manifest, this will be followed by a pair of U.S. EVAs in April 2016 to install and activate IDA-2 at the forward port of the Harmony node. In the meantime, Progress-MS was successfully launched from Baikonur Cosmodrome in Kazakhstan at 2:44 p.m. local time (3:44 a.m. EST) Monday and is currently tracking a rendezvous and docking at the Earth-facing (or “nadir”) Pirs module on Wednesday.
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