Two astronauts representing the Marine Corps and Army branches of the U.S. Armed Forces ventured outside the International Space Station (ISS), earlier today (Thursday, 5 October), to conduct the first major maintenance on the 57.7-foot-long (17.6-meter) Canadarm2 robotic arm. Expedition 53 Commander Randy “Komrade” Bresnik, making the third Extravehicular Activity (EVA) of his career, and first-time spacewalker Mark “Sabot” Vande Hei spent six hours and 55 minutes removing Latching End Effector (LEE)-A and replacing it with a spare unit. This was a change to original plans for this month’s batch of EVAs, following the 22 August “stall” of the latching mechanism at the LEE-A “end” of the arm. Bresnik and Vande Hei’s work has now positioned the 16-year-old Canadarm2 into a more operational state, ahead of its planned use in November to capture both Orbital ATK’s OA-8 Cygnus and SpaceX’s CRS-13 Dragon cargo vehicles.
As outlined earlier this week by AmericaSpace, plans for the removal and replacement of both ends of Canadarm2—known as “LEE-A” and “LEE-B”—have been in work for some time. The arm uses both LEEs to “inchworm” its way from worksite to worksite, plugging its power and data grapple fixtures into receptacles on the expansive Integrated Truss Structure (ITS) and allowing it to perform operations in support of science, maintenance and visiting vehicles. Unsurprisingly, in recent years, “wear-and-tear” degradation in both LEEs has manifested itself through increased motor currents within the latches, which draw more motor current than should ordinarily be the case. According to Jacklyn Kagey, lead spacewalk officer for today’s EVA, the original intent when planning got underway in July 2017 was to remove and replace the LEE-B end. Then, on 22 August, during a walkoff operation of the arm in support of a maintenance task, the LEE-A latches stalled, posing a more immediate risk to the system. It was decided that LEE-A would be replaced first and LEE-B will be changed out during an EVA in January-February 2018.
Canadarm2 is, in the words of ISS Operations Integration Manager Kenny Todd, an “absolutely critical asset” to the station program. Since its launch aboard shuttle Endeavour in April 2001, it has supported the delivery of several major components—beginning with the Quest airlock—in addition to the capture and berthing of 25 unpiloted cargo ships, including six Japanese H-II Tranfer Vehicles (HTVs), 12 SpaceX Dragons and seven Orbital ATK Cygnuses. Designed for a ten-to-15-year lifespan, the arm has operated with surprisingly few anomalies. During initial checkout in May-June 2001, it endured a spate of backup software glitches, associated with its shoulder pitch joint, and in March 2002 a failure occurred in its wrist roll joint, which triggered LEE degradation. The wrist roll joint was later replaced by spacewalkers on the STS-111 shuttle mission in June 2002. Since then, Canadarm2 has operated admirably, most recently receiving lubrication of its LEEs during Expedition 42 in February 2015 and Expedition 50, earlier this year.
Preparations for today’s spacewalk, designated “U.S. EVA-44”—the 44th excursion, carried out in U.S.-built Extravehicular Mobility Units (EMUs), in the absence of the Space Shuttle—formally got underway several weeks ago, when the incumbent Expedition 53 crew set to work readying their suits, tools and procedures. Although Randy Bresnik has chalked up 11 hours and 50 minutes of previous spacewalking time, his colleague Mark Vande Hei was making his first foray into open space. And the excitement certainly showed. “Spacewalk coming up!” Vande Hei tweeted. “@AstroKomrade and I, with a whole lotta support, will change the end effector on that (big) puppy for a better one.”
And that “puppy” certainly is big. Described by Canadian Space Agency (CSA) liaison Tim Braithwaite as “one of the most complex electromechanical packages that we’ve flown in space”, the LEE weighs around 500 pounds (225 kg). In addition to the trouble-prone end-effectors, there were two “spares” aboard the station, one affixed to the Payload Orbital Replacement Unit (ORU) Accommodation (POA) on the Mobile Base System (MBS) and the other on ExPRESS Logistics Carrier (ELC)-1 on the port side of the truss. The spare on the MBS POA would be used by Bresnik and Vande Hei.
With a unique situation of four crew members on the U.S. Orbital Segment (USOS) “side” of the station, the spacewalkers had plenty of support this morning, with Joe Acaba assisting them with the suiting-up process in the Quest airlock, assisted by Italian astronaut Paolo Nespoli, who pulled double-duty at the controls of Canadarm2. Bresnik and Vande Hei spent about 60 minutes “pre-breathing” on masks and the inner “equipment lock” was depressed from its ambient 14.7 psi to 10.2 psi, allowing for suit checks and purging. It was then repressurized back up to 14.7 psi, allowing the astronauts to undertake a nominal pre-breathing regimen and 50 minutes of In-Suit Light Exercise (ISLE).
Just after 7 a.m. EDT, Acaba and Nespoli transferred the fully-suited duo from the equipment lock into the outer “crew lock” and closed the connecting hatches. Depressurization of the crew lock got underway shortly thereafter and reached a condition of near-vacuum at 0.5 psi. Bresnik and Vande Hei transferred their suits’ life-support utilities to battery power and U.S. EVA-44 officially began at 8:05 a.m. Today’s activities were led by the Orbit-2 Team in the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas, led by Flight Director Tony Ceccacci, with veteran astronaut Mike Hopkins serving as Capcom. The spacewalkers were greeted by the glorious view of Egypt and Israel, passing “beneath” them.
“One small step for man and one giant leap for Sabot,” was the summary of Vande Hei’s first translation as a spacewalker, using his nickname. The initial task upon leaving Quest was to perform “buddy checks” of each other’s suits, including gloves and Helmet Absorption Pads (HAPs), together with tethers and tools. Bresnik then headed along the airlock “spur” to reach the worksite at the P-1 truss and Vande Hei moved to collect two Articulating Portable Foot Restraints (APFRs) from External Stowage Platform (ESP)-2. He then joined Bresnik, with both spacewalkers at the worksite and given a “Go” to egress their APFRs shortly before 9 a.m. Meanwhile, Nespoli—based at a Robotics Workstation (RWS) in the U.S. Destiny lab—expertly maneuvred Canadarm2 into position, between them.
This established the proper conditions for the spacewalkers to conduct the LEE-A removal task and Bresnik first released a pair of Multi-Layered Insulation (MLI) blankets to uncover the joint interface. The astronauts then worked together to release two of six Expandable Diameter Fasteners (EDFs), a process completed by 9:15 a.m. The arm was then rotated and powered-down a few minutes later, allowing them to reach and release the remaining four EDFs and the mate-demate mechanism. With these fasteners released, the LEE-A was detached from the end of the arm shortly before 9:30 a.m. and temporarily stowed on the Port Crew and Equipment Translation Aid (CETA) cart on the truss.
By this stage, the astronauts were working about 15 minutes ahead of the timeline. Bresnik and Vande Hei headed to the MBS, where they released the six EDFs holding the spare LEE in place. The new end-effector was freed from the MBS POA by 10:15 a.m., a little over two hours into the EVA. They transferred it to the worksite, inspected its interfaces and installed four EDFs to an “initial torque”. When this was complete, Canadarm2 was powered-up shortly before 11 a.m. and rotated to enable them to install the other two EDFs and perform a “final torque” on all six.
After photographing their work, the duo completed the installation of MLI blankets at 11:30 a.m. and began cleaning up the worksite and heading back to Quest. They were notified that the newly powered-up Canadarm2 was performing beautifully, to which both spacewalkers exulted: “Awesome!” Working well ahead of the timeline, the astronauts were assigned a couple of get-ahead tasks. Bresnik removed some MLI from the Direct Current Switching Unit (DCSU) on ESP-2, whilst Vande Hei worked to prepare a spare 900-pound (400 kg) Flex-Hose Rotary Coupler (FHRC). This work was designed to alleviate pressures on spacewalking and Mission Control teams further down the road.
Wrapping up the third EVA of his career, Randy Bresnik has now accrued 18 hours and 45 minutes, whilst Mark Vande Hei has logged six hours and 55 minutes from his first spacewalk. Uniquely, Vande Hei’s astronaut class, selected in June 2009, is chalking up an impressive EVA experience base. Every U.S. member of the class flown to date—Mike Hopkins, Reid Wiseman, Kjell Lindgren, Kate Rubins and Jack Fischer—has performed two spacewalks, with Vande Hei’s second excursion slated for Tuesday, 10 October, with Bresnik.