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Spacewalkers replace ‘hand’ on space station robotic arm

Randy Bresnik, bottom, and Mark Vande Hei work to replace the Latching End Effector for the station's robotic arm. Photo Credit: NASA

NASA astronauts Randy Bresnik, bottom, and Mark Vande Hei work to replace a Latching End Effector for the station’s robotic arm. Photo Credit: NASA

Expedition 53 Commander Randy Bresnik and Flight Engineer Mark Vande Hei wrapped up the first of three spacewalks planned for the next two weeks. The October 5, 2017, spacewalk was nearly seven hours long and saw the replacement of one of the two Latching End Effectors (LEE) on the International Space Station’s robotic arm.

The robotic Canadarm2 has been in orbit since 2001. It was launched inside the payload bay of Space Shuttle Endeavour during the STS-100 mission to the ISS. Each end effector was designed with a 10-year lifetime. However, spacewalks in 2015 helped extend their life expectancies.

The Cygnus capsule and Canadarm2 during rendezvous and berthing operations on Jan. 12, 2014. The station's robotic arm is used for a variety of tasks ranging from spacecraft berthing to helping astronauts during spacewalks. Photo Credit: NASA

The Cygnus capsule and Canadarm2 during rendezvous and berthing operations on Jan. 12, 2014. The station’s robotic arm is used for a variety of tasks ranging from berthing spacecraft to assisting astronauts during spacewalks. Photo Credit: NASA

It was originally planned that LEE-B would be replaced before LEE-A; however, in August 2017, the latter suffered a motor stall within its latches, which prevented it from successfully completing base changes across the outpost.

Starting at 8:05 a.m. EDT (12:05 GMT) Oct. 5, the astronauts switched to suit-battery power on their Extravehicular Mobility Units to begin U.S. EVA-44. Bresnik was the lead spacewalker and wore the suit with red stripes; Vande Hei wore the suit with no stripes.

Once outside, the two made their way to the P1 truss segment on the port side of the outpost. There, already prepositioned, was the LEE-A side of the robotic arm. After installing foot restraints on the truss segment, the two began working to remove the end effector.

The LEE is attached to the arm wrist joint via six Expandable Diameter Fasteners. These were released by the astronauts using the space-grade equivalent of a power drill called a Pistol Grip Tool (PGT).

Once the first two fasteners were released, the LEE was commanded to rotate so that the spacewalkers could reach the other four. Once that maneuver was completed, the robotic arm was powered down.

With no problems, the duo removed the 440-pound (200-kilogram) end effector and tethered it to a temporary stowage location near the work area. The new LEE, located on the Mobile Base Unit, was removed from its current location and attached to the arm in a reverse fashion. Once four of the bolts were driven using the PGT, ground teams powered the robotic arm back on. This allowed for a 10-minute break for the astronauts.

After the power-up, the remaining bolts were driven and the primary task of the spacewalk was completed, some three hours into the EVA. While the duo began cleaning up their workspace and attaching the old LEE on the Mobile Base Unit, ground teams decided to give each astronaut a get-ahead task.

The two tasks involved removing a protective cover from a spare Direct Current Switching Unit, allowing it to be removed robotically in the future, and to prepare a Flex Hose Rotary Coupler for future operations. By the time those were finished, it was time to call it a day. The two astronauts made their way back to the airlock to conclude the spacewalk after 6 hours, 55 minutes outside the outpost.

Two more spacewalks are planned in October: one on the 10th; the other on the 18th. Both will be led by Bresnik; however, the second spacewalker will be Vande Hei on U.S. EVA-45 and Flight Engineer Joe Acaba for U.S. EVA-46. The second and third spacewalk of this series will be devoted to lubricating the newly replaced LEE as well as replacing cameras on the left side of the station’s truss and the right side of the Destiny laboratory module.

Today’s spacewalk was the 203rd in support of ISS assembly and maintenance since 1998. It was Bresnik’s third EVA of his career and Vande Hei’s first. Bresnik’s total is now at 18 hours, 45 minutes.



Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity. You can find him on twitter @TheSpaceWriter.

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