The first spacewalk of 2018, U.S. EVA-47, is now in the history books after two NASA astronauts completed a nearly 7.5 hour extravehicular activity to replace an aging latching end effector on the International Space Station’s robotic Canadarm2.
Canadarm2 has a latching end effector, also called a LEE, on either side of the 17-meter robotic arm to either grab onto the exterior of the station, move objects around the outpost, or grab visiting spacecraft.
Launched in 2001 during Space Shuttle Endeavour’s STS-100 mission, the Canadian-built arm was designed to be serviced and refurbished in orbit. As such, in 2015, both end effectors, LEE-A and LEE-B, were lubricated during several spacewalks to extend the life of the “hands” of the outpost.
But with the LEEs more than 15 years in age, it was time to replace them. LEE-A was replaced over the course of three spacewalks in October 2017.
LEE-B was replaced during this spacewalk, U.S. EVA-47. LEE-B was originally planned to be replaced first, but a motor stall in the latches of LEE-A prompted NASA to switch the order.
The two Expedition 54 astronauts that performed this spacewalk were NASA’s Mark Vande Hei, who wore the spacesuit with red stripes and was designated EV-1, and Scott Tingle, who wore a space suit with no stripes and was designated EV-2.
After suiting up and squeezing inside the station’s Quest airlock, the chamber that leads to the exterior of the outpost, was sealed off from the rest of the lab with the duo inside and slowly depressurized.
U.S. EVA 47 began at 6:49 a.m. EST (11:49 GMT) Jan. 23, 2018, when Vande Hei and Tingle switched their spacesuits to battery power.
Not long after the start of the spacewalk, the first of several time-delaying issues cropped up. Vande Hei’s Display and Control Module on his suit locked up requiring him to completely reboot his suit.
Once it was verified his equipment was working, he and Tingle moved to External Stowage Platform 2 to set up their work area. This involved placing two foot restraints on the platform so that the duo would be able to work on Canadarm2 with their feet attached to the station.
LEE-B was also at ESP-2. It was brought to the outpost during Space Shuttle Atlantis’ STS-129 mission in 2009.
The first order of business for the crew was to prepare the spare LEE for installation. This included removing insulation blankets and opening four launch locks to rotate the end effector upright allowing the astronauts to get to the ring where six bolts are holding it to the platform.
The first few bolts were released before the astronauts got onto their foot restraints to focus on the LEE-B attached to Canadarm2.
Just like on the spare, insulation blankets were removed to gain access to the ring attaching LEE-B to the arm’s wrist joint. The first two bolts were removed using the Pistol Grip Tool, a space-grade power tool. Once the bolts were released, Japanese astronaut Norishige Kanai, who was inside the station, commanded Canadarm2 to rotate LEE-B to give Vandi Hei access to the next set of bolts.
Once four were release, the LEE was rotated again to allow the final two of six to be released. Then Canadarm2 was powered down to prepare for the LEE-B to be removed.
Once released, Vande Hei held the 190 kilogram LEE-B while TIngle rotated Vande Hei’s restraint to put him in front of the temporary stow location at ESP-2. Four of six bolt’s were attached to secure LEE-B on ESP-2 until the next spacewalk, where it will be relocated to the Mobile Base System.
With the spare LEE and LEE-B side-by-side, the duo worked to remove a guidance camera from the old LEE and attach it to the new LEE.
Once that was completed, the three remaining bolt’s on the new LEE were detached and Vande Hei grabbed onto the now-released end effector. Tingle again rotated Vande Hei’s restraint to push him, and the new LEE, back to Canadarm2.
In a reverse fashion, the duo worked methodically to attached the new LEE. However, difficult access to the six bolts caused the timeline to slip even more. Once the end effector was attached, all the bolts were manually started and four tightened by the PGT.
It was then time to power Canadarm2 back up. Unfortunately, robotics controllers on the ground said the arm’s software wasn’t able to communicate with the new LEE-B. This necessitated the crew to cycle the mechanism that pushes electrical and data connectors in the LEE to attach to ports in the wrist-portion of the arm, according to Spaceflight101.
The spaceflight version of unplugging and plugging a device back in – worked. Once the arm was powered back on, ground controllers confirmed all was operating well and the new LEE-B was in a healthy condition. Over the next several days, more checkouts will be performed to verify all is indeed well with the new end effector.
With the initial indication that the arm was installed correctly, the spacewalking astronauts continued to tighten the bolts and replace the insulation blankets. By this time, the duo was more than an hour behind the planned timeline. As such, no get-ahead tasks were performed and the crew was directed to clean up their work space and return to the airlock.
Once the spacewalking duo was back inside Quest, the hatch was closed. U.S. EVA-47 officially ended at 2:13 p.m. EST (19:13 GMT) when the airlock began repressurizing.
Once the lock pressure was the same as the station’s interior, the interior hatch was opened. Vande Hei and Tingle were then helped out of their suits byKanai and NASA astronaut Joe Acaba.
This was the 206th spacewalk in support of space station assembly and maintenance, according to NASA. The agency said spacewalker’s have now spent a total of 53 days, 13 hours, and 49 minutes working outside the space station since 1998. The 7-hour, 24-minute U.S. EVA-47 was Vande Hei’s third extravehicular activity of his career and the first for Tingle.
One more spacewalk is required in this series to completely finish the job of replacing the end effector. The old LEE-B still needs to be stowed onto the Mobile Base System where it will remain as an emergency on-orbit spare, if needed. The old LEE-A, which was replaced during the trio of October 2017 spacewalks, will eventually be returned to Earth via a future SpaceX Dragon capsule for inspection and refurbishment, according to NASA.
NOTE: While this article was written by Derek Richardson, it was originally published at SpaceFlight Insider. Feel free to head over there to read all the stuff they write about!