NASA planning 2 spacewalks to replace Canadarm2 ‘hand’ despite US government shutdown
Despite budget battles in Washington, D.C. resulting in a temporary shutdown of the U.S. federal government, NASA and the International Space Station’s Expedition 54 crew still plan to carry out a pair of spacewalks to replace one of the 16-year-old “hands” on the outpost’s robotic arm.
Canadarm2, the space station’s robotic arm, has been attached to the outpost since 2001. In that time, the 57.7-foot (17-meter) long Canadian-built remote manipulator system has been used to assembled the ISS, relocate the Dextre robotic “repairman” as needed, and now helps with maintenance and spacecraft berthing tasks.
At each end of Canadarm2 is a latching end effector (LEE), which can serve one of two functions: it can attach to the station or Mobile Base System (MBS) to serve as the base of the arm or it can grapple onto Dextre or a spacecraft and move it where needed near or on the exterior of the complex.
The arm and its end effectors have lasted well beyond their planned 10-year lifespans. As such, the latching mechanisms were lubricated in 2015 to extend their service life, but both ends were due to be replaced eventually.
After a successful trio of spacewalks to replace LEE-A in October 2017, two more spacewalks are on the docket to be performed on Jan. 24 and Jan. 29, 2018, to replace LEE-B.
LEE-B was originally scheduled to be replaced first. However LEE-A suffered a motor stall within its latches, preventing it from successfully completing base changes across the outpost. This prompted NASA to switch which effector was to get replaced first.
In 2009, a spare LEE was sent up to ISS aboard a Space Shuttle, it was placed into storage on the exterior of the ISS, and kept covered and warm until needed. After 16 years of moving about hardware in the hard vacuum of space, that spare LEE is now needed.
During a Jan. 18 briefing, NASA previewed the upcoming spacewalks. On Jan. 24, astronauts Mark Vande Hei and Scott Tingle are scheduled to perform U.S. EVA-47 to replace the current LEE-B with the unit that’s been in storage. On Jan. 29, Vande Hei and Japan Aerospace Exploration Agency (JAXA) astronaut Norishige Kanai will perform U.S. EVA-48 to attach the original LEE-B to the Mobile Base System. Each spacewalk is expected to last about six and a half hours.
Part of the EVA activities will include removing the camera that is attached to the LEE to help astronauts guide it to its target. The camera will be removed from the old LEE, placed in a bag for storage, and then attached to the new LEE once it’s been attached to Canadarm2 during U.S. EVA-47. The second spacewalk, U.S. EVA-48, will focus on attaching the former LEE-B to the Mobile Base System. As it is still considered to be in decent shape, it will remain on the outpost as an on-orbit spare. This should eliminate the need for another to be brought up from Earth.
The meter-long, 441-pound (200-kilogram) LEE removed in October, on the other hand, will be shipped back to Earth aboard a SpaceX Dragon spacecraft in the future, after which it will be returned to the original manufacturer for inspection and refurbishment.
What’s coming next?
In his opening remarks, ISS Operations & Integration Manager Kenny Todd laid out the next couple of months of the station’s operations, which are expected to be quite busy and will require a fully functional robotic arm. Future activities include the following:
- A Russian EVA is slated to be performed on Feb. 2 to remove and replace an antenna on the outside of the Russian segment of the station.
- A new Progress spacecraft is currently scheduled to deliver supplies on Feb. 11.
- Soyuz MS-06 will return three members of Expedition 54 to Earth on Feb. 27.
- In the middle of March, Soyuz MS-08 will launch astronauts Andrew Feustel and Richard Arnold as well as cosmonaut Oleg Artemyev to the outpost.
- Once the crew of Soyuz MS-08 arrives at the outpost, Orbital ATK’s OA-9 and then SpaceX’s CRS-14 flights are slated to be sent to the ISS.
- Two or three EVAs are planned for the April-May time frame.
Lots of questions
The EVA briefing team consisted of Todd; Tim Braithwaite, the Canadian Space Agency ISS program liaison; Zeb Scoville, the U.S. spacewalk flight director; and Sarah Korona, the lead spacewalk officer for U.S. EVA 47 and 48.
The bulk of the questions directed at the team were about the possible impact of a government shutdown, which ultimately began midnight Jan. 19. However, Todd made it clear NASA would continue to staff Mission Control in Houston with the mission-critical personnel needed to support the spacewalk and the station’s regular operations.
“We’ll continue to handle the EVA and other operations, so no impact,” Todd said.
Individuals on social media using the #AskNASA hashtag asked a variety of questions related to astronaut safety, including inquiries about oxygen systems, safety tethers, and radiation due to solar storms.
Spaceflight Insider asked: “Given the heavy workload the LEEs have taken on over the last 16 years, have the new parts been upgraded in any way?”
Braithwaite responded that they have gotten into the practice of lubricating the arm’s end effectors as well as refining techniques for the way Canadarm2 is operated.
“We’re a lot smarter today than we were in 2001 about how to handle the effector,” Braithwaite said. “We have reduced the rate at which these things bottom out. And we’ve updated the software quite a bit.”
Additionally, Braithwaite said the robotics team is a lot gentler on the end effectors than they were when it was first placed in orbit.
“These two new end effectors will outlast the remainder of the program,” Braithwaite said.
Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.