It was In August that astronauts noticed that a one of the two Latching End Effector’s (LEE) on the station’s Canadarm2 was stalling. These LEE’s are often referred to as a robotic “hand” because of their location (see diagram below) and functionality.
LEE “A” was acting up and it meant that a spacewalk would be needed to replace it. ISS planners worked out a plan that necessitated three spacewalks to accomplish the task of replacing the “hand” and preparing it for service. The crew would also perform other tasks while spacewalking.
The Canadarm2 is one of three robotic components Canada contributed to the International Space Station that make up the Mobile Servicing System which is critical to space station operations. The other two components are the Mobile Base System and Dextre, the “handyman”.
There are five Latching End Effector’s on the ISS. There are two on the Canadarm2, one at each end. There’s also one on the Mobile Base System, one on Dextre and a spare one.
The Canadarm2 uses its Latching End Effector’s to connect to the Mobile Base System and Dextre and to perform other functions needed by the robotic “hand”. Because the Canadarm2 “hands” are used quite often, they have more wear and tear than the one on Dextre and the Mobile Base System. So when LEE “A” on the Canadarm2 started to show some problems it didn’t come as a complete surprise.
SpaceQ spoke with Ken Podwalski , Director, Space Exploration Operations and Infrastructure at the Canadian Space Agency to get a better idea what the astronauts would be doing.
It turns out the astronauts did not replace LEE “A” with the onboard spare. It was decided to save that Latching End Effector for possible future use. In part the decision was made because Canadarm2 is used often and it so critical that they wanted to use a proven LEE to replace the problematic one.
So they instead took the Latching End Effector from the Mobile Base System and replaced LEE “A” on the Canadarm2 with it. But that meant that the problematic LEE “A” was now being used by the Mobile Base System.
Wouldn’t that be a problem I asked Ken?
No. It turns out that for now the problems with LEE “A” wouldn’t be a big issue when used on the Mobile Base System as the “hand” functionality needed for the Mobile Base System isn’t the same for the Canadarm2.
The merry-go-round of moving Latching End Effector’s isn’t over yet. in 2018 LEE “A”, which is now on the Mobile Base System, will be removed and stowed in a Dragon cargo spacecraft for a return to Earth. The current spare on-orbit will be then be put into service.
In the meantime, the lone ground spare will be launched to ISS to act as the on-orbit spare. The problematic LEE “A” will undergo refurbishment by MDA in Brampton and will become the ground spare. Refurbishment will take a minimum of one year, possibly up to two years.
The ISS will be used until at least 2024. There are only six Latching End Effector in existence and the design is close to 25 years old. I asked Ken if needed, could new Latching End Effector’s be built. He said yes, but qualified that by saying some of the production used 20 years ago doesn’t exist anymore. So yes it could be done, but it would take many years and be very costly.
Ken said he is confident that the existing “fleet” of six Latching End Effector’s can do the job for the lifetime of the station.
The first spacewalk took place on Thursday, October 5th by astronauts Randy Bresnik, the current ISS Commander, and Flight Engineer Mark Vande Hei of NASA.
The astronauts successfully removed the problematic Latching End Effector and replaced it with the Mobile Base System LEE in a spacewalk that lasted 6 hours and 55 minutes.
The two astronauts astronauts also removed a multi-layer insulation from a spare direct current switching unit and prepared a flex hose rotary coupler for future use.
On October 10th, Bresnik and Vande Hei completed the second spacewalk in 6 hours, 26 minutes. They lubricated components of the LEE they installed on the Canadarm2 from the first spacewalk. They also had to replace the camera on the LEE. This was an additional task added to the second spacewalk and was a result of the camera not functioning properly after it had been moved from the Mobile Base System and installed on the Canadarm2 during the first spacewalk.
The astronauts also performed other station maintenance “including replacing a smudged lens cover and removing two handrails from outside the tranquility module in preparation for a future wireless antenna installation”.
The third spacewalk was performed once again by Expedition 53 Commander Randy Bresnik who this time was joined by Flight Engineer Joe Acaba. They completed the spacewalk in 6 hours, 49 minutes on October 20th.
During the spacewalk they replaced a camera light assembly on the recently installed Canadarm2 LEE and greased the LEE. They also installed another HD camera on the starboard truss of the space station and replaced a fuse on the Dextre robotic arm.
Adding to the Knowledge Base
With the trio of spacewalks completed the Canadarm2 and Mobile Servicing System should now be ready for more work.
The Latching End Effector that was moved from the Canadarm2 to the Mobile Base System should work fine for what it needs to do. Sometime in 2018 it will be removed, stowed in Dragon spacecraft, and returned to Earth for refurbishment.
Having the SpaceX Dragon spacecraft return cargo from the ISS was not originally in the builders plans as SpaceX didn’t exist at the time. Now MDA will have the opportunity to see their flown hardware firsthand, learn from the wear and tear, and add that information to their knowledge base as they prepare to build future robotic tools for use in space.