As you get older, some of your joints might get a little crunchy. The same is apparently true of robots. NASA has just sent two astronauts out on a multi-hour spacewalk to repair the International Space Station’s aging Canadian-built robotic arm, part of which broke down in late September. While the arm still works for certain applications, it will need to be fully operational in advance of the station’s upcoming supply drop next month.
This is the second major repair on the Canadarm-2 since the Space Shuttle Endeavor delivered it to the ISS in 2001. Just one year later in 2002, the wrist joint malfunctioned and needed replacement in orbit. It’s impressive such a sophisticated device has required only two major repairs in that time–it has seven independent joints, giving the arm seven degrees of freedom.
On September 22nd, ISS mission control reported that one of the arm’s two Latching End Effectors (LEE-A) failed to engage fully. The Canadarm 2 is 57.7 feet long and weighs in at 4,000 pounds. When it’s fully operational, operators use the arm to grapple spacecraft and other objects outside the station, and it’s vital to safely docking supply craft that arrive at the station. The issue with Canadarm 2 right now is not the part that does the grappling, but the part that connects it to the ISS. The arm is needed in different places, so it uses the LEE-A mechanisms to inch along from one fixture to the next as it moves across the station’s hull. With only one active LEE, it can’t get where it needs to be.
According to Tim Braithwaite of the Canadian Space Agency, each Latching End Effector is a “very complex package” because of all the included functionality. It not only latches onto the station, it transmits avionics data, camera feeds, and other sensor data from the rest of the arm. Thus, the procedure conducted by astronauts Randy Bresnik and Mark Vande Hei was rather involved. Two thermal blankets needed the be removed from the arm’s base first, and then the six bolts holding the LEE-A in place were disconnected. Attaching a new LEE is the same thing in reverse. It may sound simple, but everything takes longer in a weightless environment when you’re wearing a clunky spacesuit.
Another spacewalk is currently slated for early next year when NASA plans to replace the LEE-B device. It’s still working fine, but these parts have an expected lifespan of 10 years. The designers are pleased they’ve both lasted as long as they have, but no one wants to take any chances. NASA believes the Canadarm 2 will be ready to greet Orbital ATK’s supply ship when it arrives in a few weeks.