Earlier this year a robotics tool on the ISS failed a checkout and recently it was declared failed and unusable. The Robot Micro-Conical Tool (RMCT) is used by the 12 foot tall Special Purpose Dexterous Manipulator (SPDM) to interface with several payloads and parts that cannot be grasped directly by the SPDM arm.
Two RMCTs were launched in with the SPDM in 2008: Spacewalkers will add tool kit to space station robot
One of the main operations the tool is used for is to move/replace power control modules that semi-regularly experience failures. Below you can see a module being replaced; the gray cylinder grasping the box is the RMCT and the white edge of the SPDM arm is visible in the far top right.
The tool was acting erratically last year after being stowed for several years. For that reason a checkout was scheduled before a planned SPDM power module swap activity to make sure the tool would work. It did NOT work correctly during the checkout, and as a result all of the robotics control procedures had to be rewritten to use only one RMCT instead of both (hundreds of pages - lots of work).
The issue is that the tool does no longer reliably release from fixtures - at the end are little flaps called collets that grip the fixture. Sometimes when commanded to open, they wouldn't; this is a big problem because the tool could get stuck on something and could be in the way for future operations.
March 2015 troubleshooting excerpt:
Special Purpose Dexterous Manipulator (SPDM) Diagnostics/Robot Micro Conical Tool (RMCT) 1 Troubleshooting:
In preparation for the Pump Module relocation scheduled for March 6-7, yesterday Ground Controllers positioned the SPDM and stowed RMCT2. They engaged launch locks on RMCT1 and successfully released its collets. The collets were cycled open and back to close one time for data collection. Following review of preliminary data, the robotics team determined that having the launch locks engaged was affecting the data so no further cycles were performed. Ground teams will plan further data collection activities.
After some troubleshooting and looking at data, RMCT1 has been declared no-go for use. It isn't clear yet exactly what is causing the problem, but a leading theory is physical deformation of the internal mechanisms (possibly related to lengthy disuse). RMCT2 is still good and in use. Now the problem, however, is that we don't have redundancy; if RMCT2 fails for any reason, it won't be possible to do any robotics with these type of parts. Any replacement would have to be done via Extra Vehicular Activity which is expensive in consumables and crew time.
Fingers crossed that we'll be able to launch and deploy a spare soon via a SpaceX Dragon or other vehicle.
Sources:
- Canada’s Dextre Completes Marathon Week of Robotics Ops on ISS
- Robotic Transfer and Interfaces for External ISS Payloads: Page on nasa.gov
- Dextre Completes RPCM R&R