The term Drive Lock Assembly or DLA is used to refer to the mechanisms present in each Solar Alpha Rotary Joint or SARJ which allow the outer segments of the Integrated Truss Structure, a component of the International Space Station or ISS, to rotate and track the Sun. A component of the DLA is a pinion which engages with the race ring that serves as a bull gear. There are two race rings and two DLAs in each SARJ providing on-orbit redundancy, however a series of space walks would be required to reposition the DLAs and the Trundle Bearing Assemblies (TBAs) to utilize the alternate race ring.
Currently NASA is investigating damage to the Starboard SARJ of the ISS. It is not known whether the DLA is damaged, however a spare DLA was brought to the ISS on STS-122.[1]