NASA reported that on 11 December, the pump module on one of the International Space Station’s (ISS) two external cooling loops automatically shut down when it reached pre-set (lower) temperature limits. These loops circulate ammonia outside the station to keep both internal and external equipment cool. The flight control teams worked to get the cooling loop (Loop B) back up and running, and they suspect a flow control valve actually inside the pump module itself might not be functioning correctly.
NASA notes that at no time was the crew or the station itself in any danger, but the ground teams did work to move certain electrical systems over to the second loop. Some non-critical systems have been powered down inside the Harmony node, the Kibo laboratory and the Columbus laboratory while the teams of engineers work to figure out what caused the valve to not function correctly and how to fix it.