In this image provided by NASA astronaut Nicole Stott, Expedition 20 flight engineer, participates in the STS-128 mission's first session of extravehicular activity on the International Space Station Sept. 1, 2009.(AP Photo/NASA)
CAPE CANAVERAL, Fla. (AP) -- NASA is scrambling to figure out what's wrong with a key cooling unit on the International Space Station.
On Wednesday, one of two identical cooling loops shut down. The system uses ammonia to dissipate heat from on-board equipment. One line was getting too cold. Engineers suspect a bad valve.
Mission Control ordered the six-man crew to turn off some science experiments and other non-critical equipment. Those instruments stayed off Thursday, while the astronauts remained safe and comfortable.
The suspect valve is in a pump that was replaced by spacewalking astronauts three years ago. Flight controllers are looking at ways to fix the valve. A software repair would be the easiest option, a spacewalk the most complicated.