Space station cooling system suddenly shuts down

After huddling Sunday, NASA managers gave preliminary approval for a pair of spacewalks, the first of which would take place later this week. Two of the Americans on board were already scheduled to conduct a spacewalk Thursday for routine maintenance, though the repairs would supersede the original chores.

Officials stressed that the six occupants were in no danger, and that the orbiting complex was in a stable situation. Much of the station is operating on a single string, however, with no safeguard in case of further cooling system failures.

The trouble arose Saturday night, when one of the two ammonia-fed cooling loops shut down. Alarms sounded throughout the sprawling outpost as the circuit breaker for the pump in that line tripped, causing the pump to stop working.

The cooling system is critical for on-board operations. The two ammonia lines ensure that all the station's electronic equipment does not overheat.