Florida -- One of two cooling systems serving the International Space Station's U.S., European and Japanese laboratories broke down, setting off a wave of equipment shutdowns to cut the heat generated on board, NASA said on Sunday.
The three Russian cosmonauts and three NASA astronauts aboard the station are not in any danger, NASA's flight controllers said in a statement. The crew members, who were asleep at the time, were roused by alarms about 8 p.m. EDT Saturday and immediately set to work powering down equipment to prevent the sole remaining cooling loop from overloading.
The shutdown, however, means that many systems aboard the station are now without working backups.
"It's pretty clear that we're going to want to have a course of action to take as quickly as possible. This is not something we want to linger over," said NASA spokesman Rob Navias at the Johnson Space Center in Houston.
After an attempt to revive the cooling loop failed, NASA on Sunday scrambled teams to begin choreographing a pair of spacewalks later this week to make repairs.
The station, a $100 billion project of 16 nations, has two ammonia-fed cooling loops to dissipate heat generated by equipment. One loop shut down after a power spike in a pump module, which is needed to funnel ammonia through the lines.
The loss of the cooling system triggered the shutdown of several pieces of equipment, including two of the station's four gyroscopes, which keep the complex properly orientated in orbit, one of two communications systems, one of two Global Positioning System receivers, power converters and routers.
On Sunday, the astronauts set up a jumper cable to make sure key control functions in the Russian Zarya module have backup power.
The station has two spare pump modules in storage on platforms outside the station.
Flight engineers Doug Wheelock and Tracy Caldwell Dyson had been preparing for a spacewalk on Thursday to install part of a new robotic crane onto the Zarya module and to configure the station for a storage closet that is due to be delivered by the shuttle Discovery crew in November on NASA's next-to-last shuttle flight.
That work will be deferred, NASA said Sunday, with the astronauts likely dispatched to replace the cooling loop's failed pump instead.
The work is expected to take two spacewalks, the first of which would be staged no earlier than Thursday to replace the pump module and bolt it in place. A second spacewalk would follow two or three days later to hook up electrical connections and fluid lines.
In addition to Wheelock and Dyson, the station crew includes commander Alexander Skvortsov, cosmonauts Mikhail Kornienko and Fyodor Yurchikhin and NASA astronaut Shannon Walker.