The International Space Station suffered a cooling systemmalfunction late Saturday that forced its astronaut crew to power down some vitalsystems while engineers on Earth study the problem.

A power spike led to the shutdown of a pump module in oneof two liquid ammonia cooling loops on the space station, setting off alarmsthat awoke the six astronauts living aboard the orbiting lab, NASA officialssaid in a statement. The malfunction occurred Saturday at about 8 p.m. EDT(0000 Sunday GMT) while the crew was sleeping.

Once awake, spacestation astronauts powered down some attitude control systems, as well as redundantcommunications and global position system gear to balance the heat loads on theoutpost's backup cooling system, which is working well.

"The crew is in no danger, but will need to workadditional troubleshooting on Sunday to keep the station in a stableconfiguration, including the installation of a jumper cable to maintain propercooling to the Zarya module in the Russian segment," NASA officials said.The InternationalSpace Station is currently home three American astronauts, representingNASA, and three cosmonauts with Russia's Federal Space Agency.

Most of the crew returned to sleep after powering downstation systems in response to the glitch, though American astronautTracy Caldwell Dyson remained awake well into the wee hours of Sundaymorning to help Mission Control troubleshoot the malfunction.

In all, the astronauts shut down two of the station'sfour American control moment gyroscopes, which are used to adjust the orbitinglab's orientation in space without using thrusters. They also turned off anS-band communications systems, a GPS system, several power current convertersin the station's Tranquility module (a room that houses much of its lifesupport gear) and some gear that routes commands to ?other parts of the spacestation.

The pump module malfunction affected the space station'sCooling Loop A only, with the backup Cooling Loop B working as designed, NASAofficials said.

The space station is also equipped with two spare pumpmodules should a replacement be required in a future spacewalk. They are storedoutside the station on spare parts platforms attached to the orbitinglaboratory's backbone-like main truss.

Astronauts have been living aboard the $100 billionInternational Space Station, which is being built by five international spaceagencies representing 16 different countries, for nearly 10 years. Constructionbegan on the orbiting laboratory in 1998.

NASA plans to fly two space shuttle missions (in Novemberand February, respectively) to complete construction of the space stationbefore retiring the shuttle fleet next year. Congress is discussing thepossible addition of a third and finalshuttle mission, which if approved would likely carry spare parts and othersupplies to the space station in next summer.