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

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

Once awake, space station astronauts powered down some attitude control systems, as well as redundant communications and global position system gear to balance the heat loads on the outpost's backup cooling system, which is working well.

"The crew is in no danger, but will need to work additional troubleshooting on Sunday to keep the station in a stable configuration, including the installation of a jumper cable to maintain proper cooling to the Zarya module in the Russian segment," NASA officials said.

The International Space Station is currently home three American astronauts, representing NASA, and three cosmonauts with Russia's Federal Space Agency.

Most of the crew returned to sleep after powering down station systems in response to the glitch, though American astronaut Tracy Caldwell Dyson remained awake well into the wee hours of Sunday morning to help Mission Control troubleshoot the malfunction.

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

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

The space station is also equipped with two spare pump modules should a replacement be required in a future spacewalk. They are stored outside the station on spare parts platforms attached to the orbiting laboratory's backbone-like main truss.

Astronauts have been living aboard the $100 billion International Space Station, which is being built by five international space agencies representing 16 different countries, for nearly 10 years. Construction began on the orbiting laboratory in 1998.

NASA plans to fly two space shuttle missions (in November and February, respectively) to complete construction of the space station before retiring the shuttle fleet next year. Congress is discussing the possible addition of a third and final shuttle mission, which if approved would likely carry spare parts and other supplies to the space station in next summer.