Computers that control navigation and key life-support systems on the International Space Station were partially restored on Thursday after failing the day before.

Flight controllers were able to re-establish some communication with the computers overnight, with Russian engineers working Thursday to restore the rest of the system, NASA space station flight director Holly Ridings said.

Astronaut Sunita Williams uses a computer in the Unity node of the space station while Atlantis was docked on Tuesday. The crew of the shuttle and station are working to restore computers that failed earlier this week.
(NASA/Associated Press)

"They've made a lot of progress," she said. "There are some cleanup steps to do still and some investigation."

The U.S. space agency and Russian officials are still trying to determine the cause of a failure affecting multiple computers in the Russian network — computers that control the navigation and control systems that help the station's gyroscopes maintain its orientation in space and also supply oxygen and water to the station.

The computer failure occurred in the Russian segment of the orbital outpost, which relies on the resources of 16 nations. While computers had failed before, these failures had never happened all at once, nor to the point where none could reboot.

Some of the computers were able to restart Thursday morning, though the reconnection gave the crew a scare by setting off a false fire alarm about an hour and 20 minutes before Thursday's wake-up call.

Without the computer systems to operate the machines that supply oxygen, the station has only a 56-day supply of oxygen.

Since an earlier failure on Monday, thrusters on the space shuttle Atlantis have been fired periodically to help maintain the station's position.

The Russian and U.S. space agencies said they could extend Atlantis's mission by one or two days to fix the problem. In the worst-case scenario, NASA said the ISS crew members — two Russians and an American — may be evacuated from the station.

Atlantis launched last Friday on the mission to the space station to install a set of solar arrays and a new truss segment that will allow the arrays to rotate to catch more of the sun's energy.

Russian engineers are investigating whether the computer failures could have been triggered by the new set of solar arrays.

NASA has already extended Atlantis's mission to the station from 11 to 13 days, and also scheduled an extra spacewalk to fix a tear in the peeled-back thermal blanket near Atlantis's tail.

On Wednesday, NASA gave the go-ahead for astronauts to repair the torn thermal blanket during a spacewalk on Friday. The astronauts will be using surgical staples and pins to secure it in place.

With files from the Associated Press