Atlantis arrived at the space station on June 8 to continue working on the international project scheduled for completion in 2010, but has been subsequently dogged by its own technical problems.

No abandonment

Mike Suffredini, programme manager for the space station, said despite the computer failure, he had "no plans to de-man the space station".

Two Russian and an American astronaut are currently living at the station along with the seven visting astronauts from Atlantis.

"There is nobody in this agency, or as far as I know in the Russian agency, that thinks this vehicle is at risk of being lost, not even remotely," Suffredini said.

In the past, Nasa and Russia have talked about operating the space station without people. But Suffredini said if astronauts did have to leave, they would be able to come back safely.

Breakdown in space

Six computers started crashing on the Russian side of the International Space Station (ISS) on Tuesday.

The spacecraft's ability to manoeuvre and produce oxygen have been affected.

The eight astronauts and two cosmonauts currently at the station have plenty of oxygen and supplies.

There is concern because the ISS needs the computers to remain positioned towards the sun for its power and so it can move to avoid flying debris.

If all the computers cannot be repaired the crew will stay where they are in the short run.

The space shuttle's thrusters help the ISS stay in place while the spacecraft is docked there.

Once Atlantis leaves on Tuesday, the space station's gyroscopes and thrusters on two Russian spacecraft docked at the ISS can help maintain control.

A Russian cargo ship, now set to launch in July, can deliver new computers to replace the failed ones.

 

The computers control the station's positioning in space so that it can draw power from the sun, maintain proper temperatures and position antennas for communicating with ground controllers.

The German-built computers also command critical life-support equipment, such as the oxygen generators and scrubbers that remove deadly carbon dioxide.

Suspect connector

The spacewalking Atlantis astronauts were disconnecting a connector on a newly installed power-conducting truss that is suspected of being responsible for the computer glitch.

Nasa suspects the connector because the Russian computers blinked out at about the same time the connector went on line. The connector is not required for station operations until a later power hook-up, Suffredini said.

"It's circumstantial," he said. "We don't know if that's the cause."

The astronauts were also repairing a torn thermal blanket that helps protect the shuttle from heat on its return flight to Earth next week.

Atlantis launched June 8 with a crew of seven to the space station to continue work on the long-running project.

But plans for the 11-day mission were first disrupted by discovery of a rip in the thermal blanket a problem that has extended the mission by two days so that a repair spacewalk could be worked into the mission.

The computer breakdown added to the work assignment for the two spacewalkers.

The thermal blanket damage is a concern given the Columbia shuttle disintegrated as it returned to Earth in February 2003 caused by breaks in the shuttle's heat shield due to foam insulation peeling off its fuel tank and striking a wing during the launch.

Nasa has also played down concerns over the tear to the blanket but it could decide to delay the return of Atlantis to buy more time for engineers to fix the problem.

Enormous complexity

Francisco Diego, a space expert from University College London, told Al Jazeera that while the problems will be a temporary setback for the space station, they are to be expected given the complexity of the project and the difficult working conditions astronauts face in a limited amount of time.

He said: "This is one of the most complex engineering tasks ever achieved in the history of mankind."

"There are so many systems and different nations contributing to the station ... so the complexity is enormous and I think we would expect problems like this in the future."

Diego said in a way it was fortunate the computer failure occurred while the extra astronauts from Atlantis were around.

He also said he thought the space station would be completed on time and would be a "major achievement".