You can rest assured that everybody that knows anything about a computer is now at Johnson Space Center

Space station flight director

A computer program prevented astronauts from testing the station's new giant robot arm and resulted in a cascade of other problems, the US space agency Nasa said.

The three main computers on board were either not working or not communicating, while the orbiting outpost was left to fly on autopilot.

A spokesman said there was no immediate danger to the astronauts on board, but reports say that if the space shuttle Endeavour was not docked with the platform, ground controllers would be completely cut off from the space station's crew.

Successful task

"Doesn't sound like you're going to get much sleep tonight," said Susan Helms, a flight engineer on the station.

Those on board the station were not in danger

"No, and I think you can rest assured that everybody that knows anything about a computer is now at Johnson Space Center in Houston, and we're all working hard on it," said space station flight director Mark Ferring.

As scientists struggled to try to put the fault right, they were encouraged at one point when they successfully commanded a light to switch off on the station - but they were unable to repeat the task.

Exercise rescheduled

"The situation is strange to us at this point, and we are trying to sort that out, yet it doesn't appear to be causing any huge problems on board the station," a Nasa operations manager, Milt Heflin, said.

Meanwhile, the station continued to perform its automatic tasks, such as pointing its solar panels to the Sun and maintaining life support.

But Nasa had to cancel the first operational test of the new robotics system aboard the station.

If the trouble persists, the exercise will be rescheduled for Friday, ground controllers told the station crew.

Nasa said it would keep the shuttle at the station for an extra day, if necessary.