Spacewalking astronauts make critical repair

A pair of spacewalking astronauts found success in Earth orbit on Wednesday, making a critical repair to the International Space Station after meeting with frustration just one week earlier.

Russian Gennady Padalka and American Michael Fincke made quick work of what had been a scheduled six-hour mission, completing their repair about one hour ahead of schedule, Nasa said.

Replacing a transistorised switch box the size of a DVD player restored one of the space station's four large gyroscopes needed to keep it stable in flight and its arrays of solar-power panels always aimed at the sun.

With two of the gyroscopes down, the 200-tonne station was just one failure away from having to consume its precious store of fuel, which must be launched by rocket from Earth.

The other broken gyro will need to be replaced, and that must wait until Nasa's space shuttles, with their enormous cargo bays, are returned to flight.

"We have power. Great job, you guys," radioed Mission Control in Houston.

The gyro passed a one-minute test and was yesterday spun up to its normal rate of 6,600 rpm.

An earlier attempt ended prematurely last Thursday, when less than two minutes after Mr Fincke departed the air lock, Russian ground controllers detected a steady drop in the pressure inside his primary oxygen tank and ordered him to return to the station.

The problem proved to be a back-up valve stuck in the "on" position after it had been tested.

This was an "empty can" spacewalk with no one inside the station to aid the astronauts in an emergency. The complex was designed for a minimum crew of three, but there is only enough life support for two.

That situation, as well as the eventual completion of the orbiting laboratory, also depends on the space shuttles, grounded since the crash of the Columbia in 2003.

Although the astronauts worked on the US segment of the station, they wore Russian spacesuits because two of the three US suits on board are not working.

There were concerns that they would not be able to communicate with ground controllers or one another so far from the Russian segment, but communications never became a problem.

As a contingency, the pair had worked out simple hand signals to communicate with one another. Mission Control had arranged to waive the station's $1 billion robot arm if ground controllers needed to get the astronauts' attention.

The astronauts spoke Russian when talking to Mission Control Moscow and English to Mission Control Houston.