Test takes spacewalking astronauts out on limb

A Nasa TV video grab shows spacewalker Piers Sellers entering the hatch of the International Space Station's Qwest airlock.

HOUSTON - Two spacewalking astronauts spent this morning twisting and bending at the end of a spindly pole to make sure the device provides a stable platform for future repair work on the US space shuttle fleet.

British-born shuttle astronaut Piers Sellers and American colleague Michael Fossum strapped their feet into a foot clamp and dangled from the end of a 30-metre boom.

"It's like being in a very slow elevator," Sellers radioed to ground controllers as he rode atop the end of the boom, which is a combination of the space shuttle Discovery's 15-metre robot arm and a 15-metre extension.

The exercise, performed at 28,000km/h, 357km above the Earth, was part of Nasa's efforts to recover from the 2003 Columbia disaster and make certain there are options if a shuttle is too damaged to return home.

Seven astronauts aboard Columbia died without knowing their shuttle was critically damaged by falling insulation foam during liftoff. The vessel fell apart over Texas as it returned to Earth.

Sellers and Fossum, who along with five other astronauts on Discovery docked with the International Space Station on Thursday, were to be out in space more than 6 hours. Their spacewalk was the first of three on the shuttle's 13-day flight.

Before bouncing on the boom, they worked briefly on a broken space station transport system needed to complete the half-finished, US$100 billion ($164.1 billion) space outpost.

Since Discovery's launch from Florida on Wednesday, Nasa has been poring over the shuttle with cameras and sensors looking for any Columbia-like damage.

On the only other post-Columbia shuttle flight, which flew last summer, foam also fell off the fuel tank at launch, but did not harm the spacecraft. Nasa has spent US$1.3 billion on safety upgrades since Columbia.

No major damage has been spotted on this flight, but engineers are still studying filler material protruding slightly from between heat-protecting tiles on the shuttle skin.

If Nasa decides to remove the protruding "gap fillers," it would likely happen on the third spacewalk, scheduled for Thursday.

Today's work on the end of the boom was delayed slightly by what the spacewalkers thought was a jammed safety tether. In case the extension should break off the arm, Nasa wanted the astronauts to be tethered to the payload bay as a precaution.

But as the astronauts prepared to retrieve a spare tether, flight directors asked them to double-check if the device was unlocked.

"Oh, that's pretty embarrassing," Fossum said, realizing their mistake and quickly moving the switch.

The moonlit Earth appeared over the shuttle's left wing and the astronauts quickly regained their composure. An orbital sunrise hit them full face.

"That's so beautiful," Fossum said.

As the two astronauts pretended to fix a damaged spaceship, they appeared to be comfortable working at the end of the boom. They ended their exercise at one of the station's truss segments, which they used as a stand-in heat shield to practice applying putty and drilling and patching holes.

- REUTERS