NASA taps British astronaut for key spacewalk

CAPE CANAVERAL, Fla, June 30 (Reuters) Perched on the end of a 100-foot pole, shrouded in darkness and floating in space, British astronaut Piers Sellers may be forgiven a moment of trepidation.

Not that the 51-year-old scientist is expecting one. As the lead spacewalker on Discovery's upcoming mission to the International Space Station, Sellers, and Michael Fossum, 48, have trained for a most unusual task: testing a spindly pole laden with sensors.

The pole is normally used for in-flight inspections of the shuttle's heat shield but can do double duty as a platform for potential repairs.

NASA added the boom and developed heat shield repair kits after the Columbia accident in 2003.

Columbia had been hit by a piece of falling debris during launch.

Even if NASA had suspected damage, which it did not, the Columbia astronauts had few means to inspect their ship and no options for repair. The shuttle was destroyed as it returned through the atmosphere for landing, killing the seven astronauts aboard.

It will be a long time before astronauts will be able to easily repair a spaceship during flight. NASA's plan for astronauts aboard seriously damaged shuttles is to shelter them aboard the space station until a rescue mission can get there.

But there is no plan to help a crew servicing the Hubble Space Telescope, which is in a different orbit from the space station.

NASA wants to fly one more mission to the ageing telescope before the shuttle fleet is retired in 2010.

First, however, engineers need to know if the 50-foot boom, which is mounted on the shuttle's 50-foot robotic arm, is stable enough to support spacewalkers working on the slippery slopes of the ship's wings and belly.

First Sellers and then Fossum will step into a foot clamp attached to the end of the extended boom. They will sway and bounce and lean in all directions so engineers can determine if the pole could be used for an actual heat shield repair job.

''I'm pretty optimistic it's going to work,'' Sellers said in an interview.

A DIFFERENT KIND OF SPACEWALK Previously, astronauts on spacewalks would only manoeuvre using handholds attached to the shuttle. Sellers expects that being at the end of the probe, with his foot securely clamped into a foothold, will be similar to three previous spacewalks he has done during the day.

But by night, with little to fix his gaze upon, things could get weird.

''All you have are your eyes in space. That's the only thing to tell you which way up you are. And if your eyes can't lock with something, you might feel you're falling in any direction. You might feel like you're tumbling in any axis. It could happen. It's not predictable,'' he said.

The spacewalkers will be connected with 85-foot tethers to iscovery's payload bay so there is no chance they would float off into space. If the tethers fail, the astronauts could manoeuvre themselves back to the shuttle using their jet backpacks.

Additional spacewalks to repair the station's mobile transporter, which is critical to future assembly missions, and to test a technique to repair heat shields also are planned during Discovery's next flight.

Sellers was born in England and trained as a pilot by the Royal Air Force. He earned degrees in ecology and biometeorology -- the interrelation between weather and living things -- and was recruited in 1982 to work as a climate modeller at NASA's Goddard Space Flight Center in Maryland.

Sellers became a US citizen in 1991 and joined NASA's astronaut corps five years later. With the shuttle's retirement looming and a long list of rookie astronauts awaiting flights, Sellers realizes his upcoming space mission could be his last.

Having experienced what he calls the sheer joy of being in space, he said his only regret would be that he didn't get to bring his family and friends along.

REUTERS SRS KN0931