Astronauts prepare for first spacewalk of Endeavour mission

WASHINGTON (AFP) - US astronauts prepared early Saturday for the first spacewalk of the shuttle Endeavour mission following discovery of damage in the spacecraft's protective shield.

The two spacewalkers, mission specialists Rick Mastracchio and Dave Williams, were to spend the night at a special airlock to prevent decompression sickness.

The walk, which will be undertaken with the purpose of installing and activating a new truss aboard the International Space Station, was set to begin at 12:31 pm.

Preparations included transfer of spacewalk equipment and a review of procedures. Also, the two crews used the shuttle robot arm to lift the truss out of the payload bay and hand it off to the station robotic arm.

On Friday, NASA detected an apparent gouge on shuttle Endeavour's heat shield during a routine inspection, after the orbiter docked with the station.

A piece of ice struck the shuttle shortly after Wednesday's liftoff from Cape Canaveral, Florida, leaving what appears to be a three square inch gouge near the hatch of one of the shuttle's landing gears, mission manager John Shannon said.

Small white marks were also visible on other thermal tiles surrounding the gouged area, he told a news conference.

He said NASA was trying to determine the extent of the apparent damage, adding: "What this means, I don't know at this point."