Astronauts begin space walk

Two astronauts from the shuttle Endeavour have begun a spacewalk to replace equipment on the international space station.

Dave Williams and Rick Mastracchio began the mission's second spacewalk, floating out of the £50 billion space station to replace one of the four gyroscopes that help control the orbiting outpost's orientation.

The astronauts will replace the broken gyroscope with equipment they brought aboard the shuttle Endeavour.

Nasa experts are also calculating whether Endeavour's crew need to repair a gouge on the ship's belly. A chunk of insulating foam hit the craft at lift-off last week in an unlucky ricochet off the fuel tank.

The unevenly shaped gouge penetrates all the way through the ship's thermal shielding on its underside.

Former teacher Barbara Morgan and other crew members spent much of Sunday using a laser boom attached to the shuttle's robot arm to create 3-D images of the gash and a few other damaged areas that Nasa officials say pose no threat.

Mission managers expect to decide later whether to send astronauts out to patch the gouge.

Engineers are trying to determine whether the marred area can withstand the searing heat of atmospheric re-entry at flight's end and heating tests will be conducted on similarly damaged samples.

Space shuttle Columbia was destroyed and its seven crew members killed in 2003 when hot atmospheric gases seeped into a hole in its wing and melted the wing from the inside out. A foam strike at lift-off caused the gash.

John Shannon, chairman of the mission management team, said: "We have really prepared for exactly this case, since Columbia.

"We have spent a lot of money in the programme and a lot of time and a lot of people's efforts to be ready to handle exactly this case."

Astronauts plan to conduct two more spacewalks on Wednesday and Friday, and they could add the gouge repairs to their to-do list.

Depending on the extent of the damage, astronauts can apply protective paint, screw on a shielding panel, or squirt in filler.

© Independent Television News Limited 2007. All rights reserved.