Debra L. Wabnik

Debra L. Wabnik

Two astronauts began a spacewalk Monday to replace equipment on the international space station as NASA worked feverishly to decide whether the shuttle Endeavour's crew would need to repair a gouge on the ship's belly later this week.

A chunk of insulating foam smacked the shuttle during liftoff last week, creating a 3 1/2-inch-long gouge that penetrates all the way through the thermal shielding on the ship's underside.

Teacher-turned-astronaut 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 Monday, or Tuesday at the latest, 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. Actual heating tests will be conducted on similarly damaged samples.

The space shuttle Columbia was destroyed 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 liftoff caused the gash.

"We have really prepared for exactly this case, since Columbia," said John Shannon, chairman of the mission management team. "We have spent a lot of money in the program and a lot of time and a lot of people's efforts to be ready to handle exactly this case."