to another Columbia-type disaster. Columbia was destroyed in 2003 when hot atmospheric gases seeped into a hole in its wing and melted the wing from

to another Columbia-type disaster. 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.

Teacher-astronaut Barbara Morgan — who was the backup for Challenger's Christa McAuliffe in 1986 — conducted the slow and painstaking survey, along with crewmate Tracy Caldwell. They used the 100-foot robotic arm and extension boom that flew up on Endeavour, steering the instrument to a spot just above the gouge and keeping it hovered there.

Laser sensors and cameras zoomed in on the damage, white and easily visible against the black tiles, from a variety of views.

Four other damaged areas also were scanned. Engineers believe the piece of foam struck the shuttle's underside, creating the big gouge, then skimmed along the bottom and nicked it in at least three spots. Those smaller gouges pose no threat, Shannon said.

The foam came off a bracket on the external fuel tank 58 seconds after Wednesday's launch, fell down onto a strut on the tank, then bounced up, right into Endeavour's belly. Ice apparently formed before liftoff near the bracket, which helps hold the long fuel feed line to the tank, and caused the foam to pop off when subjected to the vibrations of launch.

It's possible some ice was attached to the foam, which would have made the impact even harder. The debris that came off is believed to have been grapefruit-sized.

These brackets have lost foam in previous launches, a concern for NASA, Shannon said. A switch to titanium brackets, eliminating foam, will not occur before next year.

Shannon said he did not know whether the recurring foam problem would delay the next shuttle flight, currently scheduled for October.

"We have a lot of discussion to have before we decide to fly the next tank," he said.

The inspection consumed much of the astronauts' day. On Monday, two of them will go back out for the second spacewalk of the mission to replace a broken gyroscope at the international space station.

Endeavour has been docked at the space station since Friday. It will remain there until Aug. 20 for a record 10-day stay. Mission managers on Sunday approved the prolonged visit based on the successful testing of a new power transfer system flying on Endeavour. The system is drawing power from the station and converting it for use aboard the shuttle.

On the space station, meanwhile, two cosmonauts continued repairs to a Russian computer system that failed during shuttle Atlantis' visit in June. Condensation from an air conditioning unit apparently is collecting behind the panels where the computer equipment is located.

And a U.S. command-and-control computer that shut down during Saturday's spacewalk was working again Sunday.

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On the Net:

NASA: http://spaceflight.nasa.gov

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Rasha Madkour and Liz Austin Peterson contributed to this report from Houston.