In this photo made available by NASA, Space Shuttle Endeavour and the shuttle's Remote Manipulator System/Orbiter Boom Sensor System are shown against the blackness of space and Earth's horizon during flight activities.

Cape Canavarel, Fla. ? NASA discovered a worrisome gouge on Endeavour’s belly soon after the shuttle docked with the international space station Friday, possibly caused by ice that broke off the fuel tank a minute after liftoff.

The gouge – about 3 inches square – was spotted in zoom-in photography taken by the space station crew shortly before Endeavour delivered teacher-astronaut Barbara Morgan and her six crewmates to the orbiting outpost.

“What does this mean? I don’t know at this point,” said John Shannon, chairman of the mission management team. If the gouge is deep enough, the shuttle astronauts may have to patch it during a spacewalk, he said.

Columbia was destroyed during re-entry four years ago because of a hole in its wing, the result of a large chunk of foam insulation that broke off the external fuel tank and slammed into the wing at liftoff. Ice is heavier than foam, however, and would cause more damage to the thermal cover that protects the shuttle from the intense heat of re-entry at flight’s end.

NASA was still rejoicing over the shuttle’s arrival at the space station, and the grand entrance by Morgan, Christa McAuliffe’s backup for Challenger’s tragic mission in 1986, when engineers saw photos of the gouge.

On Sunday, the astronauts will inspect the area, using Endeavour’s 100-foot robot arm and extension beam. Lasers on the end of the beam will gauge the exact size and depth of the gouge, Shannon said, and then engineering analyses will determine whether the damage is severe enough to warrant repairs. The astronauts got a chance to see the damage after Mission Control sent them pictures late Friday.

If the gouge is deemed serious and cannot be fixed, the shuttle astronauts would have to remain at the space station. They have more than two months of supplies with them, and a rescue shuttle could be launched by early October, Shannon said.

The astronauts have three methods for repairing tile damage, if necessary: They could apply black paint, screw on a protective plate or squirt in goo.

The gouge – white against the black tiles on the underside of Endeavour – is four or five feet from the starboard main landing gear door. It appears to be the result of ice, although engineers are not positive; the damage could have been caused by a piece of foam insulation that came off the fuel tank.

Radar images show a white spray or streak coming off Endeavour 58 seconds after liftoff. Engineers theorize that if the debris was ice, it pierced the tile and then broke up, scraping the area downwind.

“It looks like it was an ice impact to me,” Shannon told reporters.

Even though it was an extremely hot day in Florida when Endeavour lifted off, the fuel tank was loaded with super-cold fuel, which could have allowed dangerously big chunks of ice to form on its surface.