Cape Canaveral, Fla. ? A routine shuttle mission, highlighted by a teacher’s first spaceflight and space station construction, is now overshadowed by a potentially serious gash in Endeavour’s thermal shield.

A detailed laser inspection today of the difficult-to-reach area on Endeavour’s belly may send astronauts out to repair the 3-inch wound later in the week. A severe penetration could let in searing gases when the shuttle returns to Earth in a possible replay of the Columbia accident.

As a pair of spacewalking astronauts installed a new beam to the international space station on Saturday, engineers back on Earth scrutinized images of the gouge, believed to be the result of a strike by ice at launch.

The ice, which would have come from the external fuel tank, is denser than the tank’s insulating foam and even a small piece could cause major damage to the shuttle’s thermal covering.

In a scene eerily reminiscent of the foam smack to Columbia four years ago, radar showed a whitish spray or streak emanating from Endeavour’s right side 58 seconds after Wednesday evening’s liftoff. The chairman of NASA’s mission management team was quick to point out that the spray looked much smaller than the one during Columbia’s launch.

Nonetheless, the similarities immediately grabbed the attention of mission managers. The 1986 Challenger launch explosion already was at the forefront of everyone’s minds, given the presence of teacher-astronaut Barbara Morgan – Christa McAuliffe’s backup – aboard Endeavour.

Mission managers promptly ordered a focused inspection of the gouged area today, using Endeavour’s 100-foot, laser-tipped robot arm and inspection boom. They also had engineers and other experts poring over the radar launch imagery as well as photographs of the damage that were taken by the space station crew right before the shuttle’s docking Friday.

The inspection boom and augmented photography became mandatory after the Columbia disaster. Every shuttle crew also has been supplied with a repair kit to handle precisely this type of damage.

Today’s inspection will ascertain the depth of the gouge, a vivid white against the surrounding black thermal tiles. If NASA decides a repair is needed, two astronauts will venture out to either cover the gouge with black paint, screw on a plate or squirt goo into the cavity.

The damaged area, just a few feet from the right main gear landing door, is subjected to as much as 2,300 degrees Fahrenheit during re-entry. The wings and nose cap get considerably hotter, and any damage there would be even more worrisome.

Columbia’s left wing ended up with a hole estimated between 6 inches and 10 inches after being slammed by a 1 1/2-pound wedge of foam shortly after liftoff.