Houston ? NASA may have to send astronauts on a special spacewalking mission to mend a 3 1/2-inch gouge on Shuttle Endeavour’s belly that appears to penetrate all the way through two heat shield tiles that protect the orbiter.

Images gathered by lasers and cameras on an extension to the shuttle’s robotic arm confirmed Sunday that the divot went through the 1.12-inch thick tile, exposing some of the heat-resistant felt-like material below. That material, as well as the tile itself, is designed to protect the orbiter from burning up during re-entry into the Earth’s atmosphere.

“It’s a fairly deep gouge,” John Shannon, chairman of the mission management team, said Sunday. That team will decide either today or Tuesday whether a repair spacewalk is needed, he said.