The U.S. space agency NASA says it has found what seems to be damage on the space shuttle Endeavour's heat shield.

Astronauts aboard the International Space Station spotted a gouge in the shuttle's heat-resistant tiles Friday as the orbiter approached for docking.

Video images beamed down from space indicate the damaged heat shield measures about 7.5 centimeters square, which is slightly less than 60 square centimeters. NASA officials suspect a piece of ice or insulating foam from the shuttle's external fuel tank hit the heat shield during launch on Wednesday.

Two astronauts are due to examine the exterior of the spacecraft later Saturday on the first of up to four spacewalks. NASA says they will gather further information about the condition of the heat shield on Sunday, using sensors attached to a robot arm.

Based on the crew's findings, engineers will determine whether the heat-shield damage is significant enough to warrant repairs in orbit.

In February of 2003, a damaged heat shield caused the fiery breakup of the shuttle Columbia. All seven astronauts aboard the craft died as it disintegrated in the upper reaches of Earth's atmosphere.

Endeavour will be docked at the space station for seven to 10 days. The crew of two women and five men includes 55-year-old school-teacher-turned-astronaut Barbara Morgan. NASA says she will create a "classroom in space" during the mission.

Some information for this report provided by AP and AFP.