A pair of spacewalking astronauts installed a new beam to the international space station Saturday as engineers back on Earth scrutinized images of a disturbing gouge in shuttle Endeavour's heat shield. The 7.6-centimeter gash in the shuttle's belly will be inspected in greater detail Sunday, when the shuttle crew pulls out its 30-meter robotic arm and extension boom and probes the difficult-to-reach area with lasers. Until then, NASA has only camera and radar images to examine. Mission managers suspect a chunk of ice flew off Endeavour's external fuel tank one minute after liftoff on Wednesday and struck tiles on the shuttle's underside, near the right main landing gear door. Ice is heavier than the tank's foam insulation, and even a small piece could cause major damage to the shuttle's thermal covering, which protects against the intense heat of atmospheric re-entry at flight's end. The area where the gouge is located is exposed to as much as 1,260 Celsius during re-entry. Sunday's laser inspection will ascertain exactly how deep the gouge is, then engineers will determine whether repairs are needed.