As a pair of astronauts float outside the international space station to replace a gyroscope, NASA is busy studying a tear on Endeavour's belly.
Engineers are trying to figure out if the gash can withstand the searing heat of atmospheric re-entry. Scientists will heat up similarly damaged samples to see if the gouge needs patching.
A piece of insulating foam crashed into the ship's belly during takeoff, tearing all the way through the thermal shield.
Teacher-turned-astronaut Barbara Morgan and other crew members spent much of yesterday operating a laser boom to generate 3-D images of the gash and other damaged areas.
Mission managers will decide no later than tomorrow whether to send astronauts out to patch the rip.
Astronauts plan to conduct two more spacewalks Wednesday and Friday, and they could add the gouge repairs to their to-do list.