(Updates with chairman comments, details)

By Ed Stoddard

DALLAS, Oct 24 (Reuters) - Astronauts used a robot arm to scan the space shuttle Discovery's heat shield for damage on Wednesday as it headed for a Thursday rendezvous with the International Space Station.

"The mission is right on track ... We look forward to docking tomorrow," mission management chairman John Shannon told a press briefing at the Johnson Space Center in Houston.

The shuttle is due to dock with the ISS at 8:33 a.m. EDT (1233 GMT) on Thursday to kick off a 10-day construction mission at the outpost that will feature five spacewalks.

Astronauts spent the morning remotely maneuvering the arm to slowly inspect the shuttle wings and nose in a now mandatory post-launch routine begun after space shuttle Columbia broke apart on its return to Earth in 2003.

The scan with lasers and digital cameras looked for any damage to the heat shield that might have occurred when Discovery hurtled into space from Florida on Tuesday.

Data collected is beamed back to Earth for study by NASA engineers who will scrutinize it over the next few days. Preliminary analysis revealed nothing amiss.

Three suspect panels were given an especially close examination. Engineers using a new X-ray analysis technique warned managers ahead of the launch that three of the wing's 44 carbon-composite panels had tiny cracks in their silicon-carbide coatings.

After a lengthy debate, managers opted to proceed with the launch and assigned teams to monitor the situation.

Columbia was doomed by a hole in its wing heat shield from a blow by fuel tank insulation foam that broke loose during takeoff. The damage was not detected and the shuttle was destroyed by the high heat of re-entry into the atmosphere, killing the seven astronauts on board.

Loose tank foam has been a recurring problem on shuttle flights. NASA says the danger cannot be eliminated, but it has taken many steps to reduce it.

Video of Tuesday's liftoff showed several pieces of insulation flying off the tank late in the ascent when debris strikes pose less danger because they occur with less force.

The shuttle is carrying the 24-foot-long Harmony, an Italian-built unit that will be installed on the station and to which Europe's Columbus and Japan's Kibo modules will be attached on space missions starting in December.

The seven-member shuttle crew is led by retired U.S. Air Force Col. Pam Melroy. They will link up with a space station crew led by NASA astronaut Peggy Whitson.

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