Astronauts Inspect Discovery Heat Shield

A robotic arm and camera boom are extended out from the Space Shuttle Discovery as it orbits Earth Sunday, Dec. 10, 2006. The camera and sensors will scan and inspect the shuttle's wings and nose cap for damage during liftoff.
The Discovery astronauts conducted an inch-by-inch inspection of the most critical sections of the shuttle's heat shield Saturday, examining the ship's nose cap and wing leading edge panels with a laser scanner on the end of a 50-foot-boom attached to the shuttle's robot arm. No obvious problems stood out, reports CBS News space analyst Bill Harwood.

But it will take engineers several more days to complete the normal (post-Columbia tragedy) assessment of launch imagery, laser scans carried out Saturday, and close-up photos of Discovery's belly during final approach to the International Space Station Sunday evening, before the heat shield is given a clean bill of health.

Docking with the International Space Station is targeted for around 9:04 p.m. EDT Sunday. As with all shuttle-station dockings, commander Frederick "C.J." Sturckow will approach from directly in front of the lab complex, manually guiding the shuttle the final 400 feet or so to a linkup with a port on the front end of the Harmony module.

But Sturckow will have a bit of an added challenge Sunday. He won't be able to use the shuttle's small vernier jets for fine attitude control because of an apparent leak in one of two small thrusters in the ship's nose. Because of the presumed leak, engineers asked the crew to close a manifold earlier Saturday to isolate the leak, taking both forward jets off line for the duration of the mission.

The shuttle's forward reaction control system, or RCS, includes 14 primary engines and two vernier jets. Two aft RCS pods feature 12 primary thrusters and two verniers each. The primary engines generate 870 pounds of thrust while the verniers produce just 24 pounds of push.

Without the verniers, "the crew just has to be a little bit more careful," flight director Tony Ceccacci said. Using the more powerful primary jets during final approach requires "just a little bit more piloting" than usual, "but nothing that's outside of our experience or what we train the crew."

Along with inspection the nose cap and wing leading edge panels Saturday, the Discovery astronauts checked out two spacesuits that will be used later in the mission by John "Danny" Olivas and Christer Fuglesang.

Early Sunday, the crew planned to test their rendezvous tools and prepare the orbiter docking system for operation before going to bed at 5:29 a.m.

For more info:
CBS News space analyst Bill Harwood's "Space Place" updates
Space Shuttle Main Page (NASA)