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.

Credit: NASA TV

No obvious problems stood out, but it will take engineers several more days to complete the normal post-Columbia assessment of launch imagery, the 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.

"We had one of our vernier jets, F5R, fail-leak last evening," lead flight director Tony Ceccacci told reporters early Sunday. "Basically, the signatures that we saw were somewhat interesting, I have to admit. I was an ex prop (propulsion officer in mission control) and what I saw didn't quite make sense. But what we did this morning after the crew woke up, we did close that manifold, No. 1, just to safe the system. We wanted to make sure the manifold was evacuated and didn't cause any contamination concerns to the station.

"Even in the loss-of-vernier case, the crew is well trained to press through the rendezvous sequence, the prox ops (proximity operations) part of it. We actually had a quick tag up with C.J. today on what to expect and what differences he will have without vernier jets."

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," 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."

Once docked, the orientation, or attitude, of the combined shuttle-station "stack" is typically controlled by the station's four control moment gyroscopes, assisted from time to time by the shuttle's vernier jets. Because of the F5R failure, Russian thrusters will be used for major changes.

"There were some other things we were looking at in the event we had to do a debris avoidance maneuver, what the best scenario and configuration would be, whether it would be on the Russian thrusters or going to the alt-DAP (digital autopilot) on the primary jets," Ceccacci said. "The folks are taking a look, making sure we have good solar array configurations, making sure that we meet all the loads constraints and such. But we have work-arounds to deal with that failure."

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.

Additional coverage for subscribers:
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VIDEO: NARRATED PREVIEW OF SHUTTLE INSPECTIONS PLAY

VIDEO: LAUNCH REPLAY: INSIDE MISSION CONTROL ROOM PLAY
VIDEO: LAUNCH REPLAY: VAB ROOF PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PRESS SITE PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD PERIMETER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: BEACH TRACKER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD CAEMRA 070 PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD CAEMRA 071 PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: UCS-23 TRACKER PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PLAYALINDA BEACH PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PAD FRONT CAMERA PLAY | HI-DEF
VIDEO: LAUNCH REPLAY: PATRICK AIR FORCE BASE PLAY | HI-DEF

VIDEO: POST-LAUNCH BRIEFING PLAY
VIDEO: FLIGHT DAY 1 HIGHLIGHTS MOVIE PLAY
VIDEO: THE FULL LAUNCH EXPERIENCE PLAY
VIDEO: LIFTOFF OF SPACE SHUTTLE DISCOVERY! PLAY | HI-DEF
VIDEO: COMMANDER RICK STURCKOW BOARDS DISCOVERY PLAY
VIDEO: PILOT KEVIN FORD BOARDS SHUTTLE DISCOVERY PLAY
VIDEO: MISSION SPECIALIST PAT FORRESTER BOARDS DISCOVERY PLAY
VIDEO: MISSION SPECIALIST JOSE HERNANDEZ BOARDS SHUTTLE PLAY
VIDEO: MISSION SPECIALIST DANNY OLIVAS BOARDS DISCOVERY PLAY
VIDEO: MISSION SPECIALIST CHRISTER FUGLESANG BOARDS PLAY
VIDEO: MISSION SPECIALIST NICOLE STOTT BOARDS DISCOVERY PLAY
VIDEO: ASTRONAUTS LEAVE CREW QUARTERS BUILDING PLAY | HI-DEF
VIDEO: CREW FINISHES GETTING SUITED UP PLAY | HI-DEF

VIDEO: NARRATED MISSION OVERVIEW MOVIE PLAY | HI-DEF
VIDEO: MEET SHUTTLE DISCOVERY'S ASTRONAUTS PLAY | HI-DEF
VIDEO: NARRATED REVIEW OF SHUTTLE'S PREPARATIONS PLAY | HI-DEF
VIDEO: NARRATED REVIEW OF PAYLOADS' PREPARATIONS PLAY | HI-DEF
VIDEO: THE "COLBERT" TREADMILL PLAY | HI-DEF

VIDEO: MANAGERS EXPLAIN REASON FOR SECOND SCRUB PLAY
VIDEO: WEATHER SCRUBS FIRST COUNTDOWN PLAY | HI-DEF
VIDEO: ASTRONAUTS DEPART QUARTERS FOR PAD 39A PLAY | HI-DEF
VIDEO: CREW GETS SUITED UP FOR LAUNCH ATTEMPT PLAY | HI-DEF
VIDEO: LAUNCH PAD SERVICE GANTRY ROLLED BACK PLAY | HI-DEF

VIDEO: PRE-LAUNCH INTERVIEW WITH RICK STURCKOW PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH KEVIN FORD PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH PAT FORRESTER PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH JOSE HERNANDEZ PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH DANNY OLIVAS PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH CHRISTER FUGLESANG PLAY
VIDEO: PRE-LAUNCH INTERVIEW WITH NICOLE STOTT PLAY

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VIDEO: FLIGHT READINESS REVIEW SETS LAUNCH DATE PLAY

VIDEO: SHUTTLE AND STATION PROGRAM UPDATE PLAY
VIDEO: THE STS-128 MISSION OVERVIEW BRIEFING PLAY
VIDEO: PREVIEW BRIEFING ON MISSION'S SPACEWALKS PLAY
VIDEO: THE ASTRONAUTS' PRE-FLIGHT NEWS BRIEFING PLAY
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VIDEO: MISSION CARGO LOADED ABOARD DISCOVERY PLAY | HI-DEF

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VIDEO: ASTRONAUTS BOARD DISCOVERY PLAY | HI-DEF
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VIDEO: PAD BUNKER TRAINING FOR THE CREW PLAY | HI-DEF
VIDEO: CREW BRIEFED ON EMERGENCY PROCEDURES PLAY | HI-DEF
VIDEO: NIGHTTIME APPROACHES IN TRAINING AIRCRAFT PLAY | HI-DEF
VIDEO: TEST-DRIVING EMERGENCY ARMORED TANK PLAY | HI-DEF
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VIDEO: SHUTTLE DISCOVERY ROLLS OUT PAD 39A PLAY | HI-DEF
VIDEO: ORBITER HOISTED FOR MATING TO TANK PLAY | HI-DEF
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VIDEO: PAYLOADS DELIVERED TO LAUNCH PAD PLAY | HI-DEF
VIDEO: LEONARDO PUT INTO TRANSPORTER PLAY | HI-DEF
VIDEO: STATION'S NEW AMMONIA TANK PLAY | HI-DEF
VIDEO: MPLM HATCH CLOSED FOR FLIGHT PLAY | HI-DEF
VIDEO: INSIDE SHUTTLE MAIN ENGINE SHOP PLAY | HI-DEF
VIDEO: CREW EQUIPMENT INTERFACE TEST PLAY | HI-DEF
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