The Discovery astronauts carried out painstaking, inch-by-inch inspections of the shuttle's carbon composite nose cap and wing leading edge panels today, using a laser sensor on the end of a long boom to look for signs of ascent impact damage. White markings thought to be bird droppings were spotted at one point, and a few other whitish streaks were visible, but no obvious signs of significant damage were seen in downlinked TV.

Officials believe white marks on one of Discovery's wing RCC panels are bird droppings. Photo: NASA TV

Along with analyzing the results of today's inspections, engineers also are poring over launch-day photographs and video, assessing data from wing leading edge impact sensors, radar data, footage from a jet equipped with a powerful telescope and imagery captured by the astronauts and by robotic cameras mounted in the belly of the orbiter.

The goal is to assess the integrity of Discovery's heat shield tiles, nose cap and wing leading edge panels to make sure the ship can safely re-enter the atmosphere at the end of the mission.

Some of the most valuable observations are yet to come. Commander Steve Lindsey and his crewmates are slowly catching up with the international space station for a rendezvous and docking Thursday. During final approach, Lindsey will oversee a slow 360-degree pitch-around maneuver 600 feet directly below the lab complex that will expose Discovery's belly to cameras wielded by station commander Pavel Vinogradov and Jeff Williams.

With resolutions between one and three inches, the cameras are expected to spot any significant damage to the shuttle's belly. But again, NASA's Mission Management Team is not expected to reach any final conclusions until after additional post-docking inspections to look at any sites of special interest.

Otherwise, it appears Discovery came through it's ground-shaking launch and climb to space in good condition. One of six small steering jets that suffered a heater failure before launch has been warmed up by exposing it to sunlight and engineers plan to use the thruster during the space station rendezvous.

With no other problems of any significance, the attention Wednesday was on the heat shield inspections, now a standard part of every shuttle flight.

Black-and-white video from today's scans of the wing leading edge panels showed several areas with whitish streaks or other markings but the grainy imagery is difficult to interpret and similar markings were seen during Discovery's last flight.

As for the apparent bird droppings, lead flight director Tony Ceccacci said he and station flight director Rick LaBrode "saw that out at the pad when we were down there a couple of weeks ago."

"Basically, it's in exactly the same place, RCC (reinforced carbon carbon) panels 18 and 19," Ceccacci said. "This is my speculation, it's bird droppings. That's what it looked like. But we'll let the LDRI (laser dynamic range imager) guys look at that."

Here is a timeline of Thursday's rendezvous with the space station (in EDT and mission elapsed time). The TI rocket firing that begins the terminal phase of the rendezvous will occur with the shuttle trailing the space station by eight nautical miles:

EDT        DD  HH  MM   EVENT

08:05 AM   01  17  27      TI rendezvous rocket firing
08:43 AM   01  18  05      Sunset
09:03 AM   01  18  25      Range: 10,000 feet
09:12 AM   01  18  34      Range: 5,000 feet
09:18 AM   01  18  40      Range: 3,000 feet
09:20 AM   01  18  42      Sunrise
09:22 AM   01  18  44      MC-4 rendezvous burn
09:26 AM   01  18  48      Range: 1,500 feet
09:31 AM   01  18  53      Range: 1,000 feet
09:34 AM   01  18  56      KU antenna to low power
09:35 AM   01  18  57      +R bar arrival 725 feet directly below ISS
09:40 AM   01  19  02      Range: 600 feet
09:47 AM   01  19  09      Noon
09:51 AM   01  19  13      Rendezvous pitch maneuver
                                      - RPM - start window open
09:51 AM   01  19  13      Start pitch maneuver
09:55 AM   01  19  17      RPM full window close
09:59 AM   01  19  21      End pitch maneuver
10:02 AM   01  19  24      Initiate TORVA pitch up maneuver to +V bar
10:04 AM   01  19  26      RPM start window close
10:13 AM   01  19  35      +V bar arrival; range: 310 feet in front of ISS
10:14 AM   01  19  36      Range: 300 feet
10:15 AM   01  19  37      Sunset
10:18 AM   01  19  40      Range: 250 feet
10:22 AM   01  19  44      Range: 200 feet
10:25 AM   01  19  47      Range: 170 feet
10:27 AM   01  19  49      Range: 150 feet
10:31 AM   01  19  53      Range: 100 feet
10:34 AM   01  19  56      Range: 75 feet
10:38 AM   01  20  00      Range: 50 feet
10:41 AM   01  20  03      Range: 30 feet; start stationkeeping
10:46 AM   01  20  08      End stationkeeping; push to dock
10:51 AM   01  20  13      Sunrise
10:51 AM   01  20  13      Range: 10 feet
10:52 AM   01  20  14      DOCKING

Additional coverage for subscribers:
VIDEO: THE FULL LAUNCH EXPERIENCE PLAY
VIDEO: RIDE ALONG DURING LAUNCH VIA CREW MODULE CAMERA PLAY
VIDEO: AMAZING FOOTAGE FROM WB-57 HIGH-ALTITUDE AIRCRAFT PLAY

VIDEO: IMAGERY QUICK-LOOK BRIEFING DIAL-UP | BROADBAND
VIDEO: SHUTTLE LANDING FACILITY TOWER PLAY
VIDEO: PLAYALINDA BEACH TRACKER PLAY
VIDEO: UCS 23 TRACKER PLAY
VIDEO: UCS 11 TRACKER PLAY
VIDEO: CS 1 TRACKER PLAY
VIDEO: VEHICLE ASSEMBLY BUILDING ROOF PLAY
VIDEO: LAUNCH PAD FRONT CAMERA PLAY
VIDEO: COMPLEX 39 PRESS SITE PLAY
VIDEO: LAUNCH PAD SIDE VIEW PLAY
MORE: STS-121 VIDEO COVERAGE
MORE: STS-121 VIDEO COVERAGE
SUBSCRIBE NOW