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Crew completes focused heat shield inspections BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: August 12, 2007 Astronaut Tracy Caldwell, operating the shuttle Endeavour's robot arm, aimed a camera and laser scanner at the belly of the orbiter today in a "focused inspection" to precisely measure the size and depth of gouges in a handful of heat shield tiles cause by external tank foam debris during launch Wednesday. While image analysts will not draw any conclusions until their assessment is complete, the most significant damage site looked relatively minor to the untrained eye, a seemingly shallow gouge in two adjacent tiles. Based on pictures snapped by the space station's crew during Endeavour's final approach Friday, mission managers had already decided the shuttle could safely re-enter as is if some other emergency forced a speedy return to Earth. The close-up pictures today seemed to confirm that judgment, showing an irregular, scooped-out area where the black surface of two tiles had been scraped away, exposing the white silica fiber interior. The tiles in question are about 1.12 inches thick and laser scans of the area will let engineers compute the depth of the damage, a key component in determining how well the damaged tiles can reject heat during re-entry. Temperatures in that region climb to more than 2,000 degrees during the return to Earth. John Shannon, chairman of NASA's Mission Management Team, said Saturday "if we have even half the tile left we won't have any issues at all." Based on close-up TV views today, the gouge appeared relatively shallow and certainly less extensive than some damage seen in earlier flights that ended with safe landings. But two-dimensional TV views can be deceiving and a full assessment is not expected until Monday, after the photography and laser data is analyzed. Engineers believe a chunk of foam from a bracket holding a 17-inch liquid oxygen feedline to the outside of the external tank broke away 58 seconds after launch. The foam slammed into an aft strut that helps hold the orbiter to the tank and broke into multiple pieces. One of them ricocheted off the strut and hit the shuttle's heat shield. Four separate impact sites of interest were seen in the rendezvous photography, the largest measuring 3.48 by 2.31 inches across and the smallest measuring 1.56 by 0.48 inches wide. The 50-foot-long instrument boom attached to the shuttle's robot arm was aimed at all four damage sites today as well as an area where a small bit of thermal barrier was seen earlier protruding from the seal around the right main landing gear door. By luck, the largest damage site is located right above an internal rib in the right wing called a stringer. Even if the tiles were gouged out all the way to their base, Shannon said, any unusual heat during re-entry that made it to the underlying aluminum skin would spread out in the structure and not result in a localized hot spot. Based on the television pictures today, the tiles in question did not appear to have suffered anywhere near that level of damage. While today's inspection work was going on, space station commander Fyodor Yurchikhin and flight engineer Oleg Kotov were busy replacing cables attached to a computer processing unit known by the English version of a Russian acronym, BOK-3. In the wake of widespread Russian computer failures in June, engineers discovered quite a bit of corrosion on cables leading to the BOK-3 unit, located near an air conditioner in the Zvezda command module. Opening access panels today, Yurchikhin reported finding a fair amount of condensation and water in the area. The BOK-3 unit itself will be removed Tuesday and replaced with a freshly delivered spare on Wednesday. Astronauts Rick Mastracchio and Canadian flier Dave Williams, meanwhile, spent part of the day preparing the tools they will use during a second spacewalk Monday to replace one of the station's four stabilizing control moment gyroscopes. The excursion is scheduled to begin around 11:30 a.m. Monday. The Mission Management Team is expected to discuss the results of today's focused inspection during a meeting Monday. Today, the MMT was briefed on the performance of a new station-to-shuttle power transfer system, or SSPTS, that is allowing the orbiter to plug into the station's solar power grid. Going into the mission, flight planners said if the SSPTS operated as expected, they would recommend extending Endeavour's mission by three days and adding a fourth spacewalk. The SSPTS has been operating flawlessly, delivering some 6 kilowatts of power to the shuttle and allowing the astronauts to reduce the consumption of liquid oxygen and hydrogen used by the ship's fuel cells. As a result, the MMT was expected to approve the mission extension, setting the stage for spacewalks Monday, Wednesday and Friday. If the extension is, in fact, approved, Endeavour would remain docked to the lab complex until Aug. 20 and return to Earth two days later. A news briefing to discuss today's inspection and the daily MMT meeting is planned for 5 p.m.
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