The Endeavour astronauts wrapped up the first phase of an extensive heat-shield survey today and mission managers say damage detected to date is minor and is not expected to jeopardize the shuttle and its crew.
"There is nothing that we have seen on the orbiter that causes us any concern," NASA Shuttle Program Manager John Shannon said today.
Digital imagery of Endeavour's external tank as it was jettisoned from the shuttle after launch Wednesday show nine to 12 spots where foam insulation came off in thin layers.Most of the loss came 377 seconds into flight -- about six-and-a-half minutes into eight-and-a-half-minutes of powered flight -- a time when the shuttle already is out of the atmosphere and debris cannot generate enough kinetic energy to strike the ship's heat shield with enough force to cause damage.
The debris came from the innerstage area of the tank -- the middle point that structurally links the liquid hydrogen and liquid oxygen vessels at the bottom and top of the tank, respectively.
Two other debris events took place earlier in the ascent, peppering the starboard chine area on the underside of the orbiter.Shannon said a cloud of multiple pieces of debris from an area near the external tank liquid oxygen feedline camera created three dings when they struck thermal tile there at one minute, 47 seconds into flight.
Another piece of debris from the same area caused a line-like dent eight seconds later -- at one minute, 55 seconds into flight.
NASA is most concerned about debris strikes that occur during a period that stretches from 45 seconds to 135 seconds -- two minute, 15 seconds -- into flight.
The damage is similar but less extensive than minor damage done to that same area on the STS-125 Atlantis/Hubble Servicing mission, Shannon said.
Engineers are uncertain why the foam peeled off. One theory is that the adhesive used to fix the foam to the primer atop the metal alloy skin of the tank is not adhering adequately.
Shannon said inspections of the tank for Discovery's mission in August will be x-rayed as part of an effort to determine the mechanism that is liberating the foam.
Discovery, which is scheduled to launch Aug. 18, is to be rolled from its processing facility to the Vehicle Assembly Building on Monday -- the 40th anniversary of the Apollo 11 moon-landing.
The x-ray shearography testing might delay the mating of Discovery to that tank -- designated ET-132. Twin solid rocket boosters already are attached to the tank.
A significant delay in the mating operation could push back the Aug. 18 target launch date.
Shuttle heat-shield inspections will continue Friday as Endeavour approaches the International Space Station.
About 600 feet from its docking port, mission commander Mark Polansky will guide the spaceship through a nose-over-tail backflip. The eight-minute maneuver will point the belly of the orbiter toward the station.
Two crew members aboard the station will use cameras with 400-millimeter and 800-millimeter lenses to document the condition of the thousands of thermal tiles that cover the underside of the orbiter and protect the ship and its astronauts during atmospheric reentry.
The high-resolution images will be downlinked to Mission Control for analyses. If any problems are detected, NASA would order up a focused inspection of any suspect area on Sunday.
ABOUT THE IMAGEs: Click to enlarge the NASA image (top) of Endeavour's external tank after it was jettisoned from the orbiter about nine minutes after its launch Wednesday from Kennedy Space Center. The image shows several areas on the tank where foam insulation peeled off during the shuttle's ascent into orbit. You can also click to enlarge the second image -- a NASA TV screen grab that shows four tile dings on the starboard chine area of the underside of the orbiter.
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