HOUSTON - The heat shield protecting the
space shuttle Discovery is fit to return to Earth in an emergency, though analysts
are still eyeing two areas for additional study, NASA mission managers said
Saturday after the spaceflight's first spacewalk.
John
Shannon, NASA's deputy space shuttle program manager, said that five of the six
heat shield sites examined by Discovery's astronaut crew during Friday's
up-close inspections have been cleared of any concerns, and that the orbiter's
thermal protection system is no longer classified as "suspect" based on the
results.
One small
protruding gap filler and a dinged thermal blanket between Discovery's two
center-most windows are all that stand between the orbiter's heat shield and a
clean bill of health, shuttle officials added.
"Yesterday
things were a little fuzzy, and today things are a lot more clear," NASA's
orbiter project manager Steve Poulos said of the image data returned by during
a briefing on Discovery's STS-121 mission.
Poulos said
high-resolution images of the six
target areas photographed Friday with a new digital camera at the end of
Discovery's orbital inspection boom allowed heat shield experts to dismiss
concerns over the health of the shuttle's reinforced carbon carbon (RCC)
covered wing leading edges and nose cap. The shuttle's heat-resistant tiles
have been cleared for several days.
The dark
areas or blotches seen along the shuttle's right wing and nose cap pre-docking
photographs taken by the Expedition 13 crew aboard the International Space
Station (ISS) appear to be little more than drips of hydraulic fluid, leftover
remnants from the motors that blast the orbiter's solid rocket boosters free
during launch or other surface
material, Poulos added.
Analysis is
still underway to determine whether a small gap filler jutting out from between
two belly tiles near one of Discovery's aft external tank umbilical doors will
present a heating concern during reentry. The gap filler appears torn in some
areas and juts a maximum of about 1.04 inches (2.6 centimeters) above the
surrounding tiles, but is expected to fold over during reentry and not pose a
large threat, NASA officials said.
Additional
tests are also underway over the damaged thermal blanket between Discovery's
forward windows to determine whether the forces expected during reentry could
rip the material free and cause a debris concern along the vehicle's aft.
"Of course
we still have to do the homework...to clear [Discovery] for the nominal end of mission,"
Shannon said. "We do expect that to be tomorrow."
Shannon added that video from four new
cameras mounted to Discovery's twin solid rocket boosters has been recovered.
The video is expected to deliver more detail on any foam shedding from the
shuttle's external tank during its July 4 launch.
Boom-tastic
spacewalk
While
imagery from Discovery's orbital boom continues has proven vital to determine the
shuttle's health, the boom itself went through a rigorous test during a
seven-hour and 31-minute spacewalk.
STS-121
mission specialists Piers Sellers and Michael Fossum bounced, swayed, pushed
and pulled while perched at the tip of the 50-foot (15-meter) boom, which
itself was attached to Discovery's 50-foot (15-meter) robotic arm.
The tests
were aimed at determining whether the boom would prove stable enough to use
during the delicate operations of a heat shield repair. Spacewalk officials
said the robotic arm-boom combination's oscillations damped out much quicker -
15 to 20 seconds rather than the anticipated minute or more - than they
expected.
"It was
above and beyond what the engineers and us thought how the arm would perform,"
said Tony Ceccacci, lead shuttle flight director for Discovery's STS-121
mission. "That's given us very good confidence in utilizing this whole platform
for [heat shield] repair."
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