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.
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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