The space shuttle Discovery will launch next week despite concerns from an independent safety group over slight defects on three of the orbiter's wing-mounted heat shield panels, top NASA's officials said late Tuesday.
Shuttle mission managers decided to proceed with Discovery's planned Oct. 23 launch while engineers root out the source of imperfections in the exterior coating of heat shield panels along the spacecraft’s wing leading edges.
"It was quite divided," shuttle program manager Wayne Hale told reporters after a day-long Flight Readiness Review meeting at NASA's Kennedy Space Center (KSC) spaceport in Cape Canaveral, Fla., today. "[There was] a preponderance of evidence, in my mind, that says we have an acceptable risk to go fly.
Hale said that engineers were about evenly split about whether to launch Discovery next week or stand down for repairs, but after a four-hour discussion top managers decided to proceed with the mission while engineers continue to pin down the mechanism that leads to exterior coating defects in shuttle heat shield panels.
Commanded by veteran spaceflyer Pamela Melroy, Discovery's STS-120 astronaut crew is now set to launch from KSC's Pad 39A at 11:38 a.m. EDT (1538 GMT) on a planned 14-day construction flight to the International Space Station (ISS). Melroy and her six crewmates plan to deliver a new connecting node and relocate an older solar array segment outside the ISS during their busy mission.
Last week, NASA's Engineering and Safety Center (NESC), an independent safety group, recommended the space agency delay Discovery's launch in order to replace three of the 44 reinforced carbon-carbon panels (RCC) – two on the right wing and one on the left – that protect the shuttle's leading wing edges from the searing hot temperatures of atmospheric reentry during landings. An inspection technique that uses heat to scan RCC panels found indications of defects in the silicone carbide coating that protects the heat shielding from being burned by super-heated gases while reentering the Earth's atmosphere, Hale said.
NESC director Ralph Roe said his group recommended NASA either replace the panels and perform additional tests before launching Discovery.
Swapping the panels, which are designed to withstand temperatures of up to 3,000 degrees Fahrenheit (1,650 degrees Celsius) during reentry, would prompt a two-month delay in order to haul Discovery from the launch pad to a maintenance hangar and back again. The work could also push the planned December flight of the shuttle Atlantis into early next year.
Discovery flew twice in 2006 with the defects and post-flight inspections found them to be unchanged after each landing, NASA officials said. That performance, and ongoing work to better understand the cause of the defects, prompted space shuttle officials to press forward with next week's shuttle launch, they added.
"It's a very complicated problem, it's a very complicated system and we absolutely need to make sure it works right," Hale said.
NASA officials have kept a close watch on space shuttle heat shield integrity, both during launch and in orbit, since the 2003 loss of the shuttle Columbia and its crew due to left wing RCC damage from fuel tank foam debris.
"I've been very adamant that we are not going to let schedule drive us to making an appropriate decision," Hale said, adding that NASA will continue to reevaluate the heat shield coating concerns as new data comes in. "If the risk grows to an unacceptable level we will take action, whether that's to change some hardware or to delay some flights while we do testing, or what have you."
Discovery's STS-120 mission will mark NASA's third of up to four planned shuttle flights for 2007. In addition to delivering the new connecting node, dubbed Harmony, the shuttle will ferry a new crewmember to ISS to relieve NASA astronaut Clayton Anderson, who has lived aboard the station since last June.
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