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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