HOUSTON -- A
preliminary analysis of the gouged heat shield tile on the belly of NASA's
space shuttle Endeavour shows promise that a spacewalk repair may not be
required, but NASA will await additional tests to be sure, mission managers
said late Tuesday.
Initial
computer modeling of the small, but deep, ding
on Endeavour's undercarriage found that the damaged area would not leave
the orbiter vulnerable to the searing hot temperatures of reentry, they added.
"We're
cautiously optimistic that we can fly as is," John Shannon, chairman of
Endeavour's mission management team, told reporters in a briefing here at NASA's
Johnson Space Center.
Shannon
said the preliminary computer analysis is undergoing an independent
verification to ensure its accuracy. Meanwhile, more tests over the next 24
hours will use subject mockups of the tile damage to the same extreme temperatures
Endeavour will face during landing, as another check of that initial study, he
added.
A final
decision on whether Endeavour's STS-118 spacewalkers will have to venture beneath
the orbiter's underbelly for to make repairs is anticipated by late Wednesday,
NASA said.
A piece of
debris fell from a fuel tank bracket and bounced off a metal strut to carved the
3 1/2-inch by 2-inch (9-centimeter by 5-centimeter) gash in Endeavour's fragile
heat-resistant tiles about one minute after the orbiter's Aug. 8
launch. The damage etched all the way through a tile to expose about one inch
(2.5 centimeters) by one-quarter inch (0.5-centimeter) wide.
Preliminary
report
According
to the preliminary look, the surface of the gouged tile on Endeavour's belly
will experience between 2,000 and 2,100 degrees Fahrenheit (1,093-1,148
degrees Celsius), with temperatures on the inner felt strip near the
shuttle's aluminum skin reaching about 325 degrees Fahrenheit (162 degrees Celsius).
The upper
limit for heating on Endeavour's hull at the damaged area is about 350 degrees
Fahrenheit (176 degrees Celsius), Shannon said. Ongoing tests planned for late
Tuesday and Wednesday should double check that initial finding, he added.
If a repair
is ultimately required, mission managers would likely delay a planned Friday
spacewalk, the fourth for Endeavour's STS-118 crew, until Saturday and possibly
extend the already extended
14-day mission. The success of a new space station-to-shuttle power
transfer system has allowed Endeavour to conserve enough supplies to stay at
the ISS three additional days, mission managers said.
The repair
plan would call for two spacewalkers to perch at the end of Endeavour's
100-foot (30-meter) robotic arm and inspection boom and coat the dinged tile
with a heat-resistant black paint, then fill it with an ablative goo-like
material called STA-54, NASA said.
Image analysts
pinned down the size and mass of that debris, finding it to be a 4-inch by
3.8-inch (10- by 9.6-centineter) piece of foam about 1.8 inches (4.5
centimeters) thick. The debris weighed about 0.021 pounds (about one-third of
an ounce), Shannon added.
Earlier
Tuesday, STS-118 commander Scott Kelly told reporters that he believed
Endeavour was safe to return to Earth as is, but felt comfortable performing a
repair if required.
"My
understanding is that this tile damage is not an issue of the safety of the
crew," Kelly said.
NASA has
kept a close watch on the shuttle heat shield damage and fuel tank debris since
a combination of both led to the catastrophic
loss of the Columbia orbiter and its crew in 2003.
Fuel
tank discussions
While
mission managers discuss whether a repair for Endeavour is required, Shannon
said shuttle officials are beginning to turn an eye to future flights to
complete assembly of the ISS by September 2010.
Since NASA
returned its three-orbiter fleet to flight after the Columbia accident, the
agency has seen an increased amount of foam shedding similar to that on
Endeavour's current flight. That history, Shannon said, has prompted some
discussions that an extra hour added to launch countdowns for fuel tank checks
may allow more ice to build up and lead to debris events, mission managers
said.
On Friday,
shuttle officials plan to discuss plans to mate a new fuel tank to its solid
rocket boosters for NASA's STS-120 mission aboard Discovery. That mission is
slated to launch in late October to deliver the new Harmony connecting node to
the ISS.
"The
program will look at what checks we need to do before we mate to the solid
rocket boosters," Shannon said.
NASA is
broadcasting Endeavour's STS-118 mission live on NASA TV. Click here for mission updates and
SPACE.com's NASA TV feed.
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