HOUSTON --
NASA engineers are running a battery of tests to determine whether Endeavour
shuttle astronauts will have to repair a deep gouge on their orbiter's underbelly,
while a separate team weighs the best of three options for any fix required,
mission managers said Monday.
John
Shannon, chairman of Endeavour's mission management team, said a decision on
whether any repair is required is expected by Wednesday.
A piece of fuel
tank debris struck Endeavour's belly-mounted tiles 58 seconds after launch
on Aug. 8, carving the 3 1/2-inch by 2-inch (9-centimeter by 5-centimeter)
gouge. The debris did penetrate through the tile to expose a small strip of
felt about one inch (2.5 centimeters) wide and 0.2 inches (0.5 centimeters)
long.
The damaged
tile, however, does not represent to risk for Endeavour's STS-118 astronaut crew,
but rather the orbiter itself, Shannon said. The shuttle's heat shield is sound
enough to return its crew to Earth safely in an emergency, but mission managers
hope to avoid causing any additional damage to the spacecraft that would
require lengthy repairs before its next construction flight to the
International Space Station (ISS), he added.
"This
is not a catastrophic loss of orbiter case at all," Shannon told reporters
during a briefing here at NASA's Johnson Space Center. "This is a case
where you want to do the prudent thing for the vehicle."
Engineers are
subjecting mockups of the damaged tile to the same searing temperatures
Endeavour will experience during its planned reentry and landing on Aug. 22, as
well as running computer model analysis. The results of those tests should
determine whether a repair is required, Shannon said.
NASA has
kept a watchful eye on fuel tank debris and the health of its shuttle heat
shields since the 2003 Columbia
accident, when a piece of foam insulation breached that orbiter's left wing
and led to the loss of the spacecraft during reentry.
Weighing
options
Meanwhile,
a second team is evaluating whether a heat-resistant paint, a carbon-composite
overlay or an ablative goo-like material would be the best method of repairing
Endeavour's dinged tile.
Joel Montalbano,
NASA's lead ISS flight director for STS-118, told reporters that any repair, if
required, would not occur before a planned Friday spacewalk.
Montalbano added
that mission managers are also eyeing options of extending Endeavour's construction
flight up to three extra days should any fix be required. Another option
includes the possibility of adding a fifth spacewalk to the already extended
mission, he added.
Endeavour's
STS-118 mission to the ISS is delivering cargo, spare parts and a new piece
to the station's starboard truss. The success of a new power
transfer system, which allows Endeavour to siphon electricity from the
station's solar power grid and conserve its own resources, led mission managers
to stretch the orbiter's flight from an initial 11 days to 14 days and add a fourth
spacewalk to the STS-118 crew's docket.
Mystery
debris
The debris
that struck Endeavour fell from a fuel tank bracket at a rate of about 204
miles an hour (328 kph) 58 seconds after the shuttle's
Aug. 8 launch, bounced of a metal strut and hit the orbiter's tiles at
about 141 miles per hour (226 kph), NASA said.
About the
size of a baseball, the debris was initially thought to be ice before engineers
shifted on foam insulation. But it may actually have been foam, ice or a piece
of ablative material a bit denser than foam, Shannon said.
"We
wouldn't expect just foam to look like that," Shannon said. "So it's
a little bit of a mystery."
That the
debris managed to damage Endeavour in the first place also surprised engineers,
since previous studies showed that foam debris from the bracket region would either
miss an orbiter entirely or be destroyed if it hit a tank strut.
Engineers
will study the debris event to determine if the foam-covered shuttle fuel tank
brackets, which secure a liquid oxygen fuel line in place, will have to be
modified in any way before NASA's next shuttle flight in October. Any lengthy
fix, if required, could temporarily stall shuttle flights and delay NASA's already
tight schedule to launch at least 11 more missions to complete assembly of the
ISS.
"The
tank is going to shed some foam," Shannon said, adding that while NASA
continues work to minimize such debris but there will also be some shedding.
"It's our challenge to understand why, and then go and fix that if
possible."
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