HOUSTON --
A chunk of foam insulation, not ice, damaged the protective belly-mounted tiles
of NASA's space shuttle Endeavour during its launch earlier this week, mission
managers said late Saturday.
Video
recorded by cameras on Endeavour's twin solid rocket boosters during its Aug. 8
launch caught a grapefruit-sized piece of fuel tank foam as it
gouged a 3-inch square (19 square centimeter) gash
into heat-resistant tiles on the orbiter's undercarriage, said John
Shannon, chair of NASA's shuttle mission management team.
"We
feel like we have the culprit," Shannon said in a mission briefing here at
NASA's Johnson Space Center. "I think we have conclusively shown where the
piece of foam came from."
The foam
piece fell
from a lower bracket attaching a 17-inch (43-centimeter) liquid oxygen feed
line to Endeavour's fuel tank about 58 seconds after liftoff, then bounced off
a metal strut to bite into two of the black ceramic tiles near the shuttle's
rear right landing gear door. In addition to the gouge, the foam debris caused
a series of other scuffs aft of the initial impact, Shannon said.
"It
was bad luck because we got a bad bounce off this [external tank] strut," he
added.
Because the
debris appears to be primarily made up of foam, and not denser ice as
originally thought, mission managers are more confident that the damage
inflicted is not be severe enough to require a spacewalk repair. But Shannon
said Endeavour's astronaut crew will conduct an in-depth inspection of the tile
damage Sunday to be sure.
"If we
even have half the tile left, then we're not going to have any issues with this
at all," Shannon said.
Initial
computer modeling, based on the assumption that the foam hit gouged deep enough
to reach close to Endeavour's aluminum skin, found that the orbiter could
return to Earth as is in the event of an emergency, Shannon said. The damage
site is also under a metal support strut, which would soak up excess heat if
the underlying tile were compromised, he added.
NASA has
kept a watchful eye on fuel tank foam debris and shuttle heat shield integrity
since 2003, when an errant chunk of insulation breached the left wing of the
space shuttle Columbia during launch. The resulting damage allowed superheated
atmospheric gases into Columbia's left wing during reentry, leading to the loss of the orbiter and its
seven-astronaut crew.
Since then,
the space agency has redesigned shuttle fuel tanks to lower the amount of foam
shed during launch and instituted mandatory in-orbit heat shield inspections
for orbiter crews.
NASA has
seen foam fall from the brackets along external tank liquid oxygen feed lines
in the past, including on four of the last six shuttle missions since the
agency returned its orbiter fleet to flight in 2005, Shannon said. The STS-26
flight in 1988, the first to fly after the 1986 Challenger accident, returned
safely with similar damage as that seen on Endeavour, he added.
The space
agency found that ice can form on the flexible liquid oxygen feed line as it is
filled with the super-cold oxidizer, which is used along with liquid hydrogen
to fuel a space shuttle's main engines during launch. The ice can later expand
to pop out nearby foam insulation, causing debris.
"It's
a little bit of a concern to us because this seems to be something that has
happened frequently," Shannon said, adding that future tanks will
rely on foam-less, titanium brackets beginning with the flight just before the September 2008 launch
to service the Hubble Space Telescope.
In the
meantime, the likelihood that a spacewalk repair will be required for Endeavour
appears to be dwindling based on the new data, Shannon said.
"I
would say that that is much more doubtful than it was yesterday," he added.
Commanded
by veteran shuttle flyer Scott Kelly, Endeavour's STS-118 mission is delivering
fresh cargo, spare parts and a new structural piece to the ISS. The mission
also marks the first flight of teacher-turned-astronaut
Barbara Morgan, who was selected as NASA's backup Teacher in Space in 1985
and will help perform Sunday's focused heat shield inspection.
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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