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Foam still vexes NASA after fixes to shuttle

June 26, 2006

By Irene Klotz

CAPE CANAVERAL, Florida (Reuters) – It’s been 3.5 years and
hundreds of millions of dollars since the space shuttle
Columbia disintegrated. Yet NASA faces the same vexing problem
that doomed the orbiter when it tries to launch shuttle
Discovery on Saturday.

Insulation foam — it seems a trivial part of launching a
complex spacecraft. But the problem of falling foam has
perplexed the U.S. space agency capable of doing what no other
country does, landing a space freighter like an airplane.

Outfitted with a second round of upgrades to its fuel tank
following the 2003 Columbia disaster, Discovery is on the
launch pad and scheduled to fly at 3:49 p.m. EDT (1949 GMT) on
July 1.

If successful, NASA plans up to 17 more shuttle missions,
including a possible servicing call to the Hubble Space
Telescope, before the shuttle fleet is retired in 2010.

If not, and if the U.S. space agency were to lose a third
shuttle to disaster, NASA Administrator Michael Griffin has
said he would likely pull the plug on all future missions.

NASA lost Challenger on January 28, 1986, due to the
failure of an O-ring seal on a solid rocket booster.

Then Columbia disintegrated during re-entry on February 1,
2003, when its wing was damaged by foam debris that fell from
its external fuel tank during launch.

The 1.6-pound (0.7 kg) chunk of insulating foam smashed
into the ship’s left wing. It pierced a hole in the orbiter’s
protective heat shield that caused its breakup and the loss of
all seven crewmembers aboard as Columbia slammed into the
atmosphere on its fatal re-entry toward Earth.

In July 2005, NASA launched shuttle Discovery to test-fly a
new fuel tank design — but the fix turned out to be nearly as
troublesome.

More foam insulation, including a piece as large as one
pound (0.4 kg), dislodged as the shuttle rocketed toward orbit.
Luckily, none of the debris struck the shuttle.

NEW TECHNIQUES

NASA has since implemented new manufacturing techniques and
removed two long foam windshields that tests showed were not
necessary to protect cables and hoses running along the outside
of the tank. The ramp-shaped structures had been used since the
first shuttle flight in 1981.

Engineers have also reworked wiring for heaters that were
installed as part of the first redesign. The heaters replaced
foam insulation where the tank is attached to the shuttle.

After Discovery’s 2005 flight, NASA discovered that
insulation around the wiring had trapped air, which turned to a
liquid in the cold and filled tiny voids in the foam. As the
pressure changed during launch, the liquid transitioned to gas
and popped off pieces of foam.

But the foam debris issue still has not been resolved. And
NASA’s top safety official, along with its chief engineer, both
recently voted against clearing Discovery for its July 1
launch. They were overruled by NASA administrator Michael
Griffin and other top managers.

The shuttles have flown 114 space missions, and only two
have ended in tragedy. But 14 astronauts died in the Challenger
and Columbia disasters and two of the five shuttles built were
lost. They cost around $2 billion each and are viewed as
irreplaceable.

As engineers learned more about the physics of foam, NASA
realized it was not going to be possible to manufacture a
shed-free tank.

The foam is needed to prevent ice buildups as the shuttle
sits awaiting liftoff with cryogenic propellants in its fuel
tank. Ice can be even more dangerous than foam if it breaks off
during launch and hits the spacecraft.

“Foam will come off. There is no way around that. It’s the
very nature of the material and the way that we use it and the
way we apply it,” said John Chapman, who oversees the external
tank project at NASA’s Marshall Space Flight Center in
Huntsville, Ala.

But Chapman said steps had been taken to minimize foam
falling off and prevent the dislodging of chunks large enough
to damage the shuttle’s heat shield.

The shuttle lifted off under the gaze of dozens of sensors
and cameras last year and will have even more this year.

It also has been outfitted with stronger windows, beefed up
tires and landing gear and more than 5,000 new cloth fillers
between the most critical heat-resistant ceramic tiles on its
belly.

During Discovery’s previous flight, photographs taken by
space station crewmembers as the shuttle approached showed two
fillers slightly protruding from the smooth surface.

Engineers grew concerned that the tiny misalignment could
cause the shuttle to heat up earlier than expected during its
plunge through the atmosphere and possibly damage its heat
shield. The shuttle crew conducted an unplanned spacewalk to
remove the cloth strips.

Cameras, both aboard the shuttle and on the ground, will
photograph and videotape every second of the launch, while
sensors aboard the ship will monitor vibrations, speeds,
temperatures and other data.

Still, when 2.5 million moving parts catapult through the
atmosphere, the odds of something going terribly wrong remain a
sobering one in 100, said shuttle program manager Wayne Hale.

“If you’re not scared when we fly the shuttle, you’re not
understanding what’s going on,” he said.


Source: reuters



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