Shuttle explosion risk?
- From: "hallerb@xxxxxxx" <hallerb@xxxxxxx>
- Date: Sun, 03 Jun 2007 23:17:12 -0000
Orbiters feel pains of aging
NASA taking precautions in fear tanks could burst
BY TODD HALVORSON
AND JOHN KELLY ADVERTISEMENT
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Warning. NASA will begin pressurizing gas tanks aboard Atlantis and
then close pad 39A to all but essential personnel as a safety
precaution. Michael R. Brown, FLORIDA TODAY
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CAPE CANAVERAL - NASA is moving to protect ground crews, astronauts
and VIPs from potential disaster, closing shuttle Atlantis' launch pad
to all but essential personnel even before a three-day countdown
starts Tuesday.
No up-close-and-personal tours will take place at Kennedy Space
Center's launch pad 39A next week after NASA finishes pressurizing
helium and nitrogen tanks aboard the 22-year-old spaceship, which is
scheduled to launch at
7:38 p.m. Friday.
The precaution is being taken to reduce the risk created by aging
pressure vessels in the orbiter that could burst, triggering a rocket
fuel fire or explosion that might injure or kill workers and seriously
damage the launch pad.
The tanks "can explode without warning at normal operating pressures,"
a safety bulletin sent to workers Friday said. Shrapnel from an
exploding tank "would be dangerous to personnel and could potentially
puncture adjacent hypergolic fuel systems resulting in fire, explosion
and toxic cloud release," the bulletin added.
NASA records obtained by FLORIDA TODAY under the Freedom of
Information Act show that the problem is one of the top risks facing
the shuttle program. It is also an example of obsolescence issues
bound to crop up before NASA retires the three orbiters in 2010.
"It's a serious problem, and it is one of a number of problems that I
would call 'aging aircraft' issues that we face with these vehicles,"
shuttle program manager Wayne Hale said. "So we're trying to
understand exactly what the hazard is, and how to accommodate it."
Here's the situation:
Shuttle orbiters are equipped with 24 helium and nitrogen gas tanks
that pressurize the shuttle's main propulsion system, orbital
maneuvering engines and nose-and-tail steering thrusters.
The spherical tanks provide pressure needed to push rocket propellants
into shuttle engines and thrusters at very specific rates required to
keep the spaceship on its proper course. Some of the propellants are
highly volatile and ignite on contact.
Ranging in diameter from 19 to 40 inches, the tanks have lightweight
titanium or steel shells wrapped with the same type of fabric used to
make bulletproof vests -- Kevlar -- or carbon graphite. They hold
helium and nitrogen gas at extremely high pressures (up to 4,600
pounds per square inch) and are extraordinarily dangerous.
"You certainly wouldn't want a 4-foot-diameter helium bottle that's
pressurized to about 4,000 psia to burst on you," Hale said. "That
would be a bad thing."
A tank rupture on the ground could lead to a fire or explosion that
could injure or kill workers in the launch pad area. A failure in
flight could lead to the loss of a shuttle and the astronauts inside.
NASA nonetheless is poised to proceed with the launch of Atlantis and
seven astronauts on an International Space Station assembly mission.
"I would characterize it as serious but not a showstopper kind of
problem," Hale said. "It's certainly not something somebody has
trumped up to get attention. I mean, this is a nontrivial engineering
problem. It's quite complex."
Built for NASA in the late 1970s and early 1980s, the copper-
colored spheres were designed, developed, manufactured and tested for
10 years of shuttle fleet operations.
The NASA records show that proper engineering analyses were done in
1988 to certify the tanks for an additional decade of use. But no
subsequent recertification was done in 1998 when the agency's extended
warranty expired.
NASA engineers raised questions about the tanks, which are named
Composite Overwrap Pressure Vessels, as the agency was struggling to
return the shuttle fleet to service after the 2003 Columbia accident.
The aerospace industry already had expressed concern about the
structural integrity of similar tanks on satellites and aircraft, and
the agency's newly anointed NASA Engineering and Safety Center took up
the cause in 2004.
The safety center's engineers concluded the orbiter tanks are much
more likely to fail than NASA previously thought.
Past NASA analyses assumed the tanks would leak before they burst. New
studies and tests show that they would explode before they leaked,
increasing the hazard considerably.
The new tests were done at NASA's White Sands Testing Facility in New
Mexico, and another series aimed at more accurately pinpointing the
risk is getting under way.
New tanks are not an option. The original vendor is out of the
business and the agency would not be able to qualify a new producer
before the shuttles' retirement. So NASA is changing the way it
operates to reduce the risk.
Pressure within the tanks aboard Atlantis will be brought up to 80
percent -- rather than 100 percent -- this weekend, a move meant to
lessen the amount of time full pressure is maintained before launch.
The launch pad will be cleared of all but essential personnel when
pressure is increased to full flight levels Monday.
"We go through our standard two-stage pressurization trick now and do
that as close to launch countdown as possible. The principal risk is
to the ground crews, and so we clear the pad when we go through the
pressurizations," launch director Mike Leinbach said.
"This is an ongoing activity," Hale said. "We believe that we have an
adequate level of safety for the upcoming flight, and we have a longer
program of engineering tests to try to more specifically indicate what
we might do to mitigate those problems."
Contact Halvorson at 639-0576 or thalvorson@xxxxxxxxxxxxxxxxx
.
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