For NASA, Misjudgments Led to Latest Shuttle Woes
FYI,
"For NASA, Misjudgments Led to Latest Shuttle Woes"
NY Times/Drudge Report
http://www.nytimes.com/2005/07/31/science/space/31foam.html?ei=5065&en=93280ea1193e7512&ex=1123387200&partner=MYWAY&pagewanted=print
: It was June 24, and William W. Parsons, NASA's shuttle program manager, was
: speaking to reporters on a telephone conference call from the Kennedy Space
: Center at Cape Canaveral, Fla. Two and a half years of study and struggle, he
: told them, were over at long last. The shuttle Discovery could blast off in July.
: At a closed-door meeting that afternoon, senior shuttle managers had ruled that
: the chances that debris from the giant external fuel tank would strike the
: Discovery at liftoff - in the kind of accident that doomed the Columbia and its
: seven astronauts in February 2003 - had been reduced to "acceptable levels."
: The possibility that a large chunk of insulating foam might break away from a
: section of the tank called the protuberance air load ramp - PAL for short -
: never came up. It had been ruled out months earlier, checked off on a long list
: of items no longer worthy of urgent action.
: Last Tuesday morning, NASA's contention that it had produced the safest fuel
: tank in shuttle history was shattered two minutes into the Discovery's mission
: to the International Space Station.
: The 0.9-pound piece of foam that fell from the PAL ramp on liftoff, which could
: have led to another catastrophe if it had ripped away a minute sooner, forced
: the immediate suspension of future shuttle flights until the problem could be
: resolved.
: How did it happen? In hindsight, it is clear that the effort to resolve the PAL
: ramp problem was a chain of missed opportunities and questionable judgments, not
: just since the Columbia disaster but over the life of the shuttle program.
: Potentially useful tests were not performed. Innovative solutions were not
: seriously pursued. Tantalizing clues were missed. In the end, the old
: engineering maxim "If it ain't broke, don't fix it" trumped vague misgivings
: about a part that had not shed any foam, as far as anyone knew, since 1983.
: At the dawn of the shuttle program, NASA rules said no foam at all should be
: allowed to hit the shuttle and possibly damage the fragile heat-resistant tiles
: that cover its aluminum skin.
: But fidelity to those standards was relaxed over time; in fact, foam fell from a
: PAL ramp in two early missions, including the one in June 1983 on which Sally
: Ride became the first American woman in space. There may have been many more
: incidents, but dozens of shuttle missions have been launched in darkness, with
: no visual record of foam, and the tanks themselves cannot be retrieved from the
: ocean for analysis.
: As the early tank was replaced with two lighter successors, the PAL ramps
: remained - one a 19-foot baffle along a channel for cables and pressurized lines
: along the forward end of the tank and the other the 37-foot strip along the
: flank of the cylindrical midsection of the fuel tank. And as experience showed
: NASA that shuttles returned safely despite well over 100 nicks and gouges
: requiring repair on many flights, the concerns abated over time.
: Until Feb. 1, 2003, the day the Columbia disintegrated on its way home to Cape
: Canaveral.
: He said that while it was premature to conclude whether mistakes were made, many
: panel members were frustrated with the lack of physical testing of the foam
: under liftoff conditions.
: NASA engineers had already seen how fixes can break things. After they made a
: minor change in the foam application process in the late 1990's to comply with
: environmental rules, small divots of foam rained off of the tank during ascent.
: The phenomenon, called popcorning, was caused by trapped bubbles; NASA solved
: the problem by venting the foam with tiny holes, but it was a reminder, if any
: was needed, that seemingly small changes could have profound effects.
: "Foam really is complicated," said Douglas D. Osheroff, a professor of physics
: at Stanford and a member of the board that investigated the Columbia accident.
: "Once you go supersonic, the top surface melts, the bottom surface is brittle as
: all hell because it's very cold, and you've got everything in between."
: Among other things, it improved the training processes for applying foam by
: hand. At the Michoud tank assembly plant in Louisiana, an observer monitors
: every worker spraying foam - "for every sprayer there's a watcher, a second pair
: of eyes," said June Malone, a NASA spokeswoman.
: But the tank that flew with the Discovery last week was made before the new
: procedures went into effect, and NASA stopped short of requiring that the ramps
: be redone, said a spokesman, Martin J. Jensen.
: At its final meeting in June, however, it also found that NASA had failed to
: meet the goal of eliminating all debris. The group took issue with the way NASA
: determined that the foam chunks that might still fall off the tank were too
: small to cause critical damage. And it criticized the agency's tendency to
: depend on computer simulations when physical experiments might yield more
: valuable data.
: At its final meeting in June, however, it also found that NASA had failed to
: meet the goal of eliminating all debris. The group took issue with the way NASA
: determined that the foam chunks that might still fall off the tank were too
: small to cause critical damage. And it criticized the agency's tendency to
: depend on computer simulations when physical experiments might yield more
: valuable data.
--
Mark Reiff <markreiff@xxxxxxxxxxxxx>
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