CAIB - Did they really get the point of

"Cause and Effect"

Extract from Air Safety Week dated 08 Sep 03

Above all, in the aftermath of an accident, the potential for a repeat is perhaps best minimized when both sides of a problem are addressed - cause and effect. In the aftermath of the 1996 fuel tank explosion that destroyed TWA Flight 800, a major hunt for ignition sources was launched (cause). More belatedly, it was recognized that inerting was necessary to nullify the vapors for full protection against explosions (effect).

In the case of the Shuttle's vulnerable RCC leading edge tiles, the CAIB has addressed cause (external tank foam shedding), while breach (effect) remains a vulnerability. The CAIB said more RCC spares should be in hand, swapping them out on the basis of postflight condition, age, tap-tests, tactile tests, and so forth. And, to be sure, the external tank's propensity to shed foam needs to be fixed. But the failure-proofing of the RCC leading edge tiles was relegated to a desirable future "fix." Although not suggested in the CAIB report, the RCC tiles might be failure-proofed from impacts during the ascent phase, and from zinc erosion from flakes landing on the Orbiter from exposed primer paint on the launch pad during the pre-launch weeks spent in the open. One source suggested a protective "glove" or fillet on the RCC tiles, covering at a minimum the vulnerable inboard leading edge areas (where the fatal damage occurred on RCC tile 8, located right where the angle of sweepback changes). Because max Q (the aerodynamic force during ascent) is relatively low, hitting just over Mach 2, a glove on the RCC tiles would protect the brittle leading-edge RCC from the locus of impact and foam penetrating the tile as easily as was demonstrated during the CAIB's impact testing. The glove could be designed to ablate away during the heat of re-entry, providing further protection. Even a leading edge coating of one inch of Silastic might be sufficient to protect the Shuttle's leading edge during ascent - from the pointy trauma of impact.. That "sacrificial" coating would soon burn away under the temperatures of re-entry - but if thin two-strand wires were embedded beneath that Silastic layer atop, beneath and along the leading edge - and could still carry their currents to the wing-tip and back once in orbit, chances are that no RCC tiles would have sustained any significant damage.

The overarching theme of cause and effect emerges from the Shuttle investigation. Culture contributed to a dilution of proactive safety (cause #1). Foam shedding was tolerated, with resulting damage to the Shuttle's "flight critical" thermal protective system (cause #2, among others). Columbia's loss with all hands was the effect.
Space Shuttle Program Needs More Spare Parts, Lawmakers Say
By Marc Selinger
September 11, 2003

A key Senate panel is pressing NASA to develop a plan to buy more spare parts for the space shuttle.

In a report accompanying the fiscal 2004 NASA appropriations bill, the Senate Appropriations Committee suggested that the agency does not have enough spares for the shuttle fleet and that a failure to address the shortages could disrupt future flight plans.

During the investigation of the Feb. 1 Columbia disaster, a reinforced carbon-carbon (RCC) panel had to be removed from the Atlantis orbiter to verify that insulating foam from the external tank could cause damage if it crashed into the wing leading edge. The shuttle's RCC panels are costly and time-consuming to make.

The committee, which approved the bill Sept. 4 (DAILY, Sept. 5, Sept. 8), told NASA to give Congress a detailed description of the shuttle parts shortages, an explanation of how the agency plans to correct the problem, and an estimate of how much the additional parts would cost. The committee said it would like to receive the information from NASA no later than 60 days after the bill is enacted.

"With the need for specialized equipment in order to maintain the safety of the remaining fleet, it is expected that NASA have appropriate inventory of parts available in order to keep the orbiter fleet from experiencing further delay," the committee wrote. "The reliance on the shuttle for at least the next decade and beyond should be reason enough to ensure appropriate levels of replacement parts in order to keep shuttles flying on schedule once the shuttle program has returned to flight."

The shuttle has been rounded since the loss of Columbia. On Sept. 8, NASA released a plan that would return the shuttle to flight no earlier than March (DAILY, Sept. 9).

The committee's recommendations echo those of the Columbia Accident Investigation Board (CAIB), which called on NASA to obtain enough RCC panel spares to ensure that decisions about RCC maintenance are based on component specifications, not cost and schedule considerations. NASA indicated in its return to flight document that it is developing a plan to acquire additional RCC panels as part of its effort to implement the CAIB's recommendations.

Long-ignored pinholes may have aided shuttle's demise / STS-107
SJ Mercury News ^ | 3/12/03 | Seth Borenstein - Knight Ridder
 

Posted on 03/12/2003 8:30 PM PST by NormsRevenge
 

WASHINGTON - Experts have told NASA for years that simply covering the wings of a space shuttle while it sits on the launch pad could prevent a problem that investigators now think may have contributed to the destruction of the shuttle Columbia.

But NASA ignored the recommendation, one of those experts told Knight Ridder on Wednesday, even though the idea had been endorsed by top materials researchers inside and outside the space agency.

Their suggestion was simple: drape the equivalent of a painter's drop cloth over the shuttle's wings to protect them from Cape Canaveral's corrosive sea air and prevent tiny pinholes from forming on the edges of the wings.

Those pinholes - about as wide as three human hairs - began to appear on the leading edges of shuttle wings in

 1992, first in Columbia, then other shuttles. Pinholes develop after about 10 flights. The oldest shuttle, Columbia, broke apart at the end of its 28th flight, and it had suffered far more pinholes than any other shuttle, according to NASA technical reports.

The Columbia Accident Investigation Board is looking at the pinholes as a possible contributing cause of the Feb. 1 tragedy that claimed the lives of seven astronauts, board member Maj. Gen. John Barry said Tuesday. Investigators are trying to find the cause of a breach in Columbia's left wing that allowed hot gas into the shuttle as it re-entered Earth's atmosphere, starting the fatal break-up.

The leading edges of the shuttles' wings are made of carbon-carbon, a composite of various types of carbon that is able to withstand ultra-high temperatures.

"When you have a pinhole, you can have oxidation (corrosion) occur inside the carbon-carbon that makes a gap," Barry said. That gap can then allow hot gas inside, and then grow bigger, experts said.

"Think of termites," board chairman Adm. Harold Gehman said. The carbon-carbon "is built up in layers, the oxidation gets inside and starts opening up gaps from the inside out."

At least five studies by NASA researchers and outside contractors have looked at the pinhole problem since 1995. The most recent ones blame the salty sea air at the Cape Canaveral, Fla., launch site, compounded by flaking paint chips from the launch platform.

Salt interacts with silicon on the carbon surface of the leading edge of the shuttle's wings to form sodium silicates, which melt at a much lower temperature than the carbon, experts said. The addition of zinc-based paint chips doubles the salt's corrosive effect, top NASA materials researcher Nathan Jacobson wrote in a 1998 study.

"The aging launch structure in the corrosive marine environment is the problem here," Jacobson wrote in an agency technical report in November 1998. "Thus the obvious solutions are physical protection of the wings and improvement of the paint on the launch structure."

In the mid-1990s, Ohio State University materials science professor Robert Rapp, who co-authored two studies with Jacobson, told NASA officials at the Johnson Space Center in Houston that the answer to their problems was to cover the wings, Rapp said.

"I don't know why they couldn't design a canvas cover to cover it and keep the salt off it," Rapp, now retired, told Knight Ridder. Jacobson would not comment, citing the ongoing investigation and worries about job security.

That solution became obvious during Houston meetings when engineers were trying to figure out why the pinholes were not found in the shuttle's nose cone, but were in the leading edges of the wings, even though both are made of the same material, Rapp said. The solution came from an off-hand remark by a NASA engineer, who noted that a metal structure that shields the shuttle from the bad weather as it sits on the launch pad is close to the nose cone and also protects it from sea spray.

"You're getting salt spray on the wings and not on the nose cone," Rapp said.

Before its fatal flight, Columbia sat on the launch pad for more than a month, during which 10.6 inches of rain, an unusually high volume, poured down on it.

Ted Paquette, president of Refractory Composites in Glen Burnie, Md., a materials scientist who helped design the wings' leading edge, said the covering solution makes sense: "It wouldn't take an awful lot, if you had some sort of sticky Saran Wrap, if you wrapped it over the leading edge."

NASA still does not cover shuttle wings and has not changed the paint's composition, said agency spokesman Bruce Buckingham. He did not know why changes were not made, he said.

NASA looks for the tiny holes after each flight and fixes them, but that doesn't stop new ones from developing as aging shuttles sit atop the launch pad at Cape Canaveral.

The U.S. Navy has also struggled with salt spray-caused pinholes on F/A-18 jets' exhaust nozzles, which are made of the same materials, Paquette said. This has forced the Navy to retire those parts earlier than it had hoped, he said.

Nowhere in any of the studies did researchers suggest that the pinholes would be a safety problem. Investigators are looking at pinholes as one of what may be many factors in the chain of events that combined to cause Columbia's demise.

During the heat of re-entry into Earth atmosphere - when temperatures rise to 3,000 degrees Fahrenheit - the pinholes could grow slightly, and researchers have replicated that effect in the lab at even lower temperatures, Rapp said.

"These holes are only millimeters, but that is a flaw in the materials for sure," Rapp said. "They don't grow catastrophically, but they enlarge."

Usually the pinholes' tiny size limits their growth because not enough oxygen gets in to feed the flames, rather as a candle flickers when its air supply is cut off, Rapp said.

But the pinholes could grow if other circumstances arose, Rapp said.

About 82 seconds after Columbia's Jan. 16 launch, a suitcase-sized chunk of foam insulation from the shuttle's external fuel tank slammed against the edge of the left wing.

"If something hard hit (the pinholes), it could break it right there," Rapp said. "Then you'd have not a capillary, but a hole and (heat-caused cracking) could really take off."

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