1990 study warned of dangers of flying ice and failing tiles

Shuttle's wheel well areas singled out as vulnerable

February 05, 2003|By NEW YORK TIMES NEWS SERVICE

The National Aeronautics and Space Administration was warned in 1990 that the protective tiles around the shuttle's wheel wells were particularly vulnerable to catastrophic failure, partly because of their proximity to fuel tanks and the shuttle's hydraulic system.

The study, conducted by experts at Stanford University and Carnegie-Mellon and financed by NASA, also identified ice that builds up on the super-cold external fuel tank as a major source of debris that could fall on the tiles and trigger a cascade of failures that could doom the spacecraft.

These two observations fit the leading theory emerging so far as investigators attempt to discover what destroyed the space shuttle Columbia. If this theory is correct, it would mean that accidents involving two vulnerable areas -- the foam and the tiles -- combined to destroy the craft.

NASA officials said yesterday that they still believed the object that hit the underside of the wing of the Columbia on takeoff was foam insulation, but there is growing speculation that it might have been mixed with ice.

Video images taken 80 seconds into the flight show the object to be white or light -- the insulation is bright orange -- fueling speculation that NASA engineers might have seriously underestimated its weight when they concluded a blow from a block of rigid foam would pose no safety hazard to the orbiter. The insulation is applied as a shaving cream-like foam, but it turns hard as a brick.

NASA officials also confirmed yesterday that Columbia sat out on its launching pad for 39 days -- more than two weeks longer than usual. That means the shuttle was on the pad for 23 days in December, when the Cape Canaveral area received four times the usual amount of rain.

The unusual weather conditions mean the foam insulation around the 15-story-high external tank was drenched. If that water soaked into insulation or cracks around it, it could have created significant ice when the tank was filled with super-cold hydrogen and liquid oxygen the day before the launch, experts said yesterday.

The study by researchers at Stanford and Carnegie Mellon was particularly significant because it determined that the two wheel areas were especially vulnerable to damage. They were often hit by flying debris, became unusually hot during the shuttle's fiery re-entry through Earth's atmosphere and covered some of the most vital -- and volatile -- sections of the orbiter.

Its helium, liquid oxygen and liquid hydrogen are stored there in pressurized tanks, any of which might explode and rupture the winged spaceship.

If even a single tile were lost in this area, the 1990 report said, a "zipper effect" could occur, stripping away other tiles. The study noted that once several tiles are gone, the resulting heat "could cause a burn through in the aluminum skin of the orbiter during re-entry, exposing and possible crippling some of the critical subsystems and leading to the loss of the vehicle and crew."

Yesterday, one of the authors of the study, Dr. Elisabeth Pate-Cornell, a researcher at Stanford, said NASA headquarters called two days ago to get a copy of the original 1990 study.

"I don't blame them," she said of the space agency's inability to find the study. "I'm the same way."

But the research does not appear to be widely understood in NASA even today. Yesterday afternoon, Maj. Gen. Michael C. Kostelnik, the deputy associate administrator for the space station and the shuttle -- who overseas safety issues -- was asked whether the tiles around the wheel wells were considered a particular safety issue. "Not really that I'm aware of," he said.

He described the protective tiles, which shed heat as the orbiter re-enters the atmosphere, as "a very robust system." Kostelnik joined the agency last year.

The two researchers, Pate-Cornell and Dr. Paul S. Fischbeck of Carnegie Mellon, analyzed the orbiter's 25,000 tiles and identified which were the most likely to fail catastrophically. They did their study for NASA in 1990 and published three academic papers on their work in 1993 and 1994.

Fischbeck was dismayed about NASA's sudden request for a copy of the study the agency itself had sought and paid for. "That was discouraging," he said in an interview.

Even so, the researchers agreed that their warnings in the 1990s had helped NASA improve its maintenance and repair of the shuttle's fragile tiles.

The federal investigation is scrutinizing the left wheel area of Columbia because it might have been hit by flying debris during the shuttle's launch. Moreover, several clues from re-entry, including rising temperatures, suggest the ship's demise might have started there.

The two scientists, who worked closely with NASA managers, engineers and technicians to produce their 1990 study, found that the shuttle's two wheel areas were among a half-dozen dangerous tile zones. Others included the nose area and either side of the shuttle's central belly.

Fifteen percent of the shuttle's tiles contributed to 85 percent of the risk, they found.

Pate-Cornell said one of the 1990 report's recommendations to NASA was to "make sure that the insulation on the external [fuel] tank is applied in a very secure way."

In their report four years later, the researchers estimated that such improvements could reduce the possibility of shuttle accidents attributable to tile failure by about 70 percent.

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