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Tie between foam heat spike { April 16 2003 } Original Source Link: (May no longer be active)
http://www.nytimes.com/2003/04/16/national/nationalspecial/16SHUT.htmlhttp://www.nytimes.com/2003/04/16/national/nationalspecial/16SHUT.html
April 16, 2003
Panel Looks at Tie Between Foam Piece and Heat Spike
By JOHN SCHWARTZ
HOUSTON, April 15 - Members of the board investigating the Columbia disaster said today that they now believed that the spot where a large piece of foam struck the shuttle during launching was very close to sensors that detected a temperature spike of hundreds of degrees in the minutes before the breakup.
The temperature readings, from a data recorder that survived the disintegration and the long fall to earth, lend support to the theory that the strike by the foam debris 80 seconds after liftoff doomed the shuttle.
At their weekly briefing here, the board members also said the debris could have broken a seal on the leading edge of the left wing, letting superheated gas flow into the wing as the Columbia re-entered the atmosphere on Feb. 1.
The board members also said they were preparing recommendations to improve safety at NASA even if they could not pinpoint a cause.
"We don't have a scenario du jour," said Adm. Harold W. Gehman Jr., who is chairman of the board. Admiral Gehman, who is retired, added that even if the inquiry failed to provide a definite chain of events, "there is no doubt that heat got in there someplace."
The board recommendations will include more thorough inspections of aging materials, as well as changing the management culture to make the space agency more open to warning signs of disaster.
This week, the investigation focused on a part of the leading edge of the wings called a T-seal because of its shape. T-seals are between each leading-edge panel on the wing. The two components are made of the same heat-resistant composite.
The piece of insulating foam that hit after liftoff might have caused a T-seal to break where the top of the T meets its trunk. That would have left a slit eight inches long and more than an inch wide that superheated gases could have poured through. That part of the seal, investigators theorize, could be the mysterious object seen on radar floating away from the shuttle on the second day of the mission.
A theory that the object was a carrier panel has largely been dismissed, because the panels in question have been accounted for in the debris, board members said.
Admiral Gehman said after the briefing that recovered T-seal fragments all broke at the same spot "like a wishbone."
A board member, G. Scott Hubbard, cited three fundamental lines of inquiry, the visual evidence of where the foam chunk hit, the physical evidence of damage on recovered debris and the heat measurements from hundreds of sensors.
"Currently," Mr. Hubbard said, "the data are not all pointing in the same direction."
He said, however, that analysis of videotape of the launching suggested that the foam struck a little farther out on the wing than earlier analysis had indicated. A recovered panel from that area bears spatters of molten metal "much heavier than elsewhere," and the half-inch-thick panels in that area were eroded "to knife edges," presumably by long exposure to high heat, Mr. Hubbard said. The heat sensor closest to that spot also showed a temperature rise of hundreds of degrees more than two minutes before sensors farther back in the wheel well showed increases.
"We're closing in on it, but it continues to evolve," he said.
Age has not been kind to the shuttle fleet. NASA has been concerned for years about the possibility of erosion in the leading-edge panels, studying pinholes and other flaws on older panels since the early 1990's. Last week, NASA released hundreds of pages of shuttle maintenance logs under Freedom of Information Act requests. The files showed, for instance, that a two-inch gash in the leading edge of the Discovery was found after a mission in March 2001.
Shuttle investigators say they have ascertained that the two-pound foam piece hit the Columbia with more than 1,700 pounds of force. Mr. Hubbard said testing could show whether the panels, especially those in worse shape, could sustain such a blow without breaking. All but three panels were original, said Rear Adm. Stephen A. Turcotte of the Navy, a board member.
The board also announced that its large-scale search for debris would wind down by April 30 and that more than one-third of the pieces by weight had been recovered.
Admiral Gehman spoke of the general fragility of reinforced carbon- carbon panels and T-seals, saying they were "designed not to be damaged in handling." A blow from a wrench or a pen could begin the process that would eventually let in heat.
"It was not designed to ever take any hits whatsoever," he said. "And the fact that it is being hit hundreds of times is a concern."
Copyright 2003 The New York Times Company |
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