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NASA Computer Program Decides Shuttle Landings

Posted on: Wednesday, 26 February 2003, 06:00 CST

NASA's Computer Evaluations Have Long History with Shuttles, Officials Say

HOUSTON (Dallas Morning News) -- Critics have questioned how it was used, but the computer program that helped NASA decide Columbia could land safely has been employed effectively since early in the space shuttle program, officials say.

"It's used in almost every instance where we have debris impact on launch," said Michael Mott, vice president-general manager of NASA systems for Boeing Co., which runs the program. "Any time we have a token amount of concern, we bring out all the big guns."

But the program, known as "crater," is only as good as the information fed into it and the quality of management evaluation after it reaches its conclusions, said Paul Fischbeck, a Carnegie Mellon University expert on the risk of damage to the shuttle's heat shield.

That decision-making has raised questions, particularly in a series of internal e-mails between NASA support personnel who focused on risks to the left landing-gear wheel well while Columbia was aloft.

The program was developed early in the shuttle program, when it became apparent NASA needed a tool to evaluate damage like that Columbia may have sustained shortly after liftoff Jan. 16 – insulation, ice or some combination falling off the external tank and striking the orbiter.

Crater, the second step in a three-step process, can provide only part of the answer, Dr. Fischbeck said.

"What it does is it determines how much tile damage would be done given an impact of a certain size angle and velocity," he said.

Estimates of the size of debris, its angle of impact and its velocity have to be fed into the program. Then, when the computer program has projected damage to the fragile tiles, mission managers must decide how much risk that represents to the shuttle and its crew.

Internal e-mails released by NASA since the Feb. 1 disaster make clear that engineers inside the agency questioned the reliability of the data that crater was fed and the thoroughness of management's evaluation of the computer program's findings.

"I am advised that the fact that this incident occurred is not being widely discussed," wrote Mark Shuart, a manager at NASA's Langley Research Center in Virginia in an e-mail Jan. 28, four days before the shuttle broke apart, killing all seven astronauts.

Noting that crater's current estimate of damage was 7 inches by 30 inches on the left wing, engineer Robert Daugherty warned Mr. Shuart of a possible breach in the left landing-gear well.

"One of the bigger concerns is that the 'gouge' may cross the main gear door thermal barrier and permit a breach there," Mr. Daugherty wrote in an e-mail.

Mr. Daugherty also warned that a hole in the shuttle's thermal protection barrier during re-entry could expose the wheel well to temperatures of about 3,000 degrees, compared with the approximate 1,000-degree melting point of aluminum.

The aluminum wheel could soften and the tire could explode, blowing open a wheel-well door or setting off the explosives used to back up hydraulic systems for lowering the wheels.

Either could damage sensitive equipment nearby, Mr. Daugherty wrote; the result could be "catastrophic."

In another e-mail, engineer Dennis Bushnell at Langley questioned why a vent pipe off the external tank hadn't been moved away from the shuttle because it had proved to be a threat – dropping ice from the supercold tank onto the orbiter.

"Why this dump line was not repositioned to the other side of the tank ... I do not understand," he wrote Feb. 5.

Another Langley engineer, Daniel Mazanek, said that if the debris that struck the wing were something denser than foam – say, ice – the impact could be "the equivalent of a 500-pound safe hitting the wing at 365 mph."

The team that ran the computer program "spent hours and hours.

... This isn't something that's not done with a lot of rigor," said Mr. Mott of Boeing.

"There is no question in my mind that these folks ... absolutely turned over every rock and made sure that they had looked at this every way humanly possible to insure the safe return of the crew," he said. "There's an unbelievable commitment to safety."

(c) 2003, The Dallas Morning News. Distributed by Knight Ridder/Tribune Business News.

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