Foam Was Largest Piece to Hit A Shuttle
Wednesday, February 5, 2003
The chunk of insulating foam that broke free from shuttle Columbia's external fuel tank Jan. 16 was the biggest piece of debris ever to hit a shuttle during launch, and only two previous launches have encountered even moderately large impacts from the tough insulating material, a NASA official said yesterday.
That suggests that NASA engineers had little practical experience to rely upon as they weighed the potential importance of the event -- and as they made their decision, days later, to write off the collision as probably no threat to the shuttle's safety.
The new detail about foam debris impact described by Michael Kostelnik, a NASA deputy associate administrator, was one of several pieces of new information to shed light yesterday on the frustrating level of uncertainty that engineers had to work with as they decided whether to ignore the incident or perhaps design a radical plan to bring the crew home safely.
Among the uncertainties were the potential effects of the debris not only on the shuttle's ceramic tiles -- the major focus of NASA's attention -- but also on the reinforced carbon leading edges of the shuttle's left wing, which are stronger than the tiles in some respects but have their own vulnerabilities.
Also yesterday, NASA officials sent teams to California and Arizona to check reports that pieces of Columbia had been found in those states, which would be the farthest west that debris from the high-altitude crash had been found. Officials are very interested in looking at the most westward pieces from the breakup, on the assumption that those pieces would reveal which part of the spacecraft was the first to fail.
Last night, local officials reported finding a portion of what they believed to be a shuttle wing in a pond in Texas. And in a tantalizing development that could offer additional clues, the military yesterday confirmed that one of its Apache helicopters flying over Texas early Saturday had caught images of the shuttle on its approach. Details of the footage were not available yesterday.
Investigators have said the apparent collision between a dislodged piece of fuel tank insulation and the shuttle's left wing -- noted on video about 80 seconds after launch -- is their leading candidate as the cause of Saturday morning's disintegration of the shuttle.
At the same time, NASA officials have repeatedly expressed doubt that such a collision would be capable of damaging the shuttle's protective surfaces enough to jeopardize the spacecraft through the heat of reentry as it hurtled back to Earth.
Their confidence, they have said, was based on both empirical evidence -- the many previous times that tank foam has pelted the craft upon liftoff with no serious effects -- and on computer modeling they conducted both before and after Columbia's voyage, which suggested the impacts did not pose a "safety of flight" issue.
But Kostelnik's comment at a Washington news briefing yesterday that the slab of hardened foam -- estimated to weigh 22/3 pounds -- "probably is the largest piece" ever to hit the shuttle on takeoff undermines the agency's supposition that the lack of trouble in the past was predictive of a safe return on this flight, experts said.
If one in only three large-scale foam impacts -- or "instances of significance," as Kostelnik called them -- can result in the loss of a shuttle and its crew, experts said yesterday, the overall safety of the shuttle may be less than NASA presumed, and it becomes important to know the probability that similar sized or even larger chunks of foam might break off on future flights.
"We need to find out how big a piece could come off and how often might this happen," said Robert K. Weatherwax, president of Sierra Energy and Risk Assessment, a Roseville, Calif., company that has analyzed shuttle safety. "This is reminiscent of the bad old NASA," he said, referring to what he said was an old habit at NASA of being overly optimistic in its assessments of dangers.