Space: Zeroing in on the O Rings

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What might have caused an O ring in the right booster to fail? Panelist Feynman demonstrated one possibility at the public hearing by conducting a simple experiment in front of the TV cameras. He placed a small section of a ring in a C-clamp and submerged it in a cup of ice water. Then, removing the section and releasing it from the clamp, he concluded, "The resilience is very much reduced when the temperature is reduced." That fact may be significant, because the booster joints that the O rings are supposed to seal shift under the enormous stresses of launch. If the rings are not resilient, ! they may not seat properly in their grooves, leaving gaps through which the hot gases can escape. Thus, Feynman asked, would the low temperature (38 degrees F) at Challenger's lift-off have increased the chance of failure?

NASA's Mulloy conceded that the rings start to lose their resiliency at a temperature of 50 degrees F. But despite some reservations expressed the day before the tragedy by booster manufacturer Morton Thiokol, Mulloy said, NASA technicians had concluded (and Thiokol experts concurred) that the seals would work. Mulloy later volunteered that even if the primary O ring failed, the backup ring "would seat as it has done in the past, even under those temperature conditions."

Mulloy's statement seemed at odds with a 1982 NASA report. The document concluded that because of shifting motions in the boosters at launch, the secondary O rings might not seat properly. But NASA decided that the shuttle could keep flying without an assured backup, knowing that the consequences of failure, in the agency's own words, could be "loss of mission, vehicle and crew."

At week's end, as NASA continued to maintain a stiff upper lip about both the rocket's defects and the shuttle's future, Rogers issued a terse but devastating statement: he had advised the President that after only one week of hearings, the commission "has found that the process (of decision making leading up to Challenger's launch) may have been flawed." As a result, NASA was being asked to exclude those of its personnel involved in the launch from any further role on the investigating teams.

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