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of political entanglements. Despite Rogers’s disapproval he insisted on conducting his own lines of inquiry and traveled alone to interview engineers at the Kennedy Space Center in Florida, the Marshall Space Flight Center in Alabama, the Johnson Space Center in Houston, and the headquarters of several contractors. In between, he made repeated visits to a Washington hospital for blood tests and medication for his worsening kidney, and he talked by telephone with his doctor in California, who complained about the difficulty of practicing medicine at long distance. “I am determined to do the job of finding out what happened—let the chips fall!” he wrote Gweneth proudly. He enjoyed the thrill of the game, and he suspected that he was being carefully managed. “But it won’t work because (1) I do technical information exchange and understanding much faster than they imagine”—he was, after all, a veteran of Los Alamos and the MIT machine shop—“and (2) I already smell certain rats that I will not forget.”

He tried to make use of his naïveté. When Rogers showed him a draft final recommendation, effusive in its praise of the space agency—

The Commission strongly recommends that NASA continue to receive the support of the Administration and the nation. The agency constitutes a national resource and plays a critical role in space exploration and development. It also provides a symbol of national pride and technological leadership. The Commission applauds NASA’s spectacular achievements of the past and anticipates impressive achievements to come… .

—he balked, saying he lacked expertise about such policy matters, and he threatened to withdraw his signature from the report.

His protest was ineffective. The language appeared virtually intact, as the commission’s “concluding thought” rather than a recommendation. Although the commission learned that the decision to launch had been made over the specific objections of engineers who knew of the critical danger from the O-rings, the final report did not attempt to hold senior space-agency officials responsible for the decision. Evidence emerged showing that the history of O-ring problems had been reported in detail to top officials, including the administrator, Beggs, in August 1985, but the commission chose not to question those officials. Feynman’s own findings, substantially harsher than the commission’s, were isolated in an appendix to the final report.

Feynman analyzed the computer system: 250,000 lines of code running on obsolete hardware. He also studied in detail the main engine of the shuttle and found serious defects, including a pattern of cracks in crucial turbine blades, that paralleled the problems with the solid rocket boosters. Overall he estimated that the engines and their parts were operating for less than one-tenth of their expected lifetimes. And he documented a history of ad hoc slippage in the standards used to certify an engine as safe: as cracks were found earlier and earlier in a turbine’s lifetime, the certification rules were repeatedly adjusted to allow engines to continue flying.

His most important contribution to the understanding of the disaster came in the area of risk and probability. He showed that the space agency and its contractors—although the essence of their decision making lay in weighing uncertainties—had ignored statistical science altogether and had used a shockingly vague style of risk assessment. The commission’s official findings could do no better than quote Feynman’s comment during the hearings that the decision making became

a kind of Russian roulette… . [The shuttle] flies [with O-ring erosion] and nothing happens. Then it is suggested, therefore, that the risk is no longer so high for the next flights. We can lower our standards a little bit because we got away with it last time… . You got away with it, but it shouldn’t be done over and over again like that.

Science has tools for such problems. NASA was not using them. A scattering of data points—for the depth of erosion in O-rings, for example—tended to be reduced to simplistic,