WASHINGTON -- The Rogers Commission, calling it 'an accident rooted in history,' Monday traced the Challenger disaster to basic design flaws in booster rocket joints dating back more than a decade and to more recent decisions to play down their significance.
'The space shuttle's solid rocket booster problem began with the faulty design of its joint and increased as NASA and contractor management failed to recognize it as a problem, then failed to fix it and finally treated it as an acceptable flight risk,' the report said.
It said Morton Thiokol Inc., which builds the solid propellant boosters, did not accept early test implications that the design 'has a serious and unanticipated flaw' and NASA did not accept the judgment of its engineers that the design was unacceptable.
'And as the joint problems grew in number and severity, NASA minimized them in management briefings and reports,' the panel said. 'At no time did management either recommend a redesign of the joint or call for the shuttle's grounding until the problem was solved.'
The commission noted that Thiokol was named winner of the $800 million booster rocket contract in November 1973, primarily because NASA believed Thiokol could produce the boosters at the lowest cost.
Four companies competed for the contractand Thiokol was rated last in the competition as far as design, development and testing were concerned, the report said. But Thiokol's 'overall mission suitability' score tied for second with United Technologies.
The other two competitors were Aerojet Solid Propulsion Co. and Lockheed Propulsion Co.
NASA selection officials at the time said Thiokol's cost advantages were substantial and they also praised the design of the joints between booster segments and their dual rubber O-ring seals.
The commission said Thiokol's joint design was based on the highly successful Titan 3 booster rocket joints but differed in that the shuttle O-ring was intended to take the brunt of hot gas pressure while the Titan O-ring was able but not intended to take the pressure.
The only other gas barrier in the shuttle design was an asbestos-filled insulating putty. The report said Thiokol believed it had 'complete, redundant seal capability.'
While pressure testing of the booster was successful, it revealed that the two key steel components of the joint, the tang and clevis, bent away from each other instead of toward each other 'and by doing so reduced -- instead of increased -- pressure on the O-ring in the milliseconds after ignition,' the report said.
This 'joint rotation' effect was reported by Thiokol to Marshall, the report said, but Thiokol engineers did not believe it would cause significant problems.
But the report said Marshall's reaction to the test results 'was rapid and totally opposite of Thiokol's.'
In a 1977 memo, Marshall engineer Leon Ray said no change in the Thiokol design was unacceptable. After that report, John Miller, chief of the solid rocket branch at Marshall, sent a memo Jan. 9, 1978 to his superior that said the design needed to be improved.
'One year later, not having received a response to his 1978 memo, Miller signed and forwarded a second memo strenuously objecting to Thiokol's solid rocket motor joint seal design,' the report said.
It said Miller's memo was sent to George Hardy, then booster project manager at Marshall, but Thiokol apparently did not get a copy.
The commission said tests in July 1978 and April 1980 again showed the joint rotation phenomenon but Thiokol continued to question the validity of the findings.
In May 1980, the report said NASA's design certification committee recommended full-scale tests to check the joint, including firings with propellant as cold as 40 degrees. But the response from NASA program officials was that the original tests and testing then under way were sufficient.
The joint design was approved and on Nov. 24, 1980, it was classified as 'criticality 1R,' meaning that it had a redundancy but that if that backup failed, there could be loss of life or a shuttle. The report said the 'R' meant NASA believed the secondary O-ring would hold if the first one did not.
Nevertheless, the report said a 1980 NASA document said redundancy of the secondary seal could not be verified after the pressure inside the rocket reaches 40 percent of its maximum operating pressure. When asked about this, Arnold Aldrich, NASA's shuttle manager in Houston, said the seal should not have been considered to have redundnancy.
Problems with the joint in flight first appeared during the second shuttle mission in November 1981, as previously disclosed. Some 'erosion' was seen in the primary O-ring, meaning hot gases had passed it.
Nevertheless, the commission said that problem was not reported at a flight readiness meeting held for the next mission. Furthermore, the problem was not reported by Marshall's problem assessment system, the report said.
The report said Marshall management finally accepted the conclusion that the O-ring was not fully redundant and the joint was listed as 'criticality 1' in Dec, 17, 1982.
But the commission said testimony in hearings and statements in interviews indicated NASA and Thiokol still considered the joint to be redundant 'in all but exceptional cases.' The report said Marshall officials Judson Lovingood, George Hardy and Lawrence Mulloy shared that view.
NASA Associate Administrator Michael Weeks signed a waiver March 28, 1983, allowing the shuttle to fly with the joint even though it had no fail-safe backup.
Additional joint problems were seen in shuttle flights and during the launch of Discovery on the 15th shuttle flight Jan. 24, 1985, when the temperature was 53 degrees, O-ring damage was seen in both boosters. This, the report said, was the first time a secondary O-ring showed the effect of heat from hot gases that passed the primary ring.
On Jan. 31, 1985, Mulloy sent an urgent message to Lawrence Wear at Marshall calling for a review of all O-ring damage before the next shuttle flight. On Feb. 8, 1985, Thiokol said there was cause for concern but, 'Its resolution was 'accept risk,'' the report said.
At a top-level NASA flight readiness review Feb. 21. 1985, the report said, there was no detailed analysis of O-ring problems not was there any reference to low temperature effects.
Joint seal problems occurred on each of the next four shuttle flights and when a booster nozzle joint flown on the 17th shuttle mission in April 1985 was taken apart and examined by Thiokol, the results were 'alarming,' the commission said.
As a result, Mulloy placed 'launch constraints' on each subsequent shuttle flight, meaning launch could not occur until the problem had been reviewed and the restriction waived. Mulloy did waive the constraint for each mission after July 10, 1985 -- a total of seven flights.
However, the report said NASA's top two levels of shuttle managers 'apparently did not realize Marshall had assigned a launch constraint.
'This communication failure was contrary to the requirement' that such restrictions should be reported to managers, the report said.
It said NASA and Thiokol engineers were increasingly concerned about the problem. On July 31, 1985, Thiokol engineer Roger Boisjoly wrote a memo saying, 'The mistakenly accepted position on the joint problem was to fly without fear of failure ...'
As a result of the April 1985 flight, Boisjoly said it is 'a jump ball' whether the joint wold hold or fail. If it failed, he said, 'The result would be a catastrophe of the highest order -- loss of human life.
'It is my honest and very real fear that if we do not take immediate action to dedicate a team to solve the problem, with the field joint having the No. 1 priority, then we stand in jeopardy of losing a flight along with all the launch pad facilities,' he said.
On Aug. 19, 1985, Thiokol and Marshall program managers briefed NASA headquarters officials on the problem and concluded that it was a critical matter, 'but it was safe to fly,' the report said.
Thiokol formed a task force Aug. 20 to work on the problem. But on Oct. 1, R. V. Ebeling, manager of Thiokol's solid motor ignition system, wrote an internal memo beginning with the word, 'HELP.' He said the company's task force was being delayed 'by every possible means.'
In December, Ebeling 'became so concerned about the gravity of the O-ring problem that he told fellow members of the seal task force that he believed Thiokol should not ship any more motors until the problem was fixed,' the report said.
The commission said the record shows that on the day before Challenger's launch, 'only limited consideration was given to the past history of O-ring damage in terms of temperature.'
The panel said, however, the data indicate that the probability of O-ring 'distress is increased to almost a certainty if the temperature of ther joint is less than 65.'
'The genesis of the Challenger accident -- the failure of the joint of the right solid rocket motor -- began with decisions made in the design of the joint and in the failure by both Thiokol and NASA's solid rocket booster project office to understand and respond to facts obtained during testing,' the report said.
'Neither Thiokol nor NASA responded adequately to internal warnings about the faulty seal design,' the panel said. 'Furthermore, Thiokol and NASA did not make a timely attempt to develop and verify a new seal after the initial design was shown to be deficient.
'NASA and Thiokol accepted escalating risk because they 'got away with it last time.''
Commissioner Richard Feynman called it 'a kind of Russian roulette.'