O-rings and production pressure

Allan McDonald's Truth, Lies, and O-Rings: Inside the Space Shuttle Challenger Disaster (2009) has given me a somewhat different understanding of the Challenger launch disaster than I've gained from other sources, including Diane Vaughan's excellent book The Challenger Launch Decision: Risky Technology, Culture, and Deviance at NASA. McDonald is a Morton Thiokol (MTI) insider who was present through virtually all aspects of the evolving solid rocket program at NASA in the two years leading up to the explosion in January 1986. He was director of the Space Shuttle Solid Rocket Motor Project during part of this time and he represented MTI at the formal Launch Readiness Review panels (LRRs) for several shuttle launches, including the fateful Challenger launch. He was senior management representative for MTI for the launch of STS-51L Challenger. His account gives a great deal of engineering detail about the Morton Thiokol engineering group's ongoing concerns about the O-rings in the months preceding the Challenger disaster. This serves as a backdrop for a detailed analysis of the dysfunctions in decision-making in both NASA and Morton Thiokol that led to an insufficient priority being given to safety assessments.

It is worth noting that O-rings were a key part of other large solid-fuel rockets, including the Titan rocket. So there was a large base of engineering and test experience with the performance of the O-rings when exposed to the high temperatures and pressures of ignition and firing.

The biggest surprise to me is the level of informed, rigorous, and evidence-based concern that MTI engineers had about the reliability of joint seal afforded by the primary and secondary seals on the solid rocket motors on the Shuttle system. These specialists had a very good and precise understanding of the mechanics of the problem. Further, there was a good engineering understanding of the expected (and required) time-sequence performance of the O-rings during ignition and firing. If the sealing action were delayed by even a few hundredths of a second, hot gas would be able to penetrate past the seal. These were not hypothetical worries, but instead were based on data from earlier launches demonstrating O-ring erosion and soot between the primary and secondary rings showing that super-hot gases had penetrated the primary seal. The worst damage and evidence of blowby had occurred on flight STS-51C January 25, 1985, one year earlier, the lowest-temperature launch yet attempted. And that launch took place when the temperature was 53 degrees.

Launch temperatures for the rescheduled January 28 launch were projected to be extremely cold -- 22-26 degrees was forecast on January 27, roughly 30 degrees colder than the previous January launch. The projected temperatures immediately raised alarm concerning the potential effects on the O-rings with the Utah-based engineering team and with McDonald himself. A teleconference meeting was scheduled for January 27 to receive recommendations from the Utah-based Morton Thiokol engineers who were focused on the O-rings problem about the minimum acceptable temperature for launch (95).

I tried to reach Larry Mulloy at his hotel but failed, so I called Cecil Houston, the NASA/MSFC Resident Manager at KSC. I alerted him of our concerns about the sealing capability of the field-joint O-rings at the predicted cold temperatures and asked him to set up the teleconference. (96)

The teleconference began at 8:30 pm on the evening before the launch. McDonald was present in Cape Canaveral for the Flight Readiness Review panel and participated in the teleconference involving the analysis and recommendations from MTI engineering, leading to a recommendation against launching in the expected cold weather conditions.

Thiokol's engineering presentation consisted of about a dozen charts summarizing the history of the performance of the field-joints, some engineering analysis on the operation of the joints, and some laboratory and full-scale static test data relative to the performance of the O-rings at various temperatures. About half the charts had been prepared by Roger Boisjoly, our chief seal expert on the O-ring Seal Task Force and staff engineer to Jack Kapp, Manager of Applied Mechanics. The remainder were presented by Arnie Thompson, the supervisor of our Structures Section under Jack Kapp, and by Brian Russell, a program manager working for Bob Ebeling. (97)

Boisjoly's next chart showed how cold temperature would reduce all the factors that helped maintain a good seal in the joint: lower O-ring squeeze due to thermal shrinkage of the O-ring; thicker and more viscous grease around the O-ring, making it slower to move across the O-ring groove; and higher O-ring hardness due to low temperature, making it more difficult for the O-ring to extrude dynamically into the gap for proper sealing. All of these things increased the dynamic actuation time, or timing function, of the O-ring, when at the very same time the O-ring could be eroding, creating a situation where the secondary seal might not be able to seal the motor, not if the primary O-ring was sufficiently eroded to prevent sealing in the joint. (99)

Based on their concerns about temperature and effectiveness of the seals in the critical half-second of ignition, MTI engineering staff prepared the foundation for a recommendation to not launch in temperatures lower than 53 degrees. Their conclusion as presented at the January 27 teleconference was unequivocal against launch under these temperature conditions:

The final chart included the recommendations, which resulted in several strong comments and many very surprising reactions from the NASA participants in the teleconference. The first statement on the “Recommendations” chart stated that the O-ring temperature must be equal to or greater than 53° at launch, and this was primarily based upon the fact that SRM-15, which was the best simulation of this condition, worked at 53 °. The chart ended with a statement that we should project the ambient conditions (temperature and wind) to determine the launch time. (102)

NASA lead Larry Mulloy contested the analysis and evidence in the slides and expressed great concern about the negative launch recommendation, and he asserted that the data were "inconclusive" in establishing a relationship between temperature and O-ring failure.

Mulloy immediately said he could not accept the rationale that was used in arriving at that recommendation. Stan Reinartz then asked George Hardy, Deputy Director of Science and Engineering at NASA/MSFC, for his opinion. Hardy said he was “appalled” that we could make such a recommendation, but that he wouldn't fly without Morton Thiokol's concurrence. Hardy also stated that we had only addressed the primary O-ring, and did not address the secondary O-ring, which was in a better position to seal because of the leak-check. Mulloy then shouted, “My God, Thiokol, when do you want me to launch, next April?” He also stated that “the eve of a launch is a helluva time to be generating new launch commit criteria!” Stan Reinartz entered the conversation by saying that he was under the impression that the solid rocket motors were qualified from 40° to 90° and that the 53° recommendation certainly was not consistent with that.” (103)

Joe Kilminster, VP of Space Booster Programs at MTI, then requested a short caucus for the engineering team in Utah to reevaluate the data and consider their response to the skepticism voiced by NASA officials. McDonald did not participate in the caucus, but his reconstruction based on the memories of persons present paints a clear picture. The engineering experts did not change their assessment, and they were overriden by MTI executives Cal Wiggins (VP and General Manager of the Space Division) and Jerry Mason (Senior VP of Wasatch Operations). In opening the caucus discussion, Mason is quoted as saying "we need to make a management decision". Engineers Boisjoly and Thompson reiterated their technical concerns about the functionality of the O-ring seals at low temperature, with no response from the senior executives. No members of the engineering team spoke up to support a decision to launch. Mason polled the senior executives, including Bob Lund (VP of Engineering), and said to Lund, "It's time for you, Bob, to take off your engineering hat and put on your management hat." (111) A positive launch recommendation was then conveyed to NASA, and the process in Florida resumed towards launch.

McDonald spends considerable time indicating the business pressure that MTI was subject to from its largest customer, NASA. NASA was considering creating a second-source option for competing companies for solid fuel motors from MTI and had also delayed signing a large contract (Buy-III fixed cost bid) for the next batch of motors. The collective impact of these actions by NASA could cost MTI over a billion dollars. So MTI management appears to have been under great pressure to accommodate to NASA managers' preferences concerning the launch decision. And it is hard to avoid the conclusion that their decision placed business interests first and the professional judgments of their safety engineers second. In doing so they placed the lives of seven astronauts at risk, with tragic consequences.

And what about NASA? Here the pressures are somewhat less fully developed than in Vaughan's account, but the driving commitment to achieve a 24-launch per year schedule seems to have been a primary motivation. Delayed launches significantly undermined this goal, which threatened both the prestige of NASA, the hope of significant commercial revenue for the program, and the assurance of continuing funding from Congress.

McDonald was not a participant in the caucus conference call. But he provides a reconstruction based on information provided by participants. In his understanding the engineers continued to defend their recommendation based on very concrete concerns about the effectiveness of the O-rings in extreme cold. Senior managers indicated their lack of support for this engineering judgment, and in the end Jerry Mason indicated that this would need to be a management decision. The FRR team was then informed that MTI has reconsidered its negative recommendation concerning launch. McDonald refused to sign the launch recommendation document, which was signed by his boss Joe Kilminster and faxed to the LRR team.

In hindsight it seems clear that both MTI executives and NASA executives deferred to business pressures of their respective organizations in the face of well-supported doubts about the safety of the launch. Is this a case of 20-20 vision after the fact? It distinctly appears not to be. The depth of knowledge, analysis, and rational concern that was present in the engineering group for at least a year prior to the Challenger disaster gave very specific and evidence-based reasons to abort this launch. This was not some intuitive, unspecific set of worries; it was an ongoing research problem that greatly concerned the engineers who were directly involved. And it appears there was no significant disagreement or uncertainty among them.

So it is hard to avoid a rather terrible conclusion, that the Challenger disaster was avoidable and should have been prevented. And the culpability lies with senior NASA and MTI executives who placed production pressures and business interests ahead of normal safety assessment procedures, and ahead of safety itself.

It is worth noting that Diane Vaughan's assessment is directly at odds with this assessment. She writes:

We now return to the eve of the launch. Accounts emphasizing valiant attempts by Thiokol engineers to stop the launch, actions of a few powerful managers who overruled a unanimous engineering position, and managerial failure to pass information about the teleconference to senior NASA administrators, coupled with news of economic strain and production pressure at NASA, led many to suspect that NASA managers had acted as amoral calculators, knowingly violating rules and taking extraordinary risk with human lives in order to keep the shuttle on schedule. However, like the history of decision making, I found that events on the eve of the launch were vastly more complex than the published accounts and media representations of it. From the profusion of information available after the accident, some actions, comments, and actors were brought repeatedly to public attention, finding their way into recorded history. Others, receiving less attention or none, were omitted. The omissions became, for me, details of social context essential for explanation. (LC 6215)

Young, Cook, Boisjoly, and Feynman. Concluding this list of puzzles and contradictions, I found that no one accused any of the NASA managers associated with the launch decision of being an amoral calculator. Although the Presidential Commission report extensively documented and decried the production pressures under which the Shuttle Program operated, no individuals were confirmed or even alleged to have placed economic interests over safety in the decision to launch the Space Shuttle Challenger. For the Commission to acknowledge production pressures and simultaneously fail to connect economic interests and individual actions is, prima facie, extremely suspect. But NASA’s most outspoken critics—Astronaut John Young, Morton Thiokol engineers Al McDonald and Roger Boisjoly, NASA Resource Analyst Richard Cook, and Presidential Commissioner Richard Feynman, who frequently aired their opinions to the media—did not accuse anyone of knowingly violating safety rules, risking lives on the night of January 27 and morning of January 28 to meet a schedule commitment. (kl 1627)

Vaughan's account includes many of the pivot-points of McDonald's narrative, but she assigns a different significance to many of them. She prefers her "normalization of deviance" explanation over the "amoral calculator" explanation.

(The Rogers Commission report and supporting documents are available online. Here is a portion of the hearings transcripts in which senior NASA officials provide testimony; link. This segment is critical to the issues raised in McDonald's account, since it addresses the January 27, 1986 teleconference FRR session in which a recommendation against launch was put forward by MTI engineering and was challenged by NASA senior administrators.)