NASA wanted to check with all of its contractors to determine if there would be any problems with launching in the cold temperatures. Alan McDonald, director of the Solid Rocket Motor Project at Morton-Thiokol, was convinced that there were cold-weather problems with the solid rocket motors and contacted two of the engineers working on the project, Robert Ebeling and Roger Boisjoly. Thiokol knew there was a problem with the boosters as early as 1977, and had initiated a redesign effort in 1985. NASA Level I management had been briefed on the problem on August 19, 1985. Almost half of the shuttle flights had experienced O-ring erosion in the booster field joints. Ebeling and Boisjoly had complained to Thiokol that management was not supporting the redesign task force.
Temperatures for the next launch date were predicted to be in the low 20°s. This prompted Alan McDonald to ask his engineers at Thiokol to prepare a presentation on the effects of cold temperature on booster performance.
A teleconference was held between engineers and management from Kennedy Space Center, Marshall Space Flight Center in Alabama, and Morton-Thiokol in Utah. Boisjoly and another engineer, Arnie Thompson, knew this would be another opportunity to express their concerns about the boosters, but they had only a short time to prepare their data for the presentation.
Thiokol’s engineers gave an hour-long presentation, presenting a convincing argument that the cold weather would exaggerate the problems of joint rotation and delayed O-ring seating. The lowest temperature experienced by the O-rings in any previous mission was 53°F, on the January 24, 1985 flight. With a predicted ambient temperature of 26°F at launch, the O-rings were estimated to be at 29°F.
After the technical presentation, Thiokol’s Engineering Vice President Bob Lund presented the conclusions and recommendations. His main conclusion was that 53°F was the only low-temperature data Thiokol had for the effects of cold on the operational boosters. The boosters had experienced O-ring erosion at this temperature. Since his engineers had no low-temperature data below 53°F, they could not prove that it was unsafe to launch at lower temperatures. He read his recommendations and commented that the predicted temperatures for the morning’s launch was outside the database and NASA should delay the launch, so the ambient temperature could rise until the O-ring temperature was at least 53°F. This confused NASA managers because the booster design specifications called for booster operation as low as 31°F. (It later came out in the investigation that Thiokol understood that the 31°F limit temperature was for storage of the booster, and that the launch temperature limit was 40°F. Because of this, dynamic tests of the boosters had never been performed below 40°F.)
Marshall’s Solid Rocket Booster Project Manager, Larry Mulloy, commented that the data was inconclusive and challenged the engineers’ logic. A heated debate went on for several minutes before Mulloy bypassed Lund and asked Joe Kilminster for his opinion. Kilminster was in management, although he had an extensive engineering background. By bypassing the engineers, Mulloy was calling for a middle-management decision, but Kilminster stood by his engineers. Several other managers at Marshall expressed their doubts about the recommendations, and finally Kilminster asked for a meeting off of the net, so Thiokol could review its data. Boisjoly and Thompson tried to convince their senior managers to stay with their original decision not to launch.
A senior executive at Thiokol, Jerald Mason, commented that a management decision was required. The managers seemed to believe the O-rings could be eroded up to one-third of their diameter and still seal properly, regardless of the temperature. The data presented to them showed no correlation between temperature and the blowby gasses which eroded the O-rings in previous missions. According to testimony by Kilminster and Boisjoly, Mason finally turned to Bob Lund and said, “Take off your engineering hat and put on your management hat.”
Joe Kilminster wrote out the new recommendation and went back online with the teleconference. The new recommendation stated that the cold was still a safety concern, but their people had found that the original data was indeed inconclusive and their “engineering assessment” was that launch was recommended, even though the engineers had no part in writing the new recommendation and refused to sign it.
Alan McDonald, who was present with NASA management in Florida, was surprised to see the recommendation to launch and appealed to NASA management not to launch. NASA managers decided to approve the boosters for launch despite the fact that the predicted launch temperature was outside of their operational specifications.
More at link:
http://www.engineering.com/Library/ArticlesPage/tabid/85/ArticleID/170/categoryId/7/The-Space-Shuttle-Challenger-Disaster.aspx
Have you ever read Edward Tufte’s “The Decision to Launch the Space Shuttle Challenger”, one of two essays in his “Visual and Statistical Thinking: Displays of Evidence for Making Decisions”?
If not, you should - it’s an excellent companion to what you provided.
I went to an Edward Tufte seminar on graphic presentation of data a couple years after the Challenger blew up. He made a good case for poor graphic presentation of the data on the part of the engineers being a cause of the decision to launch. With proper graphics, the danger could have been made too obvious even for managers to ignore.