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Challenger: An Accident Rooted in History...
Presidential Commission on the Space Shuttle Challenger Accident
There are times when history fails to have analytic power; this is one of them. Students should understand that there are circumstances that require turning to another discipline to interpret evidence bearing on a historical question. Since the task confronting the staff members involved answering a non-historical question and illustrating the results, they should have turned to a statistician and a graphic or information designer. In this case they did not, and the product was what Edward Tufte calls "chartjunk." He wrote
The staff members provided an essentially historical explanation--a time series. As Tufte points out, this was a reasonable approach but not one that answered the question. Consequently, the commission was probably as confused about the relationship between temperature and O-ring damage after the chart as they had been before. A better illustration would have been a more statistical rendering that demonstrated some predictive power:
The fatal flaw is the ordering of the data. Shown as a time-series, the rockets are sequenced by date of launching--from the first pair at upper left [SRM 1, No. A and SRM 2, No. B] to the last pair at lower right [SRM 24, No. A and SRM 24, No. B] (the launch immediately prior to Challenger). The sequential order conceals the possible link between temperature and O-ring damage, thereby throwing statistical thinking into disarray. The time-series chart...bears on the issue: Is there a time trend in O-ring damage? This is a perfectly reasonable question, but not the one on which the survival of Challenger depended. That issue was : Is there a temperature trend in O-ring damage?1
With the advent of multimedia and the Web it is also a good idea to remind students that form in which they present their material is important and that presentation glitz--like the little rockets--can often muddle clear exposition, at best, or mislead an audience, at worst.
Edward R. Tufte, Visual Explanations: Images and Quantities, Evidence and Narrative (Cheshire, CT: Graphics Press, 1997) pp. 46-47.
On the morning of January 28, 1986, the Challenger space shuttle exploded within seconds of takeoff, killing its seven astronauts. The incident sparked a presidential commission and inquiry into the causes of the disaster. The chart was prepared for the presidential commission investigating the Challenger incident. The first illustration was the legend and placed on the overhead projector initially; the second illustration, the chart proper, subsequently replaced the legend on the projector. Because the commission was interested in the relationship between temperature and O-ring damage, they directed staff members to prepare a chart that would show this relationship.
Questions to Consider
- What relationship does the chart show?
- Is it effective in presenting the data that illustrates the relationship between temperature and O-ring damage? Explain the reasons for your thinking.
- How would the mode of presentation (seeing the legend first, having it removed, and finally seeing the chart without the legend) have affected an audience's understanding of the chart?
- One shuttle manager's estimate of the odds of a Challenger-type disaster occurring were 1/100,000. If NASA were to launch one shuttle every week (i.e., 52 launches per year), approximately how long would it take for a disaster to occur if his estimate were accurate? What historic circumstances might have influenced his thinking?
Presidential Commission on the Space Shuttle Challenger Accident, vol. 5 (Washington, DC: US Government Printing Office, 1986.) pp. 895-896.
- Federation of American Scientists
Under "Education and Outreach," an excellent collection of primary sources (in Adobe Acrobat), including wills and probate inventories. A comprehensive and very useful collection of commentary and annotated web links associated with the Challenger incident.