Challenger: getting away with it last time

Through “What could have been done”: Mike’s text from the paper, pp. 17–18 and 21–23, with the Commission report it quotes.

A history of success #

We had successfully launched a number of space shuttles with O-ring erosion and hot gas blow by in the joints of the solid rocket boosters adjacent to the external tank. With sufficiently critical analysis, and better internal communication, we might have concluded that this was a dangerous situation before we had one blow up. Instead, influenced by our repeated successes, we actually expanded both the amount of blow by that was acceptable and the low temperature range at which we were willing to launch, increasing the danger of a catastrophic failure.

What the Commission found #

Quoting from the Report of the Presidential Commission on the Space Shuttle Challenger Accident:

Paper, note 8 William P. Rogers et al., Report of the Presidential Commission on the Space Shuttle Challenger Accident, NASA Historical Reference Collection, NASA History Office, NASA Headquarters, Washington, DC, June 6, 1986, http://history.nasa.gov/rogersrep/genindex.htm, ch. V, “Findings” [104].

The Commission concluded that there was a serious flaw in the decision making process leading up to the launch of flight 51-L. A well-structured and managed system emphasizing safety would have flagged the rising doubts about the Solid Rocket Booster joint seal.

Paper, note 9 Ibid., ch. VI, “Early Design.”

Neither Thiokol nor NASA expected the rubber O-rings sealing the joints to be touched by hot gases of motor ignition, much less to be partially burned. However, as tests and then flights confirmed damage to the sealing rings, the reaction by both NASA and Thiokol was to increase the amount of damage considered “acceptable.” At no time did management either recommend a redesign of the joint or call for the Shuttle’s grounding until the problem was solved.

Paper, note 10 Ibid., ch. VI, “Findings,” item 3.

NASA and Thiokol accepted escalating risk apparently because they ‘got away with it last time.’ As Commissioner Feynman observed, the decision making was: ‘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.’

The pressure to go #

In the paper, an indented aside: material beyond the talk

The existence and / or perception of pressure was referenced a number of times in the Rogers report. The commission noted for example:

Paper, note 14 Rogers et al., Report of the Presidential Commission, ch. IX, sec. VII, “Flight Rate.”

The nation’s reliance on the Shuttle as its principal space launch capability created a relentless pressure on NASA to increase the flight rate.

Roger Boisjoly, a structures engineer at Thiokol, who strongly opposed the launch of Challenger under the temperature conditions at the time, testified before the commission,

Paper, note 15 Ibid., ch. V.

I felt personally that management was under a lot of pressure to launch and that they made a very tough decision, but I didn’t agree with it.

More on this factor: Factor III · The pressure to go.

What could have been done #

One method for doing this [analyzing our successes] is to establish beforehand a quantitative metric that relates to safety, and then to set a target for performance. The target can be set so as to allow for a significant margin of safety.

Then by measuring actual performance against our target, we may identify apparently successful outcomes that did not meet our target performance, and therefore should not, perhaps, be considered successes.

This could have been done during the Shuttle program in relation to the O-ring seals, and it would have triggered a stop to the program until the problem was fixed. We might guess why that wasn’t done – the program was under performing and the pressure to go, which can exist at many levels within a complex organization, was likely significant.

Ironically, however, it’s not unlikely that the program lost more time in fixing the problem after the catastrophe than would have been lost to a proactive approach to fixing it ahead of time.

The method in full: A metric and a target, set beforehand.

Which factors it shows #

I · Deceptive mathematics

Each flight with erosion that came home safely was counted as evidence. Feynman’s “kind of Russian roulette” is the paper’s own point: a small risk on each flight, repeated, adds up to a large one.

II · Murphy’s Corollary

“The risk is no longer so high for the next flights.” Flights with erosion came home safely, so the erosion was taken as proof it could not cause a loss, and the standard was lowered: more blow-by accepted, colder launches allowed.

III · The pressure to go

The Commission found “a relentless pressure on NASA to increase the flight rate,” and Boisjoly testified that he felt management was under a lot of pressure to launch.

Questions for discussion #

1. Which limit in your program has been widened after a run of successes, and on what evidence?
2. What damage or anomaly do you now call “acceptable” that was once unexpected?
3. If you set a quantitative target for that anomaly today, with a margin of safety, would your recent successes meet it?
4. Where does the pressure to keep flying come from in your organization, and at what levels?
5. When an engineer disagrees with a go decision, how does that disagreement reach the person making it?

These questions also appear, with every other case’s, in the Briefing Kit.

@misc{meier2026challenger,
  author = {Meier, Mike},
  title  = {Challenger: Getting Away with It Last Time},
  year   = {2026},
  note   = {Edition 1.0},
  url    = {https://meiersafe.com/case-studies/challenger/}
}