Appendix F is a must read. The tl;dr summary is: Engineers at Rocketdyne, the manufacturer, estimate the total probability [of catastrophic failure] as 1/10,0

Appendix F is a must read. The tl;dr summary is: Engineers at Rocketdyne, the manufacturer, estimate the total probability [of catastrophic failure] as 1/10,000. Engineers at Marshal estimate it as 1/300, while NASA management, to whom these engineers report, claims it is 1/100,000. An independent engineer consulting for NASA thought 1 or 2 per 100 a reasonable estimate. — Personal observations on the reliability of the Shuttle by R.P. Feynman Empirical post script (as of STS-133 24 February 2011) Total launches 132 Failures 2 Successes 130 Failure rate: 1.5% Edit: add opinions: See also http://en.wikipedia.org/wiki/Rogers_Commission_Report#Role_of_Richard_Feynman http://en.wikipedia.org/wiki/Rogers_Commission_Report#Role_o... The reason for appalling and wildly inaccurate estimate of the failure probability is because the failure probability was a top-down "estimate." Someone Important apparently said "the space shuttle needs a reliability of 1/100,000". This mandate was pushed down on all the suppliers. The result was that the probability of failure was divided out onto all the systems, subsystems, subsubsystems... ad nausium all the way down to the bolts. The result was that all the subsystems had reliability numbers that could not be refuted (e.g. bolts at 1/10^12 IIRC), but could not be realistically substantiated either. Unfortunately, some of the probabilities of the major subsystems (SRB and ice damaging the heat shield tiles) were not accurate. The most accurate estimate was the engineer with a lot of experience in extremely complicated systems who gave an experience-based estimate, not a top-down (dictated) numerically derived estimate.