SAE AIR5006/2

The authors of this guidebook and the solid propulsion industry at large have long been troubled by an inability to absolute "demonstrate" SRB reliability because, under classic reliability theory, large numbers of tests are required to establish "statistically significant" reliability values. 240 tests with no failures, for instance, are required to demonstrate 0.99 reliability to a 90% confidence level if a binomial model is used. Since the testing cost for hundreds of large motors like space shuttle SRBs would be prohibitive, the solids industry has always been confronted with a vexing dilemma: (1) what is the fewest number of SRBs that can be tested to establish reliability with high confidence level for commitment to flight and (2) what should the reliability that was established with fewer-than- classical numbers of tests be called (it obviously is not "demonstrated reliability" in the strictest sense of the definition)?