NASA/SP-2011-3421

Abstract

<strong>Purpose and Scope of This Procedures Guide</strong> <br>During the past several decades, much has been written on PRA methods and applications. Several university and practitioner textbooks and sourcebooks currently exist, but they focus on applications of PRA to industries other than aerospace. Although some of the techniques used in PRA originated in work for aerospace and military applications, no comprehensive reference currently exists for PRA applications to aerospace systems. <br>This PRA Procedures Guide, in the present second edition, is neither a textbook nor an exhaustive sourcebook of PRA methods and techniques. It provides a set of recommended procedures, based on the experience of the authors, that are applicable to different levels and types of PRA that are performed for aerospace applications. It therefore serves two purposes, to: <br>1. Complement the training material taught in the NASA PRA course for practitioners, and together with the Fault Tree Handbook [1-6], the Risk-Informed Decision Making Handbook [1-1], the Bayesian Inference handbook [1-7], the Risk Management Handbook [1-8], and the System Safety Handbook [1-9] to provide quantitative risk methodology documentation, and to <br>2. Provide aerospace PRA practitioners in selecting an analysis approach that is best suited for their applications. <br>The material in this Procedures Guide is organized into five parts: <br>1. A management introduction to PRA and the Risk Management framework in which it is used is presented in Chapters 1-3. <br>2. Chapters 4-12 cover the details of PRA: methods for scenario development, data collection and parameter estimation, uncertainty analysis, dependent failure analysis, human reliability analysis, software reliability analysis, modeling of physical processes for PRA, probabilistic structural analysis, and uncertainty propagation. The Human Reliability Analysis (Chapter 8) was updated in the present edition. The Software Risk Assessment (Chapter 9) was also re-written but this area is still not mature enough to include several recommended methodology approaches. <br>3. Chapter 13 discusses the presentation of results. The discussion addresses what results should be presented and in what format. Presentation and communication of PRA results is extremely important for use in risk-informed decision making. <br>4. Given the importance of crew safety, Chapter 14 presents details on launch abort modeling including the factors that must be considered, the analysis methodologies that should be employed, and how the assessment should be included in the vehicle development process. <br>5. Finally, Appendix A through C contain basic information to supplement one's existing knowledge or self-study of probability, statistics, and Bayesian inference. Then two PRA examples are provided in Appendix D and, finally, the use of simulation in the probabilistic assessment of risk is covered in Appendix E.