RLV Reliability Analysis Guidelines Terry Hardy AST-300/Systems Engineering and Training Division October 26, 2004

2 Introduction What are reliability analyses? Why are reliability analyses important? Why develop guidelines? How are reliability analyses used? Acceptable reliability analysis methods. Typical documentation.

3 What Are Reliability Analyses? Reliability analyses are quantitative and qualitative tools used to determine whether an item will perform its intended function for a specified interval under foreseeable operating conditions. Reliability is not safety –Components may be reliable and still unsafe –Accidents arise from interactions between machines, software, humans, and the environment, as well as from component failure Reliability must be considered in the context of system safety.

4 Why Are Reliability Analyses Important? Reliability analyses are important because: Risk to the public can depend on reliability of safety- critical systems and consequences of failures of those systems. Reliability analyses can provide risk assessment data to support launch vehicle safety analyses. Reliability analyses help make decisions leading to improved reliability and safety.

5 Why Develop Guidelines? AST is developing Reliability Analyses Guidelines to: Facilitate valid RLV reliability analyses by providing a set of acceptable methods that demonstrate compliance with regulatory requirements. Provide examples of methods and approaches to assist RLV developers. Capture best practices in the aerospace community. Illustrate integration of safety and reliability analyses.

6 How Are Reliability Analyses Used? Reliability analyses can be used to: –Support the system safety process: Identify potential reliability/safety problems Compare alternate designs to improve reliability/safety Identify operational/test requirements Provide validation and verification data –Provide vehicle failure probability estimates to support E c analysis. –Help specify operating restrictions. –Evaluate whether a flight safety system will meet reliability or safety requirements. Guidelines will document how reliability analyses are applied

7 Acceptable Reliability Analysis Methods Reliability Block Diagrams Parts Count Analysis Failure Modes, Effects, and Criticality Analysis Fault Tree Analysis Event Tree Analysis Reliability Allocation Probabilistic Risk Assessment Monte Carlo Simulation Guidelines will describe each of these methods, including approach, advantages, disadvantages, and RLV-specific examples

8 Typical Documentation Reliability analysis documentation typically includes: Item identification Intended use of the analysis results Analysis methods used Analysis inputs Analysis results Confidence in analysis (assumptions, sources of uncertainty, limitations) Guidelines will provide a description of each documentation element

9 Summary AST is developing RLV Reliability Analysis Guidelines to facilitate valid reliability analysis. Guidelines will include how reliability analyses are used, acceptable methods, and RLV-specific examples. Draft guidelines posted for comment: April 2005