Probabilistic R isk Assessment and C onceptual Design

1. ProbabilisticRisk Assessment andConceptual Design Bryan C Fuqua – SAIC bryan.c.fuqua@nasa.gov 281.335.2282 Diana DeMott – SAIC diana.l.demott@nasa.gov 281.335.2056 Paul Wilson – SAIC paul.wilson-1@nasa.gov 281.335.2291

2. What is PRA? • Determining risk generally amounts to answering the following three questions: • What kinds of events or scenarios can occur (i.e., what can go wrong)? • What are the likelihoods and associated uncertainties of the events or scenarios? • What consequences could result from these events or scenarios (e.g., Loss of Crew and Loss of Mission)? • Probabilistic Risk Assessment (PRA) is a comprehensive, structured, and logical analysis method aimed at identifying and assessing risks in complex technological systems for the purpose of cost-effectively improving their safety and performance. (PRA Procedures Guide for NASA Managers and Practitioners) • They are often characterized by (but not limited to) event tree models, fault tree models, and physics based simulation models

3. Why Use PRA for Planning or Early in Concept Phase? • PRA can be applied in the conceptual design phase and not just the operational phase • PRA can be utilized as a key input to the Risk Informed Decision Making process • Identifies potential risks early to: • Determine what (equipment, process, mission, etc.) drives the risk • Mitigate or eliminate risks earlier in design to lower costs • Allows trade studies to compare design alternatives based on risk

4. Use of PRA in Trade Studies • Provide additional information for Risk Informed Decisions made by management • Compare concept/design alternatives based on risks • Determine magnitude of reduced risk due to proposed changes in: • Design • Process • Equipment / components

5. Using PRA Methodology • Develop high level PRA models of Design Reference Missions (DRMs) or early design prototypes • Models may include Event Trees, Fault Trees, or other probabilistic-based applications • Models should be based on conceptual designs and generic key system and equipment level information • Using what is known today, we can quantify the model(s) to predict magnitudes of risk, or compare risks, for different designs • Following this methodology will provide program/project management with a better understanding of the risks

6. Key PRA Parameters to Develop • Establish the scope of the model • Understand and incorporate success criteria • Use a high level approach to provide magnitude of (not specific) risk • Master Equipment List (MEL) • Find data (e.g., historical data, surrogate data, etc.) • Use placeholder data for known future considerations

7. PRA Results (Risk Drivers) Identify and characterize the key risks and challenges associated with potential high risk programs in aerospace or other industries • Loss of life • Loss of equipment or facility • Large financial loss

8. Conclusion PRA methodology is a tool that has the potential to improve both conceptual planning and early design efforts to help identify and ultimately mitigate risks in a more efficient and cost effective manner.