Choosing among safety improvement strategies: a discussion with example of risk assessment and multi-criteria decision approaches for NASA

Abstract

This paper focuses on risk assessment and multi-criteria decision making methods applicable to deciding among candidate safety improvement strategies in the face of cost, safety and other uncertainties for NASA flight vehicles, launch vehicles and ground research facilities. Deciding on the best safety improvement strategy to implement on a spacecraft involves balancing safety with other quantifiable criteria such as technical feasibility, schedule, mass, performance, volume, and cost. The strategem of a simplified example is used to illustrate the use of probabilistic risk assessment derived results with multi-criteria decision making in the face of uncertainties. The investigated decision making approaches are intuition, cost/benefit ratio, expected impact, and Analytic Hierarchy Process. A useful sensitivity study, termed Decision Trajectories, is proposed in this paper. The example, using the shuttle auxiliary power units (APUs), is limited to the following criteria: (1) safety improvement of proposed strategies, and (2) the associated recurring and non-recurring costs. These two criteria provide sufficient richness of domain to illustrate the technologies of risk assessment and decision making. Because of the general unfamiliarity of the readers with work being conducted by NASA, this paper also provides the needed background.