A risk evaluation approach for safety in aerospace preliminary design

The preliminary design phase of any program is key to its eventual successful development. The more advanced a design the more this tends to be true. For this reason the preliminary design phase is particularly important in the design of aerospace systems. Errors in preliminary design tend to be fundamental and tend to cause programs to be abandoned, or to be changed fundamentally, and at great cost later in the design development. In the past aerospace system designers have used the tools of systems engineering to enable the development of designs that were more likely to be functionally adequate. However to do so has meant the application significant resources to the review and investigation of proposed design alternatives. This labor-intensive process can no longer be afforded in the current design environment. The realization has led to the development of an approach that attempts to focus the tools of systems engineering on the risk drivers in the design. One of the most important factors in the development of successful designs is adequately addressing the safety and reliability risk. All too often these important features of the developed design are left to afterthoughts as the design gives sway to the more traditional performance focus. Thus even when a successful functional design is forthcoming significant resources are often required to reduce its reliability and safety risk to an acceptable level. This builds upon the experience base of the integrated shuttle risk assessment and its expansions and applications to the evaluation of newly proposed launcher designs. The approach used the shuttle developed PRA models and associated data sets as functional analogs for new launcher functions. The concept is that associated models would characterize the function of any launcher developed for those functions on the shuttle. Once this functional decomposition and reconstruction has been accomplished a proposed new design is compared on a function-by-function basis and specific design enhancements that have significant promise of reducing the functional risk over the shuttle are highlighted. The potential for enhancement is then incorporated into those functions by suitable modification of the shuttle models and or the associated quantification data sets representing those design features addressed by the new design. The level of risk reduction potential is then estimated by those component failure modes and mechanisms identified for the shuttle function and eliminated in the new design. In addition heritage data that would support the claims of risk reduction for those failure modes and mechanisms that remain albeit at a reduced level of risk are applied.