Applications of Relative Risk Evaluations in the Spacecraft Development

In the development of complex spacecraft, new technologies or new processes are often introduced in the design. Therefore, the problems of lack of information and data are usually encountered in the decision-making of designs selection. Relative risk evaluations can be applied in the selection of designs to cope with these problems. Also, in many instances, evaluators are more comfortable making relative decisions versus assigning absolute values. In this paper, a framework based on relative risk evaluations is presented which assists in making the decision on the design or designs to select. The proposed approach starts with applying the Fussell-Vesely measure to obtain the importance rankings of different risk contributors of different end states. The analytical hierarchy process (AHP) method is then used to determine the criteria weights of different risk end states. Accordingly, the relative importance of the particular contributors to the total risk for the reference design is calculated. On the other hand, the relative difference ratios in the contribution for alternative designs compared to reference design are calculated. Combined with the relative importance and the relative difference ratios of contributors, the relative risk difference ratios between different designs are evaluated. Finally, the optimal alternative design is determined by ranking relative risk evaluations. The performances of the proposed approaches are illustrated and validated using an example of a spacecraft propellant distribution system development. The results show that the proposed approaches are capable of helping designers to systematically consider relevant information and effectively determine the optimal design alternatives in the spacecraft development.