Failure modes and effects recognition in the Tertiary Mirror Assembly design

Abstract

It is desirable to expose and observe the implications of design decisions early in conceptual stages of design when the cost of design changes are relatively inexpensive. However, few quantitative design details are available at the conceptual design stages rendering traditional design analysis techniques ineffective. Using qualitative information, failure mode and effect recognition (FMER) analysis can expose many possible failure modes. In addition, it lays the foundation for the quantitative failure modes and effects analysis (FMEA) employed in the later stages of design. In performing FMER for a given design, system functionality and interactions between all subcomponents become better understood. The objectives, goals, and assumptions of the design become explicitly documented in the analysis. FMER design verification is based on first principles, geometric relationships, and general information about the components. This qualitative analysis can reveal critical failures due to overconstrained objects, under-constrained motions, conflicting information, and unrecognized assumptions. The designer quickly recognizes short comings of a design and is thus better able to make revisions. The designer specifies more details, making the transition from conceptual design to detailed design. Moving from qualitative to more quantitative analysis, more thorough design validations can be performed as detailed information becomes available. The effectiveness of FMER as an early design analysis tool was demonstrated. Failure modes and effects recognition (FMER) analysis was performed on the base-line (kinematic mount concept) design of the tertiary mirror assembly (TMA) of the space infra-red telescope facility (SIRTF). The findings presented here are not intended to be critiques of the design. But they did serve to identify areas of concern to the designer.