Use and Misuse of Reliability Analyses for Unmanned Spacecraft Missions

Unmanned space observatories are composed of a spacecraft “bus” and a suite of instruments. Several types of reliability analyses are used during the design process to help ensure the mission success of observatories. New designs and significantly modified existing designs need Failure Modes, Effects, and Criticality Analysis (FMECA), Parts Stress Analysis (PSA), Limited Life Items (LLI) analysis, and Worst Case Analysis (WCA), which are used as part of the design process. For reliability-proven components built by vendors known for consistent processes and whose components have been used in space without failure, the only reliability analysis listed above that is needed is an LLI analysis.