TIME-EVOLUTIONARY METHOD OF RISK ASSESSMENT FOR RELIABILITY IMPROVEMENT

摘要

High reliability is required for the space systems because of its large-scale structure, long-term operation, maintenance-free condition and extraordinary environment. In the conventional reliability analyses, Failure Mode Effect and Criticality Analysis (FMECA), Fault Tree Analysis (FTA), Event Tree Analysis (ETA) and other miscellaneous methods have been adopted. In these methods, the relationships between the failures including malfunctions, anomalies, hazards and catastrophe, and its causes are evaluated in detail at each development phase at/after the site of the accident. However, these methods cannot identify the combined causes and effects of present and previous failures. It is necessary to evaluate the reliability from the beginning of design thorough the end of on-orbit operation. Objectives of this study are to propose a new risk assessment method/tool for reliability improvement where the time-evolutional updates of system risk/reliability assessment are taken into account, focusing on the following two features. (1) Time-evolutionary evaluation of the development products/processes. (2) Information sharing system between program/project manager and engineers at the front by the computer network. A new risk assessment method for the reliability improvement, Time-tagged Risk/Reliability Assessment Program (hereinafter referred to "T-TRAP") is described. In this program, time-evolutionally evaluation process is included and this process makes possible time-tagged analysis. We expand risk assessment for all phases of the project. T-TRAP does not only refer to the conventional two-dimensional scheme of system, subsystem, and lower, but also the chronological axis threading through all the development and operation phases. T-TRAP is a generic tool of risk management applicable to any level of the project, and supports managers and engineers to assure their interfaces.