Development of a Software for the Failure Modes and Effects Analysis and Reliability Analysis of Satellite Power Generation Systems

Abstract

Cost and lifetime requirements are two of the key drivers for the development of complex systems for modern space missions. As a consequence, system reliability is a factor of primary concern, requiring appropriate analyses. A closely related topic is the study of the effects induced by failures to which the system may be subjected, necessary to identify criticalities and weaknesses within the system. Mitigation strategies may then be derived and implemented. The aforementioned activities are laborious, intensive and a significant number of iterations are needed to achieve a system design that fully complies with the dependability requirements. This research aims to perform an FMEA and reliability analysis of satellite solar arrays by developing a flexible modeling software for the simulation of the performance of any PVA configuration, able to provide a reliability assessment. These activities require the implementation of two different models: an electrical model and a reliability model.
As far as the FMEA is concerned, two types of analysis may be performed to study the effects of the failure modes. A static analysis comprises the investigation of the variations experienced by the characteristic curves of the solar array due to failures, while a dynamic analysis studies the response of the Solar Array Regulator (SAR). The outcome depends on the type of analysis performed: for the former, the characteristic curves of the healthy and faulty system are plotted. Then, the performance variations corresponding to the three main operating points (open-circuit, short-circuit, maximum power) are calculated. This allows characterizing the effects of the failures of the solar array. Furthermore, a severity classification of the failure modes is retrieved. The response of the solar array regulator is instead investigated through the dynamic analysis, where a load is connected to the solar array. Based on the wave-forms obtained, the correct implementation of the SAR may be verified and the sizing of other elements of the Electrical Power Subsystem (EPS) may be derived.
The reliability analysis, besides providing an accurate estimation of the system reliability, is also used to calculate the probability of occurrence of failures. From this, a probability classification is determined, leading to a criticality assessment of the failure modes for the selected PVA configuration. This allows highlighting weaknesses in the system and acting accordingly with the implementation of mitigation measures. Furthermore, through the sensitivity analysis, recommendations for reliability improvement may be derived.
The classification of the effects of the failure modes provides relevant insights about the synthesis of a reliable system, drawing attention to those components whose failure induces the most concerning performance degradation. Furthermore, the outcome of the research is a robust starting point for the development and analysis of a full EPS.