Research On Assessment Of Fault Risk For Attitude Control System Of Satellite

With the requirements for long-life and high reliability spacecraft,the research on quantitative fault risk assessment has become a great concern.Directed fault propagation graph mode l of satellite attitude system is built by introduc ing switching nodes and logical nodes to describe the redundancy of components.A method using virtual gravity is proposed to evaluate the importance of components in a system.A quantitative fault risk assessment is carried out in case of component failure,in which the degree of failure,the degradation of performance and the previous probabilities are included.System risk analysis is developed then with consideration of results of risk assessment and results of importance evaluation of a component when undergoing on-orbit malfunction.Firstly,by analyzing the composition structure,configuration,working mechanism and failure modes of the satellite attitude control system.Directed fault propagation graph mode l of the system is established based on switching nodes and logical nodes in order to describe the redundancy of components.The classical satellite attitude control system adopts redundant configuration.In order to reduce the complexity of modeling,the switching nodes are introduced to describe the configuration of the system when the directed fault propagation graph model is established.The logical nodes are introduced to describe the fault output of the branches,and each subsystem is approximated as a node.Then,the fault propagation directed graph is modeled for each subsystem.The system directed fault propagation graph model laid the foundation for the evaluating the importance of components in a system.Secondly,a method of evaluate the importance of components in a system is studied.Taking into account the different positiona l importance of each component in the system and the inevitable relationship between the components,the components of the system can be divided into the key components,the important components and the general components.A virtual gravitationa l mode l is proposed to represent the influence relationship among the components.Conside ring the nodes proximity and the nodes importance contribution,a method using virtua l gravity is proposed to evaluate the importance of components in a system.The simulation research of ARPA(Advanced Research Projects Agency)network is taken as an example,and the proposed method is applied to the satellite attitude control system to determine the importance of each component of the system under a certain configuration,and to provide theoretical support for the system design.Thirdly,a method of quantitative fault risk assessment is studied.Based on the importance degree of the system components,a quantitative fault risk assessment evaluation research based on the influence factors of system is carried out.The performance degradation characteristics of the components are analyzed by using the system state data and the degradation data.Then the three main influencing factors of the degree of failure,the degradation of performance and the previous probabilities are analyzed.Considering the three major influenc ing factors of the degree of failure,the degradation of performance and the previous probabilities,a Multi-factor method of system fault risk assessment based on the degree of failure,the degradation of performance and the previous probabilities is proposed.The typical multi-gyro configuration system and the multi-flywheel configuration system are taken as an example to validate the effectiveness of the proposed method.Fina lly,a method of system risk analysis based on the results of risk assessment and results of importance evaluation of a component is studied.By establishing the system risk management model and analyzing the corresponding technical approaches of system risk management,a method of system risk state partitioning based on the degree of risk and component importance is proposed.The system risk is divided into high,medium,low and norma l,and on this basis,the paper presents the on-orbit maintenance strategy based on the system risk analysis.