Investigation On Model-based Fault Diagnosis Methods For Spacecraft Propulsion System

Some key technologies involved in fault diagnosis for typical Chinese spacecraft propulsion systems such as DFH satellite propulsion system and Shenzhou propulsion system) were thoroughly investigated, analyzed and developed in the dissertation. The research works related to modeling and simulation of propulsion system dynamics, failure mode analysis and simulation, integrated qualitative and quantitative fault diagnostic methods, fault diagnosability analysis and sensor placement optimization, the integrated design, implementation and validation of fault diagnosis system.In order to investigate the dynamic characteristics of complex supply pipes of spacecraft propulsion system, a modular model library of propulsion system was established. The dynamic simulation of the priming and shutdown process for DFH satellite propulsion system was carried out. Some interesting results have been obtained as follows. Firstly, waterhammer phenomena occur obviously in almost whole propulsion system during priming and shutdown process. However, the frequency and the peak pressure of waterhammer during priming process are both lower than that of shutdown process, especially for the peak pressure. Secondly, due to the distributary of supply pipes for attitude control thrusters, peak pressure and attenuation time of waterhammer in main supply pipes decrease significantly than main supply pipes work independently. Thirdly, orifice can suppress oscillation of pressure and flow rate significantly during priming and shutdown process, bent pipe and initial blanket pressure can also suppress waterhammer effectively during priming process.Due to the lack of fault sample data, fault mode features and diagnostic knowledges, the failure mode and effect analysis(FMEA) of spacecraft propulsion system during orbit maneuver and attitude control were comprehensively studied. Aiming at two kinds of typical failure modes, leakage and blockage, respectively, 5 typical fault effects and 2 typical fault characteristics of the propulsion system were simulated. The results of numerical simulation provide solid foundation for investigation of fault effects and evaluation of parameter response and sensibility under some specific fault condition.Due to the lack of spacecraft onboard resources and measured parameters, the signed directed graph(SDG) based qualitative fault diagnostic method was investigated and developed for spacecraft propulsion system. 5 potential fault sources were obtained for the case study of DFH satellite propulsion system, while 4 potential fault sources were obtained for the case study of Shenzhou propulsion subsystem. The results show that SDG-based qualitative diagnosis method is effective, and the potential fault sources obtained can cover all possible fault sources. However, because of information loss while going from quantitative to qualitative domain, SDG-based diagnosis method has poorly discriminatory ability. In order to identify accurately fault source, this method needs further improvement by combining quantitative information.The SDG-based diagnosis method was combined with temporal information and quantitative information, in order to improve its discriminatory ability. The Temporal SDG(TSDG) model and corresponding diagnostic strategy were investigated and developed, and effect relations between SDG model nodes were analysed from the componential mathematical model and integrated into SDG model. Case studies of Shenzhou propulsion system show that the method proposed can utilize effectively the initial responses and historical information of propulsion system, and the quantitative restrictions of componential mathematical models. The discriminatory ability of the method was remarkably improved, and all of three case studies can accurately identify the only fault source.In order to provide a solid basis for the fault diagnosis applications, the fault diagnosability including fault detectability and fault isolability of spacecraft propulsion system was analysed. Case studies of spacecraft propulsion systems show that the number and location of sensors have important effect on fault diagnosability of propulsion system, and fault isolability requires much more sensor information than fault detectability. In DFH satellite scenario, which has only 5 flight telemetry parameters, the fault detectability is about 62.8%, and the fault isolability is about 30.2%. While in Shenzhou propulsion system scenario, which has 26 flight telemetry parameters, the fault detectability is 100%, and the fault isolability was about 38.2%. The optimal sensor placement method based on fault diagnosability analysis was developed, and 10 more sensors were selected for DFH satellite propulsion system. Based on the optimal sensor placement results, the fault diagnosability of DFH satellite propulsion system was re-analysed. The results showed that the method proposed can remarkably improve the fault diagnosability. In DFH satellite scenario, the fault detectability increased from 62.8% up to 100%, and the fault diagnosability increased from 30.2% up to 55.8%.In order to solve some practical engineering problems of fault diagnosis for spacecraft propulsion systems, an extensible framework for fault diagnosis system was proposed. Based on the framework, the fault diagnosis subsystem which includes data acquisition module, fault detection module, fault diagnosis module, and diagnosis database was designed and developed. The simulation subsystem which includes system dynamics simulation and fault simulation module, playback database, and analog output module was also designed and developed to meet the verification requirements of fault diagnosis subsystem. Moreover, based on combination and integration of the above mentioned research results, a fault diagnosis system for DFH satellite propulsion system was implemented. The system has been validated by telemetry data and fault simulation data. The results show that this diagnosis system is stable and reliable, and there is no false alarm and missing alarm for the 6 data group verifications. The diagnosis system can satisfy the requirements of fault diagnosis for spacecraft propulsion system ground test.The methods proposed and developed in the dissertation have laid a solid theoretical and technique foundation for the design and realization of practical ground test and on-orbit fault diagnosis system for spacecraft propulsion system. The results will provide significantly important reference to improve spacecraft propulsion system reliability and safety.