Reliability Engineering of BeiDou Navigation Satellite

Reliability engineering is a series of technical and management activities carried out to meet the reliability requirements of the product. Reliability engineering through the study of the occurrence, development, and prevention of product failure, through design, analysis, testing, and other means, to prevent and control the occurrence and development of failure, and improve the inherent reliability of products, to ensure the success of product missions and reduce life cycle costs. Reliability engineering is an important part of the whole system and life cycle management of spacecraft. It includes the determination of reliability requirements, reliability design and analysis, reliability tests, reliability management, and other aspects. It runs through the feasibility demonstration phase, preliminary definition phase, qualification and production phase, and on-orbit operation phase of the project, and is applied to spacecraft systems, subsystems, equipment, components and parts, as well as electronic, electromechanical, optoelectronic, mechanical, structural, software and other types of products.

Reliability requirements are the basis for reliability design, analysis, test, and verification. Reliability requirements can be divided into qualitative requirements and quantitative requirements. Qualitative requirements are to design, evaluate, and assure the reliability of products in a non-quantitative form. Quantitative requirements specify the reliability parameters, values, and verification methods of products, to evaluate or verify the reliability level of products with quantitative methods in the process of design, production, and use.

The task of satellite reliability modeling is to model the system behavior (fault logic) under various mission conditions (mission profile changes, system structure changes, etc.) based on reliability parameters (such as reliability) and system characteristics (such as repairable or non-repairable, static or dynamic), and to express it in the form of graphics and/or mathematical relations or simulation logic. The task of satellite reliability prediction is to estimate the value of the satellite reliability index using the system reliability model and unit product reliability prediction. The combination of reliability modeling and reliability prediction can provide a sufficient basis for reliability analysis work and reliability design improvement, which is of great significance in the process of navigation satellite preliminary design and detailed design. This is accomplished by accurately and truly describing the reliability relationship of the system and obtaining the analysis results.

The continuous availability of navigation signals is the basic condition for the successful operation of a satellite navigation system. In aviation, transportation, and other navigation applications, navigation signal interruption may bring serious consequences. Therefore, GPS of the United States, Galileo system of Europe Union, BDS of China, and other satellite navigation systems all regard the continuous availability of navigation signals as the basic requirement and the availability as the critical technical index of satellite navigation constellation.

It is necessary to evaluate quantitatively whether the availability design of navigation satellites and constellations meets the requirements and to quantitatively determine the weak links through availability analysis. In response to the availability requirements of navigation systems, it is necessary to study all situations that may cause navigation signal interruption during the operation of navigation satellites, and analyze those faults that can be recovered on-orbit. At this point, it is necessary to view the navigation satellite as a repairable system and conduct availability analysis work.

Reliability design is an integral part of navigation satellite engineering. The navigation satellites have the characteristics of complex composition, harsh environment, and high cost. If on-orbit failure occurs, it may lead to fatal consequences. Multiple navigation satellites are developed at the same time, and their inherent design faults will affect satellites with the same technical status. At least, the progress is delayed, and at worst, the system loss is incalculable.

Reliability analysis is a technical work that uses various methods to identify the critical characteristics and weaknesses of products from different aspects and improves the reliability of products by implementing design and improvement measures. The reliability analysis of navigation satellite products includes mission profile analysis, FMEA, FTA, WCCA, SCA, etc. Mission profile analysis is the basis of reliability and related critical characteristic analysis. FMEA and FTA are used to identify potential weaknesses in design or process and determine critical items. WCCA is used to find weaknesses in circuit design. SCA is used to identify potential states that cause unexpected functions or inhibit expected functions.

Reliability is designed and produced. The inherent reliability of satellite design needs to be guaranteed by the production process, and the reliability of satellite products delivered also be directly determined by the reliability assurance and quality control of the production process. According to the quality problems statistics during the development phase in recent years, production defects and design defects are the two main factors in the occurrence of quality problems. Especially for navigation satellites developed in batches, the reliability assurance of the production process is more important.

Satellite product tests can be divided into three categories: function/performance tests, environmental tests and reliability tests. The purpose of function/performance test is to verify whether the mechanical and electrical properties of the satellite meet the design requirements and whether it is compatible and coordinated with the ground support equipment. The purpose of environmental testing is to find the environmental design defects of the product, verify the adaptability of the product to extreme environments during the life, and obtain the response characteristics of the product to environmental effects.

Reliability management is an important part of satellite development management. From the perspective of system engineering, it plans, organizes, coordinates, and supervises various reliability activities in various stages of satellite development, production, and operation, and realizes the reliability requirements of products with the least resources. Reliability management involves the whole development process and life cycle stages of satellites from the feasibility phase to the end of life and involves all product levels of satellites.