Research On The Modular Design Method Of On-Board Software

Modern space missions are becoming increasingly complex and on-board computer system more sophisticated. Due to the weight, size and power consumption restrictions, simplifying the design of hardware system means that the on-board software is responsible for meeting the majority of a mission's requirements. Meanwhile, the processor technology is improved fast, and the difference of the software exists because of the differences of missions and hardware environments, so the software production is inefficient, and the maintenance is complex. Any software fault could be catastrophic. Consequently on-board software is at the heart of satellite system design and development. In order to achieve that on-board software can be updated dynamically and developed with great efficiency, this dissertation studies three problems, including on-board software architecture, modular design, and module-based dynamic on-board software updating method. The topics are as follows:1. Combining with the requirements of on-board software, this dissertation proposes an On-board Software Architecture supporting Dynamic Updating (DUOSA) based on the architecture design patterns which are applied in the Real-Time Embedded Systems put forwarded by Bruce Powel Douglass. The on-board software based on DUOSA can meet the demands which include real-time, reliability, reusability, easy maintenance and so on. Meanwhile, the modular architecture DUOSA lays a good foundation to support the dynamic updating of on-board software module.2. The multi-task design method of on-board software is gived based on DUOSA, and take an example of a small satellite, the task partition and task scheduling are designed. Prophase experiments showed that they both meet the real-time requirement of the system. Subsystems are designed using the mechanistic design pattern, take an example of a telemetry subsystem, the methods of module design, interface design and correlative problems are gived.3. In order to update the on-board software modules dynamically, the customer modules visit the server modules indirectly through the module redirection table. By modifying the contents of the table, the old modules are redirected to the new modules which the new addresses point to. Selecting a single function module and a module encapsulating some function operations as updating granularities, the former achieves dynamic updating based on indirect executing, in other words, the customer will execute the new module which is at the new entry address after modifying the entry address of the function module; the latter achieves dynamic updating by dynamic loading, in other words, dynamically load the new module by modifying the address of the first level module redirection table, and then the customer will execute the new function services which are encapsulated in the new module. Emulational experiments showed that both methods are reasonable and practical to meet the requirements which includes repairing software module faults, improving software reliability and expanding software functionalities.