Computer-Aided Software Design for Spacecraft Guidance, Navigation and Control

In the early days of space flight, the attitude and orbit control system (AOCS) was essentially a hard-wired, frozen architecture that could hardly be modified during flight. Then came the microprocessors whose on-board software, hand-coded by humans before flight, could be reprogrammed during flight. In the most recent evolutionary step, flight software can now be automatically generated by another software tool, starting from a high-level graphical representation of the AOCS functions and their interrelations. The presentation will demonstrate some of the limitations but also many of the benefits of using computer-aided software design tools for flight code generation. The impact on the quality of the flight code and on the substantial savings in development and validation time will be illustrated using the particular case of the on-board AOCS software of the PROBA-1 spacecraft. PROBA-1 was launched in October 2001 for a two-year mission and it is still successfully fulfilling its Earth-observation mission today. Flight results will be provided to illustrate the performance of the AOCS software.