From Graphs to the Science Computer of a Space Telescope

Abstract

Space system engineering has to follow a rigorous design process to manage performance/risk trade-os at each development stage and possibly across several functional and organizational domains. The process is further complicated by the co-development of multiple solutions, each contributing dierently to the goal and with dierent tradeos. Moreover, the design process is iterative, involving both changing requirements and specications along the dierent ways that lead to the set goal of the mission. The above requires rigorous modeling that, in addition, must be easily extendible and maintainable across organizational units. On the example of the PROBA-3 science computer (instrument control unit, CCB DPU), we show how Petri Nets can serve as such a simple-to-maintain, holistic model, combining nite-state characterizations with dynamic system behavior caused by hardware-software interactions, to express the component-state dependent end-to-end performance characteristics of the system. The paper elaborates on how the proposed Petri-Net-modeling scheme allows for system architecture optimization that result in safely reduced technical margins and in turn substantial savings in components costs. We show that performance metrics, obtained from simulation, correlate well with the real performance characteristics of the ight model of PROBA-3's science computer.