Resilient Operation Model for Nano-Satellite Using STPA

Abstract

Though our developed nano-satellite, HIROGARI released to orbit in March 2021 achieved the missions successfully until the end of 2021, the satellite encountered significant problems in the early operation stage. Because the satellite condition did not follow the expected behavior, the operation policy had to be decided with insufficient data. However, it was difficult to decide the operation policy rationally, since a nano-satellite has poor battery and communication margins. For the next nano-satellite development, this study constructed a resilient operation model for a nano-satellite using Systems-Theoretic Process Analysis (STPA) with lessons learned from operation experiences of HIROGARI. STPA is known as a new hazard analysis method that focuses on the interaction between a controller and the controlled object and that can be applied in conceptual design stage before detailed configurations are determined. The resilient operation model was constructed by considering the ground station as the controller and the satellite as the controlled target. Then, validity of adopting STPA to construct the operation model is discussed through comparing the unsafe control actions (UCA) and our lessons learned from operation of HIROGARI.