A systemic approach toward scalable, reliable and safe satellite constellations

Abstract

Constellations of hundreds to thousands of satellites are becoming a reality. Nevertheless, the unprecedented scale of these systems is creating new sorts of challenges and risks for the designers and operators, mainly due to the high level of automation required. This study demonstrates how architectural decisions like the constellation topology, type of connectivity, and the level of automation affect the scalability, reliability, and safety of these constellations. A survey of past, current, and planned constellations was conducted to identify key architectural decisions and create representative architectures to analyze using a novel process called Conceptual Architecture Development. These high-level conceptual architectures were refined and analyzed using Systems Theoretic Process Analysis (STPA), and a qualitative assessment and a comparison of the emergent properties were performed. The results suggest that increased automation improves the scalability of the system, mostly when human controllers' responsibilities are shifted from individual satellite management to constellation management. However, increased automation also creates new responsibilities for human controllers and does not necessarily improve the safety and reliability of the system. Human-related causal factors found in lower levels of automation are mostly translated into software-related causal factors in higher levels of automation instead of being eliminated, and new types of hazards arise from the introduction of human-automation interfaces. Moreover, other architectural decisions, such as ground connectivity type, can negatively impact the safety and reliability of the constellation, mostly for slightly automated systems. This study shows that architectural decisions can significantly affect the resulting emergent properties of a system and that there is a tradeoff between automation, safety, and reliability that should not be overlooked. Designers and operators should analyze this tradeoff and the development and operational costs in order to select the best-suited architecture for their constellations based on their expertise, technology strategy, and constellation size.