Design and Management of Satellite Power Systems

Satellites are indispensable for broadcast, weather forecast, navigation, and many other applications, but their design entails a number of stringent requirements, such as limited space and weight, impossible/costly online repairs, severe radiation, and a wide range of temperature they have to withstand. These requirements can only be met by an effective, robust co-design of physical and computing (control) parts of each satellite, making them prototypical cyber-physical systems (CPSes). Of the various CPS issues related to satellites, this paper focuses on offline design and online management of satellite power systems. Specifically, we analyze and model unique characteristics of power supply and demand of a satellite, which are dictated by the periodicity of power generation from solar panels and the nonlinear behavior of rechargeable battery cells. Based on the understanding of these characteristics, we first propose how to find the best configuration (e.g., the number, the arrangement, and the type) of solar panels and battery cells at design time, such that all tasks can be executed without power shortage throughout the satellite's mission lifetime. Second, we propose how to manage power online so as to execute the highest QoS versions of tasks (thus yielding the most power-effective performance) without compromising the power-sufficiency guarantee under a given configuration. As a case study, we study cubic-shaped nanosatellites, which have been launched multiple times since 2004. We borrow their architecture, configuration and parameters, and demonstrate the effectiveness of our design and management of satellite power systems.