Koopman Operator-Based Data-Driven Identification of Tethered Subsatellite Deployment Dynamics

Compact tether-based actuation is a suitable approach for the deployment of femto/picosatellite bodies from CubeSats using ultrasmall electrodynamic tethers for fuel-free propulsion and deorbiting. Despite the advantages of tethered satellite systems, control technologies for these have yet to mature in several domains including robustness to structural faults and unmodeled dynamics. A proposed solution for the identification of disturbances to tethered satellite dynamics is to use a data-driven algorithm to learn the system's behavior over previous orbits and then provide an estimated prediction for the evolution of system states. To achieve the goal of state prediction via a globally linearized system model, this paper employs the Koopman operator constructed from observed dynamics to extrapolate future motion of a tethered subsatellite subject to unknown disturbances while being deployed from its mothership. Numerical simulations of the constructed model versus the nonlinear model of the tethered satellite system demonstrate the effective prediction capabilities of the proposed Koopman operator-based numerical algorithm for the general flight characteristics many orbits into the future. © 2023 American Society of Civil Engineers.