George Z.H. Zhu
Professor and Chair, Department of Mechanical Engineering,
York University
Research Interest: Dynamics and control of electrodynamic tether system for space debris removal, autonomous on-orbit service robot for space debris removal, and multifunctional materials for spacecraft structures.  

Speech Title：Computational Control Framework for Tethered Space Systems

Abstract: This talk presents a new computational feedback control framework for flexible-rigid space systems. The framework integrates dynamic models, state estimation, and optimal control with a moving horizon into a cohesive and unified procedure by leveraging the finite element method as the foundational tool. The framework begins with the development of a high-fidelity dynamic model of the space tether system using the nodal position finite element method. This approach allows for accurate representation of the tether’s flexibility and dynamic behavior, ensuring precise simulations of its physical responses under varying conditions. A robust finite element Kalman state estimator is then employed to estimate the positions and velocities of the entire tether, which cannot be measured directly. This state estimation process is critical for capturing the dynamic behavior of the tether in real-time, providing the necessary data for effective control. Subsequently, optimal control in the finite element form is formulated to regulate and manage the geometrical profile of the flexible space tether system. The control strategy is derived by recasting the optimal control problem into canonical equations through Hamilton's variational principle. This transformation results in a two-point boundary value problem with a moving terminal boundary condition, allowing for the generation of control inputs numerically. These inputs are then applied in a closed-loop feedback control scheme utilizing a moving horizon. The proposed computational framework is validated through numerical simulations of an initially bent tethered space system. Simulation results demonstrate the framework's effectiveness in controlling the tether's geometry, achieving the desired configurations efficiently. Furthermore, the analysis reveals that the methodology can be easily adapted to other flexible elastic systems, showcasing its versatility and potential for broader applications in space, robotics, and mechanical systems. This framework represents a significant step forward in the control of flexible tethered structures in space exploration.

Short Biography: Dr. Zhu is a Professor and Tier 1 York Research Chair in Space Robotics and Artificial Intelligence in the Department of Mechanical Engineering at York University in Toronto, Canada. He is also the founding Director of the Manufacturing Technology Entrepreneurship Centre and the Space Engineering Lad at the same institution. From 2019 to 2022, he served as the inaugural Academic Director of the Research Commons in the Vice-President of Research and Innovation Office and was the Chair of the Department of Mechanical Engineering from 2018 to 2019. His research includes dynamics and control of tethered spacecraft, autonomous space robotics, visual servo, computational control, CubeSat, and additive manufacturing in space. He has published 227 peer-reviewed journal papers, 183 conference proceedings, 5 book chapters and edited one book. In addition, he was the Principal Investigator of two CubeSat missions. Currently, he is the Academician of the International Academy of Astronautics; College Member of the Royal Society of Canada; Fellow of the Canadian Academy of Canada; Fellow of the Engineering Institute of Canada, Canadian Society of Mechanical Engineering, and Fellow of the American Society of Mechanical Engineers; and Associate fellow of American Institute of Aeronautics and Astronautics. Dr. Zhu is the recipient of the 2024 Solid Mechanics Medal and the 2021 Robert W. Angus Medal from the Canadian Society for Mechanical Engineering; the 2024 Gold Medal and the 2019 Engineering R&D Medal of Professional Engineers from the Professional Engineers Ontario Canada; and the 2021 York University President’s Research Excellence Award. Finally, Dr. Zhu is the Editor-in-Chief of Acta Astronautica.