Multibody Dynamics and Control of Tethered Spacecraft Systems

This doctoral research conducts high-fidelity multiphysics modeling for tethered spacecraft systems, such as electrodynamic tether systems, electric solar wind sail systems, and tether transportation systems with climbers. Two models are developed based on nodal position finite element method. The first model deals with the tethered spacecraft system with fixed length tether, while the second model deals with the tethered spacecraft system with variable tether length using an arbitrary Lagrangian-Eulerian description. First, the nodal position finite element method is applied to model the orbital motion of tethered spacecraft systems with fixed tether length over a prolonged period. A Symplectic integration scheme is employed to attenuate the accumulation of error in the numerical analysis due to the long-term integration for tethered spacecraft systems, such as the space debris deorbit by electrodynamic tethers. A high fidelity multiphysics model is developed for electrodynamic tether systems by considering elastic, thermal, and electrical coupling effects of the tether. Most importantly, the calculation of electron collection by the electrodynamic tether is coupled with the tether libration and flexible deformation, where the orbital motion limited theory for electron collection is discretized simultaneously by the same finite element mesh used for the elastodynamic analysis of tether. The model is then used to investigate dynamics and libration stability of bare electrodynamic tethers in deorbiting end-of-mission spacecraft. Second, the model of tethered spacecraft system with fixed tether length is extended for the modeling of electric solar wind sail systems. The coupling effect of orbital and self-spinning motions of electric solar wind sail systems is investigated together with the interaction between the axial/transverse elastic motion of tether and Coulomb force. A modified throttling control algorithm is implemented in the finite element scheme to control the attitude motion of electric solar wind sail systems through the electric voltage modulation of main tethers. Third, the model of tethered spacecraft with variable tether length is applied to handle the tether length variation in tether transportation systems. The tether length variation results from the climber moving along tether and deployment and retrieval of tether at end spacecraft. The dynamic behavior of tether transportation systems with single or multiple climbers in characterized and the effectiveness of libration suppression scheme is tested by the high-fidelity model.