Dynamics And Control Of Orbital Transfer Of Hybrid Electrodynamic Tethered Satellites

The hybrid electrodynamic tethered satellite orbital transfer system has the ability of orbital boosting or deboosting,which generally refers to a space combination system that consists of two or more spacecraft connected by different kinds of electrodynamic tethers.As an innovative space propulsion method,the hybrid electrodynamic tethered satellite system can be applied to the space science exploration scenario,such that,satellites or spacecraft orbital transfer,mega-constellations maintenance,spacewalker,and so on.This work was funded by the Natural Science Foundation of China(NSFC)-"Coupling Multiphysics Model and Optimal Control of Electrodynamic Tether for Space Debris",China Scholarship Council(No.201806230154),and Discovery Grant of the Natural Sciences and Engineering Research Council of Canada(RGPIN-2018-05991).The multi-body system which consists of different electrodynamic tethers was studied.This research focuses on the dynamics and control of the hybrid electrodynamic tethered satellite orbital transfer system,which provides a theoretical research foundation and technical reserves for satellite autonomous orbit transfer and orbit maintenance.The main research work and innovations of this thesis include:1.To achieve orbital boosting or deboosting of the electrodynamic tethered satellite system,this work proposed a technical idea of hybrid electrodynamic tethers to realize the orbit transfer of spacecraft.The system is composed of a fully insulated conductive tether and a fully naked conductive tether.The effect of the interaction between the change in effective cutting length of the electrodynamic tethers with its surrounding electron density,Earth's magnetic field strength,and atmospheric density on the magnitude of the system electrodynamic force was also considered.2.Parker-Murphy Law is introduced into the multiphysics model to solve the current-voltage characteristic equations and system dynamics equations of the electrodynamic tethered satellite system under the orbital boosting mode.A dynamic model of an electrodynamic tethered satellite system coupled with a multiphysics model has been established,which can provide a way to study basic scientific issues such as the characteristics of the Earth's ionosphere,the characteristics of the geomagnetic field,and changes in the Earth's atmosphere.3.Based on the characteristics of in-plane/out-of-plane libration of the electrodynamic tether,this work proposed a continuous fuzzy logic electric current control method to solve the undesirable transient step response caused by the electric current switching control strategy.This strategy can effectively suppress the libration motion of the tethered system.As for the phenomenon that the initial tether libration angles is not zero,a real-time model predictive control method is proposed to optimize the in-plane and out-of-plane libration motion of the hybrid electrodynamic tethered satellite system.This model can quickly stabilize the libration angles in a balanced position.Both of the continuous control strategies can improve the continuity and real-time of electric current of the tethered system.