| Electrodynamic tether systems(EDT) have the potential to play an important role in future spacecraft systems. They can provide propulsion without any propellant, hence they can be widely applied in many space missions such as obital maneuvering, space debris removal, and satellite formation et al. EDT in stationkeeping phase are focused in this dissertation, including modeling of EDT in this phase and dynamics analysis of dynamics equations. The mian work and contributions can be summarized as followed:1. The basic principle of EDT is analyzed. Geomagnetic field and the ionosphere of Earth are described. Main components of EDT and function of every components are summarized, and the basic principle of EDT that how the electrodynamic force is generated expounded.2. Different models for EDT in stationkeeping phase are modeled. Dumbbell model for EDT are modeled using Lagrange method. The Kirchhoff equations are used in modeling the EDT. The discretized flexible EDT model is described. By analyzing the small element of tether, the consecutive flexible tether model is builded.3. A algorithm for obtaining periodic solution to EDT is introduced. The procedure of combining perturbation method and stationary point iteration method to seek periodic solutions for nonlinear equations is presented. In order to test the validity of this method, periodic solutions for dynamic equations in different conditions are calculated. By computing maximum eigenvalue of the mapping matrix the results show that periodic soluitons for nonlinear dynamic equations of EDT are all unstable.4. The control methods for unstable periodic solutions are studied. Three control methods which are state feedback control, time-delayed autosynchronization method and extended time-delayed autosynchronization method are studied. Numerical simulations show that all these control methods are able to transform the uncontrolled unstable periodic motions into asymptotically stable ones. |
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