Satellite tether systems: Dynamic modeling and control

Over the last few decades, researchers have realized many potential applications of tethered satellite systems that include atmospheric data collection, placing satellites from low earth orbits into higher orbits, capture of non-functional satellites for service and repair, satellite reboost and deorbiting. The deployment/retrieval dynamics of such systems due to gravity gradient forces is highly nonlinear in nature. Also, due to orbital motion, the longitudinal and transverse motions are coupled. With only boundary control, the tethered satellite system forms a highly underactuated system. In this thesis, we derive and validate the deployment dynamics of such a system following two different basic approaches---Newton's laws and Hamilton's principle. The complexity of the system is studied in an incremental nature using three different models. The problem of controlled deployment/retrieval is approached using a partial feedback linearizing controller. The problem of station keeping is tackled in a more novel way by developing a boundary controller based on the linearization of the infinite dimensional tether system around radial relative equilibrium configuration. Lyapunov function is used to study the stability of the controller on the linearized system. Effectiveness of controllers developed for deployment and station keeping are verified through simulations. We have also studied the dynamics of tethered satellite systems in the presence of electrodynamic forces due to the magnetic field of the earth. We propose a novel method to the control the tether configurations in the presence of electrodynamic forces.