| Uses of tethers for a variety of purposes in space have been investigated extensively for many years. Currently, interest is focused on two NASA missions, TSS-1 and TSS-2, in which, a satellite is to be deployed, by means of a tether, from the Shuttle, and performs a series of experiments. The tethers to be used in TSS-1 and TSS-2 are very long, namely, 20 km and 100 km, respectively. Hence, significant problems of dynamics and control arise in connection with all mission phases, and it is not yet clear that all of these problems possess satisfactory solutions. This must be a source of concern, given the fact that TSS-1 and TSS-2 are manned missions involving the very valuable Shuttle.;It is the purpose of this dissertation to propose alternate means to accomplish the goals of missions such as those of TSS-1 and TSS-2, a way that involves the Shuttle and astronauts either minimally or not at all. Stated most simply, the proposal is this: replace the Shuttle with an unmanned spacecraft. Although this idea was mentioned in early papers on tethered systems, its feasibility remained to be investigated. A comprehensive study of such a system is the topic of the present dissertation.;The system is composed of a primary satellite, a tether, and a secondary satellite. The primary satellite carries scientific instruments, whereas the secondary one is equipped with a set of thrusters for purposes of control. First, a 3D model, in which the tether is represented by two segments, is analyzed. Thereafter, multi-segment models for the tether are considered; only part of the system states are measured, and the other states are estimated by means of a reduced order estimator. To optimize the deployment and retrieval phases, a multi-controller, MATLAB based algorithm, is employed. The result is improved performance and a significant reduction in fuel consumption. Finally, to use electrodynamic forces for orbit transfer without exciting tether bending motions, the notion of synchronized impulses, that is, running electric current through the tether at pre-calculated instants and amplitudes, is presented. |
