The investigation reported upon in this report was undertaken to study attitude control concepts for use onboard structurally nonrigid spacecraft that must be pointed with great precision. It is an extension of work that has been carried on previously at UCLA with the same objective. The investigation was conducted in four separate areas, each of which is identified as a separate chapter.nIn Chapter 1, the task of determining the eigenproperties of a system of linear time-invariant equations (in terms of hybrid coordinates) representing the attitude motion of a flexible spacecraft is attached. Literal characterizations are developed for the associated eigenvalues and eigenvectors of the system. In Chapter 2, a method is presented for determining the poles and zeros of the transfer function describing the attitude dynamics of a flexible spacecraft characterized by hybrid coordinate equations. The investigation reported on in Chapter 3 is motivated by the need for a control design procedure which is insensitive to modeling errors. Alterations are made to linear regulator and observer theory to accommodate modeling errors. The results (some of which are yet unproven) show that a "model error vector," which evolves from an "error system," can be added to a reduced system model, estimated by an observer, and used by the control law to render the system less sensitive to uncertain magnitudes and phase relations of truncated modes and external disturbance effects. Sometimes mode shapes are provided the designer from an outside source. This chapter provides a hybrid coordinate formulation using the provided assumed mode shapes, rather than incorporating the usual finite element approach.
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