Advanced topics in structural dynamics: The maneuver of flexible spacecraft, and on-off decentralized control of flexible structures.

摘要

This dissertation describes two approaches to maneuver flexible spacecraft and it describes an approach to suppress vibration of flexible structures using decentralized feedback on-off control. The first maneuver method suppresses spacecraft motion relative to the motion of a fictitious shadow spacecraft using a decentralized feedback control. The second maneuver method is equivalent to the first method but it applies open-loop control with a decentralized feedback control suppressing motion relative to the open-loop path.; First, the dynamics of maneuvering flexible spacecraft are reviewed in general and then specifically for a non-dimensional free-free beam with well separated dimensions. For the first maneuver method, several in-plane rest-to-spin maneuvers are investigated for different choices of shadow coordinates including the maneuver corresponding to minimum fuel. In order to prescribe actual spacecraft motion, lag compensation of the shadow coordinates is introduced to account for feedback lag between the shadow and actual spacecraft coordinates. Also in-plane and out-of-plane maneuvers are investigated. For both maneuver methods the performance is demonstrated with multiple actuator failures. Using the second maneuver method, in-plane rest-to-spin and rest-to-rest maneuvers are investigated for the maneuvers corresponding to minimum fuel.; Next, on-off decentralized control is presented. Fuel minimization is achieved by turning on actuators when local kinetic energy is at a maximum and local potential energy is at a minimum. Maximum kinetic energy and potential energy at each actuator location are determined by recursively computing running standard deviations and running averages of displacements and velocities over moving intervals of time. On-off control of a uniform beam illustrates the results.