Near minimum-time maneuvers of large space structures using parameter optimization and lyapunov feedback control

Abstract

Near minimum-time attitude maneuvers for large space structures with limited fuel supplies are investigated. This study encompasses a wide range of methods to solve the practical engineering problem of performing rest-to-rest maneuvers of a large space structure. These methods include the modeling of the rigid body dynamics for the structure, control parameterization, the determination of a near-minimum time open-loop control by iterative parameter optimization methods, and the analytical determination of an asymptotically stable control to force the structure to come to rest at the final position. The open loop maneuver is determined with the Sequential Quadratic Programming (SQP) algorithm, which optimizes a control parameter set for the given maneuver. Torque shaping is used to prevent discontinuous jumps in the control which would excite the structure's flexible modes. Since iterative methods are sensitive to the initial guess, approximations for the control parameterizations are determined to provide an initial guess when no insights are available to particular problem. The closed-loop feedback control is determined to rigorously meet the desired final attitude using the Lyapunov direct method. Asymptotically stable final position regulation controls and tracking controls are developed and compared on the basis of settling time, peak closed-loop control, and smooth convergence for near-minimum time maneuvers. These theoretical solutions are verified using experimental results from tests on the Advanced Space Structures Technology Research Experiment (ASTREX) test article, located at Phillips Laboratory, Edwards AFB, CA. The ASTREX structure, with an approximate total mass of 4106 kg., is a dynamically-scaled structural model of a 3-mirror space-based laser beam expander. structure, which rests on a nearly frictionless air bearing, can perform three-axis rotations using pressurized air thrusters. The ASTREX structure is composed of graphite epoxy tube truss sections, which make this test article inherently flexible.