Nonlinear adaptive control of spacecraft maneuvers
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A novel method is presented to carry out near-minimum-time maneuvers of a spacecraft of unknown inertia. The formulation assumes the presence of three orthogonal reaction wheels located near the system mass center and oriented arbitrarily with respect to the spacecraft principal axes. Modified Rodrigues parameters along with their shadow set are used as the primary attitude coordinates. Open-loop maneuver laws are designed while solving the equations of motion hy inverse dynamics approach. This approach permits the approximate imposition of the maximum saturation torque constraint. The torque profiles are near-bang-bang, with the instantaneous switches replaced by cubic splines of specified duration. An adaptive tracking control law is developed to determine perturbations to the nominal open-loop torque commands that will ensure the actual motion to follow the nominal motion in the presence of uncertainty in the inertia matrix and errors in the initial attitude. Global stability of the overall closed-loop controller is proved analytically and demonstrated by numerical simulations.
