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Inertial-Optical Attitude Determination and Model Following Control of Manoeuvring Spacecraft,

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The paper presents an approach to on-board commanding, estimation, and control of the attitude motion of maneuvering spacecraft, based on modern control principles. Firstly the control algorithms are discussed. The control law is based on explicit model following. It comprises single-axis models of the spacecraft motion, which generate a target trajectory and associated target control. The spacecraft tracks the target trajectory by means of the target control which is fed forward to the spacecraft, and by means of state feedback control. A spacecraft state estimator provides for the estimates of the spacecraft state attitude, angular velocity, and provides for the estimate of the disturbance torque which is used for disturbance torque compensation. Secondly an algorithm for inertial-optical attitude determination and estimation of gyro parameters drift rate bias and scale factor error is presented. The algorithms were validated in software simulations of an attitude control system of the type as used in the Infra Red Astronomical Satellite IRAS. The control law and state estimator were tested inflight, in an on-board experiment with the IRAS spacecraft. The considered control system comprises a strapdown rate-integrating gyro and a slit-type star sensor for optical-inertial attitude sensing, a reaction wheel actuator, and a 16-bit on-board computer. The estimation and control algorithms are described, design trade-offs are discussed, simulation results and in-flight results are presented. Author

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