Abstract
This paper deals with the attitude control problem of a nearly axis-symmetric spacecraft actuated by two torques perpendicular to its symmetry axis. As a result, the spacecraft symmetry axis is unactuated and the rotation about it is uncontrollable. Our objective aims to stabilize the symmetry axis to an arbitrary inertial direction irrespective of the spinning motion about it. First, a non-smooth controller is derived via homogeneous techniques to align the symmetry axis in finite time when there are no uncertainties. To compensate for perturbations induced by uncertain inertias, unknown external disturbances and actuator faults, an adaptive integral sliding mode controller is developed by combining adaptive control and integral sliding modes with the non-smooth controller. The resultant adaptive controller can stabilize the system states into a small neighborhood around the sliding mode. Consequently, the performance of the non-smooth controller can be approximately recovered, even in the presence of uncertainties, which ensures significant robustness and high control accuracy. Numerical examples are presented to verify the effectiveness and advantages of the proposed methods.
Highlights
The attitude motion of a rigid spacecraft has 3 degrees-offreedom and it becomes underactuated when the available control torques are fewer than three
It is common that the uncontrollable symmetry axis has nonzero angular velocity for on-orbit spacecraft. To deal with this scenario, spin-axis stabilization was proposed to stabilize the symmetry axis of the spacecraft to an arbitrary target inertial direction irrespective of the spinning motion about the symmetry axis [22]–[24]. Such type of attitude control can have practical applications when the spacecraft symmetry axis is a normal vector of the solar panel, or the line-of-sight of an antenna, a telescope or a camera, etc
Tsiotras et al [22], [23] first derived proportionalderivative feedback laws asymptotically stabilizing the spinning axis of an axis-symmetric spacecraft with two torques
Summary
The attitude motion of a rigid spacecraft has 3 degrees-offreedom and it becomes underactuated when the available control torques are fewer than three. Tsiotras et al [22], [23] first derived proportionalderivative feedback laws asymptotically stabilizing the spinning axis of an axis-symmetric spacecraft with two torques In spite of their remarkable simplicity, these algorithms have poor robustness against inertia uncertainties and external disturbances. A Hölder-continuous controller with a nonlinear proportional-derivative structure is designed by means of the homogeneous theory to stabilize the spinning axis to the target direction in finite time, when there is no system uncertainties. It is developed into an adaptive controller with significant robustness against uncertain inertia, unknown external disturbances, and actuator faults by combining integral sliding mode (ISM) methods and adaptive techniques.
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