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A sliding mode control-based robust control law is proposed to deal with the problem of spacecraft attitude tracking considering actuator misalignments and external disturbances. The control torque errors due to actuator misalignments are considered in the proposed control law, and its effects on attitude control performance are suppressed. Besides showing stability, explicit bound on the attitude tracking errors is given in terms of design parameters. Simulation results show the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Attitude tracking problem with unknown friction torques of reaction wheels and external disturbances is addressed. A robust adaptive controller with parameter update law is proposed and analyzed. An indirect (nonregressorbased) approach used to deal with the effects of unknown friction torque and external disturbances is explored for the attitude control law. This is done by not focusing on friction torques and external disturbances, but on their bound, thus allowing the core information on friction torque and external disturbances to be extracted and used for controller design. The stability of the resulting closed-loop system is proved by application of Barbalat ' s Lemma. Numerical simulations are presented to show the effectiveness of the proposed attitude tracking approach. [ABSTRACT FROM AUTHOR]

For the attitude control system of a spacecraft, non-smooth control technique is utilized to improve the robustness and dynamic performance. A continuous attitude control law is given to ensure the homogeneity of the closed-loop attitude control system with a negative degree of homogeneity. The resulting attitude control system is finite-time stable, thus guaranteeing the dynamic performance of state variables. Simulation is carried out under the cases of the nominal system and the systems with parameter uncertainties and external disturbances, respectively. The simulation results show that, under the designed control law, the nominal system is finite-time stable, and uncertain systems are robust against uncertainties and disturbances. [ABSTRACT FROM AUTHOR]