In this paper, three dimensional coupled engagement dynamics are firstly transformed into a state-space form without decoupling three dimensional engagement dynamics into two mutually orthogonal planes to avoid degrading the performance of the guidance law. Specially, fixed-time guidance laws are proposed to guarantee that the line-of-sight (LOS) angular rates can be steered to zero before the final time of the guidance process at the same time. The exact convergence time can be set beforehand with respect to the LOS rates, and it is independent of initial conditions with respect to the guidance system. Moreover, impact angle constraint is taken into account, and these guidance laws are robust against maneuvering targets by sliding mode techniques. Simulation results validate the effectiveness of the proposed algorithms.
This paper investigates an attitude tracking maneuver problem for a rigid spacecraft with external disturbances, uncertain inertia parameters, actuator misalignments, and faults. First, all the uncertainty terms are split from the desired commanded control torque, and then, the nonsingular terminal sliding mode is implemented to design a fixed-time attitude tracking controller. Subsequently, an adaptive law is drawn into the attitude tracking controller to form a new control scheme, which eliminates the requirement of the upper bounds of all the uncertain terms. Besides, in the light of the concept of fixed-time stabilization, practical fixed-time convergence is achieved for attitude tracking errors. Finally, the numerical simulations are demonstrated to highlight the performance of the proposed controllers.
This paper investigates spacecraft attitude control problem to achieve global fast tracking maneuvers. The concept of state-space form is initially introduced into spacecraft attitude dynamics and kinematics based on the unit quaternion, and then robust finite-time controllers are proposed based on geometric homogeneity and integral sliding mode. Furthermore, gain adaptation laws are employed and developed to eliminate the requirement of boundaries with respect to the lumped uncertainties, while there is no overestimation of the gains. Moreover, global finite-time controllers are designed to get across the singular point caused by the unit quaternion. Finally, simulations are presented to illustrate the effectiveness of the control strategies.
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