Robust Attitude Tracking Control of Spacecraft in the Presence of Disturbances

Abstract

I T IS well known that spacecraft usually operate in the presence of various disturbances and that their control input usually is limited because of actuator saturation. Therefore, two problems, disturbance rejection and saturation constraint accommodation, should be addressed in attitude control. Both problems have attracted considerable research interest in the existing literature. However, only limited results explicitly dealt with them simultaneously [1–5]. Di Gennaro [1] designed a dynamic controller that can globally asymptotically stabilize the spacecraft in the presence of saturation constraint and gravity gradient torque. However, the rejection of other disturbances is not guaranteed. Boskovic et al. [2,3] designed sliding-mode controllers, which are discontinuous and can cause chattering [6]. To avoid chattering, the boundary layer method was used in [2,3]. However, this method can only guarantee bounded attitude and angular velocity errors. To achieve global asymptotic stability with a smooth controller, Boskovic et al. [4] designed a continuous adaptive tracking controller with a condition necessary for guaranteeing the convergence of the attitude error to zero. However, it is difficult to know in what cases that condition can be satisfied. Moreover, according to [7], there do exist some disturbances in the presence of which that condition cannot be satisfied. Wallsgrove and Akella [5] designed a smooth controller using a hyperbolic tangent function. Although the angular velocity error converges to zero, the convergence of the attitude error to zero is not proved in [5]. Moreover, this controller gives rise to numerical problems in simulations of long duration. This paper proposes a controller without the aforementioned drawbacks. II. Spacecraft Attitude Dynamics