Sliding mode attitude control using thrusters and pulse modulation for the ASTER mission

Abstract

ASTER, the first Brazilian mission to the deep space, targets the exploration of the triple asteroid system known as 2001 SN263. The mission requires an attitude controller robust and capable of coping with the non-linearities and the uncertainties present during the exploration phase. For such requirements, this paper studies the applicability of two controllers, designed based on the sliding mode control (SMC) technique, one of the controllers include an adaptive law used to compensate for the spacecraft’s inertia variation. One application is performed where gain scheduling is used for controlling two different phases: exit from tumbling and track a dynamic reference. The actuators of the attitude control loops are impulsive thrusters. They are activated by pulse width modulation (PWM) or pulse width pulse frequency modulation (PWPFM). Simulation studies, performed in realistic scenarios, show that the SMC can maintain stability and performance when these modulation techniques are used to approximate the continuous commands. It is also shown that PWM can provide better performance, but at a higher control cost. In this sense, PWPFM is more appropriate with respect to the fuel consumption and activation times.