Flexible Spacecraft Attitude Control using Hybrid Control Scheme of H∞ and Sliding Mode Control

In this paper, based on the Lagrange method, attitude motion equations for a flexible spacecraft have been derived. Flexible appendages are modeled by Euler-Bernoulli beam. Hybrid control scheme of H∞ and sliding mode are used for attitude regulation. Switching between these to algorithm is determined using absolute error parameter, so that when this parameter is large (i.e. the attitude is far from its desired conditions) the sliding mode control is used. in contrast, when the spacecraft is close to the desired attitude, the control is based on H∞ method. This hybrid scheme leads to a fast response and also robustness against uncertainty. Switching surface has been designed so that a certain cost function is minimized. In H∞ controller design, the first three vibration modes of the flexible spacecraft are considered as well as the Euler angles and their rates.