Improved adaptive sliding mode control for rigid spacecraft attitude tracking

This paper considers the attitude tracking problem of a rigid spacecraft involving inertia matrix uncertainty and external disturbance. First, an adaptive integral sliding mode control (ISMC) is proposed for when the upper bound on the lumped uncertainty is unknown in advance. It is shown that such a combination can produce a much smaller switching gain than the current adaptive sliding mode control (ASMC); hence, the overadaptation problem in existing ASMC design is effectively solved. Additionally, the system performance is improved by virtue of the global sliding mode feature of ISMC. A similar, but more flexible, ASMC design is introduced to further enhance the results; this design is developed on the basis of the reference trajectory scheme. The validity of the proposed strategies is verified by both theoretical analysis and simulation results.