Variable Structure Control of Spacecraft based on Nonlinear Sliding Surface

Attitude measurement sensors' (sun-sensor, magnetometer and etc.) accuracy play a significant role in the performance of the spacecraft attitude control system (ACS). On the other hand, the continuous use of attitude sensors is not possible due to their intrinsic limitations. So achieving the suitable performance of the ACS in the absence of the attitude sensor's data is an important problem that is addressed in this paper. The abovementioned problem is more challenging in the case of agile and high-angle non-smooth maneuvers. In this regard, a new approach for designing a variable structure control (VSC) based on the nonlinear sliding surface is presented to deal with high nonlinear effects of non-smooth maneuvers in the absence of attitude sensors. Accordingly, a new term is added to the standard conventional sliding mode controller (SMC), turning it into a practical solution for the proposed problem. This term also gives more flexibility to the controller designer to adjust the gains of the control law, which may lead to (i)faster time-responses of the spacecraft without an increase in overshoot, and (ii)also a lower steady-state error.