Application of the Nonlinear SDRE Approach to Control Smal Satellite During Detumble Orbit Phase

Resumo

Attitude Control of small satellite during detumbling orbit phase is of fundamental importance for the mission's success. In general, the small satellite starts this phase with high angular velocity and the Attitude Control System (ACS) needs to maneuver it to the normal mode of operation, which is has attitude of small angles. The ACS performs this operation between these two phases modes which has nonlinear dynamics due to the high angular velocities and perturbations using cold gas thrusters. As a result, the application of linear control techniques can compromise the performance and robustness requirements of the SAC System. To mitigate this problem, we apply the State-Dependent Riccati Equation (SDRE) method which can deal with such a nonlinear system. The SDRE controller is based on cold gas thruster torques to perform the large-angle maneuver in order to reduce the high angular velocities. The investigation serves to validate the numerical simulator model and to verify the functionality of the control algorithm as well as the signal between the controller and the actuators designed by the SDRE technique. In this study the SDRE controller is designed as a continuous time system for a full Monte Carlo perturbation model to test the adequacy of the control strategy adopted. The ACS is ready for the next step of this study, which is the analysis of discretization techniques, in which the sampling rate should be evaluated for the digital version of the SDRE technique aiming at its implementation in on-board computer.