Modified Variable Structure Estimation and Control for Constrained Landing on Mars

Landing on Mars is one the most important space missions undergoing various system and environmental uncertainties. Subsequently, an exact model to represent the dynamic system cannot be provided in advance. In this regard, the present paper has focused on designing an integrated estimation and control algorithm bringing accurate navigation in the presence of uncertainties for the landing problem. The proposed algorithm has been shaped based on the variable structure control framework. This algorithm alleviates the requirement of Jacobian via substituting statistical linearization for the analytical one and utilizing generalized matrix inverse theory. Performance of the proposed algorithm has been investigated via Monte Carlo simulations in the presence of different uncertainties including stochastic initial conditions of the coupled Mars lander dynamics, atmosphere instability and modeling errors of the exerted forces and moments, time delay of actuators, geometric constraint of the landing site as well as the saturation limitations of actuators. In addition, the obtained results have been compared to the results obtained from combination of well-known extended Kalman filter and PID controller. This study clearly shows the precise and robust performance of the proposed integrated estimation and control algorithm and proves its superiority against existing widespread algorithms.