Integrated Guidance and Fault Tolerant Adaptive Control for Mars Entry Vehicle

Reconflgurable guidance and control are major keys for reliable and safe planetary entry of space exploration vehicles. Major challenges in these missions are posed by uncertainties in atmospheric properties like density and winds. A guidance algorithm based on optimal control theory and integrated with a nonlinear Structured Adaptive Model Inversion controller is developed, implemented and evaluated in this paper. The guidance algorithm uses B-spline parametrization of states to generate dynamically feasible optimal trajectories which steer the vehicle from entry interface conditions to a Final Approach Corridor, while simultaneously satisfying terminal conditions. Guidance trajectory acts as a reference trajectory for nonlinear adaptive controller which further generates the commanded moments based on reference input. Reaction control jet selection is accomplished using discrete control allocation. Discrete control allocation method can also handle various types of control failures. Performance is evaluated with a Mars Ellipsled vehicle non real-time simulation for a complete Mars entry trajectory tracking scenario. Simulation results presented in the paper demonstrate that the guidance algorithm generates the optimal trajectory under various terminal constraints while the fault tolerant control algorithm satisfactorily track this optimal trajectory in the presence of plant and environment uncertainties, in addition to control failures. Copyright 2009 by Monika Marwaha.

Integrated Guidance and Fault Tolerant Adaptive Control for Mars Entry Vehicle Conference Paper