Fault Tolerant Control Allocation for Mars Entry Vehicle using Adaptive Control Monika Marwaha * , and John Valasek † Texas A&M University, College Station, TX. Accurate and reliable control of planetary entry is a major challenge for planetary ex- ploration vehicles. For Mars entry, uncertainties in atmospheric properties like winds aloft and density pose a major problem for meeting precision landing requirements. Antici- pated manned missions to Mars will also require levels of safety and fault tolerance not required during earlier robotic missions. This paper develops a nonlinear fault tolerant adaptive controller specifically tailored for addressing the unique environmental and mis- sion demands of future Mars entry vehicles. The controller tracks a desired trajectory from entry interface to parachute deployment, and has an adaptation mechanism that reduces tracking errors in the presence of uncertain parameters such as atmospheric density, and vehicle properties such as aerodynamic coefficients and inertias. This nonlinear control law generates the commanded moments for a discrete control allocation algorithm, which then generates the optimal controls required to follow the desired trajectory. The reaction control system acts as a non-uniform quantizer, which generates applied moments that approximate the desired moments generated by a continuous adaptive control law. If a fault is detected in the control jets, it reconfigures the controls and minimizes the impact of control failures or damage on trajectory tracking. A stability analysis is presented, and a nonlinear dynamical model of the Mars ellipsled vehicle is developed. Fault tolerance per- formance is evaluated with non real-time simulation for a complete Mars entry trajectory tracking scenario using various scenarios of control effector failures. Results presented in the paper demonstrate that the control algorithm has satisfactory performance for track- ing a pre-defined trajectory in the presence of control failures, in addition to plant and environment uncertainties. * Graduate Research Assistant, Vehicle Systems and Control Laboratory, Aerospace Engineering Department, Student Mem- ber AIAA, monika marwaha@tamu.edu † Associate Professor and Director, Vehicle Systems & Control Laboratory, Aerospace Engineering Department. Associate Fellow AIAA. valasek@tamu.edu, http://jungfrau.tamu.edu/valasek 1 of 35 American Institute of Aeronautics and Astronautics AIAA/AAS Astrodynamics Specialist Conference and Exhibit 18 - 21 August 2008, Honolulu, Hawaii AIAA 2008-7351 Copyright © 2008 by Monika Marwaha and John Valasek. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.