Aerodynamic-angle attitude control for atmospheric planetary entry

The paper describes the attitude control system of a low lift-to-drag biconic atmospheric entry capsule based on the Embedded Model Control methodology. The control structure derives from the development of the attitude dynamics and kinematics written in terms of the aerodynamic angles, instead of the Euler/quaternion kinematics. A detailed development of a simplified set of equations linking the torques generated by the reaction control system to aerodynamic angles is provided. The simplified set of equations is used as the core of the control algorithms. The bank angle dynamics is shown to be a fourth-order dynamics forced by yaw and roll torques, and a dynamic dispatching technique is proposed to convert the fourth-order dynamics into a simpler second order. Non linear dynamic inversion and active disturbance rejection are used to handle gyroscopic torques, parametric errors and to compensate for the angular variation of the longitudinal velocity. The performance of the attitude control algorithms is tested on a high fidelity simulator and the results are presented.