Model-based aerodynamic-angle attitude control of an atmospheric entry capsule

Abstract

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 aerodynamic angles, instead of Euler/quaternion kinematics. A detailed development of the simplified set of equations linking the torques generated by the reaction control system with the time evolution of the aerodynamic angles is provided. The simplified set of equations becomes the core of the control algorithm. The bank angle dynamics is shown to be fourthorder and forced by yaw and roll torques. A dynamic dispatching technique is proposed for converting fourth-order dynamics into a pair of second order systems. Nonlinear dynamic inversion and active disturbance rejection are employed to handle gyroscopic torques, parametric errors and to compensate for angular variation of translational velocity. A bank reversal logic is designed to reduce the effect of bank reversals on the translational motion. The performance of the attitude control algorithm has been tested on a high fidelity simulator and relevant results are presented. Nomenclature = aerodynamic bank angle  = total angle of attack  = aerodynamic roll l m n    = angular rate components in the body frame , T l m n M   = components of the attitude command torque in the body frame geo  = geometric bank angle geo  = angle of attack geo  = sideslip   = angular velocity vector l m n u   = components of the angular acceleration in the body frame , a l m n M   = components of the aerodynamic torque in the body frame a x = center-of-mass displacement along the body x axis (symmetry axis) a y = center-of-mass displacement along the body y axis A c = axial aerodynamic coefficient N c = normal aerodynamic coefficient , l m n a c   = aerodynamic torque coefficients in the aerodynamic frame , l m n CoM c   = aerodynamic torque coefficients in the body frame L = equivalent length from the aerodynamic data base S = equivalent surface from the aerodynamic data base

Model-based guidance and control for atmospheric guided entry

“…The time evolution of the tracking law, combined with the path-planning algorithm and the attitude control in Canuto et al 25 is shown below assuming a 10 % dispersion of the drag aerodynamic coefficient. This should be a worst-case condition since 10 % corresponds to the 3 dispersion of the capsule aerodynamic database.…”

“…The paper provides a description of the selected solution for the path planning and reference-path tracking algorithms, and the output of a simulation campaign using a high-fidelity 6 degrees-of-freedom simulator. The attitude control, in charge of actuating a reaction control system for regulating the vehicle bank angle is described by the same authors in 25 . A preliminary description of the selected solution can be found in 26 .…”