Terminal Intertial Attitude Control for a Spacecraft

Abstract

This paper addresses a terminal control scheme for a basic attitude maneuver of a spacecraft, formation of an "inertial attitude" mode in the finite time bounds. The algorithm is based on determination of the angular velocity program values. This determination uses the analytical expressions obtained by means of the boundary solution proposed in the authors' previous works. The solution assumes discrete model parameters' identification by the modal control decomposition method in the observer synthesis. The further stabilization of the attitude and angular velocity parameters is necessary. The angular motion control process is described by the kinematic equations in Rodrigues-Hamilton parameters and Euler's dynamic equations. Analytical solution of the kinematic equations with the constant values of the angular velocity is used to determine the program values of the angular velocity. This allows us to obtain new values of the program angular velocity in every onboard computer cycle. These values ensure forming up of the inertial attitude for the given time. The next step is to calculate an appropriate momentum control values. Linearized Euler's equations are used to get the control values. Linearization is performed at every cycle of the onboard computer. It gives a high degree approximation to the nonlinear model of a spacecraft angular motion. All the synthesized control laws and observer feedback coefficient matrices have simple analytic forms and can be implemented on the onboard digital computer for a real-time execution to form-up the inertial attitude mode. Numerical examples are presented to demonstrate the successful work of the developed control algorithms for a wide variety of the initial conditions (initial attitude, maneuver time) in the inertial coordinate system.