A NONLINEAR CONTROL DESIGN FOR ENERGY SINK SIMULATION IN THE EULER-POINSOT PROBLEM

A nonlinear control design is presented for the purpose of quantitativ ely simulating the effects of internal damping mechanisms modeled as e nergy sinks on the attitude dynamics of rigid body spacecraft. Damping is important because it is often the driving mechanism behind passive attitude acquisition maneuvers. Introduction of the controller into t he Euler attitude equations of motion allows for the explicit represen tation of damping without the introduction of additional degrees of fr eedom required for a physical damping mechanism. This result is signif icant because perturbation techniques which rely on the closed form so lution of the unperturbed problem can then be used to analyze the effe cts of perturbations upon a damped system. The controller is designed to dissipate kinetic energy while maintaining the magnitude of the ang ular momentum vector. Control torques are nonlinear functions of the a ngular momentum components expressed in a body-fixed frame. A numerica l simulation of an actual damping mechanism during a decay from minor axis spin into a flat spin is presented showing that the nonlinear con troller gives a good qualitative representation and, in many instances , a good quantitative approximation of the attitude motion of a repres entative spacecraft containing a damping mechanism.