ADAPTIVE NONLINEAR CONTROL OF SPACECRAFT

The problem of spacecraft attitude control and momentum management is addressed using nonlinear controllers based on feedback linearization. A chief limitation of the feedback linearization technique is that it requires an exact cancellation of nonlinear terms in order to obtain linear input-output behavior. Adaptive nonlinear controllers for linea rizable systems are investigated to overcome this restriction and to a chieve asymptotic linear behavior. The spacecraft attitude control and momentum management model is characterized by having uncertain parame ters appearing linearly on both sides of the dynamical equations. Ther efore, two adaptive control laws are developed for general models in w hich the parameters appear linearly on both sides of the dynamical equ ations. The spacecraft attitude control and momentum management proble m is then addressed utilizing the adaptive nonlinear control laws, ass uming uncertainties in the spacecraft principal inertias. The adaptive nonlinear approach is shown to effectively control the Space Station attitude and effector momentum, while providing accurate estimates of the principal moments of inertia. The combined tracking and prediction -error based adaptive controller is shown to have improvement over the performance of the tracking-error based adaptive controller.