Input-output Linearization, Zero Dynamics Stability and nonlinear Control of Space Station

Based on feedback linearization, a new approach to attitude control of the space station using control moment gyros (CMGs) is presented. The mathematical model of the space station is a nonlinear function of the pitch angle. For the derivation of the attitude control law, output vectors which are linear functions of attitude angles, angular rates and CMG momenta are defined. Using the nonlinear inversion technique, a control law is derived such that in the closed-loop system the input-output map is linear, and the selected output variables are independently controlled. The stability of the zero dynamics is examined and it is shown that in the closed-loop system attitude angles and the CMG momenta converge to the origin. Simulation results are presented to show attitude and CMG momenta regulation capability of the controller