SPACECRAFT NONLINEAR CONTROL

The feedback linearization technique is applied to the problem of spac ecraft attitude control and momentum management with control moment gy ros. The feedback linearization consists of a coordinate transformatio n, which transforms the system to a normal form, and a nonlinear feedb ack control law to cancel the nonlinear dynamics resulting in a linear equivalent model. Pole placement techniques are then used to place th e closed-loop poles. The coordinate transformation proposed here evolv es from three output functions of relative degree four, three, and two , respectively. The nonlinear feedback control law is presented. Stabi lity in a neighborhood of a controllable torque equilibrium attitude i s guaranteed and this fact is demonstrated by the simulation results. An investigation of the nonlinear control law shows that singularities exist due to multiple torque equilibrium attitudes. The nonlinear con trol law is simplified by a standard linearization technique and it is shown that the linearized nonlinear controller provides a natural way to select control gains for the multiple-input, multiple-output syste m. Simulation results using the linearized nonlinear controller show g ood performance relative to the nonlinear controller in the neighborho od of the torque equilibrium attitude.