Nonlinear optimul slew of a flexible spacecraft

Some of the future flexible space systems will require maneuvering through large angles followed by a quick settling time upon arrival at the target. It is desired to minimize the control energy as well as structural excitations. These slewing maneuvers are nonlinear motion by nature. Current work, however, has been concentrated on a linear and single axis model for open loop implementation. New algorithms have been obtained[1] to generate optimal control laws to account for nonlinear and cross-axis coupling effects for closed-loop implementation. Practical implications of these algorithms were demonstrated through slewing a nonlinear flexible spacecraft consisting of a rigid central body with two flexible appendages. A two level approach is presented for attitude control of large (nonlinear) slewing with superimposed small (linear) flexible vibration modes: an optimal control law is first designed for the nominal rigid body mode, and an LQG feedback law is then designed along the nominal trajectory, to dampen the vibrations. The controller is then verified via simulations of a nonlinear evaluation model including six flexible modes.