Abstract: Attitude control of rigid spacecraft without the measurement of angular velocity was proposed in the case of physical limits of actuators. First a quaternion auxiliary dynamical system was defined, and then a nonlinear feedback control law of hyperbolic tangent function with real and estimated errors of unit-quaternion was presented. The stability of the tracking error system with bounded control effort was proved. The performance of the proposed control algorithm was verified through numerical simulations. It shows that both the satellite attitude accuracy and response speed can be improved greatly compared to other methods.

Key words: Attitude control, Unit-quaternion, Motion equation, Control constraint
Spacecraft