Unit Quaternion Observer Based Attitude Stabilization of a Rigid Spacecraft without Velocity Measurement

In this paper, we propose an alternative solution to the attitude stabilization problem without velocity measurement. Our approach consists of using a unit quaternion observer and a linear feedback control law in terms of the vector parts of the actual unit quaternion and the estimation-error quaternion. The closed loop system leads to a passive mapping between the observer input and the vector part of the estimation-error quaternion, which in turns allows to choose the observer input as a simple feedback in terms of the vector part of the estimation-error quaternion. The resulting control scheme, without velocity measurement and without the use of a lead filter, guarantees global asymptotic stability. Simulation results are provided to show the effectiveness of the proposed controller