Abstract
In this paper, a
 nonlinear robust quaternion-based controller is developed to address the
 three-axis attitude tracking control problem of rigid spacecraft in presence of
 parametric uncertainties, unknown external disturbances and sensor noise. As a
 first step, a robust controller is designed that compensates parametric
 uncertainty and disturbance effects. The robust controller then reformulated to
 deal also with sensor noise. Singularity free unit quaternions are used to
 represent the attitude of the satellite in three-dimensional space. The
 Lyapunov-based stability analysis is applied to prove that a uniformly
 ultimately bounded tracking result is achieved. Simulation results are
 presented to illustrate the feasibility of the proposed control strategy.