Quaternion-based adaptive attitude tracking controller without velocity measurements

The main problem addressed is the quaternion-based, attitude tracking contr ol of rigid spacecraft without angular velocity measurements and in the pre sence of an unknown inertia matrix. As a stepping stone, an adaptive, full- state feedback controller is designed that compensates for parametric uncer tainty while ensuring asymptotic attitude tracking errors. The adaptive, fu ll-state feedback controller is then redesigned such that the need for angu lar velocity measurements is eliminated. The proposed adaptive, output feed back controller ensures asymptotic attitude tracking. A four-parameter repr esentation is used of the spacecraft attitude that does not exhibit singula r orientations as in the case of the previous three-parameter representatio n-based results. To the best of our knowledge, this represents the first so lution to the adaptive, output feedback, attitude tracking control problem for the quaternion representation. Simulation results are included to illus trate the performance of the proposed output feedback control strategy.