Hybrid attitude tracking of rigid bodies without angular velocity measurement

In this paper we address the problem of output-feedback attitude control of a rigid body in quaternion-coordinate space through a hybrid (switching) PD+ based tracking controller; we establish stability for all initial values in a compact subset which may be arbitrarily enlarged by increasing the control gains. Assumptions used in the literature such as supposing that the initial states lay in a determined compact set or that the attitude error norm is smaller than π rad for all time, are removed by including a switching law. Simulation results are presented to corroborate our theoretical findings, showing that the system stabilises as expected, even when the initial estimated velocity error is large.