  This paper provides new results for a robust adaptive tracking control of the
attitude dynamics of a rigid body. Both of the attitude dynamics and the
proposed control system are globally expressed on the special orthogonal group,
to avoid complexities and ambiguities associated with other attitude
representations such as Euler angles or quaternions. By designing an adaptive
law for the inertia matrix of a rigid body, the proposed control system can
asymptotically follow an attitude command without the knowledge of the inertia
matrix, and it is extended to guarantee boundedness of tracking errors in the
presence of unstructured disturbances. These are illustrated by numerical
examples and experiments for the attitude dynamics of a quadrotor UAV.
