Output feedback stabilization of the angular velocity of a rigid body

The problem of stabilization of the angular velocity of a rigid body using only two control signals and partial state information is addressed. It is shown that if any two (out of three) states are measured the system is not asymptotically stabilizable with (continuous) dynamic output feedback. Neve rtheless, we prove that practical stability is achievable if the measurable states fulfill a certain structural property, and that, under the same str uctural condition, a hybrid control law yielding exponential convergence ca n be constructed. Finally, we also study some geometric features of the Eul er's equations and the connection between local strong accessibility and lo cal observability. (C) 1999 Published by Elsevier Science B.V. All rights r eserved.