Output feedback control for attitude tracking

In this paper the problem of attitude tracking control for a rigid spacecra ft is addressed. It is assumed that only attitude measurements are availabl e, and thus spacecraft's angular velocity has to be properly estimated. Two alternative schemes are proposed in which the unit quaternion is adopted t o represent the orientation. In the first scheme, a second-order model-base d observer is adopted to estimate the angular velocity used in the control law. In the second scheme, an estimate of the angular velocity error is obt ained through a lead filter. Sufficient conditions ensuring local exponenti al stability of the two controllers are derived via Lyapunov analysis. (C) 1999 Elsevier Science B.V. All rights reserved.