  The paper proposes a technique to estimate the angular velocity of a rigid
body from vector measurements. Compared to the approaches presented in the
literature, it does not use attitude information nor rate gyros as inputs.
Instead, vector measurements are directly filtered through a nonlinear observer
estimating the angular velocity. Convergence is established using a detailed
analysis of the linear-time varying dynamics appearing in the estimation error
equation. This equation stems from the classic Euler equations and measurement
equations. A high gain design allows to establish local uniform exponential
convergence. Simulation results are provided to illustrate the method.
