A robust nonlinear observer for rigid body attitude estimation

This paper deals with the attitude estimation of a rigid body equipped with angular velocity sensors and reference vector sensors. A quaternion-based nonlinear observer is proposed in order to fuse all information sources and to obtain an accurate estimation of the attitude. It is shown that the observer error dynamics can break up into two passive subsystems connected in "feedback". Then, this property is used to show that the error dynamics is Input-to-State Stable (ISS) when the measurement disturbance is seen as an input and the error state as the state. These results allow affirm that the observer is robust towards non ideal inertial sensors measurements.