Nonlinear observer for real-time attitude estimation

This paper deals with the attitude estimation of a rigid body equipped with a module of GAM sensors (rate gyros, accelerometers and magnetometers). 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 error dynamics can break up into two passive subsystems connected in "feedback". This property is a first and crucial result that could be 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. The effectiveness of the observer is confirmed in a real-time application.