Current spacecraft and high performance underwater vehicles use angular rate gyros and other sensors in feedback loops to control orientation. Unfortunately, angular rate gyros often have a significant bias and substantial noise, which can lead to undesired behavior in the attitude control system or, even worse, system instability. Thienel and Sanner derived an adaptive observer that produced estimates of angular rates, orientation, and the gyro biases. Thienel and Sanner also derived the remarkable result that their observer exhibited the separation principle, meaning the estimator can be used in a certainty equivalence fashion with any stabilizing attitude controller.
The observer proposed by Thienel and Sanner was coupled to a standard eigenaxis PD regulator and implemented on the Autonomous Underwater Vehicle Tortuga which is known to have significant bias errors and noise in its gyro readings. The observer demonstrated asymptotic convergence of state estimates during a variety of single axis and three axis attitude maneuvers. The state estimates were then incorporated with the onboard attitude controller. Incorporation of angular rate estimates led to a significant improvement in attitude control while incorporation of both angular rate and position estimates led to decreased performance. A significant error source was identified and may be mitigated by a future extension of the observer.