Globally convergent relative attitude observers for three-platform formations

This paper presents relative attitude filters for a formation of three mobile platforms based on direction measurements between the platforms, in addition to rate gyro readings. In short, relative attitude estimates are initially obtained from the raw direction measurements using a computationally efficient algebraic method, which has no ambiguities. Afterwards, an attitude and rate gyro bias observer is proposed, which is also computationally efficient and that provides filtered estimates of both the relative attitude between the platforms and the rate gyro bias. The stability is analyzed and it is shown that the error converges to zero for all initial conditions under some mild constraints on the filter gains. Simulation results are presented, in the presence of sensor noise, that illustrate the achievable performance of the proposed solutions.