Fully decentralized cooperative navigation for spacecraft constellations

This paper proposes a method to decentralize the navigation burden, and improve the fault tolerance for a spacecraft constellation. The constellation body reference system is introduced, which is the perifocal frame of one satellite in the constellation. The structure of the proposed navigation method is constructed to enable each spacecraft to estimate its own orbit in this body reference system. This step is essentially the relative orbit determination based on inter-satellite range measurements. Thereafter, the approach to transfer an orbit from the constellation body reference system to inertial reference system is developed. The essential requirements on absolute measurements to realize the coordinate transfer are presented. By dividing the absolute orbit determination into relative orbit determination and coordinate transfer, each navigation sub-system operated in a spacecraft can be independent with others, and the absolute measurements collected by any spacecraft can contribute to the absolute orbit determination of the whole constellation. The proposed method applies to constellations in any geometric configuration. A Walker constellation is taken as an example for numerical simulations. The results show that the proposed method has a lower computation burden compared to an integrated navigation system. With the same type of absolute measurements, the proposed method has higher accuracy and convergence velocity than conventional decentralized algorithms. When a spacecraft occurs with fault, the orbit results of other spacecraft are not affected using the proposed method, which is beyond the ability of conventional methods.