Abstract: A federated filter is designed to fuse information from the inertial measurement unit, the star sensor, the digital sun sensor and the digital earth sensor which compose the satellite attitude determination system. The algorithm and structure of the federated filter are proposed. The error propagation equations and the each subsystem measurement equations of the satellite attitude determination system are derived. Simulation results show that the federated filter realizes the optimal estimation at the cost of low computational complexity. And when parts of attitude sensors fail, the federated filter could still give satisfied estimation uninfluenced by the information of failed attitude sensors.