Abstract: The SINS/CNS integrated navigation system based on characteristics of high-altitude and long-flight-time unpiloted aircraft is investigated. The observability analysis method of piece-wise constant system(PWCS) and the observable degree analysis of the system states based on the singular value decomposition are researched. A new method is proposed to analyze the observable degree of the system states. This method is based on the observability matrix and has nothing to do with the observation vector .The method is applied in the simulation of the SINS/CNS integrated navigation system. The results of the simulation show that this method is rational and feasible. Based on the observability degree of the states, the feedback method of the navigation system is researched and a method to improve the precision of navigation system is produced.

Key words: strapdown inertial navigation system, celestial navigation system, Kalman filter, obserbability analysis