Analysis of observability and the degree of observability in autonomous celestial navigation

The type of celestial measurement used in the autonomous celestial navigation system is one of the most important factors, which effect the precision of position determination greatly. There are two main celestial measurements. One is the angle between the lines of sight to a star and earth core. The other is the star elevation angle which is the angle between the lines of sight to a star and the edge of earth disk. These two common celestial measurements and their measurement equations were presented. The performance of the system using different kind of celestial measurement was analyzed based on the observability and the degree of observability of the celestial navigation system. The condition number of the observability matrix is adopted as a scalar measure of degree of observability. The effectiveness and the validation of this analysis method were confirmed by the results of computer simulation.