Autonomous navigation for GPS using inter-satellite ranging and relative direction measurements

This paper proposes a new method utilizing both inter-satellite ranging and relative direction measurements to realize autonomous ephemeris update of navigation satellites. The relative direction from one satellite to another is determined by utilizing a normal star sensor. A GPS satellite is equipped with a beacon which can produce a light beam. The light beacon is of sufficient apparent magnitude to be imaged by the star sensor mounted on the following GPS satellite in the same orbital plane. Only the software of star sensor needs to be improved to detect the stars and the light beacon simultaneously. Firstly, the light power consumption is analyzed, and the station keeping requirements are derived from the geometrical relationship between the light beam angle and orbit phase error. Secondly, a preprocessing procedure utilizing the Gauss-Newton iteration method is developed to determine the relative direction by using all the visible stars in the field-of-view of star sensor. Thirdly, an extended Kalman filter is developed to estimate the positions of all the GPS satellites by using both the ranging and the relative direction measurements. Finally, numerical simulations are executed to verify the validity of the proposed method.