Ephemeris determination using intersatellite ranging and ephemeris knowledge of other satellites

The present invention provides a system (200) for determining the ephemeris of a space vehicle based on distances to and ephemeris of other spacecraft. An ephemeris determining subsystem (300) obtains ephemeris data (308) for one or more reference spacecraft. Distance information (306) is obtained between the space vehicle and the reference spacecraft. The spacecraft ephemeris (312) is then calculated with ephemeris determination algorithms (302) based on the ephemeris data (308) and distance information (306). Other available information, such as stored results of previous measurements and calculations, time (310), information from other on-board sensors and attitude information may be used to enhance the accuracy or decrease the complexity of the ephemeris determination.