Ephemeris/attitude reference determination using communications links

The present invention provides a system (300) for determining the ephemeris and attitude for a spacecraft based on crosslink sensor pointing directions and the ephemeris of other satellites. An ephemeris determining subsystem (700) obtains ephemeris data (708) for one or more reference spacecraft crosslinked to the spacecraft. Crosslink sensor pointing information (706) is obtained for the crosslink sensors. The satellite ephemeris (712) is then calculated with ephemeris determination algorithms (702) based on the ephemeris data (708) and crosslink sensor pointing information (706). Other available information, such as stored results of previous measurements and calculations, time (710), spacecraft attitude (704), information from non-crosslink sensors and ranging information may be used to enhance the accuracy or decrease the complexity of the ephemeris calculations. In addition to ephemeris determination, the present invention also provides an attitude determining subsystem (800) for the determination of spacecraft attitude (810). Ephemeris data for crosslinked spacecraft (806) and sensor pointing information (802) is obtained. The satellite attitude is then calculated by attitude determination algorithms (804) based on the ephemeris of crosslinked spacecraft (806) and the crosslink sensor pointing information (802). Other available information, such as stored results of previous measurements and calculations, time (808), information from non-crosslink sensors, and ranging information may be used to enhance the accuracy or decrease the complexity of the attitude calculations.