Tracking accuracy evaluation for data relay and user satellites

Abstract The demand for almost continuous coverage for close Earth orbiting satellites necessitates the use of data relay systems. The European Space Agency is currently studying the in-orbit infrastructure and is preparing a European data relay system, not only to be used for telemetry and telecommand purposes but also for tracking support. This paper deals with the tracking aspects of the user satellites and derives the requirements on the position accuracy of the data relay satellites. This orbit accuracy requirement is about 70, 25, 10 m (along track, cross track, radial) and can be achieved in routine cases with a few ranging stations suitably distributed in the European area. However, the use of an additional ranging station outside Europe, preferably in the Southern Hemisphere would aid the determination of the orbit after manoeuvres, especially after inclination control manoeuvres. Adequate knowledge of the position could then be achieved after about 4 h of dense tracking.