Use of direct broadcasting satellite signals for time transfer and orbitography

Several time transfer experiments have been performed in Europe, to compare clocks in the 10 nanoseconds range, using TV satellites. The Observatoire de Besancon (OB) and the CNES Toulouse (CT), with the support of the LPTF-Observatoire de Paris (OF) and the Observatoire de la Cote d´Azur (OC), have conducted an experiment using the French telecommunication satellite TELECOM 2A, and four reception stations each equipped with a 80 cm diameter antenna, caesium clock and GPS time receiver. Each raw data was corrected of the motion of the satellite and others delays. Time transfer results were then compared to GPS results, the accuracy is limited by the delay uncertainty of each station equipment. Using the same measurements (TV and GPS), the position of TELECOM 2A spacecraft was calculated and compared with classical technique (Ranging and Turn-Around). This paper describes techniques, stations, uncertainty budget, time transfer results and presents a promising technique for geostationary orbit determination. As a conclusion, we propose the use of the Telecom 2 satellite for a near operational, automatic and independent to GPS time transfer system