Abstract
The DORIS system has been developed to provide high accuracy orbit determination and beacon positioning. It is fully operational and has been working for 10 years with Spot-2, Spot-3, Spot-4 and Topex-Poseidon. This uplink radio-electrical system is based upon precise doppler measurements (0.3 mm/s) made with the dual-frequency signals emitted by the 50 autonomous beacons distributed homogeneously over the Earth surface. The DORIS Control Center performs system monitoring (on board receivers and ground beacons), receivers programming, data processing and archive. On board gathering of the measurements allows a precise on board autonomous real-time computation of the orbit. Experienced on board of Spot-4 since 1998, DIODE (the Navigation software) has demonstrated that on-board real-time orbits are now feasible with a few meters accuracy and an availability better than 99% over 3 years, even through manæuvers. Today, Earth observation missions, altimetry, oceanography, imaging, etc. and satellite constellations navigation often ask for a real time on board orbit restitution with a 1 m accuracy, or even better. Including an extended force model (40×40 Earth gravitational fields, moon and sun attractions, etc.), the last issue of DIODE is able to compute the orbit in real-time on board of the satellite, with an expected accuracy of 10 cm RMS on the radial component. To be launched in 2001, Envisat-1 and Jason-1 are both equipped with a DORIS 2nd generation receiver: unfortunately, flight results will not be available in time to be presented in the paper. Future flights will occur in the next years (Spot-5, Cryosat, Pléiades, etc.).
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