DORIS-DIODE: Jason-1 has a Navigator on Board

DIODE (Doris Immediate On-board orbit DEtermination) is a series of real-time orbit determination software, which process one-way up-link Doppler measurements performed by a DORIS receiver on a satellite. The DIODE software are embedded within the DORIS receivers, and they provide orbit and time determination to the user as well as technical parameters to adjust the tracking loop within the instrument. After a first successful flight on-board SPOT4, the second generation of the family operates on-board Jason-1, with more efficient and more accurate algorithms. Similar versions have been embarked onboard SPOT5 and ENVISAT. The accuracy is between 10 and 30 centimeters RMS for the radial component, and about 50 centimeters RMS in 3D. With several Failure Detection and Incident Recovery (FDIR) enhancements implemented in the software, DIODE/Jason-1 has experienced only one anomaly in July 2004; its availability is 99.7%, after two years and a half in-orbit. This article describes the DORIS/DIODE element of the Jason-1 system. It summarizes the main results obtained from the various verification activities that concerned all parts of this navigation and time-tagging Jason-1 subsystem.