Rene Zandbergen

ERS-1 and ERS-2 tandem mission: Orbit determination, prediction and maintenance

Abstract After a short summary of the successful orbit operations during the ERS-2 Launch and Early Orbit Phase, the transition to and implementation of the tandem mission for the two satellites is described, including a comparison of the required and achieved ground track spacing. The new implementation of the routine operational and precise orbit determination and prediction systems is presented briefly, and an estimate of the current orbit prediction and determination accuracy is given. These statistics include tracking data residuals, comparison between routine and precise orbits, comparisons with the D-PAF preliminary orbit solutions, and routine orbit prediction accuracy. Some geophysical results from the altimeter data, obtained in the precise orbit determination, are presented, with special attention to the calibration of the ERS-2 instrument. This paper also introduces the information presented on the Near-Earth Navigation and Geodesy Sections WWW pages on the Internet, where information about the routine and precise orbit determination for ERS-1 and ERS-2 is updated on a daily to weekly basis. Finally, some first results of the ERS-2 PRARE data processing at ESOC are presented.

Galileo System Test Bed Validation Algorithms

During the Galileo Definition Phase, a GALILEO System Test Bed (GSTB) has been defined as an integral part of the GALILEO Development and Validation Phase to mitigate programme risks. The GSTB-V1 will use GPS data to investigate critical algorithm design issues. A scant effort will be devoted to extrapolate conclusions to the Galileo environment. paper deals with two types of algorithm: Orbit Determination and Time Synchronisation (ODT an improvement in the algorithms will enable the maximum benefits to be taken from future clocks SISA (Signal in Space Accuracy) algorithms, a new concept to provide integrity.