A GPS based Earth Troposphere Calibration System for Doppler Tracking of Deep Space Probes

ESA Deep Space Antennas are currently equipped with precise meteorological stations, capable to measuring the atmospheric parameters. Thanks to mathematical models both dry and wet components are estimated in order to remove the troposphere delay from Doppler data for deep space probe navigation purposes. Although the mentioned technique for the estimation of the troposphere delay offers high precision in the estimation of the dry component, this is not true for the wet one. In particular, the estimation of the wet component using meteorological data leaves an uncalibrated wet delay which reduces the precision in the Orbit Determination (OD) process of ESA spacecrafts (S/C). A novel GPS-based software (S/W) code has been developed at the Radio Science Laboratory of the University of Bologna in Forlì, aimed at the estimation of the troposphere delay, in particular the wet component. Thanks to the acquisition of raw data from the GPS receiver installed close to the ESA Deep Space Antenna in Cebreros, Spain, the local troposphere path delay has been estimated with this new algorithm. The obtained results have been feed into the ESOC’s interplanetary orbit determination software, and the quality of the range-rate residuals compared to those obtained with standard tropospheric calibrations. To this aim, range-rate data from the ESA deep space probe Venus Express, as acquired at the Cebreros Deep Space Antenna, while the spacecraft was close quadrature with the Earth and the Sun. This paper describes the data analysis performed on the acquired S/C range-rate and GPS-receiver measurements and the conclusions and recommendations for further studies.