Tropospheric Delay Calibration System performance during the first two
BepiColombo solar conjunctions
Abstract
Media propagation delay and delay-rate induced by the water vapor within
the Earth’s troposphere represent one of the main error sources for
radiometric measurements in deep space. In preparation for the
BepiColombo and JUICE missions, the European Space Agency has installed
the prototype of a tropospheric delay calibration system (TDCS) at the
DSA-3 ground station located in Malargüe, Argentina. An initial
characterization of the TDCS performance was realized using the orbit
determination of the Gaia spacecraft as a testbed. This work will
further characterize the system by analyzing the BepiColombo tracking
passes, which were recorded between March 2021 and February 2022 during
the first two superior solar conjunction experiments. The performance
exceeds the expectations based on the previous analysis, with an average
51% reduction of the Doppler noise when using the TDCS measurements in
place of standard calibrations based on global navigation satellite
system data. The tropospheric instability at long time scales is also
significantly reduced, with most of the tracking passes now satisfying
the Mercury orbiter radioscience experiment (MORE) requirements on
two-way Doppler stability.