Calibration and modelling of the main error sources in BepiColombo's radiometric data

Radiometric tracking of interplanetary spacecraft represents the fundamental basis of planetary science and fundamental physics investigations across the solar system. Within the field of radio-science, it provides the key measurements on which modern planetary exploration relies. Achieving such ambitious goals requires satisfying the demanding accuracy requirements of contemporary radio science experiments, such as the Mercury Orbiter Radio Science Experiment (MORE) onboard ESA’s BepiColombo mission. Meeting these standards requires a deep understanding of the error sources affecting radiometric observables, together with the adoption of advanced calibration strategies. Techniques such as multifrequency links or instruments like water vapor radiometers have proven essential to mitigate the impact of dispersive and non-dispersive propagation effects. In this framework, the present thesis focuses on the analysis of BepiColombo tracking data collected during the cruise phase, together with selected observations from the NASA/ESA/ASI Cassini mission and from ESA’s Tropospheric Delay Calibration System (TDCS), to pursue two main objectives: assess the performance of calibration techniques employed to mitigate propagation effects, and characterize and model the main error sources that limit the accuracy of the radiometric observables. The first aspect of the study evaluates the effectiveness of methods such as multifrequency links and the usage of water vapor radiometers in reducing the contribution of solar plasma and tropospheric fluctuations in terms of the reduction of noise levels in the radiometric observables. Further studies also included the testing of a novel technique aimed at improving the tropospheric noise calibration procedure. The second topic is dedicated to the study of the behaviour of the most detrimental error sources and the evaluation of their impact on radiometric tracking. Empirical models that quantify the magnitude of each error contribution, intended to serve as practical references for defining error budgets in the planning phase of future missions and experiments, are then presented.