Comparison of Plasma Calibration Techniques to Enhance Radiometric Observables Performance: BepiColombo MORE Test Case

We present and compare different techniques to isolate the dispersive noise contribution from radiometric observables in deep space missions. These techniques have been tested using range and Doppler data collected during five superior solar conjunctions of ESA's (European Space Agency) BepiColombo spacecraft in its cruise phase. First, we present the state-of-the-art of BepiColombo multifrequency link calibration scheme, which leverages on three 2-way links in X/X, X/Ka and Ka/Ka band. Then we compare its performance with alternative dual-link schemes, based on a combination of only two of the three links listed above. Our analyses find that the best dual-link configuration, achieved with the method reported in Mariotti and Tortora (2013, https://doi.org/10.1002/rds.20024), is the X/X + Ka/Ka configuration, which on average decreases the RMS noise with respect to the non-calibrated Ka/Ka residuals by ∼64% for BepiColombo's Doppler data (compressed at 60 s) and by 37% for range data (at integration time of 2 s). Finally, our analysis points out that during radio tracking passes characterized by a low plasma content, the dual link configuration X/X + Ka/Ka provides better performance on range data with respect to the classic full triple link configuration. This can be explained by the higher thermal noise contribution on range measurements due to the smaller integration time with respect to Doppler data: in fact, with the triple link scheme we have a contribution from the thermal noise of the three links while with the dual link configurations only from two.