Perturbative Analysis of the MORE Experiment During BepiColombo's Orbital Phase

The BepiColombo mission, designed by ESA/JAXA, was launched in October 2018 and is currently in the cruise phase towards Mercury. The Mercury Orbiter Radio-science Experiment (MORE), one of the scientific investigations of the mission, will exploit a multi-frequency microwave tracking system with an advanced Ka-band transponder to fulfill scientific goals in Mercury’s geodesy and fundamental physics. In particular, the precise measurements enabled by the state-of-the-art radio tracking system will allow us to estimate the gravity field and rotational state of Mercury, and to perform tests of general relativity through an accurate analysis of the spacecraft orbital motion. In this work we assess the performance of the radio science investigations addressed by MORE, focusing on the orbital phase, starting in early 2026. The reported simulations include the generation of synthetic radio observables and the estimation of the parameters of interest through a precise orbit determination process. The novelty of this work lies in the inclusion of different sources of mismodelling to reproduce a realistic scenario and a perturbed dynamical state of the probe. We include errors in the thermo-optical coefficients of the spacecraft, wheel off-loading maneuvers with unbalanced ΔVs, periodic accelerations of unknown magnitude and random fluctuations of solar irradiance, which cannot be modelled or measured by the onboard accelerometer ISA (Italian Spring Accelerometer). We report the results of the numerical simulation based on the latest mission scenario, which foresees a two-year orbital phase starting in 2026. Our results show that both the geodesy and fundamental physics experiments are not affected by the considered mismodelling effects. We show that MORE shall fulfill its scientific goals with an enhanced level of accuracy compared to past missions, improving our knowledge of Mercury’s interior.