Simulation of a pseudo drag-free system for the BepiColombo radio science experiment using ISA accelerometer data

The Mercury Orbiter Radioscience Experiment (MORE) onboard the ESA/JAXA BepiColombo mission aims at determining the gravity field and the rotational state of the planet to provide insights into its internal structure. The experiment will rely on accurate radiometric data provided by the onboard Ka-band transponder. The strong non-gravitational perturbations acting on the spacecraft during the orbital phase and the excellent accuracy of the radiometric observables, point out the necessity to host an accurate accelerometer onboard the spacecraft. The Italian Spring Accelerometer (ISA) has been selected by ESA to measure the non-gravitational perturbations with an accuracy of in the frequency band of Hz, providing MORE with valuable information about the spacecraft dynamic. This work presents a software implementation of a pseudo drag-free system including the synthetic accelerometer measurements in the orbit determination process. ISA readings have been simulated adding to the ideal measurements, the intrinsic noise of the instrument and the contribution due to thermal effects, as per requirements. The identification of a suitable calibration strategy it’s a key factor to fulfil MORE experiment goals pertaining to geodesy and geophysics since uncompensated errors in accelerometer data can affect meaningfully the accuracy of the orbit reconstruction, hence the scientific outcome of the experiment. Perturbative analysis of the 1-year orbital phase at Mercury points out that the proposed accelerometer calibration strategy allows obtaining an unbiased solution and compensating for accelerometer errors. The numerical simulation shows that MORE will be able to measure the Mercury gravity field up to degree and order 30 at all the latitude with a formal uncertainty on the determination of the Love number equal to . The Mercury rotational state will be determined with a formal uncertainty of 1.68 arcsec and 0.78 arcsec on the right ascension and declination of the pole, respectively, resulting in a formal uncertainty of 0.012 arcmin on the obliquity.