First Analysis of BepiColombo Radio Science and Accelerometer Data Acquired During Venus and Mercury Flybys

The ESA/JAXA BepiColombo mission is currently on its way to Mercury, aiming to unveil the secrets held by the innermost planet of the Solar System. The radio tracking measurements, in combination with the data acquired by the onboard accelerometer, will enable a precise navigation of the spacecraft addressing the scientific objectives of the mission. A series of planetary flybys are required during the interplanetary transfer orbit to save propellant for the orbital insertion around Mercury. We present here a joint analysis of the radio tracking and accelerometer measurements collected during the second Venus flyby and the first two Mercury flybys. A precise orbit determination process is carried out to yield a combined adjustment of the spacecraft trajectory and parameters associated with dynamical and observational modeling. The accelerometer data enabled the detection of unmodeled dynamical perturbations including outgassing and thermal recoil. Our analysis of Mercury flybys allowed us for the first time to combine BepiColombo and MESSENGER radiometric measurements, leading to significant improvements in the modeling of the gravitational forces.