Orbit determination and tests of general relativity in the cruise phase of bepicolombo

During its 6-year long cruise phase to Mercury, the ESA spacecraft BepiColombo will probe the laws of gravity during superior solar conjunctions. The Solar Conjunction Experiment (SCE) goal is to constrain the value of the Para-metrized Post Newtonian (PPN) parameter which controls the space curvature produced by a massive body. Thanks to the state of the art microwave instrumentation of the Mercury Orbiter Radioscience Experiment (MORE), the SCE will be able to improve the previous limits on set by the Cassini spacecraft. Spacecraft tests of general relativity and alternative theories of gravity require excellent accuracies in range and range rate observables and an extremely stable platform. In the case of the MORE SCE non-gravitational accelerations induced by solar radiation pressure are, an important source of spacecraft buffeting. Those accelerations cannot be fully accounted for because of the random fluctuations of the solar irradiance, whose magnitude is 0.1-0.01% of the average value. In this work we first characterize the effect of this dynamical noise on the outcome of the experiment, then we discuss a mitigation strategy based upon stochastic dynamical models, and finally we estimate a realistic uncertainty in the determination of the PPN parameter.