The gravity field of the Solar System celestial bodies is generally estimated within the orbit determination process of probes visiting them. Low altitude, high inclination and near circular orbits are best suited for this purpose. As part of a global characterization effort of the Jovian moon Europa, we studied the influence of multiple orbital parameters and configurations on the recovery of its gravity field parameters. We made use of Repetitive Ground Track Orbits (RGTO), allowing for a proper definition of the ground track coverage on the surface of Europa, which is essential to study the impact of this coverage. The results presented here rely on closed-loop simulations performed using a development version of the Bernese GNSS Software with planetary geodesy capabilities. We simulate realistic range-rate observables (2-way Doppler X-band, σ = 0.10 mm/s) from the different orbits considered over a total mission duration of 3 months. These observations are then used to reconstruct the orbit and estimate gravity field coefficients in terms of spherical harmonic coefficients and the k2 Love number. We systematically compare solutions based on different input orbital parameters and we quantify their impact on the gravity field recovery process, which is of great importance for future mission designs. Our best case scenario shows that the gravity field can be estimated up to degree and order 72 after 3 months in a circular polar orbit at 100 km over Europa's surface. Different gravity field recovery strategies are also discussed when starting with a very poor a priori knowledge of the gravity field, as it is the case for the Galileans moons. We propose and evaluate two approaches by either using pseudo-stochastic pulses (i.e., instantaneous velocity changes) to cope with the large model deficiencies, or by co-estimating low-degree gravity field coefficients and orbit parameters to bootstrap the estimation process.
