Ricerc@Sapienza

The JUpiter Icy Moons Explorer (JUICE) is an European Space Agency (ESA) mission to investigate Jupiter¿s icy satellites that will launch in 2022 and arrive in the Jovian system in 2029. The mission will perform flybys of the icy moons Europa and Callisto, before being inserted into a 4-month, circular orbit about Ganymede, at an altitude of approximately 500 km to investigate the moon¿s icy crust, interior structure, magnetic field and exosphere. The 3GM experiment on board the spacecraft will exploit accurate Doppler and range measurements to determine the moons¿ orbits, gravity fields, tides and therefore infer details about their internal structures. In this work, we focus on the last phase of the mission, when JUICE aims to provide an accurate global map of Ganymede¿s gravity field. The preliminary simulations carried out reveal that the moon¿s gravity field can be determined up to degree and order 40. The Love number k2, modelling the tidal response, is determined with an accuracy of 7e-5 (1-sigma), which will allow us to set a constraint on the internal behavior of the moon. The objective of this work is to use different techniques to further improve the results and analyze different mission scenarios: 200 km circular orbit at Ganymede at the end of the missions, 2 weeks around Ganymede uniquely dedicated to gravity measurements and evaluate the impact of wheel off loading maneuver on the experiment. The knowledge of the gravity field can be improved by setting constraints on the a priori value by using Kaula's rule. This technique has already been used in previous cases such as for Mercury gravity field reconstruction by using data from the MESSENGER mission (Mazarico et al, 2014) and in the simulation of BepiColombo mission (Imperi et al. 2018). The constrained multi-arc approach (Milani et al 2010) has already been proven effective by Imperi et al (2018) to further constraint the trajectory and estimate the daily wheel off loading maneuver.