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The upcoming JUICE and Europa Clipper missions to Jupiter's Galileansatellites will provide radio science tracking measurements of both spacecraft.Such data are expected to significantly help estimating the moons' ephemeridesand related dynamical parameters. However, the two missions will yield animbalanced dataset, with no flybys planned at Io, condensed over less than sixyears. Current ephemerides' solutions for the Galilean moons, on the otherhand, rely on ground-based astrometry collected over more than a century which,while being less accurate, bring very valuable constraints on the long-termdynamics of the system. An improved solution for the Galilean satellites'complex dynamics could however be achieved by exploiting the existing synergiesbetween these different observation sets. To quantify this, we merged simulatedJUICE and Clipper radio science data with existing ground-based astrometric andradar observations, and performed the inversion. Our study specificallyfocusses on the resulting formal uncertainties in the moons' states, as well asIo's and Jupiter's tidal dissipation parameters. Adding astrometry stabilisesthe moons' state solution, especially beyond the missions' timelines. Itfurthermore reduces the uncertainties in $1/Q$ (inverse of the tidal qualityfactor) by a factor two to four for Jupiter, and about 30-35\% for Io. Amongall data types, classical astrometry data prior to 1960 proved particularlybeneficial. We also show that ground observations of Io add the most to thesolution, confirming that ground observations can fill the lack of radioscience data for this specific moon. We obtained a noticeable solutionimprovement when exploiting the complementarity between all differentobservation sets. These promising simulation results thus motivate futureefforts to achieve a global solution from actual JUICE and Clipper radioscience data.

Combining astrometry and JUICE -- Europa Clipper radio science to improve the ephemerides of the Galilean moons