  Stellar occultations currently provide the most accurate ground-based
measurements of the positions of natural satellites (down to a few kilometres
for the Galilean moons). However, when using these observations in the
calculation of satellite ephemerides, the uncertainty in the planetary
ephemerides dominates the error budget of the occultation. We quantify the
local refinement in the central planet's position achievable by performing Very
Long Baseline Interferometry (VLBI) tracking of an in-system spacecraft
temporally close to an occultation. We demonstrate the potential of using VLBI
to enhance the science return of stellar occultations for satellite
ephemerides. We identified the most promising observation and tracking
opportunities offered by the Juno spacecraft around Jupiter as perfect test
cases, for which we ran simulations of our VLBI experiment. VLBI tracking at
Juno's perijove close to a stellar occultation locally (in time) reduces the
uncertainty in Jupiter's angular position in the sky to 250-400 m. This
represents up to an order of magnitude improvement with respect to current
solutions and is lower than the stellar occultation error, thus allowing the
moon ephemeris solution to fully benefit from the observation. Our simulations
showed that the proposed tracking and observation experiment can efficiently
use synergies between ground- and space-based observations to enhance the
science return on both ends. The reduced error budget for stellar occultations
indeed helps to improve the moons' ephemerides, which in turn benefit planetary
missions and their science products, such as the recently launched JUICE and
upcoming Europa Clipper missions.
