Mapping JUICE’s Journey: PRIDE observations from the Lunar-Earth Gravity Assist

Abstract. This paper presents the results of Planetary Radio Interferometry and Doppler Experiment (PRIDE) observations of the JUICE spacecraft during its lunar and Earth gravity-assist manoeuvres on August 19 and 20, 2024, using a network of VLBI radio telescopes. Prior to the flyby sequence, VLBI phase‑referencing observations were conducted to establish astrometric measurements and Doppler frequency calibration during the near-Earth approach. During the flyby events, the experiment successfully captured the signal ingress and egress during the lunar occultation, as well as the signal behaviour at closest approach to the lunar surface. Signal-diagnostic measurements were performed to characterise the received carrier signal and assess instrumental and propagation effects. The observed Doppler frequency measurements were subsequently compared with predicted values derived independently using the WebGeocalc service and the Tudat software framework. The close agreement between the measured Doppler observables and model predictions confirms that the tracking results are consistent with expectations for JUICE's cruise-phase configuration and the high-velocity dynamics of the Earth flyby. Finally, these measurements were also used to obtain complementary measurements of the terrestrial ionosphere and space weather conditions, and are being used for refining solar wind models using planetary spacecraft radio tracking.