Report on initial inflight data of JUICE’s 3GM radio science instrument

The JUpiter ICy moons Explorer (JUICE) is an ESA mission launched from the Kourou spaceport in French Guyana on April 14, 2023, with an Ariane 5 rocket. After the initial LEOP (Low Earth Orbit Phase) operations, completed within three days from launch, the mission entered the NECP (Near Earth Commissioning Phase) that lasted approximately 6 months and included the first functional checkout of the entire assembly of JUICE instruments, comprising 10 different scientific payloads. The spacecraft will arrive in the Jovian system in 2031, after an almost 8-year cruise phase. During the interplanetary phase, the JUICE scientific instruments will be routinely switched on and monitored during regular payload checkouts (occurring approximately twice per year), each lasting less than 2 weeks in total.

The 3GM (Gravity and Geophysics of Jupiter and the Galilean Moons) radio science instrument package comprises a Ka band Transponder (KaT), an Ultra Stable Oscillator (USO), and a High Accuracy Accelerometer (HAA). The KaT is a radio frequency equipment enabling a highly stable two-way coherent link at Ka band (34-32.5 GHz) and it is the key element of the 3GM gravity measurements. The USO will generate on board a highly stable, 57.5 MHz reference signal upconverted to both X- and Ka band to perform dual-frequency one-way downlink radio occultation experiments. The HAA will be used in support of radio science observations to calibrate the non-gravitational accelerations in the [10^-4-10^-1] Hz frequency band, mostly coming from propellant sloshing.

We report the results obtained by the analysis of the initial 3GM data collected during the NECP and the first Payload Checkout phases.