Expected performance of the 3GM gravity experiment on JUICE during the extended orbital phase at Ganymede

Abstract

The JUpiter ICy moons Explorer (JUICE), launched successfully on April 14, 2023, with an Ariane 5 launcher from the European spaceport in Kourou, French Guiana, embarks on a pioneering space mission dedicated to studying Jupiter and its Galilean moons. A key scientific investigation aboard JUICE, the Gravity and Geophysics of Jupiter and the Galilean Moons (3GM) radio science experiment, aims to unravel the interior structures of the Galilean moons Ganymede, Callisto, and Europa by retrieving their gravity fields. This gravity experiment delves into Ganymede's static gravity field, tidal response, and rotational state, utilizing the Ka-band transponder (KaT) for precise range-rate measurements accurate to 0.017 mm/s with a 60-second integration time and range measurements accurate to the level of a few centimeters. In this comprehensive study, we scrutinize the performance of the 3GM experiment specifically at Ganymede under different mission scenarios. The baseline configuration involves an 8-hour tracking pass per day during the 4-month Ganymede Circular Orbit at 500 kilometers of altitude (GCO-500). To deepen our understanding, we explore various simulation scenarios, including the GCO-200 phase and GCO-100 phase. In particular, we investigate the outcome of the experiment under different durations of the circular phases at different altitudes.  To evaluate the advantages and disadvantages of these diverse approaches in retrieving Ganymede's gravity field and rotational state, we employ thorough numerical simulations. Our results highlight the strengths and limitations of each scenario, providing valuable insights into the most effective strategies to maximize the scientific yield of the 3GM experiment.