Spacecraft charging during the 2024 Juice Earth gravity assist

We use the Spacecraft Plasma Interaction Software (SPIS) to simulate the interaction between the Juice Spacecraft and its environment during the Earth gravity assist performed on the 20^th August 2024. A world first was achieved by the Juice spacecraft with its execution of a double gravity assist with the Moon and Earth. Following the lunar gravity assist, Juice approached from the magnetotail and entered the plasmasphere. An unexpected sharp density drop was observed around the closest approach, leading to a drop in spacecraft potential also being seen. Around five hours after first entering the plasmasphere, Juice crossed the magnetopause into the magnetosheath.

In this work, we study how the interaction between the Juice spacecraft and the plasmasphere and magnetosheath environments impacts the surface charging on the spacecraft and the effect on the local particle environment. This understanding is essential as it will affect the Juice particle and field measurements and is crucial for the data analysis.

Here we present surface potentials and local electron, photoelectron, secondary electron and ion populations for four different plasma regimes in the plasmasphere and magnetosheath. We discuss the impact on the Juice RPWI and PEP particle and field measurements.  Large differential charging was observed due to the dielectric material covering the radiators on the spacecraft. We also examine the impact on the surface charging of the spacecraft due to the sudden drop in the plasma density near closest approach.