Calibration of Juice/RPWI Langmuir probe electric field measurements

Sammanfattning

JUpiter ICy moons Explorer (Juice) is a spacecraft developed by the European Space Agency (ESA) to study Jupiter and its ocean-bearing icy moons: Europa, Callisto and Ganymede. Its goals are to investigate the Jovian system for its characteristics as a gas giant archetype, and study the potential habitability of the icy moons. Juice carries multiple instrument packages, including the Radio & Plasma Wave Investigation (RPWI), led by the Swedish Institute of Space Physics (IRF) in Uppsala. Its purpose is to allow for observation of the electric field and plasma environment in the spacecraft’s vicinity. As a part of RPWI, the Langmuir Probe – Plasma Wave Instrument (LP- PWI), consisting of four Langmuir probes mounted on booms, performs the electric field measurements. However, these measurements are prone to disturbances caused by spacecraft-plasma interactions. Asymmetrical exposure to the solar radiation and solar wind can induce charge differentials between different parts of the spacecraft, which affect the surrounding electric field. This thesis presents a calibration method that compares LP-PWI measurements to the expected electric field derived from the Lorentz force law, using independent measurements of magnetic field and plasma velocity data. Calibration was performed using data collected during two periods of distinct plasma environments observed during the August 2024 Lunar-Earth Gravity Assist (LEGA): (1) a spacecraft roll in the solar wind, and (2) a pass through Earth’s plasmasphere. Results from the solar wind roll period show the promising effects of a simple DC offset calibration. However, a coordinate transformation error was identified, suggesting a potential flaw in the Juice documentation, that requires further investigation. The plasmasphere pass, where the plasma environment was less stable, indicates that a more complex calibration approach is needed. While this study does not establish a finalized calibration, it provides key insights into how RPWI/LP-PWI interacts with Juice’s surrounding plasma environment. These findings lay the groundwork for future improvements in calibration methods, contributing to the scientific quality of RPWI’s electric field measurements during Juice’s mission.