15:45 〜 16:00
[PEM10-20] Statistical Insights into Surface Charging Events and Plasma Environment in the Inner Magnetosphere
キーワード：宇宙機表面帯電、内部磁気圏、宇宙天気
Spacecraft surface charging is caused by the interaction between ambient plasma and the spacecraft surface, which can lead to spacecraft anomalies due to electrostatic discharging (ESD). We study the inner magnetospheric plasma environment that induces spacecraft surface charging using data from the Van Allen Probes. The analysis period (2012-2019) spans the solar maximum, declining, and minimum phases. Almost all surface charging events (V < -10) occurred during the solar maximum phase (early operational phase). These events were distributed from the midnight to dawn regions in local time and from GEO to approximately 4 Re in distance. The analysis of data from this solar maximum phase reveals that the integral flux of high-energy electrons (E > 8 keV) serves as a useful index for determining the necessary conditions for surface charging, as proposed in previous studies in GEO. However, even when the integral flux exceeds the threshold for charging, surface charging occurs in only about 20% of cases in MEO. This is because the low-energy electron flux increases inside GEO, generating secondary electron emissions that help mitigate surface charging. We investigated the number of events that meet the charging plasma conditions during the solar maximum phase and found that the occurrence rates in the declining and minimum phases are approximately 1.2 and 0.4 times those of the solar maximum phase, respectively. However, charging events were seldom observed in the declining and minimum phases. To explain this inconsistency, we conducted an analysis during eclipses, where secondary electron current is primarily responsible for charge mitigation due to the lack of photoelectron emission. The analysis suggested that the secondary electron emission coefficient of the satellite surface increased during the late phases compared to the early phase, likely due to surface degradation. We will investigate data from the Arase satellite to discuss whether similar phenomena are observed.