A Substorm-Dependent Negative Limit of Non-Eclipse Surface Charging of a Chinese Geosynchronous Satellite

Surface charging is one of the most common causes of spacecraft anomalies. When and to what potential the spacecraft is charged are two important questions in space weather. Here, for a Chinese geosynchronous navigation satellite, we infer the extreme negative surface charging potentials from the ion differential fluxes measured by a low-energy ion spectrometer. Without the solar eclipse effect away from the midnight, the charging potentials are found to have a negative limit which is determined by the maximum SuperMAG electrojet index in the preceding 2 hr. Such an empirical relation can be reasonably explained by the dependence of 1-50 keV electron fluxes on substorm strength. Similar relations may also exist for other inner magnetospheric spacecraft in the non-eclipse region, which would be useful for spacecraft engineering and space weather alerts. Spacecraft charging is the charging of spacecraft surfaces or components relative to the surrounding space plasma. There have been numerous reports of serious spacecraft anomalies related to the surface charging. When and to what potential the spacecraft is charged are two important questions in space weather. For a Chinese navigation satellite in the geosynchronous orbit, we show that the non-eclipse charging potentials have a negative limit determined by the maximum SuperMAG electrojet index in the preceding 2 hr. Such an empirical relation can be reasonably explained by the dependence of 1-50 keV electron fluxes on substorm strength. For other magnetospheric spacecraft, similar relations may also exist and would be useful for spacecraft engineering and space weather alerts. Negative surface charging potentials are inferred from ion energy spectrograms for a Chinese geosynchronous navigation satellite Non-eclipse extreme negative surface charging occurs primarily from pre-midnight through dawn to pre-noon magnetic local times Non-eclipse surface charging potentials have a negative limit determined by substorm strength