Analysis of the internal charging data in medium earth orbit with numerical simulation and ground experiment

The deep dielectric charging effect monitor (DDCEM) has been designed to study the internal charging effect by measuring the charging currents and potentials inside the spacecraft. It is equipped on three Chinese navigation satellites in a circular medium earth orbit (MEO) with 22000 km average height and 55° inclinations. Numerical simulation based on the Geant4-RIC method was used to evaluate the data of DDCEM. The data during May to November 2019 on one of the three satellites show that the charging currents of DDCEM were negatively enhanced when the satellite moved into the outer radiation belt. The currents reached the negative maximum during a significant electron enhancement in September 2019. Positive currents were also detected besides negative currents that were caused by the deposition of electrons in the sensor. The causation of positive currents in the space environment may be that the low-energy electrons cannot penetrate the satellite skin and make it charging to negative potential, the reference ground of DDCEM that is connected to the satellite skin drops below zero by the low-energy electrons so that the output currents turn to positive. Ground experiment was used to simulate the causation of positive currents and the result verified our theory.