Electrification of the proof mass of a drag-free or accelerometric satellite

The exploitation of the data provided by the Cactus accelerometer, which makes up the payload of the D5B Castor Satellite of CNES confirmed the existence of an electric current charging the proof mass under the influence of the magnetospheric protons, and revealed a periodic variation of this current, due to the passage of the apogee through the South Atlantic magnetic anomaly. Results of in-orbit measurements of this charging current are presented, as well as calculations made for determining this current and its variations from data on proton flux at the satellite altitudes. The comparison of measured and calculated values shows that the calculation method is valid and precise enough to be used for drag-free or accelerometric satellites.