Experimental Characterization of Internal Charging Processes in MEO-Like Electron Environment

This paper is dedicated to the characterization of internal charging and discharging processes of different systems or materials in medium earth orbit (MEO) environment. Experiments for MEO were carried out at the ONERA, Toulouse, France, using the Geostationary Dielectric Unit Radiation electron beam facilities. Assuming 2.5 mm of Al shielding on the spacecraft, a worst case electron spectrum emerging from the shielding has been calculated from previous works. Different materials or systems have been tested in this configuration: printed circuit board (PCB) and insulating materials used for cables or connectors [polyetheretherketone, ethylene tetrafluoroethylene (ETFE), and Kapton]. The experiments revealed that PCB or ETFE cables might be prone to present a high risk of charging and discharging after several days under extreme environment. Electrostatic discharges have then been detected on PCBs. An experimental and numerical method has also been defined and validated at ONERA to assess the charging levels in long-term space environment through short-duration experiments performed at higher electron current. This method requires the extraction of electric parameters (especially radiation-induced conductivity) of the tested materials. From these parameters, it was demonstrated that the extrapolation of the experimental results was feasible for most space used materials.