Degradation phenomena of electric property on polymeric materials films irradiated by proton

Spacecraft have a serious damage due to the electrostatic discharge accident. Although the polymeric materials are used for surface materials of spacecraft as a multi layer insulator (MLI) and optical solar reflector (OSR), those materials are charged up due to radioactive rays, especially electrons and protons. The charge accumulation is the origin of aging and discharging phenomena, furthermore those become a trigger for spacecraft operation anomaly. Therefore, we need to obtain the dielectric property of those materials. As the dielectric property, for example conductivity, have a great relationship between charge accumulation in the bulks, we especially focused polyimide films (PI) for MLI and fluorinated ethylene propylene copolymer (FEP) for OSR irradiated by high energy proton. We measured the space charge distribution in the bulks during and after proton beam irradiation by the pulsed electroacoustic (PEA) method. From the results, it is found that positive charge accumulations are observed in the bulk at the position of proton penetration depth. Furthermore, we measured the current through the bulk and space charge behavior in irradiated and non-irradiated PI under HV-DC by ASTM and PEA methods. From the above results, we discuss and estimate the aging of electrical insulating characteristics on the polyimide films and the fluorinated ethylene propylene copolymer films irradiated by proton.