Internal charging phenomena and change of electrical properties in electron beam irradiated insulating materials for spacecraft

The purpose of our research work is to evaluate some electrical properties of electron beam irradiated insulating materials for spacecraft. The spacecraft like a communication or a broadcasting satellite flying in GEO (Geostationary Orbit) is always exposed to plasma and/or radioactive-rays such as α-, β-, and γ-rays. When the insulating materials, in which the spacecraft is wrapped to keep temperature in it stable, are irradiated by the high energy electron beam, sometimes an unexpected accident due to an electrostatic discharge occurs. The accident sometimes causes a serious mission error of spacecraft. However, it has not known how the irradiation affects to the electrical properties of the materials. In our previous research work, we especially focused on an internal charging phenomenon which must affect to the electrical properties of irradiated polymers for spacecraft such as Polyimide (PI) and Polytetrafluoroethylene (PTFE). Judging from the measurement results, it is found that an amount of negative charge accumulation in PTFE is much larger than that in PI. It seems that the charge accumulation in polymers including fluorine by irradiation of electron beam is larger than that in other polymeric materials. Furthermore, the accumulated charge in the polymer including fluorine remains for long time after irradiation. Such results indicate that the electrical properties are changed by the irradiation. Therefore, we tried to compare the charge accumulation properties between the irradiated and non-irradiated polymeric materials including fluorine. By applying dc stress to them, space charge accumulation processes in various irradiated materials are observed. From the results, it is found that the charge accumulation processes in irradiated materials are completely different from the non-irradiated materials.