Dielectric charging research status and prospect

Abstract

Dielectric charging phenomenon, caused by the interaction effect between space environment and spacecraft material, has a severe threat to the normal operation of spacecraft. Especially, the problem becomes more serious with the improvement of spacecraft operation voltage. An overview of dielectric charging research status, exsiting problems and prospect are reviewed. Firstly, dielectric charging phenomenon, hazards, research history and new challenges are introduced. There have five development stages: the initial attention, the focus of surface dielectric charging, the focus of deep dielectric charging, the rapid development of dielectric charging and new challenges and demands. The development demands of spacecraft dielectric in China are analysed. There have several insulation positions, which are easy to occur fault in practice. They include surface flashover on insulation material bewteen solar cells of solar array, surface flashover on insulation material between electrodes of solay array drive assembly, the insulation material in cables and pulse discharge of circuit board. Secondly, the specific research status and exsiting problems of surface dielectric charging and deep dielectric charging are summarized from the following aspects: dielectric charging mechanism, dielectric charging mitigation and numerical simulation. Next, the top issues about dielectric charging experiments and material characteristics are introduced. They include in-situ surface potential decay measurement and characteristics of dielectric radiated by electrons, in-situ space charge measurement and material characteristics under electron radiation, surface flashover characteristics of dielectric radiated by electrons in vacuum. Two kinds of space charge in-situ measurement, short-circuit PEA (Pulsed Electro-Acoustic) and open PEA are introduced. At present, there do not have the mature in-situ space charge measurement setup under electron radiation in China, the difficult points in design and debugging are analysed. It is interesting of the surface flashover of dielectric under electron radiation. The latest experimental results indicated that the flashover voltage shows a distinctly different variation tendency under the two cases (after electron radiation and during electron radiation). The first case of after electron radiation, flashover voltage becomes higher than that without electron radiation. Because of the effect of deposited electrons in dielectric surface layer and the changes of trap distribution inside material. The trap distributions of polyimide after electron radiation are calculated based on surface potential decay measurement and Simmons theory. The results show that the shallow trap level increases slightly with the increase of electron energy (3–11 keV), ranging from 0.81–0.85 eV, while the deep trap level remains unchanged about 0.94 eV; the second case of during electron radiation, flashover voltage exhibited a dramatic drop from 26.9 kV (energy: 5 keV) to 10.5 kV (energy: 30 keV), due to the combined effect of incident kinetic electrons flowing to dielectric surface and deposited electrons in dielectric surface layer. Finally, the key scientific issues in the filed of space dielectric charging are put forward and prospected based on the present research status.