Effects of space environmental exposure on photoemission yield of polyimide

As photoemission plays a key role in surface potential of spacecraft materials in sunlight, the photoemission yield of spacecraft used polyimide film is required for surface potential analysis. To reveal the space environmental effects on the photoemission, the ground based degradations of polyimide film due to 500 keV electrons and 50 keV protons irradiation with 4 different fluences respectively, ultraviolet irradiation with 5 different doses, and atomic oxygen beam erosion with 2 different fluences were conducted separately. By using a developed measuring system, we measured the photoemission yield of the virgin and the 4 kinds of degraded polyimide films respectively and compared the results. It is inferred that, the variation of photoemission yield was obvious after electrons, protons and ultraviolet irradiation but slight for atomic oxygen erosion. The variation of photoemission yield has been explained from the viewpoint of surface reflectance, roughness, and the free radical concentration of the exposed samples. Besides, the Monte-Carlo analysis software Casino and SRIM were used to analysis the distribution and stopping power of electron and proton respectively. It is considered that, the degradation mechanism is the multiple effects of reflectance, free radicals and so forth.