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Aluminum film reflectors can yield a high reflectance over a broad wavelength region, and have been widely used in the spacecraft optical instruments for high quality optical applications. The reflectors, however, could deteriorate under the irradiation by charged particles in the Earth radiation belt. To understand the deterioration mechanisms, the change in surface morphology of an Al film reflector irradiated with 60 keV protons was studied in liquid nitrogen cooled vacuum environment. Proton irradiation affected strongly the Al film reflectors forming a rough surface covered with hillocks and valleys that caused an increase in the RMS roughness and light scattering that, in turn, contributed to the decrease of specular reflectance in UV and visible wavelength ranges. The studies on the changes in surface morphology of Al film reflectors induced by proton irradiation would help to understand the damage mechanism and predict the performance evolution of optical equipment used in spacecrafts under space ...