Impact of mirror local defects on system scattering in telescopes

To calculate the scattering impact of scratches on space-based telescope systems accurately, this study proposes fitting scratch scattering using an anisotropic scattering model based on actual test results. The stray light nonuniformity and total stray light of each mirror in a Cook-type off-axis three-mirror system was calculated. A scratch illuminated with unit radiation power can generate a maximum stray light level of 7 x 10-5 and can obscure dark targets with a brightness ratio of 1 x 10-5 to 8 x 10-5. Furthermore, as the wavelength decreases, the total stray light generated by this scratch can reach 5.7 x 10-4 when illuminated with unit radiation power in the 200 nm ultraviolet band. Such scratches on the mirrors of an off-axis three-mirror telescope cause 7-8 times higher nonuniformity of stray light than roughness scattering, decreasing signal-to-noise ratio and affecting target recognition and image processing.