The impact on an optical surface by a micrometeoroid gives rise to a specific type of stray light inherent only in the space optical instruments. This causes a double source of light scattering: the impact crater and the ejected contamination. We propose a method of stray light estimation and apply it to the case of the Laser Interferometer Space Antenna telescope. We estimate the backscattering fraction for nominal (4 years) and extended (10 years) mission durations.