Assessment of optical surfaces deterioration due to dust and ice impact and deposition

In space, planetary and astronomical observation systems are employed on spacecraft in orbit around the Earth, in halo orbits around the Earth-Sun, and in interplanetary missions. These instruments, in particular optical telescopes, can be strongly affected by the dust and micro-meteoroid environment and, for Earth orbits, by man-made space debris. Aside from the obvious catastrophic impact of large objects that may lead to the complete destruction of the optical surface, it is important to assess the impact hazards occurring with micron-sized and sub-mm particles, that might lead to nondestructive damage of the glass blank This paper investigates the damage generated in a cometary coma particles environment by dust particles, as well as ice droplets; with respect to the latter case, in addition to the potential craterisation, the possible phase transition during the impact may cause sublimation/deposition and optics contamination Both particle types can alter the cleanness level and the optical performances of the scientific cameras and bias the star tracker with fake detections caused by particles' glitter. The purpose of this study is the definition of a methodology where the optical performance degradation of the instrument surfaces is expressed in terms of surface damage, coating ablation, stray light production and modulation transfer function deterioration. In addition, this methodology will provide the definition of the requirements for an impact test campaign to validate and extend the craterisation models available in the literature. The output will be used for the experimental activity to be performed with the light-gas gun currently under development at the Malta College of Arts, Science and Technology.