Monte Carlo simulations of hyper-velocity particulate mechanics within silicon micropore optics

The focal planes of X-ray astronomy missions are at risk of particulate impacts from both micrometeoroids and orbital debris due to the open aperture of the narrow-angle incidence optics. Silicon micro-pore optics (MPOs) have seen significant development due to their wide-angle observing capabilities and are planned for use in future X-ray instruments such as SMILE and THESEUS. Although previous missions have seen sporadic events in detectors which are attributed to particulate impacts, the number of particulates that can traverse the new micro-pore optics and affect detector performance is not currently known. By using relevant micrometeoroid and orbital debris models, the number of particulates incident on the optics over the course of both missions can be predicted. The transmission rate of particulates through the MPOs has been calculated using a bespoke Monte Carlo simulation, based upon the method of ray-tracing with known physical mechanisms such as low angle scattering incorporated. For validity, an analytical solution is derived, which shows good agreement with the Monte Carlo simulation. Using the incident flux on the optics and the simulated mirror transmission rates, the probability of a focal plane impact can be estimated. This work, in combination with experimental micrometeoroid impact campaigns, aims to predict the overall detector performance loss as a result of the micrometeoroid environment for both the SMILE and THESEUS missions.