Grazing angle proton scattering: effects on Chandra and XMM-Newton X-ray telescopes

A proton scattering process resulted in damage to one of the Chandra X-ray telescope's focal plane detectors. In this process, incident protons were transmitted, by scattering off the telescope mirrors, to the focal plane. We identify the proton population responsible for the damage and, using a proper grazing angle formalism, we show that the standard calculations of grazing angle scattering will significantly under predict the expected proton flux at the focal plane.