Simulations of the ATHENA performance verification testing at XRCF

The X-ray and Cryogenic Facility is the baseline X-ray performance verification and calibration facility for the mirror demonstrator (MAMD), the qualification module (QM), and the flight module (FM) of the ATHENA ESA L-class mission. The ATHENA mirror will be the largest X-ray optic ever built, and due to its size and segmented nature it can only be partially illuminated during testing and calibration. Here we explore what this means for the method and procedure to align the mirror and obtain the effective area, point spread function, and focal length at the XRCF with raytracing and simulation. We will discuss the effects of gravity on such a large and heavy mirror, and investigate the challenge of stitching results together from different sectors due to sub-aperture illumination.