The VERT-X calibration facility: development of the most critical parts

The ATHENA X-ray telescope will be the largest X-ray optics ever built. The ground calibration of the mirror assembly raises significant difficulties due to its unprecedented size, mass and focal length. The VERT-X project aims at developing an innovative calibration facility which will be able to accomplish to this extremely challenging task. The design is based on an X-ray parallel beam produced by a source positioned in the focus of a highly performing X-ray collimator; the 6 cm-beam will be accurately moved by a raster-scan mechanism covering all the ATHENA optics. The main driving factor in the VERT-X design is the ATHENA calibration requirement on the accuracy in the HEW measure. The VERT-X project, started in January 2018, is financed by ESA and conducted by a consortium that includes INAF together with EIE, Media Lario, BCV Progetti and GPAP. In this paper we describe the first phases of the development of the most critical parts of the system, namely the raster-scan vertical tube, tip-tilt metrology, first translation axis together with the X-ray source - collimator system. These parts will be the core of the VERT-X testing system: the functioning of the whole system critically depends on their performance.