SALMASO, BiancaBiancaSALMASOMORETTI, AlbertoAlbertoMORETTIGaskin, JessicaJessicaGaskin2023-01-262023-01-262022978-981-16-4544-0http://hdl.handle.net/20.500.12386/33080Before launching an X-ray observatory, the performance of a telescope mirror or mirror assembly in the X-ray energy band of interest must be determined. This calibration requires a specialized facility that can approximate an astronomical point source and accommodate the mirrors and other telescope components, including an appropriate detector system. The X-ray source and telescope are typically housed in a vacuum chamber to permit easy propagation of the Xrays. X-ray test facilities around the world are being used to calibrate flagship and smaller X-ray observatories for multiple space agencies. These facilities are also regularly used to support the development of new types of optics for future missions. In this chapter, we describe currently available facilities and list some of the key missions that used them for calibration. Future facility developments needed to support the next-generation X-ray missions are also discussed.ELETTRONICOenBook part10.1007/978-981-16-4544-0_14-1https://link.springer.com/referenceworkentry/10.1007/978-981-16-4544-0_14-1FIS/05 - ASTRONOMIA E ASTROFISICA