XMM's X-ray telescopes

The XMM observatory has, at its heart, three large X-ray telescopes, which will provide a large collecting area (1430 cm(2) each at 1.5 keV, and 610 cm(2) each at 8.0 keV) with a spatial resolution of around 14-15 arcsec, At the end of 1998, three months ahead of schedule, the three flight and the two spare models of the X-ray telescope were handed over to the XMM Prime Contractor Daimler Chrysler Aerospace (D), The three flight models were integrated onto the spacecraft's optical platform at ESTEC at the end of March 1999. The X-ray telescopes show mechanical and optical performances much better than specification, which will undoubtedly bring important benefits for astronomers. The most challenging parts of their development phase were the design, manufacture and testing of the X-ray mirrors, which required four intensive years of work under ESA's direct management (see ESA Bulletin No. 89, Feb. 1997), This article focusses on the telescope design, with emphasis on the X-ray mirrors and baffles, and the X-ray and optical test results achieved with the flight models of the telescope, including stray-light reduction. Based on the lessons learnt from the XMM experience, the prospects for the next generation of ultra-thin X-ray mirrors are also addressed.