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The XEUS mission (X-ray Evolving-Universe Spectroscopy Mission) is a future ESA project currently under study. With a mirror collecting area of up to 30 m 2 @ 1 keV and 3 m 2 @ 8 keV it will outperform the x-ray space observatories like XMM-Newton. In fact it will have a source flux sensitivity and angular resolution respectively 250 times and 7.5 times better if compared to that mission. This huge collecting area is obtained with a 10 m diameter telescope of 50 m focal length. It is foreseen that the whole telescope will be formed by two free flying satellites, one for the mirror assembly and the other for the detectors. The two satellites will be kept aligned by an active tracking/orbit control system. The angular resolution of the optics is set to 5 arcsec with a goal of 2 arcsec. Of course the requirement of high resolution and large diameter of the optics create new technological problems which have to be overcome. First of all the impossibility to create closed Wolter I shells (due to the large diameter) means that the optics will be assembled using rectangular segments of ~1 m x ~0.5 m size. A set of these segments will form a petal. The petals will be assembled to form the whole mirror assembly. Another difficulty arises from the fact that the current design foresees a mass/geometric-area ratio of 0.08 kg/cm 2 , which is very small and much lower compared with XMM-Newton. Hence the use of materials that can offer both low weight and high stiffness is mandatory. The impossibility to have a thermal control for the huge area of the optics means also that the mirrors have to operate at temperatures between -30 and -40 o C. This requirement excludes the epoxy-replication method as option for their manufacturing (CTE mismatch between resin and substrate). Considering all these constrains a possible solution for the realization of the XEUS mirrors has been found that foresees the use of glass or ceramics materials. In this paper we will describe an investigation currently on-going aimed at the development of a procedure to produce large mirror segments from thin Borofloat glass and the preliminary results obtained, that corroborate the viability of the proposed approach. A previous article (1) has introduced the basic ideas and concepts behind this investigation.

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