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The Wide Field X-ray Telescope (WFXT) is a medium class mission for X-ray surveys of the sky with an unprecedented
area and sensitivity. In order to meet the effective area requirement, the design of the optical system is based on very thin
mirror shells, with thicknesses in the 1-2 mm range. In order to get the desired angular resolution (10 arcsec requirement,
5 arcsec goal) across the entire 1x1 degree FOV (Field Of View), the design of the optical system is based on nested
modified grazing incidence Wolter-I mirrors realized with polynomial profiles, focal plane curvature and plate scale
corrections. This design guarantees an increased angular resolution at large off-axis angle with respect to the normally
used Wolter I configuration, making WFXT ideal for survey purposes. The WFXT X-ray Telescope Assembly is
composed by three identical mirror modules of 78 nested shells each, with diameter up to 1.1 m. The epoxy replication
process with SiC shells has already been proved to be a valuable technology to meet the angular resolution requirement
of 10 arcsec. To further mature the telescope manufacturing technology and to achieve the goal of 5 arcsec, a
deterministic direct polishing method is under investigation. The direct polishing method has already been used for past
missions (as Einstein, Rosat, Chandra): the technological challenge now is to apply it for almost ten times thinner shells.
Under investigation is quartz glass (fused silica), a well-known material with good thermo-mechanical and polishability
characteristics that could meet our goal in terms of mass and stiffness, with significant cost and time saving with respect
to SiC. Our approach is based on two main steps: first quartz glass tubes available on the market are grinded to conical
profiles, and second the obtained shells are polished to the required polynomial profiles by CNC (Computer Numerical
Control) polishing machine. In this paper, the first results of the direct grinding and polishing of prototypes shells made
by quartz glass with low thickness, representative of the WFXT optical design, are presented.
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