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The XRT X-ray mirror assembly (XMA) consists of 4 nested grazing
incidence Wolter-I mirrors with a maximum aperture of 83.5 cm
and a focal length of 240 cm.
All of the 8 mirror shells (4 paraboloid/hyperboloid pairs)
are constructed of Zerodur, a glass ceramic with an almost
negligible thermal coefficient, and are coated with a thin
layer of gold to enhance the X-ray reflectivity.
Typical grazing angles are between and
depending upon the sub-shell considered.
The focal plane plate scale of the XRT is