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Technology Transfer - Ultra-Smooth Surfaces

The mirror system of the X-ray satellite ROSAT has been formed and polished from a glas ceramic material by the Carl Zeiss company, Oberkochen. X-ray astronomy makes great demands on the accuracy of surfaces: the X-ray mirror of almost ten square meter polished surface shows an average residual roughness of only a few atomic diameters - at the construction time of ROSAT this was the smoothest surface ever manufactured. Correspondingly large was the effort to prove the mirror quality. The Max-Planck-Institut has built a 130 meter long vaccum facility for the purpose of surveying mirrors of X-ray telescopes.
ROSAT X-ray telescope Figure 1: Look at the entrance aperture of the ROSAT telescope. Four parabolic-hyperbolic mirror pairs fitted into each other form a Wolter Type-I Telescope with a focal length of 2.4 m, of which ring segments - divided by 16 radial struts - are seen. Each mirror is 50 cm in length and the diameter of the largest mirror is 84 cm. With it, ROSAT carries the largest X-ray telescope ever built. Its mirror surfaces have a residual roughness of less than 3 , which make them, after a final polishing, the smoothest mirrors ever produced for a grazing-angle telescope.
PANTER X-ray test facility at Neuried Figure 2: The scientific success of the ROSAT Mission is greatly based on the extensive, carefully performed test and calibration phases. The development of the X-ray mirrors was propelled by measurements in MPE's PANTER test facility situated on the campus of the Pantolsky company at Neuried. This facility was also used for the ten-month continual calibration of the ROSAT telescope. The aerial photograph of the Bavaria Luftbildverlags GmbH at Eching near Munich in Germany shows the facility after reconstruction for the XMM mission, the second cornerstone of the Horizon 2000 programme of ESA. The 130 m long X-ray test line can be seen at the lower edge of the picture.
ROSAT X-ray mirror Figure 3: Integration of the ROSAT X-Ray mirror at the Carl Zeiss company in Oberkochen.

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