Constellation-X is NASA's next major X-ray observatory, planned to be launched in 2012-2013. Each of the four identical satellites contains a large diameter (1.6 m) spectroscopic X-ray telescope (SXT). The mirror assembly consists of many densely nested Wolter type 1 mirrors with segment angles of 30 and 60 degrees. The mirror segments will be made of thin, accurately shaped glass substrates onto which the reflective mirror surface is replicated from high precision, super polished mandrels. In this paper we report about design, fabrication, metrology and analyses of the optical performance of three prototype mandrels to be used by NASA in the constellation-X mirror development program. The prototype mandrels are characterized by the following features: Material: Zerodur; overall length: 1100 mm; segment angles: >30°; radius at paraboloid -hyperboloid intersection: 800mm, 600 mm and 500 mm; focal length: 10 000 mm.
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