Optical metrology for the segmented optics on the Constellation-X Spectroscopy X-ray telescope

We present the metrology requirements and metrology implementation necessary to optically characterize the reflector technology for the Constellation-X (C-X) spectroscopy x-ray telescope (SXT). This segmented, 1.6m diameter highly nested telescope presents many metrology and alignment challenges. In particular, these mirrors have a stringent imaging error budget as compared to their intrinsic stiffness. The low stiffness is seen to be implied by the required effective area and the required weight. The low mirror stiffness has implications for the metrology that can be used. A variety of contact and non-contact optical profiling and interferometric methods are combined to test the formed glass substrates before replication and the replicated reflector segments. The reflectors are tested both stand-alone and in-situ in an alignment tower. Some of these methods have not been used on prior x-ray telescopes and some are feasible only because of the segmented approach used on the SXT. Methods to be discussed include high precision coordinate measurement machines using very low force or optical probes, axial interferometric profiling, azimuthal circularity profiling, and use of advanced null optics such as conical computer generated hologram (CGHs).