Structural considerations for fabrication and mounting of the AXAF HRMA optics

The large, thin-walled grazing incidence X-ray optics for NASA's Advanced X-ray Astrophysics Facility (AXAF) present a significant challenge to maintain figure during fabrication, metrology, and final assembly. The largest of the X-ray optics is 1 m long, 1.2 m in diameter, only 23 mm thick and weighs 225 kg. Conical shells of this size and stiffness present particularly difficult mounting problems because of their local flexibility and extreme sensitivity to small loads caused by differences in thermal expansion and one-g effects. Support methods that minimize the optics distortion during fabrication, metrology and launch configuration is presented. We describe the important role that finite element modeling and breadboard testing play in determining the performance of the support structures and that of material effects such as epoxy shrinkage and moisture desorption.