Manufacture of mirror glass substrates for the NuSTAR mission

The NuSTAR (Nuclear Spectroscopy Telescope Array) observatory (Harrison et al. 2009), expected to be launched into an equatorial low earth orbit in 2011, will have two mirror assemblies capable of imaging X-rays in the hard X-ray band between 5 keV and 80 keV. It will be the first X-ray observatory using multilayer coatings to significantly expand the bandwidth of the typical X-ray telescope of 0.1 keV to 10 keV. The mirror assemblies use a segmented design to simplify the construction process, as such they require 4,680 mirror substrates coated with appropriately designed multilayers to enhance reflectivity for hard X-rays. These substrates are produced by slumping commercially available thin glass sheets. In this paper we report on our work of manufacturing these substrates at NASA Goddard Space Flight Center.