Development of X-ray reflectors for the Constellation-X observatory

The Constellation-X observatory is planned to have four identical satellites, each of which carries, among other instruments, a Spectroscopic X-ray Telescope (SXT). The SXT has a 10m focal length and 1.6m diameter aperture. It has a total effective X-ray collection area of similar to7,500cm(2) at 1 keV. Mission science requirements call for an angular resolution of 15" half-power diameter (HPD) at the observatory level. Combining the large collection area requirement, the angular resolution requirement, and a mass requirement, we are faced with an unprecedented task of fabricating X-ray mirror segments with an areal density of only 1 kg/m(2) which is typically called gossamer optics. We have adopted a two-step process for fabricating the mirror segments: (1) first slump a flat sheet of glass onto a forming mandrel to create a substrate, and then (2) epoxy-replicate the substrate off a precision replication mandrel to eliminate any defects or errors on its surface. As of the writing of this paper in late August 2003, we have demonstrated a process for reliably making excellent substrates. Best mirror segments fabricated so far, if aligned and mounted without error, have an angular resolution in the vicinity of 20" HPD, close to, but not quite, meeting requirements. We expect that in the next year, when forming mandrels that meet requirements are procured, we will be able to fabricate mirror segments that actually meet and even possibly exceed the SXT requirements. In this paper, we report on the baseline mirror fabrication method and the status of its development as of August 2003.