Spectroscopy X-ray Telescope Technology
Design Overview
Diagram showing the geometry of the Constellation-X Wolter telescope and reflection grating system.
The Constellation-X Spectroscopy X-ray Telescope (SXT) uses a Wolter Type I design of nested, grazing-incidence X-ray mirrors to focus X-rays. The incomming X-ray light will focus either on the X-ray Microcalorimeter Spectrometer (XMS) or the X-ray Grating Spectrometer (XGS), depending on which foils the light encounters.
Mirror Module Design
Illustration of the Constellation-X SXT mirror module
The Constellation-X SXT mirror will build on technologies of the state-of-the-art missions currently in space: Chandra, XMM-Newton, and Suzaku. It will consist of an inner and an outer submodule, with 163 nested shells total. While a foil mirror of the size needed for Constellation-X is within the 250-kg mass budget, the required spatial resolution has not yet been attained. Currently, the best half-power diameter (HPD) for a completed foil mirror assembly is about 1.5, based on the Suzaku foils. The limiting factors include the accuracy of mounting the foils, the relatively poor surface quality of the mandrels, and a lack of stiffness in the aluminum used as a substrate. Therefore, to meet the Constellation-X science goals, we are pursuing stiffer substrate material, better mounting designs, and higher quality mandrels.
Mirror Technology
Illustration of the glass slumping technique.
Photo of a mirror segment.
To meet the SXT challenge, a new method of manufacturing mirrors is under development using replicated segments similar to Suzaku. Over the last several years we have been developing a glass slumping method. We start with a properly figured and polished forming mandrel which has the required parabolic or hyperbolic shape and a commercially available thin (0.4mm) glass sheet. They are placed in a clean electric oven, and as the temperature rises to approximately 600 degrees centigrade, the glass sheet becomes soft and begins to sag under its own weight, wrapping itself around the mandrel. Once the mirror cools, a layer of iridium is sputtered onto the inner surface to enhance its X-ray reflectivity.
