Development of lightweight X-ray mirrors for the constellation-X mission

Constellation-X is NASA's next major X-ray astronomical observatory. Its salient features are its very large effective X-ray collecting area (about 30,000 cm(2) at 1 keV) and high resolution gratings and cryogenic detector systems. The large mirror effective area presents unique and unprecedented challenges in optical fabrication and metrology. In this paper we report on the development of very lightweight X-ray mirrors that address these challenges. We use a two-step mirror fabrication process: (1) slumping thin (0.4mm) flat glass sheets to generate high quality substrates that may have mid-frequency figure errors, and (2) reducing or eliminating the mid-frequency errors using an epoxy replication process. We discuss problems and the potential associated with each of these two steps. Based on our work to date, we expect that this technology to be able to meet the baseline Constellation-X requirements, Le, 15" HPD (half-power diameter) at the observatory level. In the next few years, we will further advance this technology and expect it to reach the Constellation-X goal: 5" HPD at the observatory level.