Design, fabrication, and testing of Wolter-I x-ray optic for Swift Solar Activity X-ray Imager (SSAXI)-Rocket

Swift Solar Activity X-ray Image (SSAXI-Rocket), mounted on the High-Resolution Coronal Imager (Hi-C) as a sub-payload, is a wide field solar X-ray imager designed to image Solar X-ray flares at high cadence (>5 Hz). SSAXI-Rocket consists of a Wolter-I optic with a focal length of 1 m, coupled with a monolithic CMOS X-ray sensor at the focal plane. The optics for SSAXI-Rocket were fabricated using the Electroformed Ni Replication (ENR) technique at Center for Astrophysics, Harvard-Smithsonian. Each optic has both parabolic and hyperbolic sections with 62 mm diameter at the inflection plane with a total optic length of 18 cm. The performance of the flight and flight spare optic mounted on a spider was measured at the Marshall Space Flight Center (MSFC) Stray Light Testing Facility (SLTF) to characterize the Point Spread Function (PSF) and Effective Area (EA). The flight optic selected for SSAXI-Rocket shows on-axis 16′′ Half Power Diameter (HPD) and 5′′ Full Width Half Maximum (FWHM) at 4.5 keV, exceeding the 23′′ HPD and 9′′ FWHM requirement. The effective area is about 0.64 cm2 at 4.5 keV. Coupled with the fast readout of an X-ray CMOS sensor, this optic enables rapid high-resolution X-ray imaging over a wide field of view (> 20′ x 20′). Here we review the design, fabrication and testing of the SSAXI-Rocket optic and summarize its performance.