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Completed TRL 2 (started at 2, targeting 3)
Project Objective
The Replicated Epoxy Ceramic X-ray Optics (RECXO) project aims to produce high-angular-resolution, lightweight, full-shell X-ray optics for high-energy astrophysics, heliophysics, and planetary science applications.
Project Description
The need for high-angular-resolution and high-throughput X-ray optics is strongly endorsed by the Astro2020, Pathways to Discovery in Astronomy and Astrophysics for the 2020s report. In pursuit of this goal, the RECXO project is merging two existing technologies to produce a novel, lightweight, high-resolution full-shell X-ray optic. Starting with lightweight, high-specific-stiffness ceramic carrier shells, the RECXO project will use a mandrel replication technique to create grazing-incidence, epoxy optical surfaces on the inside surface of the shells. The novel aspect of our approach is to pair a new ultra-low shrinkage epoxy replication technique developed for normal incidence optics by external collaborators with high-stiffness, light-weight silicon carbide (SiC) substrates, produced by industry, to produce full-shell optics. The high-resolution mandrel production starts with blank fabrication by an outside shop and will be completed with polishing by the ES23 optics shop at MSFC. The long-term goals of RECXO are to develop techniques for polishing the chosen mandrel material, produce a super-polished mandrel, procure ceramic shells, engage the external partner to perform epoxy replication, and finally X-ray test the RECXO shells at MSFC.
Project Results and Conclusions
To start the project, flat coupons of mandrel material were procured so that the MSFC ES23 optics could develop a polishing process optimized for the RECXO mandrel material. The shop accomplished this task, successfully determining a series of polishing slurries and techniques that improved the coupon surface roughness from ground finish to X-ray specular (<5 Angstroms RMS roughness). To characterize surface roughness after each polishing step, ten positions on the flat coupon were measured with a Zygo NewView 3600 microscope interferometer. To measure the stability of the surface over time, the coupon was left exposed in a lab environment for approximately one month, and the surface roughness measured at one-week intervals. Results indicate that the polishing process achieved the RECXO 5 Å RMS surface roughness requirement and that the surface roughness is stable in the lab environment for at least one month. This duration is more than sufficient for replicating RECXO shells.
Next, a mandrel blank was procured, and its shape was measured on a coordinate measuring machine (CMM) at MSFC. The shape accuracy of the mandrel blank must meet dimensional tolerances so that polishing, the next step in mandrel fabrication, will be successful.
Analysis was performed to determine error in the rough mandrel radius with respect to the nominal radius. Results indicate a taper error of approximately 25 microns along each segment, with a discontinuity at the intersection of the two segments. Note, in these CMM data, the intersection is at an axial position of 100 mm. The average radius error is out tolerance with a deviation of approximately 90 µm on a 50 µm tolerance. The 25 µm taper error is within tolerance. These data will be sent to the mandrel blank manufacturer and used to calibrate their grinding process before production of subsequent mandrel blanks. The mandrel that we currently have in possession will be used to practice the mandrel polishing process ahead of the expected receipt of in-tolerance blanks.
The objective of this project is to merge two existing mirror technologies, silicon carbide ceramic shell production and high-fidelity, epoxy-replicated optics, to create a novel, lightweight, high-angular-resolution that we call Replicated Epoxy Ceramic X-ray Optics (RECXO). Falling under TX08.2.1 Mirror Systems in the NASA Technology Taxonomy, RECXO is an evolutionary technology push because it proposes an innovative technology (high specific stiffness, high angular resolution optics) that will have high impact in an existing organizational model (grazing incidence X-ray optics for astrophysics, heliophysics, and planetary science).
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