Low Cost Fabrication, Inspection and Test Methods for Hardened Satellite Optics

Optical systems are continually being designed to meet more difficult and challenging performance specifications and applications. Specifically, airborne and space optics are employing larger diameter surfaces with more stringent figure requirements. In order to meet these demands, individual optical surfaces are being given increasingly strict tolerances. The traditional peak-to-valley (PV) and root-mean-square (RMS) metrics are no longer sufficient for determining an optical surfaces' capability of performing in a given system. Instead, surfaces must meet specifications within given spatial frequency bands in addition to the typical PV and RMS requirements. As the frequencies of interest increase, the spatial resolution of the metrology instrument used must be able to accurately characterize features of this size. Likewise, the polishing process used to finish the optic must be able to address figure errors in the specified bands. Using stitching interferometry and fourier transform techniques, a new measurement system has been developed that effectively increases the spatial resolution of an interferometer with a given CCD. Magnetorheological finishing (MRFr) is a highly deterministic polishing technique that can correct "low" and "mid-spatial" frequency surface features. Integrating these two processes will enable fabricators to correct surface features of large optics that could not previously be resolved over the full aperture using a standard interferometer.