19 October 2012 Minimizing the mirror distortion for subarcsecond imaging in the Hi-C EUV telescope
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Abstract
NASA/MSFC and SAO have developed a High Resolution EUV Solar Coronal Imaging telescope (Hi-C). The scientific objective of the mission is to determine, at higher spatial resolution than previously available, the geometric configuration and topology of the structures making up the inner corona. The Hi-C telescope launched on a rocket in early July 2012. It acts as a technology pathfinder for future satellite based missions. Key technology features of the Hi-C telescope are: (1) A 23.9 meter focal length, allowing for 0.1 arc-second pixels (2) Extremely high quality optics (3) Single wavelength multi-layer coating over the entire surface of each optic (4) Low distortion approach to mounting the primary into the telescope. The low distortion approach to mounting the primary mirror into the telescope is discussed in this paper. In previous solar EUV telescopes (TRACE, AIA, IRIS) the primary mirror is first bonded into a flexured mirror cell that is then bolted into the telescope. Techniques for bonding the mirror into the mirror cell have been well developed. If done properly, these techniques produce minimal distortion in the optic. Experience has shown, however, that bolting of the cell into the telescope produces distortions, typically in the form of astigmatism. The magnitude of the astigmatism may be acceptable for lower resolution missions, but as we approach ever higher resolutions, these astigmatisms contribute significantly to the error budget. In the Hi-C mission the mirror mounting hardware was completely assembled into the telescope tube prior to bonding the mirror to the mount. This final operation was done with the telescope tube vertical and the primary mirror surface facing up. This approach minimizes the "bolt-up" distortions typically seen, thus improving resolution.
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William A. Podgorski, William A. Podgorski, David Caldwell, David Caldwell, Kenneth McCracken, Kenneth McCracken, Mark P. Ordway, Mark P. Ordway, Peter N. Cheimets, Peter N. Cheimets, Kelly Korreck, Kelly Korreck, Leon Golub, Leon Golub, Jonathan Cirtain, Jonathan Cirtain, Ken Kobayashi, Ken Kobayashi, } "Minimizing the mirror distortion for subarcsecond imaging in the Hi-C EUV telescope", Proc. SPIE 8502, Advances in X-Ray/EUV Optics and Components VII, 85020E (19 October 2012); doi: 10.1117/12.930610; https://doi.org/10.1117/12.930610
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