SOFIA secondary mirror Hindle test analysis

Paul Kenneth Davis

doi:10.1117/12.458824

3 March 2003 SOFIA secondary mirror Hindle test analysis

Paul Kenneth Davis

Proceedings Volume 4857, Airborne Telescope Systems II; (2003) https://doi.org/10.1117/12.458824
Event: Astronomical Telescopes and Instrumentation, 2002, Waikoloa, Hawai'i, United States

Abstract

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a NASA facility, nearing completion, consisting of an infrared telescope of 2.5 meter system aperture flying in a modified Boeing 747. Its Cassegrain secondary mirror has recently completed polishing. The SOFIA Project Office at Ames Research Center considered it important to perform an independent analysis of secondary mirror figure. The polishing was controlled by the standard test for a convex hyperboloid, the Hindle test, in a modified form with a meniscus lens partially reflecting on the concave face, rather than a fully reflecting mirror with a central hole. The spacing between this meniscus lens and the secondary mirror was controlled by three peripherally located spacing spheres. This necessitated special analysis to determine what the resulting curvature and conic constant of the mirror would be, if manufacturing imprecisions of the test set-up components were to be taken into account. This set-up was specially programmed, and the resulting hyperboloid calculated for the nominal case, and all extreme cases from the reported error limits on the manufacturing of the components. The results were then verified using the standard program CODE-V of Optical Research Associates. The conclusion is that the secondary mirror has a vertex radius of curvature of 954.05 mm ± .1 mm (design value: 954.13), and a conic constant of -1.2965 ± .001 (dimensionless, design value: -1.298). Such small divergences from design are to be expected, and these are within the refocusing ability of SOFIA, and would result in an acceptably small amount of spherical aberration in the image.

Citation Download Citation

Paul Kenneth Davis "SOFIA secondary mirror Hindle test analysis", Proc. SPIE 4857, Airborne Telescope Systems II, (3 March 2003); https://doi.org/10.1117/12.458824

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KEYWORDS

Mirrors

Analytical research

Polishing

Interferometers

Manufacturing

Optical spheres

Telescopes

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