Considerations on testing of CFGT primary segments

Liyuan Jiang; Xinnan Li

doi:10.1117/12.866226

12 October 2010 Considerations on testing of CFGT primary segments

Liyuan Jiang, Xinnan Li

Proceedings Volume 7656, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment; 76566H (2010) https://doi.org/10.1117/12.866226
Event: 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies, 2010, Dalian, China

Abstract

Larger primary collect more light. Limited by the casting techniques, the largest single primary mirror can be cast is about 8.4-m. So segmented primary is widely adopted by large telescope with the aperture over 10-m since the twin 10-m KECK built or designed during the past two decades. Segmented primary creates new challenges for fabrication and measurements. Chinese Future Giant Telescope (CFGT), a 30m telescope project, has been proposed by Chinese astronomers. The primary of CFGT is a 30-meter diameter hyperboloid with a focal ratio F/1.2 and divided to 17 rings evenly from the center to the edge. Each ring is divided into several sector-shaped segments with the size about 1.1-meter in diagonal. The total amount of the off-axis sector-shaped aspheric sub-mirror is 1122 including 17 different types. In this case, how to test the large quantities of off-axis sector-shaped aspheric segments precisely and efficiently with less cost is highly required to be considered. In this paper, the parameters of the CFGT primary and the 17 different types of the segments are presented. Three potential methods of measurements for testing the large amount of CFGT primary off-axis aspherical segments are compared and analyzed. The advantages and disadvantages of these three measurements are discussed. By comparing, a method that test the segments with a standard flat mirror and another method which tests the segments with a CGH and a test plate may be served as two candidates of the measurement for CFGT primary segments. It may provide useful reference for the future research.

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Liyuan Jiang and Xinnan Li "Considerations on testing of CFGT primary segments", Proc. SPIE 7656, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment, 76566H (12 October 2010); https://doi.org/10.1117/12.866226

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KEYWORDS

Mirrors

Computer generated holography

Telescopes

Aspheric lenses

Space telescopes

Astronomical telescopes

Astronomical imaging

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