Mr. Krishna Murthy Thoutam Profile

Krishna Murthy Thoutam

at Indian Institute of Space Science and Technology

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Proceedings Article | 13 December 2020 Paper

Design, development, and analysis of segment support system for TMT primary mirror

Alikhan Basheer, S. Sriram, Vineeth Valsan, K. Sudharsan, Viswanatha Narasimhiah, T. Krishna Murthy, Mahesh P. K., G. Anupama

Proceedings Volume 11451, 114510I (2020) https://doi.org/10.1117/12.2564850

KEYWORDS: Glasses, Thirty Meter Telescope, Mirrors, Polishing, Spherical lenses, Surface finishing, Aspheric lenses, Metrology, Tolerancing

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The Thirty Meter Telescope (TMT) adopts a recently developed technology known as Stressed Mirror Polishing for the polishing of its 492 mirror segments. In this process, first the meniscus type spherical shape glass blanks are converted in to a desired aspheric shape by the application of forces around the edges using warping arms followed by spherical polishing in the stressed condition. After that, the blank edges will be cut in to its final hexagonal shape. These warping as well as the hex cutting process generate significant stress within the glass which in later stage, will cause the propagation of micro cracks and results in blank breakage. So prior and after the hex cutting process, it is essential to ensure that the glass blanks are free from stress accumulation. Hence the glass blanks need to be stress relieved before the hex cutting process. To achieve this stress relaxation, the glass blanks need to be kept over a platform or a support system which will provide a zero gravity condition for a time period of at least 48 hours. As a part of this, we designed, developed and analyzed a whiffletree based support system which will equally distribute the entire mirror blank mass into three points which are equally separated by 120⁰ from each other and thus balance itself as if it is in a floating condition. This support system which additionally gives optimized support for the glass blank which in turn minimizes the surface deformation due to its self weight sagging. This paper also discusses the positional sensitivity, reaction force sensitivity and alignment sensitivity analyses which are essential to obtain the tolerance values in the fabrication point of view.

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