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Measurement, modeling, and adjustment of the 10.4-m-diameter Leighton telescopes

Woody, David and Serabyn, Eugene and Schinckel, Anthony (1998) Measurement, modeling, and adjustment of the 10.4-m-diameter Leighton telescopes. In: Advanced Technology MMW, Radio, and Terahertz Telescopes. Proceedings of SPIE. No.3357. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, pp. 474-485. ISBN 0819428043.

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The design of the Leighton telescopes and the unique techniques used in their fabrication make these telescopes particularly amenable to precise modeling and measurement of their performance. The surface is essentially a continuous membrane supported at 99 uniformly distributed nodes by a pin joint triangular grid space frame. This structure can be accurately modeled and the surface can be adjusted using low- resolution maps. Holographic measurements of the surface figure of these telescopes at the Caltech Submillimeter Observatory (CSO) and the Owens Valley Radio Observatory (OVRO) have been made over several epochs with a repeatability of 5 - 10 micrometer over the zenith angle range from 15 to 75 degrees. The measurements are consistent with the calculated gravitational distortions. Several different surface setting strategies are evaluated and the 'second order deviation from homology,' Hd, is introduced as a measure of the gravitational degradation that can be expected for an optimally adjusted surface. Hd is defined as half of the RMS difference between the deviations from homology for the telescope pointed at the extremes of its intended sky coverage range. This parameter can be used to compare the expected performance of many different types of telescopes, including off-axis reflectors and slant-axis or polar mounts as well as standard alt-az designs. Subtle asymmetries in a telescope's structure are shown to dramatically affect its performance. The RMS surface error of the Leighton telescope is improved by more than a factor of two when optimized over the positive zenith angle quadrant compared to optimization over the negative quadrant. A global surface optimization algorithm is developed to take advantage of the long term stability and understanding of the Leighton telescopes. It significantly improves the operational performance of the telescope over that obtained using a simple 'rigging angle' adjustment. The surface errors for the CSO are now less than 22 micrometer RMS over most of the zenith angle range and the aperture efficiency at 810 GHz exceeds 33%. This illustrates the usefulness of the global surface optimization procedure.

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Additional Information:© 1998 Society of Photo-Optical Instrumentation Engineers (SPIE). We are grateful for having had the opportunity to learn about the craft of designing and fabricating telescopes from Prof. Bob Leighton. He has left us with a set of superb telescopes with performance that is just now being approached by the latest generation of sub-millimeter telescopes. Detailed study of the Leighton telescopes has revealed many innovative and subtle design features and we are sure that other significant ideas remain to be discovered in these telescopes. This work was supported by NSF grants AST96-15025 and AST96-13717.
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Subject Keywords:radio telescopes, radio holography, structural modeling, surface adjustment, telescope design
Series Name:Proceedings of SPIE
Issue or Number:3357
Record Number:CaltechAUTHORS:20200311-161942534
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Official Citation:David P. Woody, Eugene Serabyn, and Antony Schinckel "Measurement, modeling, and adjustment of the 10.4-m-diameter Leighton telescopes", Proc. SPIE 3357, Advanced Technology MMW, Radio, and Terahertz Telescopes, (31 July 1998);
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101886
Deposited By: George Porter
Deposited On:16 Mar 2020 15:37
Last Modified:16 Nov 2021 18:06

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