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Proceedings Paper

Experience of primary surface alignment for the LMT using a laser tracker in a non-metrology environment
Author(s): David M. Gale
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Paper Abstract

The 50-metre Large Millimeter Telescope (LMT) successfully completed first light observations in June 2011, operating with an initial 32.5-metre diameter collecting area. This reduced-area primary surface consists of 84 reflector panels measuring approximately 3x5m. During the construction phase, individual panels were assembled and adjusted to the specified rms surface error off-site, then installed and aligned on the antenna using a total station. Prior to first-light observations, panels were fine-tuned in piston, tip-tilt and twist using full-surface holography measurements to direct the movement of electromechanical actuators located at the four corners of each panel. In preparation for the next observing season the 32.5m primary is being refurbished and re-aligned on-site, using a commercial laser tracker for surface adjustment of each panel. For this task we have opted for the transfer of panels from the antenna surface to the telescope basement for adjustment, offering an enclosed environment with stable temperature, followed by reinstallation and measurement on the open-air antenna surface at night. In this paper we present our experiences on the use of a laser tracker to conduct panel surface measurement and adjustment on-site, at an isolated location 4,700m (15,000ft) above sea level and in the absence of dedicated metrology facilities. In section 2 we present the primary surface concept deployed at the LMT. Section 3 discusses the laser tracker equipment and data processing for panel surface measurement. Section 4 describes the panel adjustment process carried out in the site basement and presents examples of indoor panel metrology using the laser tracker. In section 5, we present our experiences to date of open-air measurement of panels installed on the antenna. Some conclusions are offered in section 6.

Paper Details

Date Published: 17 September 2012
PDF: 16 pages
Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 844453 (17 September 2012); doi: 10.1117/12.926695
Show Author Affiliations
David M. Gale, Lab. de Superficies Asféricas, Instituto Nacional de Astrofísica, Óptica y Electrónica (Mexico)

Published in SPIE Proceedings Vol. 8444:
Ground-based and Airborne Telescopes IV
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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