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Proceedings Paper

Adaptive secondary mirrors for the Large Binocular Telescope
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Paper Abstract

The two adaptive secondary (AS) mirrors for LBT (LBT672) represent the new generation of the AS technology. Their design is based on the experience earned during the extensive tests of the previous generation unit (the MMT AS mirror). Both the mechanics and the electronics have been revised, improving the stability, reliability, maintenance and computational power of the system. The deformable mirror of each unit consists of a 1.6mm-thick Zerodur shell having a diameter of 911mm. The front surface is concave to match the Gregorian design of the telescope. Its figure is controlled by 672 electro-magnetic force actuators that are supported and cooled by an aluminum plate. The actuator forces are controlled using a combination of feed-forward and de-centralized closed loop compensation, thanks to the feedback signals from the 672 co-located capacitive position sensors. The surface reference for the capacitive sensors is a 50mm-thick Zerodur shell faced to the back surface of the thin mirror and rigidly connected to the support plate of the actuators. Digital real-time control and unit monitoring is obtained using new custom-made on-board electronics based on new generation 32bit floating-point DSPs. The total computational power (121 Gflop/s) of the LBT672 units allows using the control electronics as wave-front computer without any reduction of the actuator control capability. We report the details of the new features introduced in the LBT672 design and the preliminary laboratory results obtained on a prototype used to test them. Finally the facility in Arcetri to test the final LBT672 units is presented.

Paper Details

Date Published: 7 February 2003
PDF: 12 pages
Proc. SPIE 4839, Adaptive Optical System Technologies II, (7 February 2003); doi: 10.1117/12.458961
Show Author Affiliations
Armando Riccardi, Osservatorio Astrofisico di Arcetri (Italy)
Guido Brusa, Osservatorio Astrofisico di Arcetri and Ctr. for Astronomical Adaptive Optics/Univ. of Arizona (United States)
Piero Salinari, Osservatorio Astrofisico di Arcetri (Italy)
Daniele Gallieni, ADS International S.r.l. (Italy)
Roberto Biasi, Microgate S.r.l. (Italy)
Mario Andrighettoni, Microgate S.r.l. (Italy)
Hubert M. Martin, Ctr. for Astronomical Adaptive Optics/Univ. of Arizona (United States)

Published in SPIE Proceedings Vol. 4839:
Adaptive Optical System Technologies II
Peter L. Wizinowich; Domenico Bonaccini, Editor(s)

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