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Proceedings Paper

GMT adaptive secondary design
Author(s): R. Biasi; D. Veronese; M. Andrighettoni; G. Angerer; D. Gallieni; M. Mantegazza; M. Tintori; P. Lazzarini; M. Manetti; M. W. Johns; P. M. Hinz; J. Kern
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Paper Abstract

The GMT adaptive secondary mirror (ASM) is based on a "segmented" concept following the primary segment layout: seven 1.05m diameter circular, independent adaptive mirrors are fed by the primaries and focus to the main telescope focal stations. The adaptive unit's design is based on the consolidated thin mirror, contactless technology already employed in several units (MMT, LBT, Magellan, VLT and one of the proposed E-ELT M4 designs), but nevertheless the mirror's topology reveals several design challenges. In particular, the off-axis units are strongly aspheric and therefore they require aspheric shaping of both thin mirror surfaces and of the thick reference body. The strong tilt of the off-axis units forced us to consider a peculiar fine positioning hexapod design, maximizing its stiffness and also implementing a special design of the last three rings of actuators to remain within the prescribed obstruction. From the control point of view, the actuator density of the adaptive mirrors is remarkably lower than in all previous units: 672 actuators with 36mm spacing compared to 30mm typical separation adopted so far. This choice is validated by static and dynamic performance computation though a sophisticated numerical simulator based on a full state space model incorporating mechanics, control and fluid dynamics. The control system fulfills the dimensional constraints of the unit. The design has completed the feasibility phase, including the cost estimate. The choice of making the GMT adaptive secondary mirrors similar to the already existing ones strongly reduces the implementation risks and allows shortening the remaining design path.

Paper Details

Date Published: 14 July 2010
PDF: 10 pages
Proc. SPIE 7736, Adaptive Optics Systems II, 77363O (14 July 2010); doi: 10.1117/12.857983
Show Author Affiliations
R. Biasi, Microgate S.r.l. (Italy)
D. Veronese, Microgate S.r.l. (Italy)
M. Andrighettoni, Microgate S.r.l. (Italy)
G. Angerer, Microgate S.r.l. (Italy)
D. Gallieni, A.D.S. International S.r.l. (Italy)
M. Mantegazza, A.D.S. International S.r.l. (Italy)
M. Tintori, A.D.S. International S.r.l. (Italy)
P. Lazzarini, A.D.S. International S.r.l. (Italy)
M. Manetti, Politecnico di Milano (Italy)
M. W. Johns, GMTO Corp. (United States)
P. M. Hinz, GMTO Corp. (United States)
J. Kern, GMTO Corp. (United States)


Published in SPIE Proceedings Vol. 7736:
Adaptive Optics Systems II
Brent L. Ellerbroek; Michael Hart; Norbert Hubin; Peter L. Wizinowich, Editor(s)

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