27 July 2016 E-ELT M4 adaptive unit final design and construction: a progress report
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The E-ELT M4 adaptive unit is a fundamental part of the E-ELT: it provides the facility level adaptive optics correction that compensates the wavefront distortion induced by atmospheric turbulence and partially corrects the structural deformations caused by wind. The unit is based on the contactless, voice-coil technology already successfully deployed on several large adaptive mirrors, like the LBT, Magellan and VLT adaptive secondary mirrors. It features a 2.4m diameter flat mirror, controlled by 5316 actuators and divided in six segments. The reference structure is monolithic and the cophasing between the segments is guaranteed by the contactless embedded metrology. The mirror correction commands are usually transferred as modal amplitudes, that are checked by the M4 controller through a smart real-time algorithm that is capable to handle saturation effects. A large hexapod provides the fine positioning of the unit, while a rotational mechanism allows switching between the two Nasmyth foci.

The unit has entered the final design and construction phase in July 2015, after an advanced preliminary design. The final design review is planned for fall 2017; thereafter, the unit will enter the construction and test phase. Acceptance in Europe after full optical calibration is planned for 2022, while the delivery to Cerro Armazones will occur in 2023.

Even if the fundamental concept has remained unchanged with respect to the other contactless large deformable mirrors, the specific requirements of the E-ELT unit posed new design challenges that required very peculiar solutions. Therefore, a significant part of the design phase has been focused on the validation of the new aspects, based on analysis, numerical simulations and experimental tests. Several experimental tests have been executed on the Demonstration Prototype, which is the 222 actuators prototype developed in the frame of the advanced preliminary design. We present the main project phases, the current design status and the most relevant results achieved by the validation tests.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Roberto Biasi, Roberto Biasi, Mauro Manetti, Mauro Manetti, Mario Andrighettoni, Mario Andrighettoni, Gerald Angerer, Gerald Angerer, Dietrich Pescoller, Dietrich Pescoller, Christian Patauner, Christian Patauner, Daniele Gallieni, Daniele Gallieni, Matteo Tintori, Matteo Tintori, Marco Mantegazza, Marco Mantegazza, Pierluigi Fumi, Pierluigi Fumi, Paolo Lazzarini, Paolo Lazzarini, Runa Briguglio, Runa Briguglio, Marco Xompero, Marco Xompero, Giorgio Pariani, Giorgio Pariani, Armando Riccardi, Armando Riccardi, Elise Vernet, Elise Vernet, Lorenzo Pettazzi, Lorenzo Pettazzi, Paul Lilley, Paul Lilley, Marc Cayrel, Marc Cayrel, "E-ELT M4 adaptive unit final design and construction: a progress report", Proc. SPIE 9909, Adaptive Optics Systems V, 99097Y (27 July 2016); doi: 10.1117/12.2234735; https://doi.org/10.1117/12.2234735


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