Design and status of the NGS WFS of MAORY

MAORY is the first-light multi-conjugate AO facility of the E-ELT, providing a > 30% Strehl ratio (evaluated in K band, median seeing conditions) over the MICADO 53 × 53 arcsec FoV and ensuring an overall sky coverage of 50%. MAORY will implement 3 NGS WFS having a double functionality: sensing the atmospheric low-order modes (LO-WFS) and de-trending the LGS WFS measurements (Ref-WFS). To maximize the AO sky-coverage the preliminary design of the LO-WFS foresees a 2×2 subapertures ShackHartmann sensor working in the H band, where the partial AO-correction regime and the low-noise detectors based on APD technology will enhance the WFS sensitivity. The Reference WFS will measure at slow rate (1÷10 s) the first ∼ 100 modes of the atmospheric aberration and it will correct the LGS measurements that are affected by the Sodium layer drifts. The Ref-WFS will be a 10× 10 SH making use of a CCD220-based detector. Hence it will work at visibile wavelenghts, using the same NGS of the LO-WFS. We present here the results of a study aimed to find the best design solutions for the MAORY NGS WFS in preparation of the project preliminary design review of scheduled in February 2018. We describe first the output of numerical simulations to find the best compromise between the working bandwidth and sampling of the LO-WFS and the sky-coverage corresponding to the expected performance. Then we describe the arrangement for the NGS WFS module, hosted on top of the MICADO cryostat, analyzing the static and dynamic properties of the NGS module structure. Finally we present the opto-mechanical layout for the NGS WFS and its degrees of freedom.