The Multi-AO Imaging Camera for Deep Observations (MICADO), a first light instrument for the 39 m European Extremely Large Telescope (E-ELT), is being designed and optimized to work with the Multi-Conjugate Adaptive Optics (MCAO) module MAORY (0.8-2.5 μm). The current concept of the MICADO instrument consists of a structural cryostat (2.1 m diameter and 2 m height) with the wavefront sensor (WFS) on top. The cryostat is mounted via its central flange with a direct interface to a large 2.5-m-diameter high-precision bearing, which rotates the entire camera (plus wavefront sensor) assembly to allow for image derotation without individually moving optical elements. The whole assembly is suspended at 3.6 m above the E-ELT Nasmyth platform by a Hexapod-type support structure. We describe the design of the MICADO derotator, a key mechanism that must precisely rotate the cryostat/SCAO-WFS assembly around its optical axis with an angular positioning accuracy better than 10 arcsec, in order to compensate the field rotation due to the alt-azimuth mount of the E-ELT. Special attention is being given to simulate the performance of the derotator during the design phase, in which both static and dynamics behaviors are being considered in parallel. The statics flexure analysis is done using a detailed Finite Element Model (FEM), while the dynamics simulation is being developed with the mathematical model of the derotator implemented in Matlab/Simulink. Finally, both aspects must be combined through a realistic end-to-end model. The experiment designed to prove the current concept of the MICADO derotator is also presented in this work.

Date Published: 9 August 2016
PDF: 6 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99087K (9 August 2016); doi: 10.1117/12.2231781

Published in SPIE Proceedings Vol. 9908:
Ground-based and Airborne Instrumentation for Astronomy VI
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)