MICADO will enable the ELT to perform diffraction limited near-infrared observations at first light. The instrument’s capabilities focus on imaging (including astrometric and high contrast) as well as single object spectroscopy. This contribution looks at how requirements from the observing modes have driven the instrument design and functionality. Using examples from specific science cases, and making use of the data simulation tool, an outline is presented of what we can expect the instrument to achieve.
MICADO is the Multi-AO Imaging Camera for Deep Observations, a first light instrument for the Extremely Large Telescope (ELT). It will provide the ELT with diffraction limited imaging capacity over a ~53-arcsec field of view, while operating with the Multi-Conjugate Adaptive Optics (MCAO) module MAORY (0.8-2.5 μm). Here, we present the design status of the MICADO derotator, which at the same time serves (i) as crucial mechanical interface between the cryo-opto-mechanical camera assembly and the instrument support structure and (ii) as high-precision image and wavefront sensor derotator to allow for 50 µas astrometry over the entire MCAO corrected field. Additionally, first test results are presented which were obtained with a derotator prototype based on a scaled 1:2 test bearing. The derotator test stand is essential to explore the limitations of the preferred bearing type in the context of the given requirements. The technical difficulties addressed by the design include: (i) design of adequate mechanical interfaces to minimize mass, deformation and the effect of the warping moment on the bearing and (ii) analysis of the friction-related stick-slip effects at low tracking velocities for the implementation of a suitable position-velocity closed-loop control system. Furthermore, our prototype setup is used to develop and test the required control concept of this high-precision application.
The paper describes the preliminary design of the MICADO calibration assembly. MICADO, the Multi-AO Imaging CAmera for Deep Observations, is targeted to be one of the first light instruments of the Extremely Large Telescope (ELT) and it will embrace imaging, spectroscopic and astrometric capabilities including their calibration. The astrometric requirements are particularly ambitious aiming for ~ 50 μas differential precision within and between single epochs. The MICADO Calibration Assembly (MCA) shall deliver flat-field, wavelength and astrometric calibration and it will support the instrument alignment to the Single-Conjugate Adaptive Optics wavefront sensor. After a complete overview of the MCA subsystems, their functionalities, design and status, we will concentrate on the ongoing prototype testing of the most challenging components. Particular emphasis is put on the development and test of the Warm Astrometric Mask (WAM) for the calibration of the optical distortions within MICADO and MAORY, the multiconjugate AO module.
The Multi-AO Imaging Camera for Deep Observations (MICADO) is one of the three first light instruments of the Extremely Large Telescope (ELT). Based on the Multi Conjugate Adaptive Optics (MCAO) modul MAORY MICADO offers diffraction-limited near-infrared imagery with a maximum field of view of 53 arcsec. In order to maintain diffraction-limited performance at the edge of the field, a precise image derotator is needed, which compensates the field rotation due to alt-azimuth mount of the telescope. In MICADO a four-point contact ball bearing is foreseen to rotate the cryostat for the compensation of the field rotation. Due to the heavy load and the high precision positioning of the ball bearing a control concept for the derotator is needed. The main challenge of positioning the ball bearing is the handling of friction effects. In this paper we present a control concept based on a velocity feedforward and a PID feedback control to rotate the bearing in the required position performance. At a scaled-down laboratory setup we demonstrate the position accuracy. To further improve the position accuracy we also study an additional friction compensation, which is based on a dynamical friction model.
MICADO will equip the E-ELT with a first light capability for diffraction limited imaging at near-infrared wavelengths. The instrument’s observing modes focus on various flavours of imaging, including astrometric, high contrast, and time resolved. There is also a single object spectroscopic mode optimised for wavelength coverage at moderately high resolution. This contribution provides an overview of the key functionality of the instrument, outlining the scientific rationale for its observing modes. The interface between MICADO and the adaptive optics system MAORY that feeds it is summarised. The design of the instrument is discussed, focusing on the optics and mechanisms inside the cryostat, together with a brief overview of the other key sub-systems.
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.