The Universitäts-Sternwarte M¨unchen (USM) was responsible for the procurement of a big Liquid Nitrogen (LN2) continuous-flow test cryostat, equipped with a 1600 mm diameter optical bench. This cryostat is planned to perform cryogenic tests of the two large cryogenic mechanisms of the MICADO instrument, the Main Selection Mechanism (MSM) and Central Wheel Mechanism (CWM), and of some of the instrument cold optics (COI) modules. The Big Test Cryostat was delivered at the end of 2021, and is currently installed at the Max Planck Institute for Extraterrestrial Physics (MPE) laboratories. In this paper we present the design, specifications and measured cold performances of the cryostat. We also provide an overview of the tests planned inside the cryostat, which will start at the beginning of 2024 and will run until beginning of 2026, when the mechanisms and the cold optics modules will be finally integrated inside the MICADO Instrument Cryostat.
MICADO is a first light instrument for the Extremely Large Telescope (ELT), set to start operating later this decade. It will provide diffraction limited imaging, astrometry, high contrast imaging, and long slit spectroscopy at near-infrared wavelengths. During the initial phase operations, adaptive optics (AO) correction will be provided by its own natural guide star wavefront sensor. In its final configuration, that AO system will be retained and complemented by the laser guide star multi-conjugate adaptive optics module MORFEO (formerly known as MAORY). Among many other things, MICADO will study exoplanets, distant galaxies and stars, and investigate black holes, such as Sagittarius A* at the centre of the Milky Way. After their final design phase, most components of MICADO have moved on to the manufacturing and assembly phase. Here we summarize the final design of the instrument and provide an overview about its current manufacturing status and the timeline. Some lessons learned from the final design review process will be presented in order to help future instrumentation projects to cope with the challenges arising from the substantial differences between projects for 8-10m class telescopes (e.g. ESO’s VLT) and the next generation Extremely Large Telescopes (e.g. ESO’s ELT). Finally, MICADO's expected performance will be discussed in the context of the current landscape of astronomical observatories and instruments. For instance, MICADO will have similar sensitivity as the James Webb Space Telescope (JWST), but with six times the spatial resolution.
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