The European Solar Telescope (EST) is a 4.2-m telescope which has been redesigned with a fully integrated Multi-Conjugate Adaptive Optics (MCAO) into the optical path right after the EST primary mirror. The current baseline configuration considers four altitude Deformable Mirrors (DM) conjugated to 5, 9, 12 and 20 km above the telescope entrance pupil and an Adaptive Secondary Mirror (ASM) conjugated to the entrance pupil. The wavefront sensing will be performed by a set of correlation-based Shack Hartmann wavefront sensors (WFS) combining an on-axis High-Order WFS (HOWFS) to be used either in Single Conjugate AO (SCAO) to drive the ASM as well as operating simultaneously with a Multi-Directional WFS (MDWFS) to drive the MCAO. Beyond the current baseline configuration, different alternatives are currently being investigated both in the wavefront sensing strategy by evolving from a HOWFS+MDWFS into possibly a single High Order Multi Directional WFS (HOMDWFS) and/or wavefront sensors operating at different observing bands.
The European Solar Telescope (EST) aims to become the most ambitious ground-based solar telescope in Europe. Its roots lie in the knowledge and expertise gained from building and running previous infrastructures like, among others, the Vacuum Tower Telescope, Swedish Solar Telescope, or the GREGOR telescope. They are installed in the Canary Islands observatories, the selected EST site. Furthermore, the telescope has a novel optical design, including an adaptive secondary mirror (ASM) that allows reducing the number of optical surfaces to 6 mirrors (plus two lenses) before the instruments’ focal plane. The latter, combined with a configuration of mirrors that are located orthogonally oriented to compensate for the instrumental polarisation induced by each surface, makes EST a reference telescope in terms of throughput and polarimetric accuracy. In its main core design, EST also includes a Multi-Conjugated Adaptive Optics (MCAO) system where the ASM compensates for the ground layer turbulence. The rest of the mirrors on the optical train correct for the atmospheric turbulence at different layers of the atmosphere. The MCAO guarantees that the large theoretical spatial resolution of the 4-metre EST primary mirror is achieved over a circular FOV of 60 arcsec. Those main elements, combined with a set of instruments with capabilities for spectropolarimetry, make EST the next frontier in solar ground-based astronomy. In this contribution, we will cover the main properties and status of all the mentioned sub-systems and the following steps that will lead to the construction phase.
The European Solar Telescope (EST) is a next generation large-aperture solar telescope, to be located in the Canary Islands. It will be optimized for studies of the magnetic coupling of the solar atmosphere. This will require diagnostics of the thermal, dynamic and magnetic properties of the plasma over many scale heights, by using multi-wavelength imaging, spectroscopy and spectropolarimetry. The optical design of the EST is based on an aplanatic Gregorian telescope, characterized by a 4.2-metre primary mirror, installed above the elevation axis with the aim of enhancing the natural air flushing. The EST works in open configuration, requiring an active/passive thermal control at telescope level to comply with the maximum temperature gradients of ±2°C. The telescope will be placed on the top of a tower to improve the local seeing conditions. The open configuration exposes the telescope to wind disturbances, higher than in other telescopes. The natural frequency of the global modes affecting the position servosystem bandwidth of the telescope are stablished in 12-15 Hz to ensure pointing and tracking accuracy of 2.3 arcsec and 0.8 arsec during 10 mins, respectively. Sophisticated end-to-end control analysis have been carried out to assess in detail the effects of the wind disturbances, but also the impact of non-linear friction, cogging and torque ripple, among others. CFD analyses and wind tunnel test campaigns have been performed to verify the performance of the telescope in operational conditions. The main axes of the telescope must be in parking position before the closure of the retractable enclosure in order to optimize its size. This requires a robust design, including redundancy in azimuth and elevation mechanisms to ensure the protection of the telescope in case of failure. The detailed maintenance strategy has been also established to ensure that every operation can be performed with the closed enclosure.
Text-based requirements management tools are widely used in engineering today. The concept behind it is quite simple, but this simplicity does not mean that these tools are affordable. In most cases, the cost of a requirements management tool license is similar to the cost of a CAD software license, the latter pertaining to a much more complex software tool. At cosmoBots.eu we have developed a plugin for a free and open project management tool (Redmine) that turns it into a powerful requirements management tool, including automatic and instant hierarchy and dependency diagrams, import/export from/to spreadsheets, full interoperability with other tools using the REST API, also including role-based lifecycle management and reporting. Several projects in IAC (EST, MICAL, NRT...) are officially using cosmoSys-Req to manage their requirements, and other projects or institutions (GTC, IACTEC...) are currently evaluating their use.
The European Solar Telescope (EST) is a 4.2-m solar telescope, based on an aplanatic Gregorian configuration with an alt-azimuthal mount. This contribution presents the status of EST and describes the baseline for the preliminary design of the Telescope Structure (Telescope Mount), Enclosure and Pier. It also introduces the systems engineering, model and tools. In addition, it explains the rationale of the main specifications. The optical design has undergone major changes since the conceptual design. The M2 Assembly has become an Adaptive Secondary Mirror, the f-number has been changed and the number of optical surfaces has been reduced to 6 mirrors and 2 lens barrels. Therefore, part of the system has been updated and new assemblies have appeared: The Transfer Optics and Calibration Assembly (TOCA) and the Pier Optical Path (POP). Some requirements make this telescope unique: the primary mirror is above the elevation axis, the multi-conjugated adaptive optics is integrated in the telescope, the telescope instrumental polarization is minimized and the telescope will observe in open enclosure configuration to improve the natural air flushing. The drawback of the open configuration is that the telescope structure, M1 and M2 will be exposed to the wind load and the thermal load by radiation, forcing the development of a stiffer Telescope Structure, a specific thermal control to achieve the pointing and tracking performances and a low local seeing degradation. The Preliminary Design phase of the Telescope Structure, Enclosure and Pier have been developed by IDOM throughout 2021 and 2022, following technical requirements by the EST Project Office.
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