The interferometric calibration and measurement of deformable mirrors for adaptive optics are often performed on complex optical system with spider arms. The spider shadows may divide the mirror surface into separate islands on the detector, so the interferometer fails in reconnecting them to a common phase value. The calibration measurements then suffer from such artificial differential pistons across islands, which is converted into a wrong actuator command and in general into a poor calibration. We review the effects of spider arms shadowing as experienced during the optical calibration of large format adaptive mirrors, such as the Large Binocular Telescope and Very Large Telescope ones; we describe the procedures that we tested to cope with these issues and their effectiveness; and we present a laboratory assessment of the effect of such a shadowing with a dedicated test setup. Our work is part of a preparatory activity for the optical test of the European Extremely Large Telescope adaptive mirror M4.
Enhanced Resolution Imager and Spectrograph is an instrument currently under commissioning at the Cassegrain focus of the Very Large Telescope UT4. Its mission is to replace the suite of instruments NAOS-CONICA and SINFONI and push to the edge the capabilities of this 8-meter class telescope, by leveraging the adaptive optics module. The instrument has been designed for maximum lifetime and reliability and minimum downtime. We will present the instrument constraints and our approach to the reliability, availability, and maintainability (RAM) analysis. We identified the main actors in the system, then for each of them, we compiled a database of reliability parameters in order to build-up the reliability diagram, describing the failure sources. Starting from this information, we computed the system-wide reliability parameters and compared them with the requirements by the customer. Such a scheme is very general and may be taken as an example of RAM analysis for astronomical instrumentation; it may be also customized for the needs of other projects. In the end, we summarize the lessons learned.
The Deformable Mirror Simulator (DMS) is an optical device reproducing the F/13 beam from the adaptive secondary mirror of the Very Large Telescope UT4. The system has been designed and integrated as a test tool for the calibration and functional verification of the WaveFront sensor module of the ERIS instrument (or ERIS-AO). To this purpose the DSMSim includes a high order deformable mirror and two sources to mimic the laser and natural asterisms and illuminate the WFS optics.
In this paper we report the design of the DSMSim, the integration, verification and alignment procedure with the ERIS-AO; in the end we outline a roadmap for future improvements of the system. This work is intended to be a reference for future instrumentation projects (e.g. MAVIS-AO) for the VLT.
MAVIS will be part of the next generation of VLT instrumentation and it will include a visible imager and a spectrograph, both fed by a common Adaptive Optics Module. The AOM consists in a MCAO system, whose challenge is to provide a 30” AO-corrected FoV in the visible domain, with good performance in a 50% sky coverage at the Galactic Pole. To reach the required performance, the current AOM scheme includes the use of up to 11 reference sources at the same time (8 LGSs + 3 NGSs) to drive more than 5000 actuators, divided into 3 deformable mirrors (one of them being UT4 secondary mirror). The system also includes some auxiliary loops, that are meant to compensate for internal instabilities (including WFSs focus signal, LGS tip-tilt signal and pupil position) so to push the stability of the main AO loop and the overall performance. Here we present the Preliminary Design of the AOM, which evolved, since the previous phase, as the result of further trade-offs and optimizations. We also introduce the main calibration strategy for the loops and sub-systems, including NCPA calibration approach. Finally, we present a summary of the main results of the performance and stability analyses performed for the current design phase, in order to show compliance to the performance requirements.
The paper describes the design of the NGS WFS sub-module of MAVIS, an instrument for the VLT UT4 that aims to provide diffraction limited imaging and spectroscopy at visible wavelengths. In this framework the NGS WFS provides means for the tomographic measurement of the lower-orders of the atmospheric turbulence allowing MAVIS to reach the required performances in terms of sky coverage and resolution. We present the optical design and performance of the NGS WFS probes and acquisition camera, the actuators embedded in the subsystem and their control hardware. Finally, we show the mechanical arrangement of the submodule.
We investigate the interferometric measure-ability of the silicon carbide Reference Body of the ELT adaptive
mirror M4. The sampling is technically challenging, because of the low fringes modulation due to poor surface
finish and to the extremely large number of holes in the aperture. We describe our approach to face and solve
such criticalities, based on laboratory experimentations with a Twyman Green interferometer on a dedicated
optical setup; we comment the feasibility of such measurement in a real environment and present in the end a
checklist to enable interferometer measurements in such unfavourable conditions.
The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs (UBV, RIZ, YJH) providing a spectral resolution of ∼100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 µm with the goal of extending it to 0.35-2.4 µm with the addition of a K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Its modularity will ensure that ANDES can be placed entirely on the ELT Nasmyth platform, if enough mass and volume is available, or partly in the Coudé room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of more than 200 scientists and engineers which represent the majority of the scientific and technical expertise in the field among ESO member states.
At the end of 2021, the ESO council approved the start of the construction phase for a High Resolution Spectrograph for the ELT, formerly known as ELT-HIRES, renamed recently as ANDES (ArmazoNes high Dispersion Echelle Spectrograph). The current initial schedule foresees a 9-years development aimed to bring the instrument on-sky soon after the first-generation ELT instruments. ANDES combines high spectral resolution (up to 100,000), wide spectral range (0.4 µm to 1.8 µm with a goal from 0.35 µm to 2.4 µm) and extreme stability in wavelength calibration accuracy (better than 0.02 m/s rms over a 10-year period in a selected wavelength range) with massive optical collecting power of the ELT thus enabling to achieve possible breakthrough groundbreaking scientific discoveries. The main science cases cover a possible detection of life signatures in exoplanets, the study of the stability of Nature’s physical constants along the universe lifetime and a first direct measurement of the cosmic acceleration. The reference design of this instrument in its extended version (with goals included) foresees 4 spectrographic modules fed by fibers, operating in seeing and diffraction limited (adaptive optics assisted) mode carried out by an international consortium composed by 24 institutes from 13 countries which poses big challenges in several areas. In this paper we will describe the approach we intend to pursue to master management and system engineering aspects of this challenging instrument focused mainly on the preliminary design phase, but looking also ahead towards its final construction.
System engineering and project-team management are essential tools to ensure the project success and the Redmine is a valuable platform for the work organization and for a system engineered approach. We review in this work the management needs related to our project, and suggest the possibility that they fit to many research activities with a similar scenario: small team, technical difficulties (or unknowns), intense activity sprints and long pauses due to external schedule management, a large degree of shared leadership. We will then present our implementation with the Redmine, showing that the use of the platform resulted in a strong engagement and commitment of the team. The explicit goal of this work is also to rise, at least internally, the awareness about team needs and available organizational tools and methods; and to highlight a shareable approach to team management and small scale system engineering.
The ELT M4 is the telescope-facility adaptive unit for the European ELT. Final design and construction were awarded in 2015 to AdOptica, a consortium of Microgate and ADS International; on-site delivery is planned for 2024. The unit is based on a monolithic, structural reference body manufactured by Mersen Boostec. The flat thin mirror, controlled using the contactless voice-coil-motor based technology, is split in 6 segments produced by Safran Reosc. The M4 unit is ready for integration: we report here the results of the construction and component level testing, introducing also the forthcoming integration and system-level tests.
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