In Solar Adaptive Optics (AO), it is common to work with a wide Field of View (FoV), which necessitates special control techniques to enhance system performance. Ground-Layer Adaptive Optics (GLAO) configurations lack sufficient degrees of freedom to correct altitude layers individually, resulting in an averaged correction across the entire FoV. In this work, we introduce alternative, intelligent control schemes to explore options for overcoming current limitations in GLAO.
Instrument rotators provide high accuracy instrument rotation at a commanded angle to ensure telescope pupil tracking. Structural support and mechanical interfaces must be provided and services (electrical and communications subsystems) routed from the stationary platform to the rotating platform for heavy instruments (which can exceed 1,500 kg). Cannot transmit vibrations to instruments. The experience gained over the years in working with several types of rotators is summarized in this paper. Not only experimental methods, but also mechanical and control models have allowed us to understand the system in depth. The paper focuses on rotators with two servomotors working together to counteract backlash and rotators with directly coupled motors. For the latter, balanced and unbalanced loads are studied. The mechanical model used to control the servo is explained and analyzed. During the development of the study, different rotator work schedules will be investigated. Tracking will be the focus of the study. The HARMONI rotator and the QUIJOTE telescopes (telescopes built by the Spanish company IDOM) in operation at the Teide Observatory (Tenerife) will therefore be the focus of our attention.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450 nm to 2450 nm with resolving powers from 3500 to 18000 and spatial sampling from 60 mas to 4 mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. HARMONI is a work-horse instrument that provides efficient, spatially resolved spectroscopy of extended objects or crowded fields of view. The gigantic leap in sensitivity and spatial resolution that HARMONI at the ELT will enable promises to transform the landscape in observational astrophysics in the coming decade. The project has undergone some key changes to the leadership and management structure over the last two years. We present the salient elements of the project restructuring, and modifications to the technical specifications. The instrument design is very mature in the lead up to the final design review. In this paper, we provide an overview of the instrument's capabilities, details of recent technical changes during the red flag period, and an update of sensitivities.
The High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI) is planned as a first light instrument for the Extremely Large Telescope (ELT). The Instrument Control Electronics (ICE) subsystem plays a vital role in HARMONI, housing all control devices and ensuring they function optimally. However, limited space within the instrument necessitates a unique design approach for the electronic cabinets. This paper details the design of these bespoke cabinets, emphasizing the thermal analysis and insulation technologies implemented to maintain proper operating temperatures for the electronics within the compact instrument volume.
The European Solar Telescope (EST) is a 4.2-metre telescope that will be equipped with a multi-conjugate adaptive optics (MCAO) system to provide a high spatial resolution over a circular field of view with 60” diameter. The EST-MCAO testbed is a downscaled demonstrator of solar MCAO with similar requirements to those defined for EST. It has been designed and developed to identify and better understand the capabilities of this system. Before MCAO implementation, different AO configurations must be first evaluated in the testbed. Single conjugate adaptive optics for point-like sources has been identified as the first step towards MCAO for the EST. This configuration is based on the use of a deformable mirror with 820 actuators and a Shack-Hartmann wavefront sensor with 33x33 subapertures. The main objective of this paper is to present the results obtained in the EST-MCAO testbed when testing different phase reconstruction algorithms and closed-loop schemes to deal with SCAO for point-like sources. Center of gravity technique was proposed for local slope computation when using point-like sources. Both zonal and modal approaches, including SVD and their regularized least-squares versions, were evaluated and tested for the reconstruction. A closed-loop strategy based on a proportional-integral controller was initially proposed. The benefits of pseudo open-loop control were also evaluated. The performance of the algorithms was tested considering different seeing conditions. Finally, a comparison based on RMS wavefront error and Strehl Ratio was conducted.
Once the design phase of the Multi-Conjugated Adaptive Optics (MCAO) testbed for the European Solar Telescope (EST) is completed, the system has been assembled and integrated at the Instituto de Astrofísica de Canarias (IAC). The aim of this highly configurable optical testbed is to study different solar adaptive optics solutions, including Single Conjugated Adaptive Optics (SCAO), Ground Layer Adaptive Optics (GLAO), and MCAO. The testbed will be used to evaluate the performance of different wavefront sensing and correction strategies. It consists of different subsystems that are being integrated with high precision by using optomechanical elements mostly developed at IAC. The testbed emulates a 4-m telescope with a Field of View (FoV) of 70 arcseconds. It currently operates as a SCAO configuration consisting of: an illumination system with point-like and extended source capability coupled with a configurable turbulence simulator based on Phase Screens (PS); a pupil-conjugated Deformable Mirror (DM) with 820 actuators; a high order Shack-Hartmann Wavefront Sensor (SH-WFS) with 33 subapertures across the pupil, which measures on-axis aberrations with a FoV of 10 arcseconds; and the science detector. The next steps include the integration of the elements that will provide GLAO and MCAO capabilities, such as two SH-WFSs with a FoV of 70 arcseconds, and two DMs conjugated to different atmospheric layers. This contribution describes the optomechanical components designed and the alignment procedure carried out to set up each subsystem and configuration to be studied.
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.
HARMONI is the first light, adaptive optics assisted, integral field spectrograph for the European Southern Observatory’s Extremely Large Telescope (ELT). A work-horse instrument, it provides the ELT’s diffraction limited spectroscopic capability across the near-infrared wavelength range. HARMONI will exploit the ELT’s unique combination of exquisite spatial resolution and enormous collecting area, enabling transformational science. The design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, and provide a summary of the instrument’s design. We also include recent changes to the project, both technical and programmatic, that have resulted from red-flag actions. Finally, we outline some of the simulated HARMONI observations currently being analyzed.
HARMONI is the Extremely Large Telescope visible and near infrared integral field spectrograph and will be one of the first light instruments. The instrument supports four operational modes called No Adaptive Optics (NOAO), Single Conjugated Adaptive Optics (SCAO), High Contrast Adaptive Optics (HCAO), and Laser Tomography Adaptive Optics (LTAO). These operational modes are closely related to the wavefront correction topology used to support the performance required for each of the science cases. By following a novel function model-based systems engineering (FBSE) methodology in conjunction with observing the software computer system golden rule of design; namely having tight cohesion within software modules and loose coupling between modules, a system architecture has emerged. In this paper, we present the design of the HARMONI Control System (HCS). Although this is not the first time (for example NACO on VLT and NIRC2 on Keck) that the adaptive optics required to correct the atmospheric turbulence is part of a general instrument design, and not tailored for a very specific science case, this will be the first instrument of this size and complexity in the era of extremely large ground-based telescopes. The instrument control design must be compatible with the ELT instrument control system framework while there is also an expectation that the adaptive optics (AO) real-time computer toolkit (RTC-TK) should be used for the realization of the AO real-time control software and hardware. The HCS is composed of the instrument control electronics (ICE), the Instrument Control System (ICS), and the AO Control Sub-system (AOCS). The operation concept of the instrument is also novel in that for each mode the instrument creates an instantiation of a virtual system composed of only the system blocks required to provide the selected mode of operation. Therefore, each mode supports a unique system composition in terms of hardware, software, and the sequencing of activities.
The performance of the “weighted Fourier phase slope” centroiding algorithm at the subpupil image of a Shack–Hartmann wavefront sensor for point-like astronomical guiding sources is explored. This algorithm estimates the image’s displacement in the Fourier domain by directly computing the phase slope at several spatial frequencies, without the intermediate step of computing the phase; it then applies optimized weights to the phase slopes at each spatial frequency obtained by a Bayesian estimation method. The idea was inspired by cepstrum deconvolution techniques, and this relationship is illustrated. The algorithm’s tilt estimation performance is characterized and contrasted with other known centroiding algorithms, such as thresholded centre of gravity (TCoG) and cross correlation (CC), first through numerical simulations at the subpupil level, then at the pupil level, and finally at the laboratory test bench. Results show a similar sensitivity to that of the CC algorithm, which is superior to that of the TCoG algorithm when large fields of view are necessary, i.e., in an open-loop configured adaptive optics system, thereby increasing the guide star limiting magnitude by 0.6 to 0.7 mag. On the other side, its advantage over the CC algorithm is its lower computational cost by approximately an order of magnitude.
This paper reviews the EDiFiSE (Equalized and Diffraction-limited Field Spectrograph Experiment) full-FPGA (Field Programmable Gate Array) adaptive optics (AO) system and presents its first laboratory results. EDiFiSE is a prototype equalized integral field unit (EIFU) spectrograph for the observation of high-contrast systems in the Willian Herschel Telescope (WHT). Its AO system comprises two independent parallel full-FPGA control loops, one for tip-tilt and one for higher order aberrations. Xilinx's Virtex-4 and Virtex-5 FPGA's fixed point arithmetic and their interfacing with the rest of the AO components and the user have been adequately dealt with, and a very deterministic system with a negligible computational delay has been obtained. The AO system has been recently integrated in laboratory and verified using the IACAT (IAC Atmosphere and Telescope) optical ground support equipment. Closed loop correction bandwidths of 65 Hz for the tip-tilt and 25 Hz for higher order aberrations are obtained. The system has been tested in the visible range for the WHT with a 9 x 9 subpupil configuration, low star magnitude, wind speeds up to 10 m/s and Fried parameter down to 18 cm, and a resolution below the EIFU’s fiber section has been obtained.
EDIFISE is a technology demonstrator instrument developed at the Institute of Astrophysics of the Canary Islands
(IAC), intended to explore the feasibility of combining Adaptive Optics with attenuated optical fibers in order to obtain
high spatial resolution spectra at the surroundings of a star, as an alternative to coronagraphy. A simplified version with
only tip tilt correction has been tested at the OGS telescope in Observatorio del Teide (Canary islands, Spain) and a
complete version is intended to be tested at the OGS and at the WHT telescope in Observatorio del Roque de los
Muchachos, (Canary Islands, Spain).
This paper describes the FPGA-based real time control of the High Order unit, responsible of the computation of the
actuation values of a 97-actuactor deformable mirror (11x11) with the information provided by a configurable wavefront
sensor of up to 16x16 subpupils at 500 Hz (128x128 pixels). The reconfigurable logic hardware will allow both zonal
and modal control approaches, will full access to select which mode loops should be closed and with a number of
utilities for influence matrix and open loop response measurements. The system has been designed in a modular way to
allow for easy upgrade to faster frame rates (1500 Hz) and bigger wavefront sensors (240x240 pixels), accepting also
several interfaces from the WFS and towards the mirror driver.
The FPGA-based (Field Programmable Gate Array) real time controller provides bias and flat-fielding corrections,
subpupil slopes to modal matrix computation for up to 97 modes, independent servo loop controllers for each mode with
user control for independent loop opening or closing, mode to actuator matrix computation and non-common path
aberration correction capability. It also provides full housekeeping control via UPD/IP for matrix reloading and full
system data logging.
This communication reviews the participation of the Instituto de Astrofísica de Canarias (IAC) in the design of the
European Solar Telescope. Apart of being the coordinator institution of the whole project, and, as such, responsible for
the project managing, the IAC leads several tasks like overall instrument definition or characterization of the
atmospheric turbulence profile with height or the definition of adequate detectors. More in particular, the IAC will
design and build two long-base SHABAR (SHAdow BAnd Ranger), instruments to measure medium-altitude seeing.
The IAC is also responsible for the design, together with other institutions, of the design of grating spectropolarimeters
suitable for multiwavelength high spatial and spectral resolution.
KEYWORDS: Sensors, Control systems, Mirrors, Actuators, Control systems design, Telescopes, Segmented mirrors, Prototyping, Computer simulations, Sensing systems
Within the preliminary developments related to the Gran Telescopio Canarias, a test rig is being designed for the active control of the support system of the segmented primary mirror. The construction of this test rig will be divided in two phases: the first one will basically consist in the implementation and testing of a displacement sensor prototype as well as an actuator prototype. Phase 2 will consist in the development and characterization of the whole test rig, including two segment simulators and a number of displacement sensors and actuators. Also, a non contact optical system for the test rig behavior verification will be constructed during phase 2. This paper presents the conceptual design adopted for the active control system proposed for the telescope and a brief description of the development program, including the requirements of the displacement sensors and actuators. We intend the test rig not only for testing the active control system components, but also for checking different control strategies.
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