The ELT primary mirror is a 39m diameter concave mirror composed of 798 mirror segments. Each mirror segment is equipped with edge sensors, position actuators and a surface deformation warping harness, independently controlled by their backend electronics. The controllers are mounted in cabinets grouping up to seven segments. Each cabinet contains a network switch and a PLC for power control, telemetry and auxiliary tasks. There are in total 132 cabinets, named segment concentrators, grouped in six sectors. This constitutes a system of more than 2600 networked endpoints, including micro controllers, PLCs and network switches, to be controlled and supervised.
The M1 Local Control System (LCS) is the subsystem of the ELT responsible for the monitoring and control of M1 segments. Its main goal is to enable the phasing of the M1 mirror to compensate for the presence of disturbances such as changing gravity vector, thermal expansion and wind forces. M1 LCS will provide a reliable and deterministic infrastructure to collect edge sensor and position actuators measurements and to distribute new position references at a frequency of 500 Hz. In addition, the software is responsible for devices synchronization, monitoring, configuration management as well as failure detection, isolation and notification.
The M1 LCS passed its final design review and the development commenced. The present paper summarizes the M1 LCS software design, including adopted patterns and technologies, and the current development status.
The construction of a diffraction limitable telescope as large as the ESO’s ELT is enabled by its embedded deformable quaternary mirror. Besides its essential function in the telescope control, M4 also contributes to compensating the free atmosphere aberrations for all post-focal AO applications. The paper presents how the telescope manages M4 to maintain its optical performance while offering to the instruments a clean wavefront interface, supporting the desired AO functionalities. The paper reviews the telescope strategy to derive its wavefront dynamic properties directly from the analysis of the control data collected in science mode, with the goal to minimize the observatory time spent on dedicated wavefront calibration tasks.
In the last years the ELT Program has entered construction phase. For the large 39 meter segmented primary mirror unit with thousands of components this means that the start of the series production is getting closer, where the final hardware will be built. The M1 Unit has been broken down in products and a procurement strategy has been developed. Most of the major design decisions have been frozen and component specifications have been settled. Most of the suppliers have already been selected and contracts have been kicked off. This paper describes the ELT M1 Unit product breakdown and the procurement baseline for each product and its status. The production contracts would not have been possible without intense prototyping and verification strategies independent of the component contracts. Therefore, the paper also takes a look back at the prototypes and de-risking strategies, which had been put in place to prepare for construction phase. Ramping up the construction contracts involves finishing design details for some products while setting up production lines for others. This requires controlling interfaces and cross-contract dependencies, a challenge described in this paper. For continuous de-risking similar verification strategies than during the design phase are planned in parallel with the production until telescope assembly, integration and verification. These measures will increase confidence in the design choices, allow early discovery of remaining design flaws and provide training means for assembly and integration long time before all components of the ELT M1 are complete and being installed on Cerro Armazones in Chile. The paper will also give an outlook on these running and planned activities.
The Extremely Large Telescope (ELT) is a 39 meters optical telescope under construction at an altitude of about 3000m in the Chilean Atacama desert. The optical design is based on a novel five-mirror scheme and incorporates adaptive optics mirrors. The primary mirror consists of 798 segments, each 1.4 meters wide. The architecture of the control system is split in layers and in a high number of subsystems/components developed by different parties. This implies a high number of interfaces that must be designed and maintained under configuration control, to ensure a flawless integration of the different parts. Having interfaces (and data) definitions in a flexible central place allows us to extract several different artifacts (for example Interface Control Documents (ICDs), Interface Definition Language (IDL) files, tabular spreadsheets, help files, other generated code formats like code stubs or state machine implementations). In this paper, we explain how selecting a graphical modeling language like SysML and using graphical and tabular editing features made available by state of the art modeling tools presents a number of advantages with respect to other solutions like spreadsheets, a relational database, or a custom textual DSL. Still, using standard export/import formats (EMF XMI), we do not bind ourselves to a specific vendor. We describe the workflow that we have identified for the definition of interfaces, what artifacts we want to automatically produce and why. We also describe what technologies we are using to reach these objectives. A key aspect of this work is the selection of interface design patterns that are formal enough to allow automatic generation of the artifacts and, at the same time, pragmatic and simple to gain acceptance from all users and not incur in overhead.
The Extremely Large Telescope (ELT) is a 39 meters optical telescope under construction at an altitude of about 3000m in the Chilean Atacama desert. The optical design is based on a novel five-mirror scheme and incorporates adaptive optics mirrors. The primary mirror consists of 798 segments, each 1.4 meters wide. The control of this telescope and of the instruments that will be mounted on it is very challenging, because of its size, the number of sensors and actuators, the computing performance required for the phasing of the primary mirror, the adaptive optics and the correlation between all the elements in the optical path. In this paper we describe the control system architecture, emerging from scientific and technical requirements. We also describe how the procurement strategy (centered on industrial contracts at subsystem level) affects the definition of the architecture and the technological choices. We first introduce the global architecture of the system, with Local Control Systems and a Supervisory Control layer. The Local Control Systems is astronomy-agnostic and isolate the control of the subsystems procured through industrial contracts. The Supervisory Control layer is instead responsible for coordinating the operation of the different subsystems to realize the observation cases identified for the operation of the telescope. The control systems of the instruments interface with the telescope using a well-defined and standardized interface. To facilitate the work of the Consortia responsible for the construction of the instruments, we provide an Instrumentation Control Software Framework. This will ensure uniformity in the design of the control systems across instruments, making maintenance easier. This approach was successfully adopted for the instrumentation of the Very Large Telescope facility. We will analyze the process that was followed for defining the architecture from the requirements and use cases and to produce a design that addresses the technical challenges.
We present an optomechanical test bench setup (MELT) for testing and validating key functionalities to be used on the Extremely Large Telescope (ELT) during the periods of system verification, wavefront control commissioning, through the handover to science, up to regular diagnostic, monitoring, and validation tasks during operations. <p> </p>The main objectives of MELT are to deploy and validate the telescope control system, to deploy and validate wavefront control algorithms for commissioning and operations, as well as to produce and validate key requirements for the phasing and diagnostic station (PDS) of the ELT.<p> </p> The purpose of MELT is to deploy optomechanical key components such as a segmented primary mirror, a secondary mirror on a hexapod, an adaptive fourth mirror, and a fast tip/tilt mirror together with their control interfaces that emulate the real telescope optomechanical conditions. The telescope control system, deployed on MELT can test control schemes with the active mounts emulating the real ELT optomechanical control interfaces. <p> </p>The presented optomechanical setup uses the Active Segmented Mirror (ASM) with its piezo-driven 61 segments and a diameter of 15 cm. It was designed, built, and used on sky during the Active Phasing Experiment (APE). <p> </p>Several beam paths after the telescope optical train on MELT are conditioned and guided to wavefront sensors and cameras, sensitive to wavelength bands in the visible and infrared to emulate wavefront commissioning and phasing tasks. This optical path resembles part of the phasing and diagnostics station (PDS) of the ELT, which is used to acquire the first star photons through the ELT and to learn the usage and control of all the ELT optomechanics. The PDS will be developed, designed, and built in-house at ESO. MELT helps its design by providing a detailed test setup for defining and deploying system engineering tasks, such as detailed functional analysis, definition of tasks to be carried out, and technical requirements, as well as operational commissioning aspects. <p> </p>The bench test facility MELT will in the end help us to be as much as possible prepared when the telescope sends the first star light through the optical train to be able to tackle the unforeseeable problems and not be caught up with the foreseeable ones.
The primary mirror of the E-ELT is composed of 798 hexagonal segments of about 1.45 meters across. Each segment can be moved in piston and tip-tilt using three position actuators. Inductive edge sensors are used to provide feedback for global reconstruction of the mirror shape. The E-ELT M1 Local Control System will provide a deterministic infrastructure for collecting edge sensor and actuators readings and distribute the new position actuators references while at the same time providing failure detection, isolation and notification, synchronization, monitoring and configuration management. The present paper describes the prototyping activities carried out to verify the feasibility of the E-ELT M1 local control system communication architecture design and assess its performance and potential limitations.
In this paper we will briefly revisit the optical vibration measurement system (OVMS) at the Large Binocular Telescope (LBT) and how these values are used for disturbance compensation and particularly for the LBT Interferometer (LBTI) and the LBT Interferometric Camera for Near-Infrared and Visible Adaptive Interferometry for Astronomy (LINC-NIRVANA). We present the now centralized software architecture, called OVMS+, on which our approach is based and illustrate several challenges faced during the implementation phase. Finally, we will present measurement results from LBTI proving the effectiveness of the approach and the ability to compensate for a large fraction of the telescope induced vibrations.
For highly segmented primary mirrors, as that of the European Extremely Large Telescope (E-ELT) with its 798 segments, the capability to update regularly the optical phasing solution is essential for robust operations. The duration of standard phasing procedures is driven by the difficulty of maintaining the registration of the image of the primary on the phasing sensor with tolerances of ~0.02% of the mirror diameter. The paper describes a re-phasing procedure with a dynamic range of about ±1.5 microns. This is based on a standard Shack-Hartmann phasing sensor operated at 2 narrow bands filters with wavelength separation of 30%. Controlled registration offsets are applied during the acquisitions, allowing the registration parameters to be estimated from the phasing data. The procedure has been successfully validated at the Gran Telescopio de Canarias (GTC).
During the last 2 years ESO has operated the “M1 Test Facility”, a test stand consisting of a representative section of the E-ELT primary mirror equipped with 4 complete prototype segment subunits including sensors, actuators and control system. The purpose of the test facility is twofold: it serves to study and get familiar with component and system aspects like calibration, alignment and handling procedures and suitable control strategies on real hardware long before the primary mirror (hereafter M1) components are commissioned. Secondly, and of major benefit to the project, it offered the possibility to evaluate component and subsystem performance and interface issues in a system context in such detail, that issues could be identified early enough to feed back into the subsystem and component specifications. This considerably reduces risk and cost of the production units and allows refocusing the project team on important issues for the follow-up of the production contracts. Experiences are presented in which areas the results of the M1 Test Facility particularly helped to improve subsystem specifications and areas, where additional tests were adopted independent of the main test facility. Presented are the key experiences of the M1 Test Facility which lead to improved specifications or identified the need for additional testing outside of the M1 Test Facility.
The fifth mirror of the European Extremely Large Telescope optical train is a field stabilization tip/tilt unit responsible for correcting the dynamical tip and tilt caused mainly by wind load on the telescope. A scale-one prototype including the inclined support, the fixed frame and a basic control system was designed and manufactured by NTE-SENER (Spain) and CSEM (Switzerland) as part of the prototyping and design activities. All interfaces to the mirror have been reproduced on a dummy structure reproducing the inertial characteristics of the optical element. The M5 unit is required to have sufficient bandwidth for tip/tilt reference commands coming from the wavefront control system. Such a bandwidth can be achieved using local active damping loop to damp the low frequency mechanical modes before closing a position loop. Prototyping on the M5 unit has been undertaken in order to demonstrate the E-ELT control system architecture, concepts and development standards and to further study active damping strategies. The control system consists of two nested loops: a local damping loop and a position loop. The development of this control system was undertaken following the E-ELT control system development standards in order to determine their applicability and performance and includes hardware selection, communication, synchronization, configuration, and data logging. In this paper we present the current status of the prototype M5 control system and the latest results on the active damping control strategy, in particular the promising results obtained with the method of positive position feedback.
This paper aims at giving an update on the most versatile Adaptive Optics fed instrument to date, the well
known and successful NACO*. Although NACO is only scheduled for about two more years<sup>†</sup> at the Very Large
Telescope (VLT), it keeps on evolving with additional operation modes bringing original astronomical results.
The high contrast imaging community uses it creatively as a test-bench for SPHERE<sup>‡</sup> and other second generation
planet imagers. A new visible wavefront sensor (WFS) optimized for Laser Guide Star (LGS) operations has
been installed and tested, the cube mode is more and more required for frame selection on bright sources, a
seeing enhancer mode (no tip/tilt correction) is now offered to provide full sky coverage and welcome all kind
of extragalactic applications, etc. The Instrument Operations Team (IOT) and Paranal engineers are currently
working hard at maintaining the instrument overall performances but also at improving them and offering new
capabilities, providing the community with a well tuned and original instrument for the remaining time it is
being used. The present contribution delivers a non-exhaustive overview of the new modes and experiments that
have been carried out in the past months.
The new operational mode of aperture masking interferometry has been added to the CONICA camera which
lies downstream of the Adaptive Optics (AO) corrected focus provided by NAOS on the VLT-UT4 telescope.
Masking has been shown to deliver superior PSF calibration, rejection of atmospheric noise and robust recovery
of phase information through the use of closure phases. Over the resolution range from about half to several
resolution elements, masking interferometry is presently unsurpassed in delivering high fidelity imaging and
direct detection of faint companions. Here we present results from commissioning data using this powerful new
operational mode, and discuss the utility for masking in a variety of scientific contexts. Of particular interest is
the combination of the CONICA polarimetry capabilities together with SAM mode operation, which has revealed
structures never seen before in the immediate circumstellar environments of dusty evolved stars.
We have developed an PSF reconstruction algorithm for the NAOS adaptive optics system that is coupled with CONICA at ESO/VLT. We have modified the algorithm of Véran et al. (1997), originally written for PUEO at CFHT, to make use of the specific real-time wavefront-related data that observers with NACO receive together with their scientific images. In addition, we use the Vii algorithm introduced by Clénet et al. (2006) and Gendron et al. (2006) instead of the Uij algorithm originally used by Véran et al. (1997).
Until now, tests on NAOS has been undertaken during technical time thanks to the NACO team at Paranal. A first test has been successfully performed to calibrate the orientation of reconstructed PSFs with respect to NACO images. We have also obtained two sets of PSF reconstruction test data with NACO in November 2006 and September 2007 to reconstruct PSFs. Discrepancies exist between the observed and reconstructed PSFs: their Strehl ratios are ~31% and ~39% respectively in Nov. 2006, ~31% and ~19% respectively in Sept. 2007. These differences may be at least partly explained by reconstructions that either did not account for the aliasing contribution or poorly estimated the noise contribution with the available noise information at that time.
We have additionally just started to test our algorithm using the AO bench Sésame, at LESIA. Results are promising but need to be extended to a larger set of atmospheric conditions or AO correction qualities.
The Laser Guide Star Facility (LGSF) is installed on the UT4 (Yepun) telescope at Paranal Observatory in Chile. On the
same telescope, two instruments are equipped with adaptive optics: an infrared spectro imager (CONICA) below the
adaptive optics module NAOS; and an integral field spectrograph (SINFONI). The LGSF is tuned to the sodium D2 line
to generate an artificial reference star, for both CONICA and SINFONI.
Although the LGSF is a complex laser system, rather different from the other instruments at Paranal, it has been
designed to run remotely without any hand-on tuning for a period of one week. The LGSF system has now been in
operation for several months, in conjunction with the Aircraft camera Avoidance System (AAS).
In this article, we report on the technical performance achieved by the LGSF in operational conditions. We also provide
a summary of the technical problems and operational constraints we have faced so far. We present the current operations
and maintenance procedures implemented at Paranal.
We also present the evolution of the human resources needed to operate and maintain the LGSF operational from
commissioning to routine operations.
Finally, we discuss possible improvements to reduce the workload to maintain and operate the LGSF.
All ESO Science Operations teams operate on Observing Runs, loosely defined as blocks of observing time on a specific instrument. Observing Runs are submitted as part of an Observing Proposal and executed in Service or Visitor Mode. As an Observing Run progresses through its life-cycle, more and more information gets associated to it: Referee reports, feasibility and technical evaluations, constraints, pre-observation data, science and calibration frames, etc. The Manager of Observing Runs project (Moor) will develop a system to collect operational information in a database, offer integrated access to information stored in several independent databases, and allow HTML-based navigation over the whole information set. Some Moor services are also offered as extensions to, or complemented by, existing desktop applications.
The European Southern Observatory (ESO) develops and maintains a large number of instrument-specific data processing pipelines. These pipelines must produce standard-format output and meet the need for data archiving and the computation and logging of quality assurance parameters. As the number, complexity and data-output-rate of instrument increases, so does the challenge to develop and maintain the associated processing software. ESO has developed the Common Pipeline Library (CPL) in order to unify the pipeline production effort and to minimise code duplication. The CPL is a self-contained ISO-C library, designed for use in a C/C++ environment. It is designed to work with FITS data, extensions and meta-data, and provides a template for standard algorithms, thus unifying the look-and-feel of pipelines. It has been written in such a way to make it extremely robust, fast and generic, in order to cope with the operation-critical online data reduction requirements of modern observatories. The CPL has now been successfully incorporated into several new and existing instrument systems. In order to achieve such success, it is essential to go beyond simply making the code publicly available, but also engage in training, support and promotion. There must be a commitment to maintenance, development, standards-compliance, optimisation, consistency and testing. This paper describes in detail the experiences of the CPL in all these areas. It covers the general principles applicable to any such software project and the specific challenges and solutions, that make the CPL unique.
The Data Flow System (DFS) for the ESO VLT provides a global approach to handle the flow of science related data in the VLT environment. It is a distributed system composed of a collection of components for preparation and scheduling of observations, archiving of data, pipeline data reduction and quality control. Although the first version of the system became operational in 1999 together with the first UT, additional developments were necessary to address new operational requirements originating from new and complex instruments which generate large amounts of data. This paper presents the hardware and software changes made to meet those challenges within the back-end infrastructure, including on-line and off-line archive facilities, parallel/distributed pipeline processing and improved association technologies.
The VLT Data Flow System (DFS) has been developed to maximize the scientific output from the operation of the ESO observatory facilities. From its original conception in the mid 90s till the system now in production at Paranal, at La Silla, at the ESO HQ and externally at home institutes of astronomers, extensive efforts, iteration and retrofitting have been invested in the DFS to maintain a good level of performance and to keep it up to date. In the end what has been obtained is a robust, efficient and reliable 'science support engine', without which it would be difficult, if not impossible, to operate the VLT in a manner as efficient and with such great success as is the case today. Of course, in the end the symbiosis between the VLT Control System (VCS) and the DFS plus the hard work of dedicated development and operational staff, is what made the success of the VLT possible. Although the basic framework of DFS can be considered as 'completed' and that DFS has been in operation for approximately 3 years by now, the implementation of improvements and enhancements is an ongoing process mostly due to the appearance of new requirements. This article describes the origin of such new requirements towards DFS and discusses the challenges that have been faced adapting the DFS to an ever-changing operational environment. Examples of recent, new concepts designed and implemented to make the base part of DFS more generic and flexible are given. Also the general adaptation of the DFS at system level to reduce maintenance costs and increase robustness and reliability and to some extend to keep it conform with industry standards is mentioned. Finally the general infrastructure needed to cope with a changing system is discussed in depth.