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 New Adaptive Optics Module for Interferometry (NAOMI) is ready to be installed at the 1.8-metre Auxiliary Telescopes (ATs) at ESO Paranal. NAOMI will make the existing interferometer performance less dependent on the seeing conditions. Fed with higher and more stable Strehl, the fringe tracker will achieve the fringe stability necessary to reach the full performance of the second-generation instruments GRAVITY and MATISSE. All four ATs will be equipped between September and November 2018 with a Deformable mirror (ALPAO DM-241), a 4*4 Shack– Hartmann adaptive optics system operating in the visible and an RTC based on SPARTA Light. During the last 6 months thorough system test has been made in laboratory to demonstrate the Adaptive Optics and chopping capability of NAOMI.
The near-infrared GRAVITY instrument has become a fully operational spectro-imager, while expanding its capability to support astrometry of the key Galactic Centre science. The mid-infrared MATISSE instrument has just arrived on Paranal and is starting its commissioning phase. NAOMI, the new adaptive optics for the Auxiliary Telescopes, is about to leave Europe for an installation in the fall of 2018. Meanwhile, the interferometer infrastructure has continuously improved in performance, in term of transmission and vibrations, when used with both the Unit Telescopes and Auxiliary Telescopes. These are the highlights of the last two years of the VLTI 2nd generation upgrade started in 2015.
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 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.
The New Adaptive Optics Module for Interferometry (NAOMI) will be developed for and installed at the 1.8-metre Auxiliary Telescopes (ATs) at ESO Paranal. The goal of the project is to equip all four ATs with a low-order Shack– Hartmann adaptive optics system operating in the visible. By improving the wavefront quality delivered by the ATs for guide stars brighter than R = 13 mag, NAOMI will make the existing interferometer performance less dependent on the seeing conditions. Fed with higher and more stable Strehl, the fringe tracker(s) will achieve the fringe stability necessary to reach the full performance of the second-generation instruments GRAVITY and MATISSE.
ESO is undertaking a large upgrade of the infrastructure on Cerro Paranal in order to integrate the 2nd generation of interferometric instruments Gravity and MATISSE, and increase its performance. This upgrade started mid 2014 with the construction of a service station for the Auxiliary Telescopes and will end with the implementation of the adaptive optics system for the Auxiliary telescope (NAOMI) in 2018. This upgrade has an impact on the infrastructure of the VLTI, as well as its sub-systems and scientific instruments.
Model Based Systems Engineering (MBSE) is an emerging field of systems engineering for which the System Modeling Language (SysML) is a key enabler for descriptive, prescriptive and predictive models. This paper surveys some of the capabilities, expectations and peculiarities of tools-assisted MBSE experienced in real-life astronomical projects. The examples range in depth and scope across a wide spectrum of applications (for example documentation, requirements, analysis, trade studies) and purposes (addressing a particular development need, or accompanying a project throughout many - if not all - its lifecycle phases, fostering reuse and minimizing ambiguity). From the beginnings of the Active Phasing Experiment, through VLT instrumentation, VLTI infrastructure, Telescope Control System for the E-ELT, until Wavefront Control for the E-ELT, we show how stepwise refinements of tools, processes and methods have provided tangible benefits to customary system engineering activities like requirement flow-down, design trade studies, interfaces definition, and validation, by means of a variety of approaches (like Model Checking, Simulation, Model Transformation) and methodologies (like OOSEM, State Analysis)
The New Adaptive Optics Module for Interferometry (NAOMI)<sup>1</sup> is the future low order adaptive optics system to be developed for and installed at the ESO 1.8 m Auxiliary Telescopes (ATs). The four ATs<sup>2</sup> are designed for interferometry which they are essentially dedicated for. Currently the AT’s are equipped with a fast, visible tip-tilt sensor called STRAP<sup>3</sup> (System for Tip/tilt Removal with Avalanche Photodiodes), and the corrections are applied through a tip-tilt mirror. The goal is to equip all four ATs with a low-order Shack-Hartmann system operating in the visible for the VLTI dual feed light beams in place of the current tip-tilt correction. Because of the limited size of the ATs (1.8m diameter), a low-order system will be sufficient. The goal is to concentrate the energy into a coherent core and to make the encircled energy (into the single mode fibers) stable and less dependent on the atmospheric conditions in order to increase the sensitivity of the interferometric instruments. The system will use the ESO real time computer platform Sparta-light as the baseline. This paper presents the preliminary design concept and outlines the benefits to current and future VLTI instruments.
In the summer of 2011, the first on-sky astrometric commissioning of PRIMA-Astrometry delivered a performance of 3 m″ for a 10 ″ separation on bright objects, orders of magnitude away from its exoplanet requirement of 50 μ″ ~ 20 μ″ on objects as faint as 11 mag ~ 13 mag in K band. This contribution focuses on upgrades and characterizations carried out since then. The astrometric metrology was extended from the Coudé focus of the Auxillary Telescopes to their secondary mirror, in order to reduce the baseline instabilities and improve the astrometric performance. While carrying out this extension, it was realized that the polarization retardance of the star separator derotator had a major impact on both the astrometric metrology and the fringe sensors. A local compensation of this retardance and the operation on a symmetric baseline allowed a new astrometric commissioning. In October 2013, an improved astrometric performance of 160 μ″ was demonstrated, still short of the requirements. Instabilities in the astrometric baseline still appear to be the dominating factor. In preparation to a review held in January 2014, a plan was developed to further improve the astrometric and faint target performance of PRIMA Astrometry. On the astrometric aspect, it involved the extension of the internal longitudinal metrology to primary space, the design and implementation of an external baseline metrology, and the development of an astrometric internal fringes mode. On the faint target aspect, investigations of the performance of the fringe sensor units and the development of an AO system (NAOMI) were in the plan. Following this review, ESO decided to take a proposal to the April 2014 STC that PRIMA be cancelled, and that ESO resources be concentrated on ensuring that Gravity and Matisse are a success. This proposal was recommended by the STC in May 2014, and endorsed by ESO.
We present the latest update of the European Southern Observatory's Very Large Telescope interferometer (VLTI). The operations of VLTI have greatly improved in the past years: reduction of the execution time; better offering of telescopes configurations; improvements on AMBER limiting magnitudes; study of polarization effects and control for single mode fibres; fringe tracking real time data, etc. We present some of these improvements and also quantify the operational improvements using a performance metric. We take the opportunity of the first decade of operations to reflect on the VLTI community which is analyzed quantitatively and qualitatively. Finally, we present briefly the preparatory work for the arrival of the second generation instruments GRAVITY and MATISSE.
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and
the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in
northern Chile. The two VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the
operation, the instruments developments are pursued, and new modes are studied and commissioned to offer
a wider range of scientific possibilities to the community and increase sensitivity. New configurations of the
ATs have been offered and are frequently discussed with the science users of the VLTI and implemented to
optimize the scientific return. The PRIMA instrument, bringing astrometry capability to the VLTI and phase
referencing to the instruments is being commissioned. The visitor instrument PIONIER is now fully operational
and bringing imaging capability to the VLTI.
The current status of the VLTI is described with successes and scientific results, and prospects on future
evolution are presented.
The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope
Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Since January 2011 the
integration and individual testing of the different subsystem has come to a necessary minimum. At the same
time the astrometric commissioning phase has begun.
In this contribution we give an update on the status of the facility and present some highlights and difficulties
on our way from first dual-feed fringe detection to first astrometric measurements. We focus on technical and
operational aspects. In particular, within the context of the latter we are going to present a modified mode of
operation that scans across the fringes. We will show that this mode, originally only intended for calibration
purposes, facilitates the detection of dual-fringes.
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four
1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two
VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the operation, the instruments
developments are pursued, and new modes are studied and commissioned to offer a wider range of scientific possibilities
to the community. New configurations of the ATs array are discussed with the science users of the VLTI and
implemented to optimize the scientific return. The monitoring and improvement of the different systems of the VLTI is a
continuous work. The PRIMA instrument, bringing astrometry capability to the VLTI and phase referencing to the
instruments has been successfully installed and the commissioning is ongoing. The possibility for visiting instruments
has been opened to the VLTI facility.
The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope
Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Most of the tests have been
concentrated on the characterization of the Fringe Sensor Unit (FSU) and on the automation of the fringe
tracking in preparation of dual-field observations. The status of the facility, an analysis of the FSU performance
and the first attempts towards dual-field observations will be presented in this paper. In the FSU, the phase
information is spatially encoded into four independent combined beams (ABCD) and the group delay comes from
their spectral dispersion over 5 spectral channels covering the K-band. During fringe tracking the state machine
of the optical path difference controller is driven by the Signal to Noise Ratio (SNR) derived from the 4 ABCD
measurements. We will describe the strategy used to define SNR thresholds depending on the star magnitude
for automatically detecting and locking the fringes. Further, the SNR as well as the phase delay measurements
are affected by differential effects occurring between the four beams. We will shortly discuss the contributions
of these effects on the measured phase and SNR noises. We will also assess the sensitivity of the group delay
linearity to various instrumental parameters and discuss the corresponding calibration procedures. Finally we
will describe how these calibrations and detection thresholds are being automated to make PRIMA as much as
possible a user-friendly and efficient facility.
ESPRI is a project which aims at searching for and characterizing extra-solar planets by dual-beam astrometry with
PRIMA@VLTI. Differential Delay Lines (DDL) are fundamental for achieving the micro-arcseconds accuracy required
by the scientific objective. Our Consortium, consisting of the Geneva Observatory, the Max-Planck Institut for
Astronomy Heidelberg, and the Landessternwarte Heidelberg, in collaboration with ESO, has built and tested these
DDLs successfully and will install them in summer 2008 at the VLTI. These DDLs consist of high quality cat's eyes
displaced on a parallel beam-mechanics and by means of a two-stage actuation with a precision of 5 nm over a stroke
length of 70 mm. Over the full range, a bandwidth of about 400 Hz is achieved. The DDLs are operated in vacuum. We
shall present, in this paper, their design and their exceptional performances.
PRIMA, the instrument for Phase-Referenced Imaging and Micro-arcsecond Astrometry at the VLTI, is currently being
developed at ESO. PRIMA will implement the dual-feed capability, at first for two UTs or ATs, to enable simultaneous
interferometric observations of two objects that are separated by up to 1 arcmin. PRIMA is designed to perform narrow-angle
astrometry in K-band with two ATs as well as phase-referenced aperture synthesis imaging with instruments like
Amber and Midi. In order to speed up the full implementation of the 10 microarcsec astrometric capability of the VLTI
and to carry out a large astrometric planet search program, a consortium lead by the Observatoire de Genève, Max
Planck Institute for Astronomy, and Landessternwarte Heidelberg, has built Differential Delay Lines for PRIMA and is
developing the astrometric observation preparation and data reduction software. When the facility becomes fully
operational in 2009, we will use PRIMA to carry out a systematic astrometric Exoplanet Search program, called ESPRI.
In this paper, we describe the narrow-angle astrometry measurement principle, give an overview of the ongoing hardand
software developments, and outline our anticipated astrometric exoplanet search program.
The Workstation Software Framework (WSF) is a state machine model driven development toolkit designed to generate
event driven applications based on ESO VLT software. State machine models are used to generate executables. The
toolkit provides versatile code generation options and it supports Mealy, Moore and hierarchical state machines.
Generated code is readable and maintainable since it combines well known design patterns such as the State and the
Template patterns. WSF promotes a development process that is based on model reusability through the creation of a
catalog of state machine patterns.
The Very Large Telescope Interferometer (VLTI)<sup>1</sup> that coherently combines the four VLT 8.2-m Unit Telescopes (UT's) is on the point to be fully equipped with its dedicated array of Auxiliary Telescopes (AT's). This array includes four 1.8-m telescopes which can be relocated on thirty observing stations distributed on the top of the Paranal Observatory. This array, albeit less sensitive than the array of UT's, is a key element for the scientific operation of the VLTI. Indeed, it will provide the best imaging capability thanks to the many possible baselines (up to 200m), it will be used for the Narrow Angle Astrometry mode which requires long term monitoring and the longest baselines not accessible with the UT's, and it will enable full-time use of the VLTI facilities even when the UT's are used for stand-alone observation.
The Auxiliary Telescopes have been designed, manufactured and tested in Europe by the company AMOS (Belgium) under ESO contract. After acceptance in Europe, ESO takes over the responsibility for the transport to Paranal, reassembly and final commissioning. Currently the first three AT's have been put into operation on Paranal while the fourth one is scheduled to arrive at the observatory in August 2006.
This paper presents the actual performances of the Auxiliary Telescopes, as measured during the commissioning of the first three AT's. An emphasis is given to the requirements dictated by the interferometer needs, including the ease and accuracy with which the telescopes can be relocated, the excellent image quality, and the nanometer-level stability for Optical Path Length.
PRIMA, the Phase-Referenced Imaging and Micro-arcsecond Astrometry facility for the Very Large Telescope Interferometer, is now nearing the end of its manufacturing phase. An intensive test period of the various sub-systems (star separators, fringe sensor units and incremental metrology) and of their interactions in the global system will start in Garching as soon as they are delivered. The status and performances of the individual sub-systems are presented in this paper as well as the proposed observation and calibration strategy to reach the challenging goal of high-accuracy differential astrometry at 10 μas level.
In the framework of the Phase-Referenced Imaging and Micro-arcsecond Astrometry facility (PRIMA) developed for the Very Large Telescope Interferometer (VLTI), a sophisticated opto-mechanical system has been developed by TNO-TPD. It will be placed at the Coudé focus of the telescopes and will allow picking up two stars anywhere in a 2 arcmin field-of-view and collimating their light into two beams that will propagate through the rest of the interferometer toward the instrument. These Star Separator systems have a very high optical quality, fast and accurate pointing and chopping, independent high speed remote control of the beam tip-tilt and of the pupil position. They are very rigid, accurate mechanical systems non-sensitive to temperature variations The Star Separator systems are described in this paper.
The Very Large Telescope Interferometer (VLTI) on Cerro Paranal (2635 m) in Northern Chile reached a major milestone in September 2003 when the mid infrared instrument MIDI was offered for scientific observations to the community. This was only nine months after MIDI had recorded first fringes. In the meantime, the near infrared instrument AMBER saw first fringes in March 2004, and it is planned to offer AMBER in September 2004.
The large number of subsystems that have been installed in the last two years - amongst them adaptive optics for the 8-m Unit Telescopes (UT), the first 1.8-m Auxiliary Telescope (AT), the fringe tracker FINITO and three more Delay Lines for a total of six, only to name the major ones - will be described in this article. We will also discuss the next steps of the VLTI mainly concerned with the dual feed system PRIMA and we will give an outlook to possible future extensions.