During the development of the VLT instrumentation program, ESO acquired considerable expertise in the area of infrared detectors, their testing and optimizing their performance. This can mainly be attributed to a very competent team and most importantly to the availability of a very well suited test facility, namely, IRATEC. This test facility was designed more than 15 years ago, specifically for 1K × 1K detectors such as the Aladdin device, with a maximum field of only 30 mm square. Unfortunately, this facility is no longer suited for the testing of the new larger format detectors that are going to be used to equip the future E-ELT instruments. It is projected that over the next 20 years, there will be of the order of 50-100 very large format detectors to be procured and tested for use with E-ELT first and second generation instruments and VLT third generation instruments. For this reason ESO has initiated the in-house design and construction of a dedicated new IR detector arrays test facility: the Facility for Infrared Array Testing (FIAT). It will be possible to mount up to four 60 mm square detectors in the facility, as well as mosaics of smaller detectors. It is being designed to have a very low thermal background such that detectors with 5.3 μm cut-off material can routinely be tested. The paper introduces the most important use cases for which FIAT is designed: they range from performing routine performance measurements on acquired devices, optimization setups for custom applications (like spot scan intra-pixel response, persistence and surface reflectivity measurements), test of new complex operation modes (e.g. high speed subwindowing mode for low order sensing, flexure control, etc.) and the development of new tests and calibration procedures to support the scientific requirements of the E-ELT and to allow troubleshooting the unexpected challenges that arise when a new detector system is brought online. The facility is also being designed to minimize the downtime required to change to a new detector and then cool it down, ready for testing. The status of the opto-mechanical and cryogenic design is also described in detail, with particular emphasis on the technical solutions identified to fulfill the FIAT top level requirements. We will also describe how the FIAT project has been set-up as a training facility for the younger generation of engineers who are expected to take over the job from the experienced engineers and ensure that the lessons learnt in so many years of successful IR instrumentation projects at ESO are captured for this next generation.
The Four Laser Guide Star Facility (4LGSF) is part of the ESO Adaptive Optics Facility, in which one of the VLT telescopes, UT4, is transformed in an adaptive telescope-equipped with a deformable secondary mirror, two adaptive optics systems at the Nasmyth focii and four sodium laser guide star modular units. In this paper we present the design, the assembly and validation test performed so far in Europe on the first laser guide star unit.
The Adaptive Optics Facility project is completing the integration of its systems at ESO Headquarters in Garching. The main test bench ASSIST and the 2<sup>nd</sup> Generation M2-Unit (hosting the Deformable Secondary Mirror) have been granted acceptance late 2012. The DSM has undergone a series of tests on ASSIST in 2013 which have validated its optical performance and launched the System Test Phase of the AOF. This has been followed by the performance evaluation of the GRAAL natural guide star mode on-axis and will continue in 2014 with its Ground Layer AO mode. The GALACSI module (for MUSE) Wide-Field-Mode (GLAO) and the more challenging Narrow-Field-Mode (LTAO) will then be tested. The AOF has also taken delivery of the second scientific thin shell mirror and the first 22 Watt Sodium laser Unit. We will report on the system tests status, the performances evaluated on the ASSIST bench and advancement of the 4Laser Guide Star Facility. We will also present the near future plans for commissioning on the telescope and some considerations on tools to ensure an efficient operation of the Facility in Paranal.
The ESO Adaptive Optics Facility (AOF) consists in an evolution of one of the ESO VLT unit telescopes to a laser
driven adaptive telescope with a deformable mirror in its optical train.
The project has completed the procurement phase and several large structures have been delivered to Garching
(Germany) and are being integrated (the AO modules GRAAL and GALACSI and the ASSIST test bench). The 4LGSF
Laser (TOPTICA) has undergone final design review and a pre-production unit has been built and successfully tested.
The Deformable Secondary Mirror is fully integrated and system tests have started with the first science grade thin shell
mirror delivered by SAGEM. The integrated modules will be tested in stand-alone mode in 2012 and upon delivery of
the DSM in late 2012, the system test phase will start. A commissioning strategy has been developed and will be updated
before delivery to Paranal. A substantial effort has been spent in 2011-2012 to prepare the unit telescope to receive the
AOF by preparing the mechanical interfaces and upgrading the cooling and electrical network. This preparation will also
simplify the final installation of the facility on the telescope.
A lot of attention is given to the system calibration, how to record and correct any misalignment and control the whole
facility. A plan is being developed to efficiently operate the AOF after commissioning. This includes monitoring a
relevant set of atmospheric parameters for scheduling and a Laser Traffic control system to assist the operator during the
night and help/support the observing block preparation.
The ESO Adaptive Optics Facility (AOF) consists in an evolution of one of the ESO VLT unit telescopes to a laser
driven adaptive telescope with a deformable mirror in its optical train, in this case the secondary 1.1m mirror, and four
Laser Guide Stars (LGSs). This evolution implements many challenging technologies like the Deformable Secondary
Mirror (DSM) including a thin shell mirror (1.1 m diameter and 2mm thin), the high power Na lasers (20W), the low
Read-Out Noise (RON) WaveFront Sensor (WFS) camera (< 1e-) and SPARTA the new generation of Real Time
Computers (RTC) for adaptive control. It also faces many problematic similar to any Extremely Large Telescope (ELT)
and as such, will validate many technologies and solutions needed for the European ELT (E-ELT) 42m telescope. The
AOF will offer a very large (7 arcmin) Field Of View (FOV) GLAO correction in J, H and K bands (GRAAL+Hawk-I),
a visible integral field spectrograph with a 1 arcmin GLAO corrected FOV (GALACSI-MUSE WFM) and finally a
LTAO 7.5" FOV (GALACSI-MUSE NFM). Most systems of the AOF have completed final design and are in
manufacturing phase. Specific activities are linked to the modification of the 8m telescope in order to accommodate the
new DSM and the 4 LGS Units assembled on its Center-Piece. A one year test period in Europe is planned to test and
validate all modes and their performance followed by a commissioning phase in Paranal scheduled for 2014.
The Wind Evaluation Breadboard (WEB) for the European Extremely Large Telescope (ELT) is a primary mirror and
telescope simulator formed by seven segments simulators, including position sensors, electromechanical support systems
and support structures. The purpose of the WEB is to evaluate the performance of the control of wind buffeting
disturbance on ELT segmented mirrors using an electro-mechanical set-up which simulates the real operational
constrains applied to large segmented mirrors. The instrument has been designed and developed by IAC, ALTRAN,
JUPASA and ESO, with FOGALE responsible of the Edge Sensors, and TNO of the Position Actuators. This paper
describes the mechanical design and analysis, the control architecture, the dynamic model generated based on the Finite
Element Model and the close loop performance achieved in simulations. A comparison in control performance between
segments modal control and actuators local control is also presented.
Telescope enclosures are used to limit the disturbance caused by the wind on the pointing and tracking performances of
telescopes and to preserve primary mirror optical shape.
Within the framework of the EC program "ELT Design Study - Contract No. 011863", extended wind tunnel test have
been performed to characterize wind turbulent structure inside two different types of enclosures and with different wind
screen positions. Also Power Spectral Densities of the turbulent flow have been directly measured. In this paper the
results are summarized, together with the limitations associated to the use of scaled models. Mean speed distributions
and turbulent energy distributions have been measured. The results are compared with the fields determined with quasisteady
approach based on existing turbulence models (namely von Karman). Measurements obtained on the field in the
VST enclosure at Paranal are crossed checked with the results obtained in the Boundary Layer wind tunnel.
Two teams of scientists and engineers at Max Planck Institut fuer Extraterrestrische Physik and at the European Southern Observatory have joined forces to design, build and install the Laser Guide Star Facility for the VLT.
The Laser Guide Star Facility has now been completed and installed on the VLT Yepun telescope at Cerro Paranal. In this paper we report on the first light and first results from the Commissioning of the LGSF.
The conceptual design of a sliding enclosure, which allows open air operation at night, has been completed for the ESO 100m telescope (OWL). The design has been performed both using classical structural design and using an interesting technology based on supporting the beams with low pressure air cushions (Tensairity), which allows enormous savings in structural material and therefore in costs. Implications of the sliding hangar on the project are discussed; the radome concept as architectural alternative is taken in consideration and compared from the performance point of view.
The "phase A" of the opto-mechanical design, which started in 1997, is now basically completed. It provides a clean, symmetrical geometry of the pupil, with a near-circular outer edge. The modular design of the mechanical structure is built on the size of the hexagonal segments, provides a perfect match with the optical elements and allows production at reasonable costs. This paper is a summary of the various design iterations. A discussion is devoted to the evaluation of the design assumptions and principles which have been set at the beginning of the study, and to their validity after the completion of this first phase. This includes a discussion about specific aspects whose criticality had been under- or overestimated, and the methodology applied to define system and sub-system requirements. Finally, we present a summary of the present and future activities, which are mainly devoted to sub-systems definition.
ESO will measure pressure fluctations on the surface of the 76m radio telescope at Jodrell bank and on a scaled down model of this telescope in a wind tunnel. The data will be used to calculate the effect of pressure variations on the overall deformation of the mirror and in particular the effect on segment to segment misalignments taking into account the correction capabilities of the segment supports.
We report on the ongoing VLT Laser Guide Star Facility project, which will allow the ESO UT4 telescope to produce an artificial reference star for the Adaptive Optics systems NAOS-CONICA and SINFONI. A custom developed dye laser producing >10W CW at 589nm is installed on-board of the UT4 telescope, then relayed by means of a single mode optical fiber behind the secondary mirror, where a 500mm diameter lightweight, f/1 launch telescope is projecting the laser beam at 90 km altitude.
We described the design tradeoffs and provide some details of the chosen subsystems. This paper is an update including subsystems results, to be read together with our previous paper on LGSF design description.
MACAO stands for Multi Application Curvature Adaptive Optics. A similar concept is applied to fulfill the need for wavefront correction for several VLT instruments. MACAO-VLTI is one of these built in 4 copies in order to equip the Coude focii of the ESO VLT's. The optical beams will then be corrected before interferometric recombination in the VLTI (Very Large Telescope Interferometer) laboratory. MACAO-VLTI uses a 60 elements bimorph mirror and curvature wavefront sensor. A custom made board processes the signals provided by the wavefront detectors, 60 Avalanche Photo-diodes, and transfer them to a commercial Power PC CPU board for Real Time Calculation. Mirrors Commands are sent to a High Voltage amplifier unit through an optical fiber link. The tip-tilt correction is done by a dedicated Tip-tilt mount holding the deformable mirror. The whole wavefront is located at the Coude focus. Software is developed in house and is ESO compatible. Expected performance is a Strehl ratio sligthly under 60% at 2.2 micron for bright reference sources (star V<10) and a limiting magnitude of 17.5 (Strehl ~0.1). The four systems will be installed in Paranal successively, the first one being planned for June 2003 and the last one for June 2004.
The 100-m OWL telescope being considered for open-air operation, wind is an essential disturbance affecting the tracking performance and figure of the primary and secondary mirrors. ESO has undertaken a study to build up a reliable and flexible computer model of the telescope and its environment. This model can, in a cost-effective way, be used to assess the wind loading under different conditions and configurations, before entering into more expensive wind tunnel testing. This paper presents the first preliminary results obtained with Computational Fluid Dynamic (CFD) methods about the wind action on the OWL 100-m telescope, in terms of pressure time histories and in the frequency domain. Preliminary conclusions on the effect of the wind loading on the design are also drafted.
Preliminary requirements and possible technological solutions for the next generation of ground-based optical telescopes were laid down at ESO in 1998. Since then, a phase A study has been commissioned, the objective of which is to produce a conceptual design compatible, to the maximum possible extent, with proven technology, and establish realistic plans for detailed design, site selection, construction and operation for a 100-m class optical, diffraction-limited telescope. There was no doubt about how daunting such a challenge would be, but, somewhat surprisingly, it turns out to be firmly confined to adaptive optics concepts and technologies. The telescope itself appears to be feasible within the allocated budget and without reliance on exotic assumptions. Fabrication of key subsystems is fully within the reach of a properly engineered, industrialized process. A consolidated baseline is taking shape, and alternative system and subsystem solutions are being explored, strengthening the confidence that requirements could be met. Extensive development of wavefront measurement techniques enlarges the palette of solutions available for active wavefront control of a segmented, active telescope. At system level, ESO is developing enabling experiments to validate multi-conjugate adaptive optics (MAD for Multi-conjugate Adaptive optics Demonstrator) and telescope wavefront control (APE, for Active Phasing Experiment).
We report in this paper on the design and progress of the ESO Laser Guide Star Facility. The project will create a user facility embedded in UT4, to produce in the Earth's Mesosphere Laser Guide Stars, which extend the sky coverage of Adaptive Optics systems on the VLT UT4 telescope. Embedded into the project are provisions for multiple LGS to cope with second generation MCAO instruments.
The paper discusses the requirements of the enclosure and infrastructure for OWL. Although predicted to have no serious technological risks, these items will constitute a significant investment within the OWL project. An enclosure for such a large telescope does not have to provide the same functions as the actual enclosures built as of today. Protection from wind disturbance is not provided as efficiently as by enclosures with dimensions in the order of 30 m. The conditioning of such large volumes is economically not viable. A none co-rotating enclosure is shortly discussed as a solution and the reasons, which could make it effective are analyzed. The pier of the telescope is sketched and its effect on the telescope dynamics is discussed.
The baseline concept for the OWL mechanical structure is further developed and studied on the basis of the `six mirrors optical concept'. The primary mirror supporting structure is elaborated in deeper detail, the impact on the design of using lightweight mirrors is analyzed and also a trade-off among the so-called iso-static and hyper-static configurations is discussed. The performance of the telescope under seismic and wind survival load cases is analyzed.
We explore the scientific case and the conceptual feasibility of giant filled aperture telescopes, in the light of science goals needing an order of magnitude increase in aperture size, and investigate the requirements (and challenges) these imply for possible technical options in the case of a 100 m telescope. The 100-m f/6.4 telescope optical concept is of a four mirror design with segmented, spherical primary and secondary mirrors, and 8-m class aspheric tertiary and quaternary mirrors, providing a 3 arc minutes field of view. Building on the experience of the VLT and other large telescope projects, we investigate mirror fabrication issues, a possible mechanical solution, the requirements for the absolutely essential adaptive optics system and for the instrumentation package, and the implications for budget and schedule.
The main structure is defined as the telescope mechanical structure including the drives, the encoder system, the hydrostatic bearing system and all those subsystems which make the system self standing safe and testable as an electromechanical system, with the exclusion of the velocity and position control loops. The main structure is now almost completely assembled in Milan. The tests of the main mechanical performances (dynamic and static) have been carried out to gather information at the earliest possible stage of the assembling activities. The drives and the hydrostatic bearing system have been tested concerning their functionality. This paper aims to summarize concisely the results of the tests, to compare them to the design calculations and to show some possible design changes which could improve the performances of the telescope.
The main structure is defined as the telescope mechanical structure including the drives, the encoder system, the hydrostatic bearing system and all those subsystems which make the system self standing safe and testable as an electromechanical system. Since the conceptual design started the main goal was to design a telescope structure with high first locked rotor eigenfrequencies and to eliminate all possible causes of non linear effects on the telescope motion (stick-slip effect in ball bearings and dragging of cable wraps). Moreover the previous experience had shown the superiority from the repeatability point of view of the direct coupled encoders. The paper describes the resulting final design performed by the Italian Consortium AES (Ansaldo GIE-Genova, EIE-Venezia and SOIMI-Milano) which could provide all the features necessary to meet the demanding requirements of ESO's technical specifications.