The Prefocal Station (PFS) is the last opto-mechanical unit before the telescope focal plane in the Extremely Large Telescope (ELT) optical train. The PFS distributes the telescope optical beam to the Nasmyth and Coudé instrument focal stations and it contains all of the sky metrology (imaging and wavefront sensing) that will be used by the active optics of the telescope and to support operations such as phasing the primary mirror (phasing and diagnostic station). It also hosts local metrology that will be used for coarse alignment and maintenance. We present the main results of a concept design study for the Nasmyth A prefocal station.
The Nasmyth platforms of the E-ELT will contain one Prefocal Station (PFS) each. The main PFS functional requirements are to provide a focal plane to the three Nasmyth focal stations and the Coudé focus, optical sensing supporting telescope low order optimisation and seeing limited image quality, and optical sensing supporting characterising and phasing of M1 and other telescope subsystems. The PFS user requirements are used to derive the PFS technical requirements specification that will form the basis for design, development and production of the system. This specification process includes high-level architectural decisions and technical performance budget allocations. The mechanical design concepts reported here have been developed in order to validate key system specifications and associated technical budgets.
During the last year a modified baseline design for the E-ELT has been developed. The aim of this revision was both to
achieve a significant cost saving and to reduce risk on major items. The primary mirror diameter was slightly reduced to
39 m and the total height of the telescope also decreased accordingly. This paper describes the work performed by ESO
and a variety of contractors to review the EELT design to match the modified baseline. Detailed design and construction
planning, as well as detailed cost estimates were updated for the 39-metre baseline design. In June 2011, ESO Council
formally endorsed this modified design as the E-ELT revised baseline.
The design drivers and balancing cost factors will be described along with the risk reduction measures taken during this
phase. This will culminate in the design which has been agreed as being ready to move forward to construction once
approval from ESO Council has been achieved.
KEYWORDS: Optical instrument design, Telescopes, Domes, Large telescopes, Buildings, Observatories, 3D modeling, Manufacturing, Camera shutters, Space telescopes
As a continuation of the Preliminary Design of the Dome for the European Extremely Large Telescope (E-ELT)
proposed by IDOM, the Detail Design for the E-ELT Dome has been developed with the objective of optimizing the
design to minimize the manufacturing, erection and operation costs.
The proposed design is based on a hemispherical dome tightly fitted to the dome design volume to minimize the
enclosed volume and consequently the cost. The large observing slit, large as compared to the dome diameter, is covered
by means of two horizontal biparting doors.
This paper summarizes the most significative changes in the design and the approach followed by IDOM for the detailed
design process, with emphasis in the construction process. The design work presented in this paper has been performed
under contract with the European Southern Observatory (ESO).
Associated to tracking capabilities, the main axes control system of the E-ELT is the first correcting system in the
chain of control loops for reducing the image motion (tip/tilt) caused by perturbations on the telescope. The main
objective of the closed-loop performance analysis of the axes is to evaluate the trade offs for the choice of control
system hardware, i.e. specification and location of the motors and sensors (encoders/tachometers). In addition,
it defines the design constraints and requirements (actuator stroke and bandwidth) of other correcting systems
in the chain: the field stabilization (M5 unit) and adaptive deformable mirror (M4 unit). In this paper the main
axes control analysis of E-ELT is presented and the performance of telescope in face of external perturbations
such as wind and imperfections of the drive (cogging/ripple) and sensing (noise) systems is evaluated. The
performance metric is the wavefront error at the focal plane which is derived from the mechanical motion of the
telescope's optical elements together with their respective optical sensitivities.
The drive and bearing technologies have a major impact on the static and dynamic performance of steerable
structures such as telescope and dome. Merging drive and bearing system into friction drive mechanical devices
(bogie) can reduce the complexity and cost of the design. In the framework of ELT design study (European
FP6) a breadboard test setup was realized to test and evaluate the static and dynamic behavior of such bogies.
In this paper some of the characterization test results are presented. Characterization of the bogies and the
setup structure in the frequency domain, quantification and measure of the most important parameters of the
friction forces, the control of the bogies and the tracking performance of the test setup are among the main
results discussed in this paper.
The upper part of the European Extremely Large Telescope (E-ELT) altitude structure is one of the most critical areas of
the telescope's structure. This part hosts sensitive optical elements of the telescope. Its structural performance has a
major impact on the whole system. The most critical requirements are low optical path obscuration, high static and
dynamic performance (high specific modulus), high mechanical safety (high specific strength), low wind cross section
and low weight.
Composite materials are ideally suited to meet these requirements. This study is carried out in order to quantify the
relative advantage of composite material over mild steel, in terms of performance and costs. The mechanical behavior of
the steel structure can be easily improved with a structure manufactured with composite materials. This structure is
significantly lighter than the steel one and reduces relative displacements between primary and secondary mirror.
Consequently, optical performance is improved, assembly process is simplified and transport cost is reduced.
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.
KEYWORDS: Control systems, Photonic integrated circuits, Chemical elements, Manufacturing, Composites, Interfaces, Telescopes, Mechanical efficiency, Large telescopes, System integration
The European Extremely Large Telescope (E-ELT) structural rope system will be integrated in a mechanical structure,
which can be made of mild steel and/or composite material. The following critical problems shall be solved by the rope
system: matching of differential thermal expansion and tensioning forces calibration and control.
The structural rope system consists of ropes, thermal compensation and tension control devices, and mechanical
interfaces with the telescope structure.
The objective of this study is to provide solutions to stabilize slender structural elements located in the upper part of the
E-ELT Altitude Structure and increase global mode frequencies of the upper part of the E-ELT Altitude Structure. An
appropriate rope system is developed to avoid local mode shapes and loss of stiffness that could lead to the failure of the
whole structure under operational loads. The pre-tension level of the ropes needs to be controlled before operation to
reach that objective.
Progress in the conceptual design phase of ESO's OWL 100-m optical and near-infrared telescope is reported, with emphasis on the development of the science case. The Phase A opto-mechanical design is now basically completed, and provides a clean, symmetrical geometry of the pupil, with a near-circular outer edge. We also report about the latest outcome of industrial studies, introduce the essential definition of the wavefront control systems, and outline operational concepts and instruments priorities. Finally, we elaborate on the favorable cost factors associated to the telescope design, its compatibility with low industrial risks, and argue that progressive implementation allows for competitive timescales. In particular, we show that suitable fabrication and integration schemes should accommodate for a start of science operation at unequalled potential and within a time frame comparable to that of smaller designs, while at the same time maximizing R&D time for critical subsystems.
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.
Even as a number of 8- to 10-m class telescopes come into operation worldwide, the scientific challenges these instruments and their space-based counterparts already address imply that future increases in light-gathering power and resolution will have to exceed conventional scaling factors. Indeed, it can be expected that the same progress in telescope diameter and resolution achieved throughout the century must now be realized within, at most, one or two decades. The technologies required to assert the validity of such an extrapolation appear to be within reach. Large telescopes successfully comissioned within the last decade have demonstrated key technologies such as active optics and segmentation. Furthermore, current design methods and fabrication processes imply that the technological challenge of constructing telescopes up to the 100-m range could, in some critical areas, be lower than those underlying, two decades ago, the design and construction of 8 to 10-m class telescopes. At system level, however, such giants are no size-extrapolated fusion of VLT and Keck, but fully integrated adaptive systems. In this paper we elaborate on some of the science drivers behind the OWL concept of a 100-m telescope with integrated adaptive optics capability. We identify major conceptual differences with classical, non-adaptive telescopes, and derive design drivers accordingly. We also discuss critical system and fabrication aspects, and the possible timeline for the concept to be realized.
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.
The drive and bearing technologies have a major impact on the static and dynamic performances of a steerable telescope. The costs related to the complexity of the design and its Reliability, Availability, Maintainability and Safety (RAMS) are not negligible. The design constraints of Extremely Large Telescopes (ELT) depart from those applicable to the current generation of 8 to 10 meter class telescopes, thus suggesting that alternative solutions should be investigated. This paper discusses the feasibility of implementing a design based on friction drives and bogies, tailored to OWL’s azimuthal and altitude degrees of freedom. The estimated static and dynamic performance of the mechanical structure, the achievable angular resolution, the optimal distribution of loads and stresses, the RAMS performance and finally its cost efficiency, make this solution particularly attractive.
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 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.
Two siderostats having 40 cm input pupil have been developed for the early commissioning phase of the VLT Interferometer at Paranal. Performances, design and development of the system are briefly introduced. First results obtained in Europe are discussed.
Each of the 12 Nasmyth and Cassegrain foci of the ESO very large telescope (VLT) will be equipped with an 'adapter/rotator' which provides the mechanical interface for the science instruments and several key functions for the control of the telescope, namely a CCD sensor for acquisition and guiding, and a separate CCD sensor as wavefront sensor for the active optics control system. This paper describes the origins and concept for the VLT adapter/rotators, and the principal design drivers and constraints.
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