Calibration of the ATHENA telescope is a critical aspect of the project and raises significant difficulties due to the unprecedented size, mass and focal length of the mirror assembly. The VERT-X project, financed by ESA and started in January 2019 by a Consortium led by INAF and which includes EIE, Media Lario Technologies, GPAP, and BCV Progetti, aims to design an innovative calibration facility. In the VERT-X design the parallel beam, needed for calibration, is produced placing a source in the focus of an X-ray collimator. This system is mounted on a raster-scan mechanism which covers the entire ATHENA optics. The compactness of the VERT-X design allows a vertical geometry for the ATHENA calibration facility, with several potential benefits with respect to the long horizontal tube calibration facilities.
The ATHENA X-ray observatory is a large-class ESA approved mission, with launch scheduled in 2028. The technology of Silicon Pore Optics (SPO) was selected since 2004 as the baseline for making the X-ray Mirror Assembly. Up to 700 mirror modules to obtain a nested Wolter like optics. The maximum diameter of the shells will be 2.5 m while the focal length is 12 m. The requirements for on-axis angular resolution and effective area at 1 keV are 5 arcsec HEW and 1.4 m2, while the field of view will be 40 arcmin in diameter (50 % vignetting). While in this moment there an on-going effort aiming at demonstrating the feasibility of a so large optics with so stringent scientific requirements, an important aspect to be considered regards the scientific calibrations of the X-ray optics. In this respect, the Point Spread Function and effective area have to be correctly measured and calibrated on-ground at different energies across the entire field of view, with a low vignetting. The approach considered so far foresees the use of a long (several hundreds of meters) facility to allow a full illumination with low divergence of the entire optics module (or at least of large sections of it). The implementation of similar configurations in a completely new facility to be realized in Europe (friendly called "super Panter") or the retrofitting existing facilities like the XRCF at NASA/MSFC are being considered. In both cases the costs and the programmatic risks related to the implementation of these huge facilities, with their special jigs for the alignment of the ATHENA optics, represent important aspects to be considered. Moreover, the horizontal position of the optics to be used in full illumination facilities would determine gravitational deformations, not easy to be removed with actuators or by modeling. In this talk we will discuss a completely different concept, based on the mount of the optics in vertical position and the use of a raster scan of the ATHENA optics with a small (a few cm2 wide) highly collimated (1 arcsec or so) white beam X-ray. This system will allow us to operate a much compact system. The use of a vertical configuration will imply smaller gravitational deformations, that can be controlled with actuators able to compensate them. A proper camera system with a sufficient energy resolution will be able to grant a correct measurement of both PSF and effective area of the Mirror Assembly within the calibration requirements and in a reasonable integration time. Moreover, it may allow us also to perform end-to-end tests using the two flight focal plane instruments of ATHENA. The cost and risks for the implementation would be much lower than for the full illumination systems. The conceptual configuration and preliminary expected performance of the facility will be discussed.
The ELT Telescope defines new levels of performances for all the engineering fields involved in the design and realization of the telescope. This is true also for the Telescope axes Control System that has to meet the requirements while guaranteeing robustness of the control loops and avoiding the resonances excitation.
The telescope requirements include slewing and offsetting time, trajectory rate limits, tracking accuracy, wind disturbances rejection and the avoidance of resonances excitation.
To evaluate the Control System behavior, a State Space Matrix has been estimated from the modal analysis of a finite element model of the complete telescope, including also the pier, in the “free rotor” condition.
The plant transfer functions of the Azimuth and Altitude axes have been analyzed to evaluate the more critical resonances that can affect the control loops bandwidth. The velocity and the position loops architectures have been designed and tuned to evaluate how the control bandwidth influences the structural resonances.
Different loops architectures have been implemented to compare the results, also including feedforward control to enhance the tracking performance and low pass filters to minimize the structural modes excitation. The control design results are presented.
A telescope model, including Azimuth and Altitude axes, frictions and motor torque disturbances, encoders quantization, loops sampling and latencies, has been created. The wind disturbance has been implemented as a time-varying force acting directly on the telescope structure, generated using a velocity time history with the requested PSD.
Several simulations, here presented, with and without the wind disturbance, have been done to analyze the performances respect to all the requirements and to assess the structural behavior. The simulations consider the axes moving at the same time to evaluate the cross coupling effect following all the foreseen trajectories.
The European Extremely Large Telescope (E-ELT), with its primary mirror diameter of 39 meters, will be the largest optical/near-infrared telescope in the world and will allow scientists to investigate important unsolved issues of the universe.
The dome and telescope (DMS) are designed to ensure high performance in one of the most seismic active areas in the world, Cerro Armazones in Chile.
The Dome diameter is 86 m and sits on the top of a stiff concrete pier, which has been designed with horizontal seismic devices to reduce the seismic accelerations on the structures. The isolation system consists of a combination of High Damping Rubber Bearings (HDRBs) and lubricated spherical bearings.
The Telescope structure has been designed to be adaptive, during operation it is extremely stiff with low damping to guarantee the pointing and tracking (fixed condition) and when subjected to strong earthquakes it is flexible with high damping (isolated condition) to reduce the accelerations on the mirrors and instruments.
To fulfill these requirements, a 3D adaptive seismic isolation system has been designed with unique features. The telescope natural frequencies and damping change suddenly when the telescope is subjected to a 1-year return period seismic event, which is the maximum threshold acceleration acceptable without isolation. In the isolated configuration, the telescope frequencies range between 0.3 Hz (isolation frequency) and 30 Hz (highest frequency of interest), while in the fixed configurations the frequencies range between 2.6 Hz and 30Hz.
The vertical and horizontal acceleration reduction is obtained with special devices designed for this type of applications.
This paper presents the design and shows the results of the sophisticated nonlinear time history analyses performed on the DMS. The large finite element models consist of about 75000 nodes and over 110000 elements and include nonlinear spring damper elements calibrated experimentally to model the vertical and horizontal behavior of the seismic devices.
The Extremely Large Telescope (ELT) is the largest near- and mid- infrared telescope of the world.
The performance check of the preliminary design of the ELT has been completed through a variety of analyses: structural static analysis (FEM), modal and harmonic analysis (FEM), seismic spectrum and transient analysis (FEM), wind analysis (CFD and Wind Tunnel Test), thermal analysis (FEM), vibration analysis (FEM + State Space model), Servo analysis for pointing and tracking (State Space model).
A FEM model of the telescope has been created to analyze the telescope behavior against all the significant actions: gravity, wind, seism, thermal, manufacturing and alignment errors. The model includes the telescope pier and the pier foundations.
A Wind Tunnel Test campaign has been carried out on a scaled model of the Dome and Telescope to assess the wind action on the structures. The campaign has been supported by a detailed CFD analysis with several cases of Dome orientation, Dome configuration, wind velocity and turbulence intensity.
A State Space model of the telescope has been set up to perform the Servo analysis of the azimuth and altitude control system. A comprehensive State Space model of the Dome, the Ground, and the Main Structure has been set up to perform the vibration analysis of the whole observatory (including the machinery in the auxiliary building and the erratic vibrations from the ground).
The present paper provides a synthetic description of the generated models and the most significant results.
The ELT, Extremely Large Telescope, a 40m class optical, near and mid-infrared telescope that will be installed on Cerro Armazones, on the Chilean Andes, will be characterized by a an alt-azimuthal steel structure mounting weighting about 3700 tons. The telescope design consists of a highly optimized, space-frame structure, whose deflection characteristics have been carefully tuned to facilitate the performance of the oil film associated with the hydrostatic bearing system and the performance of the rotation associated with the drive and encoder systems. The Altitude structure design incorporates the M1 Mirror cell and hosts all the telescope optics. The major challenges in the design are the need to keep the primary mirror segments within a reasonable range from the prescribed locations and the need to minimize the static and dynamic deflections of the secondary mirror. The telescope rotates on tracks fixed to a concrete pier with a diameter of about 52m, completely isolated from the ground by means of special seismic devices. Power, data, control cables and fluid hoses follow the azimuth range of 550 degrees by means of the 18m diameter cable wrap, and the altitude range of 96 degrees with two lateral cable drapes. The rotation of the Azimuth and Altitude axes are possible thanks to the Direct Drive System and kept in place by high precision incremental tape encoders. The telescope is equipped with a very performing Control System that implements state of the art automation technologies, such as isochronous real time fieldbus, communication protocols, absolute time synchronization and safety, state of the art software engineering methods, such as object oriented design and iterative AGILE software development methodology.
The ELT Dome has been conceived for protecting the 39m ELT telescope, with its 86m base diameter and its almost 80m height. The rotating Dome is spherical to enhance the aerodynamic behavior; it weights about 6000 tons and it is provided with a 42m wide slit, to allow the telescope observation.
The bearing structure of the Dome is a truss structure made of steel, having a base ring and a series of arch girders as its main elements.
The Dome Rotation is performed by 36 trolleys, which are fixed to the top of the reinforced concrete Dome Base. Safety against seismic events is guaranteed by a dedicated Isolation and Damping System at the Dome Pier.
The Dome is covered by a custom Cladding System, that has been tailored in order to provide the required thermal insulation and withstand the harsh Environmental Conditions of the ELT Site.
With the aim of controlling the airflow around the Telescope, the ELT Dome is provided with a series of 89 Louvers, which are distributed among the rotating and the fixed structures. Besides, a Windscreen made of four permeable aluminum panels protects the Telescope; each panel spans over the 42m slit and is 10m high. The Windscreen is able to track with the Telescope on a 20 to 70deg range of the altitude angle.
The Auxiliary Building is a ring surrounding the Dome Pier and houses the Dome Technical Rooms, thus guaranteeing a radial distribution of all the Services. Among the Dome Supplies, a custom HVAC System is able to control the Telescope Chamber temperature with a ±2°C precision. The ELT Dome is provided with specific Plants so to supply Power to all the relevant loads and to the Electrical Equipment, as well as with a custom Global Control System and a series of Safety Systems.