LEONARDO SpA is leading an Italian Space Industry Team, funded by ASI, collaborating to the ESA mission PLATO (PLAnetary Transits and Oscillation of stars). Its aim is the study of extrasolar planetary systems, with a focus on the discovery of exo-planets hosted by bright, nearby stars. PLATO is composed by 26 fully dioptric designed cameras, each composed of a telescope optical unit (TOU) and a focal plane array (FPA). The FPA is integrated with the TOU at ambient temperature by other Partners of the PLATO CAM-Team, although we determine the best image plane (BIP) of each TOU during test at cryo-vacuum operative conditions. This poses a metrology challenge at TOU manufacturing and testing facilities, with relatively high production rate of the flight units. At cold temperature (-80°C), the orientation and location of the FPA is found out as the BIP, meanwhile at ambient temperature, them are co-registered by using Hartmann masks. The results of this approach show a correspondence between the two analysis methods and give an input for subsequent FPA integration at PLATO CAM level.
Leonardo SpA is leading an Italian Space Industry Team, funded by ASI, collaborating to the ESA mission PLATO program for the realization of the 26 telescopes, which will fly on a single platform, aimed to discover, observe and analyze the exoplanets. The mission is based on a challenging telescope design with peculiar optical performance to be assured at very low operative temperature (-80°C). The “large” number of telescopes, produced in high rate (up to 3 telescopes every 2 months), is quite unusual for the production of scientific payloads. It has imposed a change with respect the prototypical manufacturing and test approach, generally a few flight units for space equipment, addressing the implementation of smart and fast methodologies for aligning and focusing each telescope, based on simulation of the peculiar “as-built” data. The opto-mechanical design of the telescope has been optimized to implement an industrial approach for all the manufacturing, assembly, integration and test (MAIT) phases. The number, production rate and the performance results of the flight units so far delivered by Leonardo to the PLATO Consortium, are validating the selected design solutions and all the selected MAIT processes. All the units already delivered present very similar performance, full specs and very close to the theoretical design.
Within the ESA PLATO M3 mission, the Telescope Optical Unit (TOU), i.e. the opto-mechanical unit, is a fully refractive optical system. The 26 TOU Flight Models (FM) to be delivered to the upper level, the PLATO Camera, make it a series production. The first Flight Models production faced many initial challenges from a Product Assurance point of view, mostly related to MAIT activities, while moving forward these challenges decreased. Discrepancies and nonconformities associated with, mainly, but not only, materials and processes, cleanliness and contamination control, safety, qualifications and validations, are the object of this proceeding. Thus, showing that serial production adds one more variable to possible failures, but at the same time, when root causes are corrected and solved, yields less difficulties in subsequent FMs MAIT and final production. Product Assurance, in monitoring the product in failure-proofing aspects, aims at mitigating criticalities and arranging for corrective and preventive actions that allow improving the likelihood of success of the mission.
Thermal and dynamic qualification loads on spacecraft are usually very high and the design of space components requires to use strong material to withstand them. However optical payloads usually mount brittle materials for optics and lenses. Two of them are the crystal CaF2 and the OHARA glass S-FPL51. Allowable design values for this kind of materials are hard to define, also considering that the numerical values for strength are low and the safety factor to use for design of brittle materials are really high. These two optical glass/crystal shall be used for three of the s ix lens es mounted on each one of the 26 Telescope Optical Units (TOU) of PLATO (PLAnetary Transits and Oscillation of stars), an ESA satellite that will be launched in 2026 to discover exoplanets. These brittle lenses, together with the mounts on which they are bonded, have been tested on a breadboards campaign checking their resistance to cryogenic temperatures (down to -115 °C), random loads up to failure and their behavior under shock loads. The results presented in this article show an unexpected and very high performance of each lens and its mount considering both thermal and dynamical behavior.
KEYWORDS: Sensors, Modulation transfer functions, Point spread functions, Stars, Telescopes, Detection and tracking algorithms, Cameras, Imaging systems, Exoplanets, Data modeling
The ESA M-size mission PLATO (PLAnetary Transits and Oscillation of stars) is scheduled for launch in 2026. During its 4-year mission orbiting Sun-Earth L2 is aimed at the discovery of exo-planets in nearby star systems. Its 26 cameras will be looking toward deep space, covering a wide area of the sky. Each camera is based on a fully dioptric design. Each camera is composed of a telescope optical unit (TOU) and a focal plane array (FPA). Here the procedure for the characterization of the best imaging plane (BIP) for each TOU is described. Camera manufacturing activity faces the challenge, by design, of locating the BIP for each TOU with high precision (±30 μm). Strict tolerances for accommodating the FPA are in fact in place in terms of inter-distances with respect to the mechanical mounts and tilts. Localization of the BIP will be carried out by mathematical optimization of the enclosed energy performances that will be evaluated at a pre-defined set of 45 field positions. Given the relatively big field-of-view of each camera (1037 deg2 for 24 normal-type and 610 deg2 for the 2 fast-type), this poses a challenge for a single service detector. Instead, an approach based on stitching single views of a smaller active area detector will be carried out. To circumvent performance limitations of detectors, for example, image degradation due to finite-size pixel sampling, dithering will be performed by leveraging a very precise mechanical positioner (hexapods) on which the detector is mounted.
PLATO (PLAnetary Transits and Oscillation of stars) is the ESA M-size mission aimed to the discovery of exo-planets hosted by bright, nearby stars. The launch of PLATO spaceship is scheduled for 2026. It will orbit Sun-Earth L2 for 4 years, looking towards deep space and covering a wide (2132 deg 2 total) area of space. To do so, PLATO will use 26 fully dioptric designed cameras, each composed of a telescope optical unit (TOU) and a focal plane array (FPA). For manufacturing purposes, the FPA will be assembled at ambient temperature, although the best image plane (BIP) of the TOU will be determined during test at cryo-vacuum conditions (-80°C). This poses a metrology challenge at TOU manufacturing and testing and at FPA integration facilities. To this extent, the procedures for the precise characterization and localization of the BIP during TOU tests are presented. In order to circumvent the thermal effects of contraction of the fixture, which in part operate at ambient and in part are cooled at -80°C (operation temperature), the final measurement will be derived by the repeated assessment of the coordinates of a set of fiducials at ambient and operation temperature. Compliance with a strict error budget is achieved by using a combination of sensors (confocal, focusvariation), mounted on very precise and repeatable hexapods. Hartmann masks are also used to co-register the position and orientation of mounting of the FPA between facilities.
PLATO is an exoplanet hunting mission of the European Space Agency. It is a medium-class mission, with a launch foreseen in 2026. Its prime objective is to uncover Earth-sized planets residing in their habitable zone. The payload consists in 26 cameras with a very wide field of view. These cameras consist in a Telescope Optical Unit, aligned at ambient and characterised at the operational temperature, and a Focal Plane Array bearing the detectors, and delivered after coupling with the Front End Electronics. In this contribution, we report on the alignment of the Engineering Model camera of Plato, i.e., the input metrology, the mechanical alignment of the optical unit with the focal plane array, the test environment and the optical characterisation throughout the process until the integrity check after delivery to the cryo-vacuum testing facility where the camera underwent a thorough performance demonstration. We also give a detailed description of the bolting process and the associated error budget.
PLATO is an exoplanet hunting mission of the European Space Agency. It is a medium-class mission, with a launch foreseen in 2026. Its prime objective is to uncover Earth-sized planets residing in their habitable zone. The payload consists of 26 cameras with a very wide field of view. These cameras consist of a Telescope Optical Unit (TOU), aligned at ambient and characterized at the operational temperature, and a Focal Plane Array bearing the detectors and delivered after coupling with the Front End Electronics. In this contribution, we report on the methods used at TOU level to characterize Focal Plane using a Hartmann Mask, i.e. we illustrate the analysis pipeline after data collection in the cryo-vacuum chamber at Leonardo (LDO), the implementation of new algorithms, and an extended uncertainties study for the Hartmann analysis.
Leonardo SpA is leading an Italian Space Industry Team, funded by ASI, collaborating to the ESA mission PLATO program for the development of the 26 telescopes, that will fly on a single platform, aimed to discover, observe and analyze the exoplanets. The mission is based on a challenging telescope design with peculiar optical performance to be assured at very low operative temperature. The “large” number of telescopes is quite unusual for the production of scientific payload; therefore, it has imposed a change with respect the prototypical manufacturing and test approach as standard for a few Flight Models, addressing the implementation of smart and fast methodologies for the aligning and focusing of the telescopes based on simulation of the as-built data. The paper describes that approach.
The ESA M size mission PLATO (PLAnetary Transits and Oscillation of stars) is planned to be launched in the 2026, with the aim of discover exoplanets that will be characterized with unprecedented precision. The optical elements of PLATO are 26 small telescopes, the TOUs (Telescope Optical Units), that using partially overlapping Fields of View will permit instantaneous sky coverage larger than 2100 square degrees. Each TOU has an aperture of 120 mm diameter assured by an internal stop, and it is composed by 6 lenses, the frontal one having an aspherical surface and the last acting as field flattener. The mechanical structure is realized mainly in AlBeMet. We here describe the optical design, summarizing several optical properties (materials, coatings, etc.), and report on nominal performances of the TOU system.
KEYWORDS: Contamination, Manufacturing, Cameras, Space operations, Picture Archiving and Communication System, Optics manufacturing, Materials processing, Telescopes, Inspection, Contamination control
The TOU is the Telescope Optical Unit for the PLATO ESA mission, consisting of the opto-mechanical unit for each of the 26 Cameras of which PLATO is composed. The TOU is currently in the manufacturing, assembly, integration and testing (MAIT) phase for the Proto Flight Model (PFM) and for Flight Models (FMs). We present the design processes as seen from the Product Assurance (PA) point of view: PA aims at monitoring the design and addresses specific issues related to, among others, materials and processes (these shall be suitable for the purpose and for the life-time of the mission), cleanliness and contamination control (to limit the loss of optical performance), safety, monitoring of qualifications/validations. PA supports the project in failure-proofing aspects to mitigate criticalities, e.g. in the elaboration of non-conformances and deviations that can arise during the design and MAIT process, and/or are highlighted during the reviews for manufacturing, test, and delivery of the related hardware. PA ensures early detection of potential problems and risks for the TOU and arranges for corrective actions that aim at improving the likelihood of success of the mission.
PLATO (PLAnetary Transits and Oscillation of stars) is the ESA Medium size dedicated to exo-planets discovery and cataloguing, adopted in the framework of the Cosmic Vision 2015-2025. The PLATO launch is planned in 2026 and the mission will last at least 4 years in the Lagrangian point L2. The primary scientific goal of PLATO is to discover and characterize a large amount of exo-planets hosted by bright nearby stars. The PLATO strategy is to split the collecting area into 24(+2) identical 120 mm aperture diameter fully refractive cameras with partially overlapped Field of View delivering an overall instantaneous sky covered area of about >2100 square degrees. The opto-mechanical sub-system of each camera, namely Telescope Optical Unit (TOU), is basically composed by a 6 lenses fully refractive optical system, presenting one aspheric surface on the front lens, and by a mechanical structure made in AlBeMet. In this paper we will update on the current working status of the TOUs.
.We describe the main tasks of the Product Assurance process for the Telescope Optical Unit (TOU) of the ESA PLATO mission, that starts from the design phase and proceeds through all phases, up to the final product, with the aim of improving the likelihood of success of the mission. When dealing with the opto-mechanical components of the TOU, several aspects regarding safety and performance have to be analyzed and tracked. From the PA point of view, we focus in this paper on materials and processes selection that shall be suitable and robust enough for the space environment. Cleanliness and contamination control is needed to overcome loss of optical performance. Validations and qualifications on prototypes is fundamental to assess the reliability of the instrument for its purpose and for the lifetime of the mission.
CHEOPS (CHaracterizing ExOPlanets Satellite) is an ESA Small Mission, planned to be launched in early 2019 and whose main goal is the photometric precise characterization of the radii of exoplanets orbiting bright stars (V<12) already known to host planets. The telescope is composed by two optical systems: a compact on-axis F/5 Ritchey-Chrétien, with an aperture of 320 mm and a Back-End Optics, reshaping a defocused PSF on the detector. In this paper we describe how alignment and integration, as well as ground support equipment, realized on a demonstrator model at INAF Padova, evolved and were successfully applied during the AIV phase of the flight model telescope subsystem at LEONARDO, the Italian industrial prime contractor premises.
PLATO (Planetary Transits and Oscillations of stars) is a new space telescope selected by ESA to detect terrestrial exoplanets in nearby solar-type stars. The telescope is composed by 26 small telescopes to achieve a large instantaneous field of view. INAF-OAPD is directly involved in the optical design and in the definition and testing of the alignment strategy. A prototype of the Telescope Optical Unis (TOU) was assembled and integrated in warm condition (room temperature) and then the performance is tested in warm and cold temperature (-80C). The mechanical structure of the TOU is representative in terms of thermal expansion coefficient and Young's modulus with respect to the actual one. A dedicated GSE (Ground Support Equipment) is used to manipulate the lenses. By co-align an interferometer and a laser with respect to the center of the third CaF2 lens, a several observables references are used to define the position and tilt of the chief ray. The total procedure tolerances for every lens is 30'' in tilt, between 15-40 μm for focus and 22 μm for decentering and the total error budget of the optical setup bench is below this requirement. In this paper, we describe the AIV procedure and test performed on the prototype of the TOU in the INAF laboratory.
PLATO (PLAnetary Transits and Oscillation of stars) is the ESA Medium size dedicated to exo-planets discovery, adopted in the framework of the Cosmic Vision program. The PLATO launch is planned in 2026 and the mission will last at least 4 years in the Lagrangian point L2. The primary scientific goal of PLATO is to discover and characterize a large amount of exo-planets hosted by bright nearby stars, constraining with unprecedented precision their radii by mean of transits technique and the age of the stars through by asteroseismology. By coupling the radius information with the mass knowledge, provided by a dedicated ground-based spectroscopy radial velocity measurements campaign, it would be possible to determine the planet density. Ultimately, PLATO will deliver the largest samples ever of well characterized exo-planets, discriminating among their ‘zoology’. The large amount of required bright stars can be achieved by a relatively small aperture telescope (about 1 meter class) with a wide Field of View (about 1000 square degrees). The PLATO strategy is to split the collecting area into 24 identical 120 mm aperture diameter fully refractive cameras with partially overlapped Field of View delivering an overall instantaneous sky covered area of about 2232 square degrees. The opto-mechanical sub-system of each camera, namely Telescope Optical Unit, is basically composed by a 6 lenses fully refractive optical system, presenting one aspheric surface on the front lens, and by a mechanical structure made in AlBeMet.
CHEOPS (CHaracterizing ExOPlanets Satellite) is an ESA Small Mission, planned to be launched in mid-2018 and
whose main goal is the photometric precise characterization of radii of exoplanets orbiting bright stars (V<12) already
known to host planets.
Given the fast-track nature of this mission, we developed a non-flying Demonstration Model, whose optics are flight
representative and whose mechanics provides the same interfaces of the flight model, but is not thermally representative.
In this paper, we describe CHEOPS Demonstration Model handling, integration, tests, alignment and characterization,
emphasizing the verification of the uncertainties in the optical quality measurements introduced by the starlight simulator
and the way the alignment and optical surfaces are measured.
The optical quality of the LLT unit of SUBARU NAOJ telescope was improved by new athermalized supports of the
optics, in order to operate at the best performance at temperatures below 0°C. The ultimate wavefront correction of
the whole LLT, that expands a laser beam from 40 mm to 500 mm, was made by Ion Beam Figuring on the small 40
mm LLT entrance window, in accordance to the WFE measured in operating conditions. The correction of small
optics including high spatial frequencies, resulting by the LLT expanding ratio, was possible by a special technique
of IBF process developed at the Astronomical Observatory of Brera (INAF-OAB), using a concentrator of the ion
beam size, able to force the broader beam emitted from an ion source into a smaller spot having large removal rate.
This paper reports some details about the optical technologies used for manufacturing the mirrors of the Refocusing
Mechanism Assembly (RMA). The RMA is a novel cryogenic mechanism designed by Galileo Avionica for the Near
Infrared Spectrograph (NIRSpec), one of the instruments of the James Webb Space Telescope (JWST). The RMA
contains two flat mirrors in Zerodur coated with Protected Silver. Severe constraints for accommodation in the
Nirspec imposed very lightweighted substrates to the RMA mirrors and required state of art technologies in order to
achieve the specified quality and its maintenance at cryogenic temperatures.
A new technology has been developed to grow layers of amorphous hydrogenated Silicon Carbide in vacuum, at
temperatures below 100-120°C by Physical Enhanced Chemical Vapour Deposition (PE-CVD) technology. The layers
have been used either to improve the surface quality of SiC mirror substrates (produced by methods different of the
CVD approach, like e.g. sintered SiC) as a super-polishable cladding coatings, or to form self-sustaining thin mirrors in
SiC. It should be noted that the PE-CVD claddings can be applied also to substrates different than SiC, as e.g. metals
like Al or Kanigen, in order to create a high durability polishable external layer. It this paper we present the results of a
wide characterization of the new material, considering the mechanical, structural and optical properties that are the most
indicative parameters for its application in optics, with particular reference to the production of mirrors for ground and
space astronomical applications.
The Ion Beam Figuring is a well known technique able to correct shape errors on optical surfaces with high accuracy.
The size of the ion beam dictates strongly the higher spatial frequencies that can be corrected on the optical surface. The
correction of small optics of some cm in diameter or containing high spatial frequencies can be very time consuming or
impossible. A system that permits the Ion Beam Figuring of small optical components has been developed in the
Astronomical Observatory of Brera (INAF-OAB). It has a small ion beam size and large removal rate. The system
employs a concentrator able to force the broader beam emitted from an ion source into a smaller spot having large
removal rate. The concentrator is placed between the ion source and the optical surface to be figured and doesn't
influence the long term stability of the source. It consists of a conical cavity in which is injected the beam extracted from
the grids of the source. The grazing incidence angle of impact of the ions with the walls of the cone ensure a very low
level of sputtering of the cone material and meanwhile permits the creation of a very small spot removal function having
large removal rate. To demonstrate its functionality a number of test optics has been figured using this system with very
good results.
The Launch Telescope Assembly (LTA) consists of a 50 cm class beam expander (angular magnification 12.5x) and it is an essential subsystem of Laser Guide Star Facility (LGSF), which provides an artificial reference star for adaptive compensation of atmospheric turbulence for one of the VLT (Very Large Telescope) 8-meters telescopes of ESO (European Southern Observatory). LTA is an afocal system, with parabolic primary and secondary mirrors, a flat 45° tertiary mirror and an exit window. It is fed with collimated Sodium laser beam, expanding and directing it along the line of sight of the 8-m telescope. Resonance backscatter from atmospheric Sodium layer at about 90 km altitude produces a point like artificial source at this altitude. The high optical quality requested for very fast optics, the severe constraints of the layout accommodation and the mass reduction made LTA a technological challenge that Galileo Avionica has been able to design, realise, align and test as requested. LTA will be positioned atop the secondary mirror unit of one of the four VLTs.
Mirror prototypes in cold-pressed sintered SiC-54 and in Carbon-SiC (Cesic) have been designed, manufactured and optically tested. The scope of the work was the development of materials, technologies and manufacturing processes to get high quality optics very stable at cryotemperatures. The activity has been performed under ESA funding in the frame of the technology development for the JWST/NIRSpec program. A description of the polishing performance and final testing results are discussed.
In view of the NIRSpec-JWST program, a trade-off study is currently in progress under an ESA-ESTEC contract, to select design, blank materials, coatings and relevant technologies for high quality mirrors operating at cryogenic temperatures. The behavior of two prototype lightweight mirrors, made in cold- pressed-sintered SiC and in Carbon-SiC (Cesic) are compared by interferometric measurements at 20 K. The prototypes are spherical mirrors, but realized using optical manufacturing technologies suitable for highly demanding aspherics (i.e. computer controlled polishing, ion beam figuring), in the perspective of the foreseen NIRSpec-TMA(s) optics.
By combining the excellent intrinsic thermo-mechanical properties of the silicon carbide (SiC) with a structural design based on a sandwich structure composed of two SiC face sheets deposited on a foam core of the same material, it is possible to manufacture very light and stiff mirrors for space applications. This paper presents some results of a technological development study, including the realization of a lightweight athermalized SiC telescope with a 310 mm diameter foamed-SiC primary mirror. An ion beam figuring equipment has been developed to improve the optical quality of the mirror.
Aspherics up to 500 nm diameter in optical glass or in ceramic substrates have been fabricated using area- compensated polishing tools and conventional optical shop machines. The tool forms are derived starting from the actual shape of the part under figuring. The figure error is measured using an interferometer mounted on-line with the polishing machine. Measurements are taken after each polishing step to compute the new tool form. The process speeds up the fabrication of aspheres and it improves repeatability in the manufacturing of axisymmetrical optics using moderate cost equipment's up to astronomical requirements. In the paper we present some examples of polishing results using the above mentioned approach on different aspherics for space applications.
The in-flight radiometric calibration of satellite multispectral sensor for earth and atmospheric observations can be conveniently based on solar diffusers. Theoretically, a knowledge of the spectral bi-directional scatter distribution function (BSDF) of the diffuser panel, and the solar incidence angle is all that is needed to allow the retrieval of the earth albedo in the observed direction. At the request of the ESA, the Centre Spatial de Liege, with the support of Officine Galileo as subcontractor, is currently designing a high-versatility high-accuracy BSDF measurement set-up with application to the calibration of space solar diffusers. This instrument will allow a BSDF measurements uncertainty within 1 percent for any angle in the wavelength range from 200 nm to 2400 nm. Vacuum measurements, polarization analysis capabilities and thermalization of the test sample between 200K and 300K are other unique features of this set-up.
The Optical Monitor is an ancillary instrument of the JET-X experiment on board of the satellite SPECTRUM-X-GAMMA. It consists of a Ritchey-Chretien telescope with an aperture of 230 mm, and two CCD detectors. The scientific objectives are the observations in the optical and UV band simultaneously with X-ray observations, the real time identification of X- ray sources with Mv <EQ 22 and detection of their variability, the improvement of the post-facto spacecraft attitude reconstruction (as a backup of the Attitude Monitor), and the serendipitous mode search for microvariability of the bright stars falling in the field of view.
The XMM Optical Monitor (XMM/OM) is a co-aligned telescope devoted to make observations of the X-ray sources both in the UV, visible and near-IR spectral bands, simultaneously with the X-ray instrument on the X-ray Multi-Mirror (XMM) satellite. The OM telescope is a Ritchey-Chretien with 300 mm clear aperture, for real time identification of sources up to magnitude mv equals 24. In the design of the telescope, particular care was paid in the selection of the optomechanical architecture and in the thermal and structural analysis, since the adopted optical scheme requires high stability of the structure. The paper highlights the major critical aspects and the criteria followed in the trade-off and design phases.
HRTIR for High Resolution Thermal Infrared Radiometer is an earth observation instrument candidate to the European Space Agency polar platform beyond Envisat 1. A preliminary design of the instrument has been performed in order to identify the most critical points and breadboard them. The instrument is a push broom concept providing an on ground spatial resolution of 50 m for a swath width of 50 km and a temperature sensitivity of 0.1 K in 3 spectral bands in the 8 to 12.5 micrometers range. A compact dioptric system has been selected for the optics and the focal plane consists of three linear arrays of 1000 HgCeTe photovoltaic elements hybridized on a CCD multiplexer and cooled down to 50 K inside a cryostat by mechanical cryocoolers. The HgCdTe IRCCD with a cut-off wavelength longer than 12.5 micrometers has been identified as the most critical technology and breadboarded. A complete detection chain with a long wavelength linear array of 222 pixels obtained by butting of three sub-arrays, a CCD multiplexer, a driving and processing electronics up to digital signal has been manufactured. The linear array is housed in a cryostat similar to the foreseen flight model but coupled to a laboratory cryogenic system. The IRCCD has been tested at unit level and the complete detection chain have been characterized in laboratory in conditions close to the flight. The test results have demonstrated the feasibility of the IRCCD at long wavelength with excellent performances. The instrument radiometric performances have been validated from the breadboard test results.
HRIS is proposed as a spaceborne, high-resolution imaging spectrometer designed to image a variable (+/- 30 degree(s)) 30 km swath with 40 m SSP pixel size in the spectral range from 450 to 2340 nm with an average 10 nm spectral bandwidth. HRIS is conceived as a push-broom imager with two-dimensional detector arrays for spectral and spatial coverage. The challenging requirements for this instrument will be discussed as well as the concept derived against these requirements. Emphasis is on the optical definition, particularly the spectrometer optics, the focal plane assembly--here mostly the hybrid SWIR CMT detector array--and the calibration concept which includes two external references, ratioing radiometers and an internal reference. The other subunits will be described briefly only. The presentation will conclude with a preliminary development plan.
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