Mirror Telescope Research Articles

Study of linear phase shift algorithms and application to deflectometry

For a number of optical methods, including deflectometry, information is encoded in fringe patterns. To extract the phase data from intensity values, a number of phase shift algorithms have been designed. In deflectometry, the nonlinearity of the fringe display implies that the displayed fringe pattern presents a harmonic content even if the input pattern is perfectly sinusoidal. The propagation of these harmonics through phase shift algorithms creates parasitic fringe patterns, reminiscent of the initial fringe pattern on the estimated phase. This phenomenon, known as print-through, has been identified as a serious performance limitation.In this paper, we revisit Surrel’s work on harmonic insensitive phase shift algorithms and demonstrate that the class of Discrete Fourier Transform (DFT) phase shift algorithms he defines is very appropriate for the field of deflectometry. We show how to choose the most suitable one depending on the application by performing a complete modeling of the harmonic print-through phenomenon for these DFT algorithms and studying the error propagation for shot noise and temporal perturbations. In a deflectometry context, we demonstrate by means of simulations that carefully chosen DFT algorithms can simultaneously be robust to print-through and perform better with respect to noise than the state of the art nonlinear phase shift algorithms.Lastly, by comparing experimental mirror shape measurements of the matrix of the secondary mirror of the European Extremely Large Telescope made on the one hand by DFT deflectometry and on the other hand by phase shift interferometry, we demonstrate that the use of DFT algorithms can substantially improve the high spatial frequency measurement capabilities of a deflectometry setup, without the need for a calibration of the display’s nonlinearities.

Risk assessment for landslide of FAST site based on GIS and fuzzy hierarchical method

In the context of circular high steep slopes within a 500-m aperture spherical radio telescope (FAST) site in Pingtang, Guizhou Province in southwest China, a pertinent small-area karst landslide risk assessment is carried out based on geographic information system and fuzzy analytical hierarchy process. Results show the following: (a) The AUC value of hazard assessment is 0.826, which means a good adaptability and a relatively higher accuracy, and the AUC value of risk assessment is 0.803, which means the accuracy of landslide risk assessment is within acceptable level. (b) The slopes of FAST area are generally at the medium or low-hazard level, with high-hazard region accounting for only 3.17% of the total area. High-hazard regions are primarily found in two locations, one is located in nearby the Guangmingding slope where the dangerous rock masses were basically cleared away, the other is located in nearby feed tower 5H where potentially unstable rock masses were reinforced to improve the stability of slope. (c) High-vulnerability area of FAST accounts for approximately 43.62%. As a direct result, the high-risk area of FAST site accounts for 34.36% based on the overlap of vulnerability and hazard. The high risk is concentrated in the surrounding areas such as the feed tower, support pillar, and telescope mirror, and the high-risk area overlaps most of the fault fracture zone in the study area. Our findings provide meaningful references for landslide prevention and monitoring of FAST areas and are instructive in theory and practice.

Об осесимметричном нагружении пластины на локальной опоре в рамках теории Родионовой – Титаева – Черных

The problem of an axisymmetric bending of a plate with constant thickness under its own weight is considered. The plate has a circular support. The problem is solved in an axisymmetric statement using a nonclassical shell theory of Rodionova-Titaev-Chernykh (RTCh), which takes plate compression in thickness into account. The solution for this theory is obtained using Godunov's orthogonal sweep method. This solution is compared with the solution obtained using the general three-dimensional theory of elasticity, implemented in an open-source package Code_Aster using axisymmetric finite elements. The motivation for this study is the description of a stress-strain state of some variants of primary mirrors of large optical telescopes under the action of gravity. The obtained results characterizing the optical quality of the mirror surface are: the peak value (PV) and the root-mean square (RMS) of its displacement. A parametric study was carried out, i.e., the thickness of the plate and the half-width of the support were varied. The two methods were compared. It is shown that, as the plate thickness increases or the half-width of the support decreases, non-physical behaviour of the mirror surface takes place within the limits of the nonclassical theory of RTCh. A criterion of its applicability is therefore proposed.

Jacques Beckers (1934–2021)

Beckers’ interests included many aspects of solar physics and a variety of topics in astronomical instrumentation. His appointments included leadership positions at the Multiple Mirror Telescope, the National New Technology Telescope project, and the National Solar Observatory.

Alignment of the active secondary mirror of a space telescope using model-based wavefront sensorless adaptive optics.

The precise alignment of the space telescope with an active secondary mirror (ASM) is essential to high-quality imaging. The traditional alignment methods either require a dedicated wavefront sensor or a lot of iterations to optimize a metric function, which is not suitable for on-orbit instant alignment. A model-based wavefront sensorless adaptive optics method is proposed for the alignment of the ASM of a wide field-of-view space telescope. In our method, the aberration is estimated by introducing a series of modal biases successively into the system using the ASM. Unlike the traditional wavefront sensing methods that intend to measure all aberration modes, only five aberration modes that can be compensated by the ASM are estimated. Two alignment schemes either using single-field or multi-field images are proposed to calculate the control signals of the ASM, depending on if the aberration is mainly caused by the ASM. Simulations are made to evaluate the performance of our method under different scenarios. The influence of image sampling frequency, image size, and image noise on alignment are also investigated.

Симуляционная модель системы адаптивного управления сегментами составного зеркала космического телескопа и ее метрологическая аттестация

The paper concerns a measurement problem of identifying inadequacy in a mathematical model of an adaptive control system driving segments of a deformable mirror in a large telescope. This is necessary to assess the validity of this model. A dual-axis servo drive unit utilising permanent magnet synchronous machines controls the mirror segments. The servo unit rotates each segment of the deformable mirror with respect to its axis of symmetry and tilts each segment relative to the fixed central reference segment. The paper provides general descriptions of the model structure and the feedback in the current control loop employing phase current measurement and coordinate transformations. We present initial data sets for metrological certification of the model. We used the MMK-stat M software to perform the metrological certification so that we could check empirical equations, determine the scope of application for the model and validate it. The metrological certification allowed us to confirm that the model of an adaptive control system for a segmented deformable telescope mirror is valid, and to find the model structure that ensures a more accurate description of the measurement problem that concerns controlling the spatial position of the object simulated

Thermal control of primary mirror of Space Solar Telescope

The space-based Lyman-alpha Solar Telescope (LST) developed by China will conduct in-depth observation and research on solar activity and internal dynamics of the sun. Thermal control of the primary mirror is the core of the LST and ensures normal and efficient operation of the LST primary mirror. The primary mirror directly receives solar energy. Its element is produced from fused silica, and the multilayer coatings have high heat absorption. The primary mirror is connected with the front of the piezoelectric actuator for high-frequency image stabilization. According to these characteristics, we study the thermal properties of the primary mirror by attaching a high-thermal-conductivity graphite membrane to its back and connecting the annular bracket. We conduct a thermal equilibrium test and finite element network simulation in high-temperature mode, and their results differ by < 1 °C. High- and low-temperature simulations of the primary mirror in orbital operation show that it meets the thermal control target of < 40 °C. Therefore, applying a graphite membrane to the LST primary mirror well meets the needs of thermal control. This provides a theoretical basis for improving the reliability and thermal optimization of the primary mirror.

临近空间望远镜次镜优化设计

临近空间望远镜次镜优化设计

临近空间望远镜次镜优化设计

临近空间望远镜次镜优化设计

Солнечный телескоп вакуумного ультрафиолетового диапазона для наноспутников

Within the Universat program, a set of solar vacuum ultraviolet (VUV) telescopes has been developed for deployment on 6U nanosatellites. Telescopes are designed to get images of the solar corona. The spectral ranges of observations is considered, the characteristics of the nanosatellite from the point of view of the observations feasibility are opmized, the optical scheme of the telescope and VUV multilayer mirrors coatings and thin-film filters are modelled.

Advances in optical engineering for future telescopes

Significant optical engineering advances at the University of Arizona are being made for design, fabrication, and construction of next generation astronomical telescopes. This summary review paper focuses on the technological advances in three key areas. First is the optical fabrication technique used for constructing next-generation telescope mirrors. Advances in ground-based telescope control and instrumentation comprise the second area of development. This includes active alignment of the laser truss-based Large Binocular Telescope (LBT) prime focus camera, the new MOBIUS modular cross-dispersion spectroscopy unit used at the prime focal plane of the LBT, and topological pupil segment optimization. Lastly, future space telescope concepts and enabling technologies are discussed. Among these, the Nautilus space observatory requires challenging alignment of segmented multi-order diffractive elements. The OASIS terahertz space telescope presents unique challenges for characterizing the inflatable primary mirror, and the Hyperion space telescope pushes the limits of high spectral resolution, far-UV spectroscopy. The Coronagraphic Debris and Exoplanet Exploring Pioneer (CDEEP) is a Small Satellite (SmallSat) mission concept for high-contrast imaging of circumstellar disks and exoplanets using vector vortex coronagraph. These advances in optical engineering technologies will help mankind to probe, explore, and understand the scientific beauty of our universe.

Complex elements of aerospace equipment from reaction silicon carbide ceramics

The results of studying the process of obtaining complex-profile elements of the substrate of mirrors of optical telescopes from reaction-sintered silicon carbide ceramics are presented. It is shown that the strength of silicon carbide ceramics depends on the dispersion of the silicon carbide powder and on the temperature of reaction sintering. An increase in the sintering temperature from 1500 to 1650 °C leads to an increase in strength by 60 MPa, and to 1800 °C – to a decrease in strength by 40 MPa. An increase in strength is explained by a decrease in free silicon and an increase in the content of secondary silicon carbide, a decrease in strength is explained by an increase in the size of carbide grains. The study of the influence of the modes of soldering of hexagonal elements to obtain a complex-profile element of the substrate of the mirror of an optical telescope on the strength of the soldered seam showed that the introduction of silicon carbide powder 7 μm in size and amorphous boron in an amount of 6 % into the solder composition based on silicon carbide has a positive effect on the strength of the soldered seam. Tests of the brazed specimens at three-point bending showed that fracture occurs along the body of the specimens being brazed, and not the brazed seam. The structure of the brazed joint depends on the composition of the braze alloy and the gap between the samples to be brazed.

Terahertz Reflectivity of YBa2Cu3O7-δ at Cryogenic Temperatures

Modern space-based telescopes operating in the terahertz (THz) spectral range require highly reflecting and cryogenically cooled optics ensuring extremely low noise. The idea of using high-temperature superconductor YBa 2 Cu 3 O 7-δ as a telescope's mirror coating for providing low dissipation and high reflectivity of the surface for the subTHz frequency band has been explored. We are presenting here some results of measurements of the reflection losses in YBa 2 Cu 3 O 7-δ at cryogenic and room temperatures (4.2-300 K) in the frequency band 0.166-0.23 THz. High-accuracy measurements of the absolute value of reflectivity have been performed with the help of the resonance technique. The measured reflection losses in the given frequency band were below 1%. For the same frequency range, these values are well above the reflection losses in normal metals such as copper or aluminum, which are normally used to cover mirrors of telescopes. We, therefore, conclude that the use of high-Tc superconductors YBa 2 Cu 3 O 7-δ as a highly reflecting coating for the THz telescope's mirror is not advisable.

Preliminary estimate of instrumental polarization effects in the LST-3 Large Solar Telescope

This article presents a polarization calculation for the LST-3 large solar telescope. It describes the interaction of the telescope mirrors and includes a calculation of the transmittance of the telescope’s optical system for incident radiation with various polarization states. It estimates the instrumental polarization, cross-talk, and depolarization at Gregorian focus F2 and after tilted mirror M4 of the telescope. The estimate is made using modeling of an aluminum coating on the mirrors for axial and peripheral image points at reference wavelengths in the 400–2000 nm region. The mean Mueller matrices are found at Gregorian focus F2 and after tilted mirror M4. The polarization distortions at the Gregorian focus are insignificant, but they are substantial after tilted flat mirror M4.

The First Extensive Spectroscopic Study of Young Stars in the North America and Pelican Nebulae

Abstract We present a spectroscopic survey of over 3400 potential members in the North America and Pelican Nebulae (NAP) using several low-resolution (R ≈ 1300–2000) spectrographs: Palomar/Norris, WIYN/Hydra, Keck/DEep Imaging Multi-Object Spectrograph (DEIMOS), and the Multiple Mirror Telescope (MMT)/Hectospec. We identify 580 young stars as likely members of the NAP region based on criteria involving infrared excess, Li I 6708 Å absorption, X-ray emission, parallax, and proper motions. The spectral types of individual spectra are derived by fitting them with templates that are either empirical spectra of pre-main-sequence stars or model atmospheres. The templates are artificially veiled, and a best-fit combination of spectral type and veiling parameter is derived for each star. We use the spectral types with archival photometry to derive V-band extinction and stellar luminosity. From the Hertzsprung–Russell diagram, the median age of the young stars is about 1 Myr, with a luminosity dispersion of ∼0.3–0.4 dex. We investigate the photometric variability of the spectroscopic member sample using Zwicky Transient Facility data and conclude that photometric variability, while present, does not significantly contribute to the luminosity dispersion. While larger than the formal errors, the luminosity dispersion is smaller than if veiling were not taken into account in our spectral typing process. The measured ages of the stellar kinematic groups, combined with the inferred ages for embedded stellar populations revealed by Spitzer, suggest a sequential history of star formation in the NAP region.

Evaluation of dimensional stability of metering truss structure using built-in laser interferometric dilatometer

Dimensional stability in a space telescope is one of the important factors for performing high-resolution observations. The supporting structures between the primary and the secondary mirrors in a space telescope are required to maintain the mirror positions with the proper focus for minimizing the optical alignment error. In orbit, the harsh environment subjects a space telescope to temperature variations that can lead to deformation of those structures and degradation of the telescope’s optical performance. Several approaches are available for achieving high dimensional stability. They include minimizing temperature variations with active thermal control, designing the structure with low thermal expansion materials, and correcting the shape and/or position of the structure with actuators. An optimum combination of these measures is determined based on an accurate evaluation of the dimensional stability of the structures. This paper proposes a displacement measuring interferometer system with a simple, robust, and compact sensor that can monitor the dimensional stability of the precise structure by integrating the sensor into the structure. In this technique, a Fabry–Perot displacement sensor was built into the end of a strut that is a component of a metering truss structure. Two types of truss struts were tested to verify the performance of the proposed technique in measuring thermal expansions. The first one was the prototype that was made of stainless steel (SUS304). The other strut was made of a low thermal expansion ceramic (SiAlON) that is one of the most promising materials for a highly thermo-stable satellite structure. The thermal dimensional stability of these struts was evaluated by using the proposed technique and compared with conventional dilatometers for validating this new technique. The results showed that the technique has similar precision to the conventional measurement system and provide a more convenient and stable measurement system.

A review on Zerodur material strength behaviour with lightweighted design

Zerodur is well-recognized glass–ceramic utilized for optical elements because of excellent dimensions stamina under varying temperature. There is a big span of material for light weighted elements made with the help of Zerodur glass. For specimen, it is work for mirrors of space astronomical working telescopes, and configuration parts for space working instruments, mechanical configurations for industrial revolution works. Due to process parameter some surface defects like micro cracks, scratches etc are obtained that identify by mechanical profilometer. In order to satisfy provision of the light weight ratios and huge size control for space working mirror, the finite element analysis for mirror assembly with structural and thermal analysis calculation.

RESEARCH OF OPTOELECTRONIC SYSTEMS ON THE BASIS OF A TELESCOPE WITH A LIGHT FIELD DIGITAL CAMERA

Within the framework of solving the problems of developing intelligent optoelectronic systems for monitoring remote objects, the possibilities of constructing schemes for registering remote objects with a telescopic system based on a light field digital camera are considered. A technique for calculating a two-component optical scheme for registering distant objects by an optoelectronic system based on a digital camera of a light field is presented, and a layout of an experimental setup for registering a scale model of an object with a two-component optical system consisting of a main mirror of a Newtonian telescope and a digital camera of a light field is presented. The principles of constructing algorithms for determining the main parameters of controlled objects and high-precision calibration of the optical system of the recorder have been developed. The fundamental possibility of constructing a light field correlator on the basis of a telescope is shown. An example of processing a light field file is given. The possibility of high-precision determination of the parameters of remote objects has been investigated.

Toward Solving the Puzzle: Dissecting the Complex Merger A521 with Multiwavelength Data

Abstract A521 has been a subject of extensive panchromatic studies from X-ray to radio. The cluster possesses a number of remarkable features, including a bright radio relic with a steep spectrum, more than three distinct galaxy groups forming a filament, and two disturbed X-ray peaks at odds with the distant position and tilted orientation of the radio relic. These lines of evidence indicate a complex merger. In this paper, we present a multiwavelength study of A521 based on Subaru optical, Hubble Space Telescope infrared, Chandra X-ray, Giant Metrewave Radio Telescope radio, and Multiple Mirror Telescope optical spectroscopic observations. Our weak-lensing (WL) analysis with improved systematics control reveals that A521 is mainly composed of three substructures aligned in the northwest to southeast orientation. These WL mass substructures are remarkably well-aligned with the cluster optical luminosity distribution constructed from our new enhanced cluster member catalog. These individual substructure masses are determined by simultaneously fitting three Navarro–Frenk–White profiles. We find that the total mass of A521 modeled by the superposition of the three halos is , a factor of 2 higher than the previous WL measurement. With these WL mass constraints combined with X-ray and radio features, we consider two merging scenarios, carry out the corresponding numerical simulations, and discuss the strengths and weaknesses of each case.

The Faint Optical Counterparts Catalog at 19.4 < r < 22 mag from Herschel-ATLAS SDP Field

We carry out a spectroscopic survey with Hectospec mounted on the 6.5 m Multiple Mirror Telescope to obtain redshifts of optical counterparts of the Herschel-ATLAS sources in the science demonstration phase field. Our work concerns counterparts with a magnitude range at mag. The observation covers two pointings. In total, we newly obtain redshifts of 158 potential counterparts. Among these counterparts, there are 59 high reliability counterparts. For these high reliability counterparts, we do a SED fitting using MAGPHYS with our spectroscopic redshifts and five Herschel band fluxes, and discover 46 new luminous infra-red galaxies and 10 new ultra luminous infra-red galaxies, including two infra-red QSOs.