Large Optical Telescopes Research Articles

Hybrid minigrid system comprising energy storage systems with optimal frequency control empowering the new Egypt large optical telescope site

Proposed hybrid minigrid two area system simulation model encompassing Photo Voltaic (PV) system, Wind Turbines (WT), diesel generators and Energy Storage Systems with intelligent based optimal Frequency Controllers (FCs) empowering the new Egypt large optical telescope (ELOT) site is presented in this research. Technical study and specifications for a PV solar system of 1000 Kw is introduced. Intelligent fine optimized Proportional Integral Derivative (PID) and Fuzzy self-tuned PID (FSTPID) controllers are designed through applying Harris Hawk optimizer (HHO). The proposed HHO employed method performance is validated under number of eventualities which include vacillations of load, sun radiation and wind speed. The objective function and control parameters are the integral time summation of absolute deviations and the parameters of controllers, consecutively. The system dynamic response and simulation results show that the proposed HHO based FSTPID type FCs are effective in reducing frequency and tie line power signals’ deviations in a diminutive time for such minigrid hybrid system. For supplemental validations, simulation results obtained are compared with genetic algorithm to get the proposed controllers’ gains.

Development of SunVoyager Interstellar Precursor Probe Driven by Inertial Confinement Fusion Propulsion

In this paper, we present updated calculations for the SunVoyager probe, a spacecraft conceptual design for a mission to the outer solar heliosphere to a distance of 500–1000 AU, in a trip time of ∼6–10 years traveling at speeds of 720 km/s. The spacecraft is innovative, in that it uses an inertial confinement fusion propulsion engine driving a 5.76-mg pellet filled with D3He fuel detonated at 10-Hz pulse frequency, augmented with 10-mg/pellet expellant propellant for enhanced mass flow rate. The spacecraft is designed to carry a 100-ton payload to include large optical telescopes for long-range imaging of nearby exoplanets. This paper is a follow-up to the earlier one that scoped out the design space, and here we give details on a more refined design configuration, in addition to calculations relating to the pellet ignition design and laser driver with 43.5 MJ delivered to the target. We also describe the power cycle with a jet efficiency of 37.8%, for a jet power of 2.67 GW and a specific power of 3.72 kW/kg.

Trajectory tracking control of autonomous space-based simulators for the on-orbit assembly of large space optical telescopes

To enhance the precision of on-orbit assembly for large space optical telescopes, the control of attitude motion in the Autonomous Space-based Simulator (ASS) is imperative. This paper presents a robust finite-time trajectory tracking control method aimed at improving the position and attitude tracking performance of ASS. Considering the dynamic characteristics inherent in ASS, we introduce an improved non-singular fast terminal sliding mode controller (INFTSMC) incorporating an adaptive fuzzy mechanism to attain finite-time error convergence and robust control. The adaptive fuzzy logic control (AFLC) method yields an equivalent gain, eliminating discontinuous switching in terminal sliding mode control (TSMC). This reduction minimizes chattering in control inputs and compensates for uncertainties and time-varying disturbances within the dynamic model. The proposed method’s effectiveness is validated through comprehensive simulation and experimental studies.

Recent Observations of Peculiar Gamma-Ray Bursts Using the 3.6-m Devasthal Optical Telescope (DOT)

India has been actively involved in the follow-up observations of optical afterglows of gamma-ray bursts (GRBs) for more than two decades, using the country’s meter-class facilities such as the 1.04m Sampurnanand Telescope, 1.3m Devasthal Fast Optical Telescope, 2.01 m Himalayan Chandra Telescope along with many others in the country, utilizing the longitudinal advantage of the place. However, since 2016, Indian astronomers have embarked on a new era of exploration by utilizing the country’s largest optical telescope, the 3.6-m Devasthal Optical Telescope (DOT) at the Devasthal Observatory of ARIES Nainital. This unique telescope has opened up exciting opportunities for transient study. Starting from the installation itself, the DOT has been actively performing the target of opportunity (ToO) observations, leading to many interesting discoveries. Notable achievements include the contributions towards the discovery of long GRB 211211A arising from a binary merger, the discovery of the most delayed optical flare from GRB 210204A along with the very faint optical afterglow (fainter than 25 mag in g-band) of GRB 200412B. We also successfully observed the optical counterpart of the very-high-energy (VHE) detected burst GRB 201015A using DOT. Additionally, DOT has been used for follow-up observations of dark and orphan afterglows, along with the observations of host galaxies associated with peculiar GRBs. More recently, DOT’s near-IR follow-up capabilities helped us to detect the first near-IR counterpart (GRB 230409B) using an Indian telescope. In this work, we summarise the recent discoveries and observations of GRBs using the 3.6-m DOT, highlighting the significant contributions in revealing the mysteries of these cosmic transients.

An efficient astronomical seeing forecasting method by random convolutional Kernel transformation

Astronomical seeing is the primary indicator of the observation quality of large-scale optical telescopes. Forecasting astronomical seeing is an essential and challenging task in the operation of large optical telescopes, as it can help observers more efficiently arrange observation tasks as well as providing hints for mechanism optimization of optical telescopes. In this paper, we propose an efficient data-driven astronomical seeing forecasting method by leveraging the environment monitoring data from multiple sensors deployed with optical telescopes. The basic idea is to use a large number of random yet fixed convolution kernels to extract features from the original data, and then train a simple tree-based predictor based on these features. In particular, the raw monitoring data is transformed by differential operations, enabling a more explicit representation of spatial and temporal features; then an elaborate convolution mechanism, including the convolution kernel and the pooling operator, is designed to extract a variety set of features of the input time series, which serve as the foundation for constructing the time series forecasting model. In contrast to existing deep learning models, there is no need to calculate and back-propagate the gradients during the training procedure, making the proposed method much more efficient. We collect real-world monitoring data from Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST), one of the world’s largest optical reflecting telescopes, and conduct extensive empirical evaluations. The experimental results demonstrate that the proposed method can achieve state-of-the-art prediction accuracy, i.e., 0.1125 in MAE, 0.0252 in MSE, and 0.0322 in MAPE, outperforming most deep-learning-based forecasting models. Moreover, it surpasses both machine learning and deep learning approaches in terms of training efficiency with a significant margin.

Optimized Approach for Image Design Processing in Optical Networks: A Comparative Study

Abstract Deep space detection and remote sensing both require optical imaging devices. The optical imaging system often needs a bigger aperture mirror to attain high spatial resolution. As a result, several novel optical imaging systems, such as big segmented mirror telescopes, large aperture membrane diffractive optical telescopes, and others, have been researched in recent years. Real-time wavefront measurement is not required for the wavefront sensorless (WFSless) applied optics (AO) approach. The wavefront corrector is directly regulated via feedback following an image quality measure of the far-field image to correct for wavefront aberration. Integrating artificial neural networks (ANN) and deep learning plays a vital role in developing WFSless AO systems. This paper evaluated various important aspects to provide an in-depth review of the state-of-the-art machine learning-based algorithms deployed in WFSless AO systems. Finally, the applications and prospects were outlined.

Limits on Simultaneous and Delayed Optical Emission from Well-localized Fast Radio Bursts

We present the largest compilation to date of optical observations during and following fast radio bursts (FRBs). The data set includes our dedicated simultaneous and follow-up observations, as well as serendipitous archival survey observations, for a sample of 15 well-localized FRBs: eight repeating and seven one-off sources. Our simultaneous (and nearly simultaneous with a 0.4 s delay) optical observations of 13 (1) bursts from the repeating FRB 20220912A provide the deepest such limits to date for any extragalactic FRB, reaching a luminosity limit of ν L ν ≲ 1042 erg s−1 (≲2 × 1041 erg s−1) with 15–400 s exposures; an optical-flux-to-radio-fluence ratio of f opt/F radio ≲ 10−7 ms−1 (≲10−8 ms−1); and a flux ratio of f opt/f radio ≲ 0.02–≲2 × 10−5 (≲10−6) on millisecond to second timescales. These simultaneous limits provide useful constraints in the context of FRB emission models, such as the pulsar magnetosphere and pulsar nebula models. Interpreting all available optical limits in the context of the synchrotron maser model, we find that they constrain the flare energies to ≲1043–1049 erg (depending on the distances of the various repeating FRBs, with ≲1039 erg for the Galactic SGR 1935+2154). These limits are generally at least an order of magnitude larger than those inferred from the FRBs themselves, although in the case of FRB 20220912A our simultaneous and rapid follow-up observations severely restrict the model parameter space. We conclude by exploring the potential of future simultaneous and rapid-response observations with large optical telescopes.

Imaging the Inner Astronomical Unit of the Herbig Be Star HD 190073

The inner regions of protoplanetary disks host many complex physical processes such as star–disk interactions, magnetic fields, planet formation, and the migration of new planets. To study directly this region requires milliarcsecond angular resolution, beyond the diffraction limit of the world's largest optical telescopes and even too small for the millimeter-wave interferometer Atacama Large Millimeter/submillimeter Array (ALMA). However, we can use infrared interferometers to image the inner astronomical unit. Here, we present new results from the CHARA and VLTI arrays for the young and luminous Herbig Be star HD 190073. We detect a sub-astronomical unit (sub-AU) cavity surrounded by a ring-like structure that we interpret as the dust destruction front. We model the shape with six radial profiles, three symmetric and three asymmetric, and present a model-free image reconstruction. All the models are consistent with a near face-on disk with an inclination ≲20°, and we measure an average ring radius of 1.4 ± 0.2 mas (1.14 au). Around 48% of the total flux comes from the disk with 15% of that emission appearing to emerge from inside the inner rim. The cause of emission is still unclear, perhaps due to different dust grain compositions or gas emission. The skewed models and the imaging point to an off-center star, possibly due to binarity. Our image shows sub-AU structure, which seems to move between the two epochs inconsistently with Keplerian motion and we discuss possible explanations for this apparent change.

Design of a Dynamic Secondary Mirror Truss Adjustment Mechanism for Large Aperture Telescopes

This study focuses on the dynamic secondary mirror truss adjustment mechanism for large aperture telescopes. The relative positions between the primary and secondary mirrors have stringent requirements for large aperture optical telescopes, with an aperture of more than 2 m. Due to the large mass of the primary mirror, the secondary mirror system is designed as an adjustable mechanism with multiple degrees of freedom, dramatically impacting telescope imaging. The kinematic modeling is followed by a detailed description of the designed adjustment mechanism, and then a static and modal analysis of the designed mechanism is performed. Subsequently, a kinematic performance test of the experimental prototype is conducted. The developed mechanism can travel up to ±5 mm in the z-direction with an accuracy of 16 µm and deflection of ±0.574° in the xy-direction. It provides accuracy better than 6.4 arcseconds.

A Tanh Control Method for the Third Mirror’s Z Axis of Large Optical Telescope

A Tanh Control Method for the Third Mirror’s Z Axis of Large Optical Telescope

A Decoupling Synchronous Control Method of Two Motors for Large Optical Telescope

Aiming at the problem of two motors system of a large optical telescope, a feedforward friction compensated linear active disturbance rejection control (FFLADRC) algorithm is proposed in this article. The algorithm consists of a friction compensated linear active disturbance rejection control (FLADRC) and two nonlinear tracking differentiators (NTDs). The FLADRC realizes the control of the two motors system by decoupling and compensates the friction. The NTDs are used to generate reference position, velocity, and acceleration signals. First, a mathematical model of the two motors system is established. Second, the FFLADRC algorithm is derived using the idea of decoupling. Third, the parameters tuning method of the FFLADRC is given. Fourth, the stability and synchronization mechanisms of the algorithm are analyzed. Finally, the experiments are carried out on a large optical telescope. In the experiments, single motor control, master–slave control, cross-coupling control, and FFLADRC are compared. The results show that FFLADRC has the minimum synchronization error and tracking error, which verifies the effectiveness of the proposed algorithm.

Research on the Time Drift Stability of Differential Inductive Displacement Sensors with Frequency Output.

An edge displacement sensor is one of the key technologies for building large segmented mirror astronomical optical telescopes. A digital interface is one novel approach for sensor technologies, digital transformation and the Internet of Things (IoT) in particular. Frequency output sensors and inductance-to-digital converter (LDC) demonstrated significant advantages in comparison with conventional sensors with analog-to-digital converter (ADC) interfaces. In order for the differential inductive frequency output displacement (DIFOD) sensor to meet the high-stability requirements of segmented mirror astronomical telescopes, it is important to understand the factors for time drift of the sensor. This paper focuses on the investigation of key factors of sensor structure and material, signal conditioning and interface, and fixtures for time drift to permanently installed applications. First, the measurement principle and probe structural characteristics of the sensor are analyzed. Then, two kinds of signal conditioning and digitalization methods using resonance circuits and LDC chips are implemented and compared. Finally, the time drift stability experiments are performed on the sensors with different signal conditioning methods and fixtures under controlled temperature. Experimental results show that the magnetic shield ring effectively improves the sensitivity and quality factor of the sensors, the time drift stability of the sensor using the signal conditioning based on resonance circuits is better than that of the sensors using LDC chips, and the root mean square (RMS) of the sensor time drift meets the requirement of 0.01 μm/24 h. This study will help further development of high-stability of frequency output sensors and IoT-based systems for scaled-up applications in the future.

Optical turbulence in the atmospheric surface layer at the Ali Observatory, Tibet

ABSTRACT In this paper, we make use of the ultrasonic anemometers placed on a 30-m high tower at the Ali Observatory, and we obtain a preliminary set of data covering 2017 April 29 to August 18. We sample quantities at heights of 6, 12 and 18 m above the ground. This is the first analysis from the site-testing campaign to report the detailed optical turbulence in the atmospheric surface layer (ASL) at Ali. The behaviour of optical turbulence parameters (Cn2 and seeing ε) in the ASL have been investigated. The Cn2 decreases with height exponentially, with the power series mainly between 10−15 and 10−13 throughout the day, and, especially, as low as 10−17 at night. Meanwhile, the h−1.1 dependency of Cn2 varying with height in the ASL is obtained, and this is especially close to h−1.3 after midday, which is similar to the h−4/3 dependency and the dependency of h−1.27 above Dome C. We also present statistics of the contribution of the ASL to the total seeing in the whole atmosphere at Ali: the median seeing above 6 m is about 0.86 arcsec; at night, the seeing values are almost below 1.0 arcsec; the seeing below 1.2 arcsec takes an account of nearly 98 per cent of the time. On the whole, the initial calculated and observed results, with the high altitude and unique longitudinal location, show that the Ali Observatory could prove to be a promising site for large optical telescopes.

Three dimensional isolation system for large ground-based optical telescope

Three dimensional isolation system for large ground-based optical telescope

Wind disturbance simulation and optical performance prediction for large ground-based optical telescopes based on two-dimensional stochastic fields

Wind disturbance simulation and optical performance prediction for large ground-based optical telescopes based on two-dimensional stochastic fields

The search for living worlds and the connection to our cosmic origins

One of the most exciting scientific challenges is to detect Earth-like planets in the habitable zones of other stars in the galaxy and search for evidence of life. During the past 20 years the detection of exoplanets, orbiting stars beyond our own, has moved from science fiction to science fact. From the first handful of gas giants, found through radial velocity studies, detection techniques have increased in sensitivity, finding smaller planets and diverse multi-planet systems. Through enhanced ground-based spectroscopic observations, transit detection techniques and the enormous productivity of the Kepler space mission, the number of confirmed planets has increased to more than 2000. Several space missions, including TESS (NASA), now operational, and PLATO (ESA), will extend the parameter space for exoplanet discovery towards the regime of rocky Earth-like planets and take the census of such bodies in the neighbourhood of the Solar System. The ability to observe and characterise dozens of potentially rocky Earth-like planets now lies within the realm of possibility due to rapid advances in key space and imaging technologies and active studies of potential missions have been underway for a number of years. The latest of these is the Large UV Optical IR space telescope (LUVOIR), one of four flagship mission studies commissioned by NASA in support of the 2020 US Decadal Survey. LUVOIR, if selected, will be of interest to a wide scientific community and will be the only telescope capable of searching for and characterizing a sufficient number of exo-Earths to provide a meaningful answer to the question “Are we alone?”. This contribution is a White Paper that has been submitted in response to the ESA Voyage 2050 Call.

Toward the Autonomous Assembly of Large Telescopes Using CubeSat Rendezvous and Docking

This paper describes the results of a system study for the in-space assembly of large optical telescopes using a building block approach involving multiple mirror segments. Such an approach is enabled by CubeSat rendezvous and docking and mirror steering technologies for compensating misalignment of the assembly. This concept thus removes the constraints imposed by the limited volume of launchers’ fairing, and hence larger telescope dimensions can be envisaged, leading to new observation capabilities. Each mirror segment is mounted on top of a small satellite, containing the miniaturized subsystems to achieve autonomous docking to either the service module containing the science instruments or other segments to build up the primary mirror. A systems’ design of all the elements constituting the assembly is provided, including tradeoffs, optimization, as well as mass and power budgets. The proposed solution scales with the size of the telescope and can be used to build primary mirrors as large as 20 m in diameter. The critical guidance, navigation, and control function is introduced, and related docking performances are presented. The results indicate that the in-space assembly of such large telescopes is feasible once these two key technologies are demonstrated in flight in the coming years.

Primary mirror segmentation for large optical telescopes: an inverse map projection approach.

Large segmented-mirror telescopes are powerful tools used in modern astronomy. Segmentation of the primary mirror is important for support design, mirror fabrication, and construction cost reduction. A curvature study showed that a primary mirror with a solid angle of less than π/6 can be well divided by projecting identical hexagonal tilings onto a curved surface. Three approaches, based on map projection, are presented. The conformal method, preserving the angle locally, provides optimal regularity. The equal-area algorithm generates a partition having zero area variation. The equidistant projection minimizes the circumscribed diameter of the segments. These approaches are unified by a newly proposed compromise approach, which provides the necessary adjustment range for individual preferences. The performances of the three approaches are numerically verified using the Thirty Meter Telescope model. This study verifies the effectiveness of the scaling rule and sheds light on the mechanism of primary mirror segmentation.

I3T: Intensity Interferometry Imaging Telescope

ABSTRACT We propose a new approach, based on the Hanbury Brown and Twiss intensity interferometry, to transform a Cherenkov telescope to its equivalent optical telescope. We show that, based on the use of photonics components borrowed from quantum-optical applications, we can recover spatial details of the observed source down to the diffraction limit of the Cherenkov telescope, set by its diameter at the mean wavelength of observation. For this, we propose to apply aperture synthesis techniques from pairwise and triple correlation of sub-pupil intensities, in order to reconstruct the image of a celestial source from its Fourier moduli and phase information, despite atmospheric turbulence. We examine the sensitivity of the method, i.e. limiting magnitude, and its implementation on existing or future high energy arrays of Cherenkov telescopes. We show that despite its poor optical quality compared to extremely large optical telescopes under construction, a Cherenkov telescope can provide diffraction limited imaging of celestial sources, in particular at the visible, down to violet wavelengths.

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.