Single Telescope Research Articles

Inflatable On-Axis and Off-Axis Space Telescope Designs

In the realm of astronomical scientific exploration, deployable and scalable approaches in space telescope systems are reshaping our understanding of the universe. Two revolutionary membrane-based space telescope designs, on-axis OASIS (Orbiting Astronomical Satellite for Investigating Stellar Systems) and off-axis SALTUS (Single Aperture Large Telescope for Universe Studies), have been developed as mid/far-infrared telescope concepts featuring an inflatable primary mirror. Through the scalable primary aperture design, these deployable space telescopes leverage an all-encompassing optical architecture that taps into the uncharted potential of extremely large telescope apertures. These visionary mission and optical designs pave the way for the next generation scalable telescopes of unprecedented dimensions and diffraction-limited imaging resolutions.

The Large Array Survey Telescope—Pipeline. I. Basic Image Reduction and Visit Coaddition

The Large Array Survey Telescope (LAST) is a wide-field telescope designed to explore the variable and transient sky with a high cadence and to be a test-bed for cost-effective telescope design. A LAST node is composed of 48 (32 already deployed), 28 cm f/2.2 telescopes. A single telescope has a 7.4 deg2 field of view and reaches a 5σ limiting magnitude of 19.6 (21.0) in 20 (20 × 20) s (filter-less), while the entire system provides a 355 deg2 field of view. The basic strategy of LAST is to obtain multiple 20 s consecutive exposures of each field (a visit). Each telescope carries a 61 Mpix camera, and the system produces, on average, about 2.2 Gbit s−1. This high data rate is analyzed in near real-time at the observatory site, using limited computing resources (about 700 cores). Given this high data rate, we have developed a new, efficient data reduction and analysis pipeline. The LAST data pipeline includes two major parts: (i) Processing and calibration of single images, followed by a coaddition of the visit’s exposures. (ii) Building the reference images and performing image subtraction and transient detection. Here we describe in detail the first part of the pipeline. Among the products of this pipeline are photometrically and astrometrically calibrated single and coadded images, 32 bit mask images marking a wide variety of problems and states of each pixel, source catalogs built from individual and coadded images, Point-Spread Function photometry, merged source catalogs, proper motion and variability indicators, minor planets detection, calibrated light curves, and matching with external catalogs. The entire pipeline code is made public. Finally, we demonstrate the pipeline performance on real data taken by LAST.

Robust free-space optical frequency transfer in time-varying link distances conditions

Future inter-satellite clock comparison on high orbit will require optical time and frequency transmission technology between moving objects. Here, we demonstrate robust optical frequency transmission under the condition of variable link distance. This variable link is accomplished by the relative motion of a single telescope fixed on the experimental platform to a corner-cube reflector (CCR) installed on a sliding guide. Two acousto–optic modulators with different frequencies are used to separate forward signal from backward signal. With active phase noise suppression, when the CCR moves back and forth at a constant velocity of 20 cm/s and an acceleration of 20 cm/s2, we achieve the best frequency stability of 1.9 × 10−16 at 1 s and 7.9 × 10−19 at 1000 s indoors. This work paves the way for future studying optical frequency transfer between ultra-high-orbit satellites.

Experimental verification of passive radar space object detection with a single low‐frequency array radio telescope

AbstractThe paper focuses on the results of experimental research on the possibility of passive space object detection using a single radio telescope from the European Low‐Frequency Array (LOFAR) network of astronomical radio telescopes. Commercial digital television (DVB‐T) transmitters were used as illuminators of opportunity in this radar system. In the conducted experiments, one LOFAR radio telescope served both as a surveillance receiver and reference receiver in a passive radar system. The greater part of the LOFAR telescope array was used to observe a space object, while a small part of the array was directed towards the illuminator of opportunity to record the reference signal. One of the most important problems to overcome with utilising the LOFAR radio telescope in such a solution was the effective suppression of the direct‐path component in a surveillance signal coming from the illuminator of opportunity, which was relatively close to the LOFAR radio telescope. The results regarding the passive detection of the International Space Station, included in the paper, confirm the possibility of observing the space object flying in Low‐Earth Orbit using the LOFAR telescope or another receiving system with a similar antenna array.

A population of Type Ibc supernovae with massive progenitors

If high-mass stars (≳20 − 25 M⊙) are the progenitors of stripped-envelope (SE) supernovae (SNe), their massive ejecta should lead to broad, long-duration lightcurves. Instead, literature samples of SE SNe have reported relatively narrow lightcurves corresponding to ejecta masses between 1 − 4 M⊙ that favor intermediate-mass progenitors (≲20 − 25 M⊙). Working with an untargeted sample from a single telescope to better constrain their rates, we searched the Palomar Transient Factory (PTF) and intermediate-PTF (iPTF) sample of SNe for SE SNe with broad lightcurves. Using a simple observational marker of g- or r-band lightcurve stretch compared to a template to measure broadness, we identified eight significantly broader Type Ibc SNe after applying quantitative sample selection criteria. The lightcurves, broad-band colors, and spectra of these SNe are found to evolve more slowly relative to typical Type Ibc SNe, proportional with the stretch parameter. Bolometric lightcurve modeling and their nebular spectra indicate high ejecta masses and nickel masses, assuming radioactive decay powering. Additionally, these objects are preferentially located in low-metallicity host galaxies with high star formation rates, which may account for their massive progenitors, as well as their relative absence from the literature. Our study thus supports the link between broad lightcurves (as measured by stretch) and high-mass progenitor stars in SE SNe with independent evidence from bolometric lightcurve modeling, nebular spectra, host environment properties, and photometric evolution. In the first systematic search of its kind using an untargeted sample, we used the stretch distribution to identify a higher than previously appreciated fraction of SE SNe with broad lightcurves (∼13%). Correcting for Malmquist and lightcurve duration observational biases, we conservatively estimate that a minimum of ∼6% of SE SNe are consistent with high-mass progenitors. This result has implications for the progenitor channels of SE SNe, including late stages of massive stellar evolution, the origin of the observed oxygen fraction in the universe, and formation channels for stellar-mass black holes.

Low Blind Zone Atmospheric Lidar Based on Fiber Bundle Receiving

Atmospheric constituents feature a large vertical gradient in concentration, especially at the first few hundred meters over the earth’s surface. Atmospheric lidar usually cannot cover this range due to the incomplete overlap effect or the limited dynamic range of detectors. This drawback is well known as the blind zone effect, which hinders the application of atmospheric lidars in many aspects. In this work, a method based on an optical fiber bundle was proposed to mitigate the blind zone effect. An optical fiber head with several stages, installed at the focal plane of the telescope, is used to receive backscatter light from different range levels. The design of the optical fiber head is analyzed with the ray-tracing technique. The optical fiber installed at the highest stage of the fiber head can collect far-range light like a small aperture, and all the other optical fibers are bundled into a near-range detection channel to receive backscatter light from the first few hundred meters. This special design can avoid the near-range light loss in conventional lidar systems, usually equipped with a small aperture. Different optical attenuations are then applied to near-range and far-range channels to suppress the overall signal dynamic range. This light-receiving method was applied in a 1030 nm elastic lidar, in which a fiber bundle with a three-stage fiber head was fabricated and installed. A test experiment was performed to verify this approach. A good agreement between simulations and in-system results was found. Based on this design, the blind zone of the lidar system is less than 50 m, and the detectable range can be over 10 km along the lidar’s line of sight with a single telescope receiver. This approach brings a new way of designing atmospheric lidar with a low blind zone and can strengthen our ability to monitor urban pollution and promote land-atmosphere interaction research.

The Large Array Survey Telescope—Science Goals

The Large Array Survey Telescope (LAST) is designed to survey the variable and transient sky at high temporal cadence. The array is comprised of 48 F/2.2 telescopes of 27.9 cm aperture, coupled to full-frame backside-illuminated cooled CMOS detectors with 3.76 μm pixels, resulting in a pixel scale of 1.″25. A single telescope with a field of view of 7.4 deg2 reaches a 5σ limiting magnitude of 19.6 in 20 s. LAST 48 telescopes are mounted on 12 independent mounts—a modular design which allows us to conduct optimized parallel surveys. Here we provide a detailed overview of the LAST survey strategy and its key scientific goals. These include the search for gravitational-wave (GW) electromagnetic counterparts with a system that can cover the uncertainty regions of the next-generation GW detectors in a single exposure, the study of planetary systems around white dwarfs, and the search for near-Earth objects. LAST is currently being commissioned, with full scientific operations expected in mid 2023. This paper is accompanied by two complementary publications in this issue, giving an overview of the system and of the dedicated data reduction pipeline.

Phased Array Feed Experiments and Galactic H i Observations

The Phased Array Feed (PAF) is considered as one of the next generation receivers for radio telescopes, which can significantly enlarge the instantaneous Field-of-View of large aperture single dish radio telescopes and enable more flexible observing configurations. Study efforts on PAF development for radio telescopes have been made for more than two decades and have become more and more applicable. We report the development of an ambient-temperature 19 element L-band PAF system and the experimental results including its far field beam pattern and system temperature measurement, which achieve the expectations. Implementing the aperture array beam-forming method, we demonstrate a wide-field Galactic H i observations in the radio camera mode. The results indicate that this system might be applicable for strong Galactic transient detections. This system could be directly equipped to large telescopes like the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and FAST array in the future.

Research on Physical Properties in NGC 1068 Nuclear Region Based on ALMA High-resolution Multi-spectral Lines

Using the multi-spectral lines from ALMA (Atacama Large Millimeter/submillimeter Array) with high-resolution (∼ 0.2″–0.7″) and the continuum data, this work studies the physical properties of the nuclear region of nearby galaxy NGC 1068. The spectral lines include CO (1-0), CO (2-1), CO (3-2), HCN (1-0), HCO+ (1-0), HCN (3-2), HCO+ (3-2), HCN (4-3) and HCO+ (4-3). The CND (CircumNuclear Disk) shows an asymmetric ring structure with a size of ∼ 300 pc in the velocity-integrated intensity images. All the molecular lines of the CND show stronger emission at the eastern knot (E-knot) than the western knot (W-knot) of the CND. Furthermore, the E-knot shows larger velocities than the W-knot, which indicates that there is significant rotational pattern in the CND. The dense gas fraction (traced by the different transitions of HCN or HCO+ to CO (1-0) integrated intensity ratios) and dense gas ratio (HCN/HCO+) are higher at the E-knot, implying that the E- and W-knots have different physical environments or chemical compositions. The HCN emission in the CND show enhancement compared with HCO+, which could be affected by the AGN (Active Galactic Nucleus) radiation and starburst activity. The CO (3-2)/CO (1-0) integrated intensity ratio is a significant indicator of gas excitation. CO (3-2)/CO (1-0) ratios show much higher values at the E-knot, suggesting that there is molecular excitation enhancement caused by the extreme physical environment. Compared with the fluxes of HCN (4-3) and HCO+ (4-3) from the single-dish telescope JCMT (James Clerk Maxwell Telescope), the ALMA missing fluxes of dense molecular gas on 1 kpc scale are about 10%–20%. The spectral lines show that the flux ratios between E-knot and W-knot are ∼ 1.8–3.9. These differences shown between E-knot and W-knot may be associated with the AGN feedback. In addition, the CO (2-1), CO (1-0) and HCO+ (1-0) spectra show absorption features in the position of AGN. This absorption could be caused by the strong background of continuum emissions, and the gas inflow around the AGN can produce self-absorption in spectra.

Photonic beam-combiner for visible interferometry with Subaru coronagraphic extreme adaptive optics/fibered imager for a single telescope: laboratory characterization and design optimization

Photonic beam-combiner for visible interferometry with Subaru coronagraphic extreme adaptive optics/fibered imager for a single telescope: laboratory characterization and design optimization

A horn-coupled millimetre-wave on-chip spectrometer based on lumped-element kinetic inductance detectors

Context. Millimetre-wave astronomy is an important tool for both general astrophysics studies and cosmology. A large number of unidentified sources are being detected by the large field-of-view continuum instruments operating on large telescopes. Aims. New smart focal planes are needed to bridge the gap between the large bandwidth continuum instruments operating on single-dish telescopes and high spectral and angular resolution interferometers (e.g. ALMA in Chile and NOEMA in France). The aim is to perform low to medium spectral resolution observations and select a lower number of potentially interesting sources (i.e. high-redshift galaxies) for further follow-up. Methods. We have designed, fabricated, and tested an innovative on-chip spectrometer sensitive in the 85–110 GHz range. It contains 16 channels, each of which covers a frequency band of about 0.2 GHz. A conical horn antenna coupled to a slot in the ground plane collects the radiation and guides it to a millimetre-wave microstrip transmission line placed on the other side of the mono-crystalline substrate. The millimetre-wave line is coupled to a filter-bank spectrometer. Each filter is capacitively coupled to a lumped-element kinetic inductance detector (LEKID). The microstrip configuration provides the benefit of low loss, due to the mono-crystalline substrate, and protects the LEKIDs from illumination by stray un-filtered light. Results. The prototype spectrometer exhibits a spectral resolution R = λ/Δλ ≈ 300. The optical noise equivalent power is in the low 10−16 W Hz−1/2 range for an incoming power of about 0.2 pW per channel. The device is polarisation-sensitive, with a cross-polarisation lower than 1% for the best channels.

Precise Distance Measurement for a Near-Earth Asteroid by the Refined Rotational Reflex Velocity Method

The rotational reflex velocity (RRV) method was proposed by Heinze and Metchev in 2015 and was used to measure the distances of main-belt asteroids (MBAs). Later, Lin et al. generalized this method using spherical astronomy in 2016. The method measures the distances of MBAs using the observations from a single ground-based telescope over two nights. We refined this method and extend it further to the distance measurement of near-Earth asteroids (NEAs). In practice, we measure the distance of the potentially hazardous asteroid (99942) Apophis from the acquired CCD frames using the newly refined method. According to the requirement of the newly refined method, we also simulate the distance measurements of the four typical NEAs, (1221) Amor, (1862) Apollo, (2062) Aten, and (163693) Atira, on their discovery dates and follow-up dates. The measurement results of Apophis based on the newly refined RRV method show that the mean relative errors for the independent exposure frames on the successive two nights is ∼0.08% (about a factor of 2 improvement in comparison with the research of Lin et al.) compared with the distance from JPL ephemeris. Our simulation results also show that this refined method can accurately and precisely measure the distances of newly discovered NEAs in an astrometric way without performing orbital determination. The accurate and precise distances of newly discovered asteroids help us to conveniently evaluate their impact risks within a shorter time, leaving us more time to take defense precautions.

Simultaneous Time-monitoring Observations of H2O and SiO Masers toward the Supergiant VX Sagittarii

We performed simultaneous monitoring observations of the 22.2 GHz H2O and 43.1/42.8/86.2/129.3 GHz SiO masers toward the red supergiant VX Sagittarii using the Korean VLBI Network single-dish telescopes. The observations were conducted about every 2 months from 2013 May to 2019 January (30 epochs in total). They included four optical maxima in the active phase of the optical pulsation cycles. The line profile of a H2O maser always comprised various velocity components with a wider velocity range and varied from highly redshifted to blueshifted velocities with respect to the stellar velocity, in contrast to those of the SiO masers. We examined the relation between peak intensities and velocities of 11 detailed components in the line profile of the H2O maser and the pulsation phases. The peak intensity of each component generally exhibited a better correlation with the pulsation phases than that of total intensity. The peak velocities of several components gradually decreased or increased with respect to the stellar velocity, implying an accelerating motion and the development of asymmetries in the H2O maser region. The characteristics of four transition SiO maser properties were compared according to the stellar pulsation phases. The intensity and velocity variation trend of the 43.1 GHz SiO maser was similar to that of the 42.8 GHz SiO maser. However, the variation trend of the 43.1 and 42.8 GHz SiO masers was different from that of the 86.2 and 129.3 GHz SiO masers. This difference stems from the different location of each maser reflecting a different excitation condition.

Constraints on the non-thermal desorption of methanol in the cold core LDN 429-C

Context. Cold cores are one of the first steps of star formation, characterized by densities of a few 104–105 cm−3, low temperatures (15 K and below), and very low external UV radiation. In these dense environments, a rich chemistry takes place on the surfaces of dust grains. Understanding the physico-chemical processes at play in these environments is essential to tracing the origin of molecules that are predominantly formed via reactions on dust grain surfaces. Aims. We observed the cold core LDN 429-C (hereafter L429-C) with the NOEMA interferometer and the IRAM 30 m single dish telescope in order to obtain the gas-phase abundances of key species, including CO and CH3OH. Comparing the data for methanol to the methanol ice abundance previously observed with Spitzer allows us to put quantitative constraints on the efficiency of the non-thermal desorption of this species. Methods. With physical parameters determined from available Herschel data, we computed abundance maps of 11 detected molecules with a non-local thermal equilibrium (LTE) radiative transfer model. These observations allowed us to probe the molecular abundances as a function of density (ranging from a few 103 to a few 106 cm−3) and visual extinction (ranging from 7 to over 75), with the variation in temperature being restrained between 12 and 18 K. We then compared the observed abundances to the predictions of the Nautilus astrochemical model. Results. We find that all molecules have lower abundances at high densities and visual extinctions with respect to lower density regions, except for methanol, whose abundance remains around 4.5 × 10−10 with respect to H2. The CO abundance spreads over a factor of 10 (from an abundance of 10−4 with respect to H2 at low density to 1.8 × 10−5 at high density) while the CS, SO, and H2S abundances vary by several orders of magnitude. No conclusion can be drawn for CCS, HC3N, and CN because of the lack of detections at low densities. Comparing these observations with a grid of chemical models based on the local physical conditions, we were able to reproduce these observations, allowing only the parameter time to vary. Higher density regions require shorter times than lower density regions. This result can provide insights on the timescale of the dynamical evolution of this region. The increase in density up to a few 104 cm−3 may have taken approximately 105 yr, while the increase to 106 cm−3 occurs over a much shorter time span (104 yr). Comparing the observed gas-phase abundance of methanol with previous measurements of the methanol ice, we estimate a non-thermal desorption efficiency between 0.002 and 0.09%, increasing with density. The apparent increase in the desorption efficiency cannot be reproduced by our model unless the yield of cosmic-ray sputtering is altered due to the ice composition varying as a function of density.

A Multilevel Scheduling Framework for Distributed Time-domain Large-area Sky Survey Telescope Array

Telescope arrays are receiving increasing attention due to their promise of higher resource utilization, greater sky survey area, and higher frequency of full space-time monitoring than single telescopes. Compared with the ordinary coordinated operation of several telescopes, the new astronomical observation mode has an order of magnitude difference in the number of telescopes. It requires efficient coordinated observation by large-domain telescopes distributed at different sites. Coherent modeling of various abstract environmental constraints is essential for responding to multiple complex science goals. Also, due to competing science priorities and field visibility, how the telescope arrays are scheduled for observations can significantly affect observation efficiency. This paper proposes a multilevel scheduling model oriented toward the problem of telescope-array scheduling for time-domain surveys. A flexible framework is developed with basic functionality encapsulated in software components implemented on hierarchical architectures. An optimization metric is proposed to self-consistently weight contributions from time-varying observation conditions to maintain uniform coverage and efficient time utilization from a global perspective. The performance of the scheduler is evaluated through simulated instances. The experimental results show that our scheduling framework performs correctly and provides acceptable solutions considering the percentage of time allocation efficiency and sky coverage uniformity in a feasible amount of time. Using a generic version of the telescope-array scheduling framework, we also demonstrate its scalability and its potential to be applied to other astronomical applications.

FEASTS: IGM Cooling Triggered by Tidal Interactions through the Diffuse H i Phase around NGC 4631

We use the single-dish radio telescope Five-hundred meter Aperture Spherical Telescope (FAST) to map the H i in the tidally interacting NGC 4631 group with a resolution of 3.′24 (7 kpc), reaching a 5σ column density limit of 1017.9 cm−2 assuming a line width of 20 km s−1. Taking the existing interferometric H i image from the Hydrogen Accretion in LOcal GAlaxieS project of Westerbork Synthesis Radio Telescope as a reference, we are able to identify and characterize a significant excess of large-scale, low-density, and diffuse H i in the group. This diffuse H i extends more than 120 kpc across, and accounts for more than one-fourth of the total H i detected by FAST in and around the galaxy NGC 4631. In the region of the tidal tails, the diffuse H i has a typical column density above 1019.5 cm−2, and is highly turbulent with a velocity dispersion of around 50 km s−1. It increases in column density with the dense H i, and tends to be associated with the kinematically hotter part of the dense H i. Through simple modeling, we find that the majority of the diffuse H i in the tail region is likely to induce cooling out of the hot intragalactic medium (IGM) instead of evaporating or being radiatively ionized. Given these relations of gas in different phases, the diffuse H i may represent a condensing phase of the IGM. Ongoing and past active tidal interactions may have produced the wide-spreading H i distribution, and triggered the gas accretion to NGC 4631 through the phase of the diffuse H i.

The Haystack Telescope as an Astronomical Instrument

The Haystack Telescope is an antenna with a diameter of 37 m and an elevation-dependent surface accuracy of ≤100μm that is capable of millimeter-wave observations. The radome-enclosed instrument serves as a radar sensor for space situational awareness, with about one-third of the time available for research by MIT Haystack Observatory. Ongoing testing with the K-band (18–26 GHz) and W-band receivers (currently 85–93 GHz) is preparing the inclusion of the telescope into the Event Horizon Telescope (EHT) array and the use as a single-dish research telescope. Given its geographic location, the addition of the Haystack Telescope to current and future versions of the EHT array would substantially improve the image quality.

Modeling and Analysis of the Active Surface System for the Large Single-Dish Sub-mm Telescope

Enlarging antenna diameter while maintaining an accurate reflective surface is important in the development of next-generation single-dish sub-mm telescopes. In this article, we propose an emulation and optimization method of the active surface system (EOMASS) for large single-dish sub-mm telescopes. The proposed method involves three main steps: 1) building an active surface system model (ASSM) based on the whole finite element model (FEM) of the large single-dish sub-mm telescope, which includes the main reflector, realistic adjustment models of actuators, backup structure and so on; 2) emulating the reflective surface deformation compensation under gravity based on the initial distribution of the actuators with the ASSM, in consideration of the manufacturing error of panels; and 3) further optimizing the number and distribution of actuators based on the illumination function, and predicting the performance of the sub-mm antenna due to the limited number of faulty actuators. As an application example, a 60 m single-dish sub-mm telescope is analyzed under gravity with the proposed EOMASS. The results demonstrate that the proposed EOMASS is an effective and advanced method, providing a feasible precision design of the active surface system for a large single-dish sub-mm telescope.

Toward a Phase Adaptive Stabilization System for Next-Generation Single-Dish Sub-mm Telescope Part—I: Multipath Phase Measurements Based on Ultrastable Microwave Signal Distribution

Large-aperture, single-dish, submillimeter-wave (sub-mm) telescopes are important to our understanding of the universe, but it is a long-term outstanding challenge to make the single-dish sub-mm telescopes larger while keeping a high accuracy of their surfaces. A bottleneck in the context of the size and the operating wavelengths of such telescopes is the deterioration of wavefront errors (phase shift) due to the deformation of reflective surfaces. Here proposed is a phase adaptive stabilization system (PASS), functioning as adaptive optics system of radio frenquency, an essential tool for overcoming the challenge, which is based on a state-of-the-art ultra-stable microwave signal distribution (UMSD) technology. The UMSD system with a phase drift of less than 11 fsec rms over 600 sec, is specially proposed for the PASS, which is an innovation. The results of outfield experiments have shown that the PASS is sufficiently accurate to measure the changes in the excess path length down to the level of 20 μm, which is the highest accuracy reported up to now. Our study marks a major step towards the phase adaptive stabilization system.

Automated optical inspection of FAST’s reflector surface using drones and computer vision

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the world ’ s largest single-dish radio telescope. Its large reflecting surface achieves unprecedented sensitivity but is prone to damage, such as dents and holes, caused by naturally-occurring falling objects. Hence, the timely and accurate detection of surface defects is crucial for FAST’s stable operation. Conventional manual inspection involves human inspectors climbing up and examining the large surface visually, a time-consuming and potentially unreliable process. To accelerate the inspection process and increase its accuracy, this work makes the first step towards automating the inspection of FAST by integrating deep-learning techniques with drone technology. First, a drone flies over the surface along a predetermined route. Since surface defects significantly vary in scale and show high inter-class similarity, directly applying existing deep detectors to detect defects on the drone imagery is highly prone to missing and misidentifying defects. As a remedy, we introduce cross-fusion, a dedicated plug-in operation for deep detectors that enables the adaptive fusion of multi-level features in a point-wise selective fashion, depending on local defect patterns. Consequently, strong semantics and fine-grained details are dynamically fused at different positions to support the accurate detection of defects of various scales and types. Our AI-powered drone-based automated inspection is time-efficient, reliable, and has good accessibility, which guarantees the long-term and stable operation of FAST.