Showing papers in "Journal of Astronomical Instrumentation in 2022"

Radio Antenna Design for Sky-Averaged 21cm Cosmology Experiments: The REACH Case

Abstract: Following the reported detection of an absorption profile associated with the 21[Formula: see text]cm sky-averaged signal from the Cosmic Dawn by the EDGES experiment in 2018, a number of experiments have been set up to verify this result. This paper discusses the design process used for global 21[Formula: see text]cm experiments, focusing specifically on the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH). This experiment will seek to understand and compensate for systematic errors present using detailed modeling and characterization of the instrumentation. Detailed quantitative figures of merit and numerical modeling are used to assist the design process of the REACH dipole antenna (one of the two antenna designs for REACH Phase I). This design process produced a 2.5:1 frequency bandwidth dipole. The aim of this design was to balance spectral smoothness and low impedance reflections with the ability to describe and understand the antenna response to the sky signal to inform the critically important calibration during observation and data analysis.

First light of the Integral Field Unit of GRIS on the GREGOR solar telescope

Abstract: An Integral Field Unit (IFU) based on image-slicers has been added to the GREGOR Infrared Spectrograph (GRIS). This upgrade to the instrument makes possible 2D spectropolarimetry in the near-infrared by simulta-neously recording the full Stokes profiles of spectral lines (in a given spectral interval) at all the points in the field of view. It provides high-cadence spectropolarimetric observations at the instrument’s high spatial resolution and high polarization sensitivity at the GREGOR solar telescope. The IFU is ideal for observing the polarized spectrum of fast-evolving solar features at high spatial and spectral resolutions. The high observing cadence opens the possibility of time-series observations. The analysis of observations to this level of accuracy is essential for understanding the complex dynamics and interactions of solar plasma and magnetic fields. The image slicer of the IFU has eight slices of width 100 µ m, covering a total field of view of 6 (cid:48)(cid:48) × 3 (cid:48)(cid:48) . It was designed and built within the framework of the European projects SOLARNET and GREST, as a prototype for future instruments of the European Solar Telescope (EST) and was integrated into GRIS. After two commissioning campaigns in 2017 and 2018, the IFU was finally installed at the end of September 2018 and offered to all observers who use the telescope.

First Light of the Integral Field Unit of GRIS on the GREGOR Solar Telescope

Abstract: An Integral Field Unit (IFU) based on image-slicers has been added to the GREGOR Infrared Spectrograph (GRIS). This upgrade to the instrument makes possible 2D spectropolarimetry in the near-infrared by simultaneously recording the full Stokes profiles of spectral lines (in a given spectral interval) at all the points in the field of view. It provides high-cadence spectropolarimetric observations at the instrument's high spatial resolution and high polarization sensitivity at the GREGOR solar telescope. The IFU is ideal for observing the polarized spectrum of fast-evolving solar features at high spatial and spectral resolutions. The high observing cadence opens the possibility of time-series observations. The analysis of observations to this level of accuracy is essential for understanding the complex dynamics and interactions of solar plasma and magnetic fields. The image slicer of the IFU has eight slices of width 100 micron, covering a total field of view of 6" x 3". It was designed and built within the framework of the European projects SOLARNET and GREST, as a prototype for future instruments of the European Solar Telescope (EST) and was integrated into GRIS. After two commissioning campaigns in 2017 and 2018, the IFU was finally installed at the end of September 2018 and offered to all observers who use the telescope.

Overview of The Galileo Project

Abstract: The Galileo Project is the first systematic scientific research program in search for potential astro-archaeological artifacts or remnants of extraterrestrial technological civilizations (ETCs) or potentially active equipment near Earth. Taking a path not taken, it conceivably may pick some low-hanging fruit, and without asserting probabilities - make discoveries of ETC-related objects, which would have far-reaching implications for science and our worldview.

Exoplanet detection with Genesis

Abstract: Convolutional Neural Networks (CNNs) have shown to offer a consistent and reliable foundation for the automatic detection of potential exoplanets. CNNs rely on an abundance of parameters (overparameterization) to achieve their impressive detection performances. Astronet was one of the first CNNs for exoplanet detection. It takes as input folded lightcurves in two views: a local view (the transit) and a global view (the entire orbital period including the transit). A more recent CNN called Exonet-XS improved on Astronet’s performance while having considerably less parameters, thereby reducing the risk of overfitting. Exonet-XS also uses two views as input. In this paper, we propose Genesis, an even more simplified CNN for exoplanet detection from folded lightcurves using only one view. In addition, we propose to use a more reliable validation procedure that is custom in CNN-based exoplanet detection studies: the Monte Carlo Cross-Validation (MCCV) procedure. We show that the use of MCCV improves the reliability of the estimation of the detection performance by providing a (discretized) probability distribution, rather than a point estimate. Using MCCV we show that Astronet with only one view performs on a par with the original two-view version. More importantly, our fair comparative evaluation (without stellar parameters and centroids) reveals that Genesis outperforms Exonet-XS and Astronet. We conclude by stating that existing exoplanet detection CNNs are too complex for the task at hand and that future evaluations of performances should use MCCV or similar validation procedures.

The Marshall Grazing Incidence X-ray Spectrometer (<i>MaGIXS</i>)

Abstract: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket instrument that flew on July 30, 2021 from the White Sands Missile Range, NM. The instrument was designed to address specific science questions that require differential emission measures of the solar soft X-ray spectrum from 6 – 25[Formula: see text]Å(0.5 – 2.1[Formula: see text]keV). MaGIXS comprises a Wolter-I telescope, a slit-jaw imaging system, an identical pair of grazing incidence paraboloid mirrors, a planar grating and a CCD camera. While implementing this design, some limitations were encountered in the production of the X-ray mirrors, which ended up as a catalyst for the development of a deterministic polishing approach and an improved meteorological technique that utilizes a computer-generated hologram (CGH). The opto-mechanical design approach addressed the need to have adjustable and highly repeatable interfaces to allow for the complex alignment between the optical sub-assemblies. The alignment techniques employed when mounting the mirrors and throughout instrument integration and end-to-end testing are discussed. Also presented are spatial resolution measurements of the end-to-end point-spread-function that were obtained during testing in the X-ray Cryogenic Facility (XRCF) at NASA Marshall Space Flight Center. Lastly, unresolved issues and off-nominal performance are discussed.

Performance Analysis Techniques for Real-Time Broadband RFI Filtering System of uGMRT

Abstract: Electromagnetic radiation from human activities, known as man-made Radio Frequency Interference (RFI), adversely affects radio astronomy observations. In the vicinity of the Upgraded Giant Metrewave Radio Telescope (uGMRT) array, the sparking on power lines is the major cause of interference at observing frequencies less than 800[Formula: see text]MHz. A real-time broadband RFI detection and filtering system is implemented as part of the uGMRT wideband signal processing backend to mitigate the effect of broadband RFI. Performance analysis techniques used for testing and commissioning the system for observations in the beamformer and correlator modes of the uGMRT are presented. The concept and implementation of recording simultaneous unfiltered and filtered data along with data analysis and interpretation is illustrated using an example. For the beamformer mode, spectrogram, single spectral channel, and its Fourier transform is used for performance analysis whereas, in the correlator mode, the cross-correlation function, closure phase, and visibilities from the simultaneously recorded unfiltered and filtered is carried out. These techniques are used for testing the performance of the broadband RFI filter and releasing it for uGMRT users.

First Lunar Occultation Results with the TIRCAM2 Near-Infrared Imager at the Devasthal 3.6-m Telescope

Abstract: TIRCAM2 is the facility near-infrared Imager at the Devasthal 3.6-m telescope in northern India, equipped with an Aladdin III InSb array detector. We have pioneered the use of TIRCAM2 for very fast photometry, with the aim of recording Lunar Occultations (LO). This mode is now operational and publicly offered. In this paper we describe the relevant instrumental details, we provide references to the LO method and the underlying data analysis procedures, and we list the LO events recorded so far. Among the results, we highlight a few which have led to the measurement of one small-separation binary star and of two stellar angular diameters. We conclude with a brief outlook on further possible instrumental developments and an estimate of the scientific return. In particular, we find that the LO technique can detect sources down to K ≈ 9mag with SNR=1 on the DOT telescope. Angular diameters larger than ≈ 1milliarcsecond (mas) could be measured with SNR above 10, or K ≈ 6mag. These numbers are only an indication and will depend strongly on observing conditions such as lunar phase and rate of lunar limb motion. Based on statistics alone, there are several thousands LO events observable in principle with the given telescope and instrument every year.

First Light Preparations of the 4m ILMT

Abstract: The 4[Formula: see text]m International Liquid Mirror Telescope (ILMT) is a zenith-pointing optical observing facility at ARIES Devasthal observatory (Uttarakhand, India). The first light preparatory activities of the ILMT were accomplished in April 2022 followed by on-sky tests that were carried out at the beginning of May 2022. This telescope will perform a multi-band optical (SDSS [Formula: see text], [Formula: see text] and [Formula: see text]) imaging of a narrow strip ([Formula: see text]) of sky utilizing the time-delayed integration technique. Single-scan ILMT images have an integration time of 102[Formula: see text]s and consecutive-night images can be co-added to further improve the signal-to-noise ratio. An image subtraction technique will also be applied to the nightly recorded observations in order to detect transients, objects exhibiting variations in flux or position. Presently, the facility is in the commissioning phase and regular operation will commence in March 2023. This paper presents a discussion of the main preparation activities before first light, along with preliminary results obtained.

Performance Analysis Techniques for Real-time Broadband RFI Filtering System of uGMRT

Abstract: Electromagnetic man-made Frequency adversely affects radio astronomy observations. In the vicinity of the Upgraded Giant Metrewave Radio Telescope (uGMRT) array, the sparking on power lines is the major cause of interference at observing frequencies less than 800 MHz. A real-time broadband RFI detection and filtering system is implemented as part of the uGMRT wideband signal processing backend to mitigate the effect of broadband RFI. Performance analysis techniques used for testing and commissioning the system for observations in the beamformer and correlator modes of the uGMRT are presented. The concept and implementation of recording simultaneous unfiltered and filtered data along with data analysis and interpretation is illustrated using an example. For the beamformer mode, spectrogram, single spectral channel, and its Fourier transform is used for performance analysis whereas, in the correlator mode, the cross-correlation function, closure phase, and visibilities from the simultaneously recorded unfiltered and filtered is carried out. These techniques are used for testing the performance of the broadband RFI filter and releasing it for uGMRT users.

Multi-Band Acoustic Monitoring of Aerial Signatures

Abstract: The Galileo Project's acoustic monitoring, omni-directional system (AMOS) aids in the detection and characterization of aerial phenomena. It uses a multi-band microphone suite spanning infrasonic to ultrasonic frequencies, providing an independent signal modality for validation and characterization of detected objects. The system utilizes infrasonic, audible, and ultrasonic systems to cover a wide range of sounds produced by both natural and man-made aerial phenomena. Sound signals from aerial objects can be captured given certain conditions, such as when the sound level is above ambient noise and isn't excessively distorted by its transmission path. Findings suggest that audible sources can be detected up to 1 km away, infrasonic sources can be detected over much longer distances, and ultrasonic at shorter ones. Initial data collected from aircraft recordings with spectral analysis will help develop algorithms and software for quick identification of known aircraft. Future work will involve multi-sensor arrays for sound localization, larger data sets analysis, and incorporation of machine learning and AI for detection and identification of more types of phenomena in all frequency bands.

A Hardware and Software Platform for Aerial Object Localization

Abstract: To date, there are little reliable data on the position, velocity and acceleration characteristics of Unidentified Aerial Phenomena (UAP). The dual hardware and software system described in this document provides a means to address this gap. We describe a weatherized multi-camera system which can capture images in the visible, infrared and near infrared wavelengths. We then describe the software we will use to calibrate the cameras and to robustly localize objects-of-interest in three dimensions. We show how object localizations captured over time will be used to compute the velocity and acceleration of airborne objects.

Physical Considerations for an Intercept Mission to a 1I/'Oumuamua-like Interstellar Object

Abstract: In this paper, we review some of the extant literature on the study of interstellar objects (ISOs). With the forthcoming Vera C. Rubin Telescope and Legacy Survey of Space and Time (LSST), we find that 0 . 38 − 84 ‘Oumuamua-like interstellar objects are expected to be detected in the next 10 years, with 95% confidence. The feasibility of a rendezvous trajectory has been demonstrated in previous work. In this paper, we investigate the requirements for a rendezvous mission with the primary objective of producing a resolved image of an interstellar object. We outline the rendezvous distances necessary as a function of resolution elements and object size. We expand upon current population synthesis models to account for the size dependency on the detection rates for reachable interstellar objects. We assess the trade-off between object diameter and occurrence rate, and conclude that objects with the size range between a third of the size and the size of ‘Oumuamua will be optimal targets for an imaging rendezvous. We also discuss expectations for surface properties and spectral features of interstellar objects, as well as the benefits of various spacecraft storage locations.

Local Oscillator Concept for the Event Horizon Imager

Abstract: The Event Horizon Imager (EHI) is a mission concept conceived to provide a radio image of the surroundings of the event horizons of SgrA* and M87* supermassive black holes with an angular resolution at least an order of magnitude better than that achievable by radio telescopes on ground. The concept is based on performing space-to-space very long baseline interferometry (VLBI) using two satellites in medium Earth orbit at slightly different altitudes. Projected baselines up to about 26,000[Formula: see text]km and down to a few tens of kilometers can be realized. Free of atmospheric perturbations, EHI is observed in three channels: 557[Formula: see text]GHz, the main frequency to achieve the finest angular resolution by minimizing the scattering of the inter-stellar medium towards our galactic center; 230[Formula: see text]GHz, inherited from the event horizon telescope (EHT); finally, 43[Formula: see text]GHz in support of the relative delay determination. The whole EHI concept relies on very precise relative positioning between the two satellites including wavelength bootstrapping and a novel local oscillator concept that is the topic of this paper. It is shown that atomic clocks cannot provide sufficient coherence over the needed integration time. Instead, a system consisting of conventional crystal oscillators and an inter-satellite link (ISL) that can work coherently for extended periods of time, longer than required, and is therefore better suited for EHI is demonstrated.

SkyWatch: A Passive Multistatic Radar Network for the Measurement of Object Position and Velocity

Abstract: (Abridged) Quantitative three-dimensional (3D) position and velocity estimates obtained by passive radar will assist the Galileo Project in the detection and classification of aerial objects by providing critical measurements of range, location, and kinematics. These parameters will be combined with those derived from the Project{\textquoteright}s suite of electromagnetic sensors and used to separate known aerial objects from those exhibiting anomalous kinematics. SkyWatch, a passive multistatic radar system based on commercial broadcast FM radio transmitters of opportunity, is a network of receivers spaced at geographical scales that enables estimation of the 3D position and velocity time series of objects at altitudes up to 80km, horizontal distances up to 150km, and at velocities to {\textpm}2{\textpm}2km/s ({\textpm}6{\textpm}6Mach). The receivers are designed to collect useful data in a variety of environments varying by terrain, transmitter power, relative transmitter distance, adjacent channel strength, etc. In some cases, the direct signal from the transmitter may be large enough to be used as the reference with which the echoes are correlated. In other cases, the direct signal may be weak or absent, in which case a reference is communicated to the receiver from another network node via the internet for echo correlation. Various techniques are discussed specific to the two modes of operation and a hybrid mode. Delay and Doppler data are sent via internet to a central server where triangulation is used to deduce time series of 3D positions and velocities. A multiple receiver (multistatic) radar experiment is undergoing Phase 1 testing, with several receivers placed at various distances around the Harvard{\textendash}Smithsonian Center for Astrophysics (CfA), to validate full 3D position and velocity recovery.

ARIES 130-cm Devasthal Fast Optical Telescope - Operation and Outcome

Abstract: This paper studies about the 130-cm Devasthal Fast Optical Telescope (DFOT) at Devasthal, India that has been in operation for more than 10 years and is the main workhorse for the photometric observations for a wide range of scientific programs carried out at ARIES, Nainital. Having a [Formula: see text] pixel imager mounted on the prime focus of the telescope, DFOT provides a field of view of about [Formula: see text] arcmin 2 in the sky. Another frame transfer CCD imager of [Formula: see text] pixel size enables monitoring transient sources with millisecond temporal resolution. DFOT is equipped with a filter assembly having eight filters, an auto-guider, an All Sky Camera, and GPS-enabled weather monitoring system to support the observations in the most optimum way. The telescope is capable of producing sub-milimag photometric stability which has allowed us to detect many small-scale photometric variations.

SDR Pathfinder for Understanding Transient and Noise-level Interference in the Karoo (SPUTNIK)

Abstract: In this work, the SDR Pathfinder for Understanding Transient and Noise-level Interference in the Karoo (SPUTNIK) is presented. We describe how a low-cost radio frequency interference (RFI) monitoring system, using solely consumer-off-the-shelf (COTS) components, directly contributes to the analysis efforts of a precision 21[Formula: see text]cm cosmology instrument. A SPUTNIK system overview is provided, as well as a generalized software-defined radio (SDR) internal calibration technique to achieve wideband, [Formula: see text][Formula: see text]dBm-level accuracy and a measured dynamic range of [Formula: see text][Formula: see text]dB.

Low-cost, Low-loss, Ultra-wideband Compact Feed for Interferometric Radio Telescopes

Abstract: We have developed, built, and tested a new feed design for interferometric radio telescopes with"large-$N$, small-$D$"designs. Those arrays require low-cost and low-complexity feeds for mass production on reasonable timescales and budgets, and also require those feeds to be compact to minimize obstruction of the dishes, along with having ultra wide bands of operation for most current and future science goals. The feed presented in this paper modifies the exponentially tapered slot antenna (Vivaldi) and quad-ridged flared horn antenna designs by having an oversized backshort, a novel method of maintaining a small size that is well-suited for deeper dishes ($f/D\leq 0.25$). It is made of laser cut aluminum and printed circuit boards, such that it is inexpensive ($\lesssim$ 75 USD per feed in large-scale production) and quick to build; it has a 5:1 frequency ratio, and its size is approximately a third of its longest operating wavelength. We present the science and engineering constraints that went into design decisions, the development and optimization process, and the simulated performance. A version of this feed design was optimized and built for the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) prototypes. When simulated on CHORD's very deep dishes ($f/D=0.21$) and with CHORD's custom first stage amplifiers, the on-sky system temperature $T_\mathrm{sys}$ of the complete receiving system from dish to digitizer remains below 30 K over most of the 0.3-1.5 GHz band, and maintains an aperture efficiency $\eta_\mathrm{A}$ between 0.4 and 0.6. The entire receiving chain operates at ambient temperature. The feed is designed to slightly under-illuminate the CHORD dishes, in order to minimize coupling between array elements and spillover.

A Digital Calibration Source for 21 cm Cosmology Telescopes

Abstract: Foreground mitigation is critical to all next-generation radio interferometers that target cosmology using the redshifted neutral hydrogen 21 cm emission line. Attempts to remove this foreground emission have led to new analysis techniques as well as new developments in hardware specifically dedicated to instrument beam and gain calibration, including stabilized signal injection into the interferometric array and drone-based platforms for beam mapping. The radio calibration sources currently used in the literature are broad-band incoherent sources that can only be detected as excess power and with no direct sensitivity to phase information. In this paper, we describe a digital radio source which uses Global Positioning Satellite (GPS) derived time stamps to form a deterministic signal that can be broadcast from an aerial platform. A copy of this source can be deployed locally at the instrument correlator such that the received signal from the aerial platform can be correlated with the local copy, and the resulting correlation can be measured in both amplitude and phase for each interferometric element. We define the requirements for such a source, describe an initial implementation and verification of this source using commercial Software Defined Radio boards, and present beam map slices from antenna range measurements using the commercial boards. We found that the commercial board did not meet all requirements, so we also suggest future directions using a more sophisticated chipset.

Evaluation of Controllers and Development of a new in-house Controller for the Teledyne HxRG Focal Plane Array for the IRSIS satellite payload

Abstract: The Infrared Astronomy Group (Department of Astronomy and Astrophysics) at Tata Institute of Fundamental Research (TIFR) is presently developing controllers for the Teledyne HxRG Focal Plane Arrays (FPAs) to be used on board the Infrared Spectroscopic Imaging Survey (IRSIS) satellite payload. In this manuscript we discuss the results of our tests with different FPA controllers like the Astronomical Research Cameras (ARC) controller, Teledyne’s SIDECAR ASIC as well as our new in-house designed Array controller. As part of the development phase of the IRSIS instrument, which is an optical fibre based Integral Field Unit (IFU) Near-Infrared (NIR) Spectrometer, a laboratory model with limited NIR bandwidth was built which consisted of various subsystems like a Ritchey-Chretien (RC) 30 cm telescope, optical fibre IFU, spectrometer optics, and the Teledyne H2RG detector module. We discuss the various developments during the building and testing of the IRSIS laboratory model and the technical aspects of the prototype in-house H2RG controller.

Characterization and Quantum Efficiency Determination of Monocrystalline Silicon Solar Cells as Sensors for Precise Flux Calibration

Abstract: As the precision frontier of astrophysics advances toward the one millimagnitude level, flux calibration of photometric instrumentation remains an ongoing challenge. We present the results of a lab-bench assessment of the viability of monocrystalline silicon solar cells to serve as large-aperture (up to 125[Formula: see text]mm diameter), high-precision photodetectors. We measure the electrical properties, spatial response uniformity, quantum efficiency (QE), and frequency response of third-generation C60 solar cells, manufactured by Sunpower. Our new results, combined with our previous study of these cells’ linearity, dark current, and noise characteristics, suggest that these devices hold considerable promise, with QE and linearity that rival those of traditional, small-aperture photodiodes. We argue that any photocalibration project that relies on precise knowledge of the intensity of a large-diameter optical beam should consider using solar cells as calibrating photodetectors.

Experimental Validation of a Novel Concept to Reduce Optical Surface Wave Front Errors by Using Deformable Bushes at Opto-Mechanical Interfaces

Abstract: One of the major objectives of the optomechanics is to support large optics required for the purpose and also to maintain high dynamic stability in operation. This requirement calls for more number of supports, to support large optics. While addressing this issue, the mounting system tends to become non-kinematic and distorts the optical surface and leads to poor image quality. The distorted optical surfaces bring in increased RMS surface wavefront errors which will result in poor image quality. In this context, a new concept is proposed in our previous publication (Nagabhushana et al., 2021) which involves introduction of deformable bushes at the optomechanical interfaces. These are deformed by applied clamping forces and also enabling all degrees of freedom (DOF) to be arrested. This also ensures that the clamping force in axial DOF is limited to a minimal value. This technique enables to arrest of axial DOF without exerting the clamping force on the optomechanical assembly there by reduces optical aberrations and improves the mounting system’s dynamic stability. This is because deformable bushes absorb all the clamping forces and the strain has no impact on the mount and therefore does not lead deformation of the optical surface. The clamping forces are simulated by Finite Element (FE) methods. Further, in this paper, the concept is verified and validated by experiments. The simulation results are observed to be in close correlation with experiment results. Improved stability is also observed by additional constraints introduced to optomechanical mounts with no compromise in wavefront errors.

Cumulative Author Index — Volume 11 (2022)

Abstract: Journal of Astronomical InstrumentationVol. 11, No. 04, 2299001 (2022) Free AccessCumulative Author Index — Volume 11 (2022)https://doi.org/10.1142/S225117172299001XCited by:0 Previous This article is part of the issue: Special Issue: The Aryabhatta Research Institute of Observational Sciences (ARIES) Guest Editors: Dr. Brijesh Kumar, Dr. T. S. Kumar, Dr. Manish Naja and Dr. Amitesh Omar Associate Editor: Dr. Udaya Shankar Narayana Rao AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetails Recommended Vol. 11, No. 04 Metrics History PDF download

A preliminary plan to quickly restore utility to the Arecibo 305m telescope

Abstract: Since the fall of the Arecibo 305[Formula: see text]m telescope platform on 2020 December 1, there has been much discussion of building a new Arecibo telescope or rebuilding the facility that was destroyed. In the collapse, the top of the three platform support towers was sheared off, and the feed arm fell free from the swinging platform and destroyed 25% of the dish. Fortunately, the Control Building, the home of the computers, spectrometers, masers, atomic clocks, 430[Formula: see text]MHz Klystrons, etc., was spared. By replacing the main dish support cables and resurfacing with coarse mesh, the main dish can be repaired as a reflector [Formula: see text] operation. By replacing the damaged aluminum panels to make the dish whole again, RF operations at up to 500[Formula: see text]MHz can be resumed. In this paper, we outline the steps that can be taken to restore High Frequency (HF, 3–30[Formula: see text]MHz) ionospheric heating, 430[Formula: see text]MHz ionospheric incoherent scattering radar, passive radio observations of satellite arcing and pulsars, and to extend the field of regard to 47 ∘ from the zenith. This would restore and improve much of the utility of the Arecibo dish. Part of this plan involves supporting, positioning and pointing novel point feeds from lightweight football-camera-like cables, strung from the rebuilt tower tops. It is believed that the dish may thus become broadly useful long before replacement facilities can be engineered and constructed.

Parameters of a short dipole antenna placed over a two-layer lunar soil

Abstract: In this paper, the performance characteristics of a horizontal symmetrical dipole antenna, located in the immediate vicinity of the Moon’s surface, are numerically analyzed. The lunar soil is assumed as a flat-layered medium composed of two lossy dielectrics, the upper layer with a thickness of 5–10[Formula: see text]m, filled with regolith, and solid bedrock in the form of granite or basalt. Calculations were performed in the frequency range of 1–100[Formula: see text]MHz, which is interesting for low-frequency (LF) and very low-frequency (VLF) radio astronomy. The frequency dependences of the impedance, the radiation efficiency, and the effective area of a thin wire dipole with a short length are investigated. All calculations were carried out by simulation of the dipole using the well-known Altair Feko software. As a result of the calculations, it was found that the frequency characteristics of the dipole parameters above the two-layer medium have characteristic differences from the same for the dipole above a homogeneous medium, namely, they have oscillating components, the period and magnitude of which depend on the parameters of these media and the thickness of the upper layer. The presence of this oscillating component is largely manifested in the dipole efficiency and effective area but to a lesser in its impedance. The dependence of the dipole radiation pattern (RP) on the frequency also is analyzed in detail, making it possible to detect the quasi-periodic changes in its shape, which are clearly synchronized with the oscillating component of the dipole radiation efficiency.

Probing the New Generation Geodetic Radio Telescopes for FRB Observations

Abstract: We investigate the possibility of fast radio burst (FRB) observation on new special geodetic 13[Formula: see text]m wideband radio telescopes in Very Large Base Interferometry (VLBI) and single-dish modes. The Crab Pulsar Giant Pulses (GPs) were used as a reference source of FRB. In order to verify our results we use joint simultaneous observations with 32[Formula: see text]m legacy and 13[Formula: see text]m new VLBI Global Observing System (VGOS) radio telescopes of the Quasar VLBI network in the L and S/X frequency bands. The special observation session contains two 10-min scans of Crab Pulsar. We successfully detect a total of 712 pulses with flux density [Formula: see text][Formula: see text]Jy at 1653.5[Formula: see text]MHz on 32-m antenna and 262 pulses with flux density [Formula: see text][Formula: see text]Jy at 2406.3[Formula: see text]MHz on 13-m antenna in Badary observatory. The VLBI fringes were obtained for approximately every third pulse. The energy distribution of detected pulses has a break in the power law fit at [Formula: see text] and [Formula: see text]-values are [Formula: see text]0.2 and [Formula: see text]1.8 for lower and higher energies. A GP with a fluence of the order of 190[Formula: see text][Formula: see text] in L-band was detected and 48[Formula: see text][Formula: see text] in S-band. We found that the peak coincidence of right and left circular polarizations of dedispersed data on a single antenna can provide a maximum detection rate with fixed false probability. It was shown that the best GP detection rate on 13[Formula: see text]m VGOS radio telescope was achieved at Badary observatory with 13 pulses per minute in the S-band.

Life Cycle of Data Processing Center of RadioAstron Project

Abstract: This paper is about the Data Processing Center (DPC) working within the RadioAstron project. Since the launch of the space radio telescope to orbit in July 2011, the DPC underwent significant quantitative and qualitative changes as the project developed. This paper describes the schemes, structure, stages of the processing center development, current upgrades and new technologies introduced in the DPC throughout the entire period of its operation. For technical reasons, the scheduled observations in the project were terminated in January 2019. However, still the work of the DPC continued. Today, the most valuable thing we have is information. There is now a unique archive of service and scientific data of the project in our possession, and a data bank of the RadioAstron project is underway, which will ensure a proper access to scientific and service information for all interested experts, as well as provide an opportunity for an additional data analysis.

Mersenne Beam-compressor with Field-flattener optics as Main Telescope design for Extremely Large Telescopes and Telescope Arrays

Abstract: The Mersenne beam-compressor is the fundamental arrangement for two mirror reflecting telescopes. The Mersenne beam-compressor consists of two confocal paraboloids. The design produces an aberration-free, collimated output beam, which makes it easy to relocate the beam to any distant location. This property of Mersenne beam compressors makes them near-ideal for telescopes with requirements for ultra-stable instruments and interferometric applications. The only problem against such application is the Petzval field curvature that is induced in the output beam. This becomes very pronounced at very high compression ratios, which are required for interferometry with large aperture telescopes. The high compression ratio is a problem because, such large aperture telescopes are also required to deliver good performance at Nasmyth and Coude locations, to be feasible. This is not possible at high compression ratios using conventional design of Mersenne beam-compressor, due to prohibitively strong field curvature. Here, we propose powered and un-powered field-flattener optics to address the problem of field curvature in Mersenne beam-compressor. After passing through this set of optics, the output beam is completely aberration free. This arrangement can produce very high compression ratios, which are useful for various special applications. We also illustrate the performance of such a system using example designs. The performance analysis shows that such a design can give considerably high performance at distant locations of foci as compared to existing relay systems.

Compact Scintillator Array Detector (ComSAD) for Sounding Rocket and CubeSat Missions

Abstract: The development of CubeSats and more frequent launch chances of sounding rockets are a total game changer to the space program, and it allows us to build space instruments that are technologically feasible and affordable. Therefore, it gives us a good opportunity to build a small cosmic-ray detector which has capabilities to measure the flux, direction, and even energy of cosmic rays at an altitude above the limitation of balloon experiments, and it may open a new door for building a constellation of detectors to study cosmic-ray physics. Compact Scintillator Array Detector (ComSAD) is a funded sounding rocket mission of Taiwan’s National Space Organization. In this paper, we present the concept, design, and performance of ComSAD which is also suitable for future CubeSat missions.