Terrain-influenced wind flow of the Qitai radio telescope site

The wind environment of a site is one of the important factors affecting the observation performance of large aperture and high-performance radio telescopes.Exploring the relationship between the effects of different terrains on wind flow is important to optimize the wind environment of the site.The terrain of the Qitai radio telescope(QTT)site located in east Tianshan Mountains at an elevation of about 1800 m was used to study the wind flow in the adjacent zone of antenna based on numerical simulation.The area from 600m south to 600m north of the antenna is defined as the antenna adjacent zone,and three groups of boundaries with different terrains are set up upstream and downstream,respectively.Since the zone where the antenna is located is a slope terrain,in order to verify the influence of terrain on the wind flow and to clarify the relationship between the influence of boundary terrain on the wind flow,a control group of horizontal terrain is constructed.The simulation results show that the wind flow is mainly influenced by the terrain.The highest elevation of the upstream and downstream boundary terrains affects the basic wind speed.The upstream boundary terrain has a greater impact on wind flow than the downstream boundary terrain.In addition,the wind speed profile index obtained by numerical simulation is smaller than the actual index for the wind from south.Therefore,the wind speed at the upper level(about 100 m)obtained by inversion based on the measured wind speed at the bottom(about 10 m)is also smaller than the actual wind speed.

Pulsar timing observations with Haoping Radio Telescope

We report pulsar timing observations carried out in L-band with NTSC’s 40-meter Haoping Radio Telescope(HRT),which was constructed in 2014.These observations were carried out using the pulsar machine we developed.Timing observations toward millisecond pulsar J0437–4715 obtain a timing residual(r.m.s.)of 397 ns in the time span of 284 days.Our observations successfully detected Crab pulsar’s glitch that happened on 2019 July 23.

VLBI observations with the Kunming 40-meter radio telescope

The Kunming 40-meter radio telescope is situated in the yard of the Yunnan Astronomical Observatory （Longitude： 102.8° East, Latitude： 25.0° North） and saw its first light in 2006 May. The Kunming station successfully joined the VLBI tracking of China＇s first lunar probe ＂Chang＇E-1＂ together with the other Chinese telescopes： the Beijing Miyun 50-meter radio telescope, Urumqi Nanshan 25-meter radio telescope, and Shanghai Sheshan 25-meter radio telescope, and received the downlinked scientific data together with the Miyun station from October of 2007 to March of 2009. We give an introduction to the new Chinese VLBI facility and investigate its potential applications. Due to its location, the Kunming station can significantly improve the u - v coverage of the European VLBI Network （EVN）, in particular, in long baseline observations. We also report the results of the first EVN fringe-test experiment of N09SX1 with the Kunming station. The first fringes in the European telescopes were successfully detected at 2.3 GHz with the ftp-transferred data on 2009 June 17. From scheduling the observations to performing the post correlations, the Kunming station shows its good compatibility to work with the EVN. The imaging result of the extended source 1156＋295 further demonstrates that the Kunming station greatly enhances the EVN performance.

Research on actuator distribution and panels for a radio telescope

Trying to achieve the best surface accuracy control with the fewest actuators, this article mainly studies the distribution of actuators and the method of panel design. The influence of the number of faulty actuators on the accuracy of the surface shape is demonstrated. In addition, the method incorporating a triangular panel, node index and the fitting solution method of a single panel is also given. This method provides a reference for the design and realization of an active surface or a deformable sub-reflector for high performance large aperture radio telescopes.

Analyzing the capability of a radio telescope in a bistatic space debris observation system

A bistatic space debris observation system using a radio telescope as the receiving part is introduced. The detection capability of the system at different working frequencies is analyzed based on real instruments. The detection range of targets with a fixed radar cross section and the detection ability of small space debris at a fixed range are discussed. The simulations of this particular observation system at different transmitting powers are also implemented and the detection capability is discussed. The simulated results approximately match the actual experiments. The analysis in this paper provides a theoretical basis for developing a space debris observation system that can be built in China.

Non-uniform temperature distribution of the main reflector of a large radio telescope under solar radiation

The non-uniform temperature distribution of the main reflector of a large radio telescope may cause serious deformation of the main reflector,which will dramatically reduce the aperture efficiency of a radio telescope.To study the non-uniform temperature field of the main reflector of a large radio telescope,numerical calculations including thermal environment factors,the coefficients on convection and radiation,and the shadow boundary of the main reflector are first discussed.In addition,the shadow coverage and the non-uniform temperature field of the main reflector of a 70-m radio telescope under solar radiation are simulated by finite element analysis.The simulation results show that the temperature distribution of the main reflector under solar radiation is very uneven,and the maximum of the root mean square temperature is 12.3℃.To verify the simulation results,an optical camera and a thermal imaging camera are used to measure the shadow coverage and the non-uniform temperature distribution of the main reflector on a clear day.At the same time,some temperature sensors are used to measure the temperature at some points close to the main reflector on the backup structure.It has been verified that the simulation and measurement results of the shadow coverage on the main reflector are in good agreement,and the cosine similarity between the simulation and the measurement is above 90%.Despite the inevitable thermal imaging errors caused by large viewing angles,the simulated temperature field is similar to the measured temperature distribution of the main reflector to a large extent.The temperature trend measured at the test points on the backup structure close to the main reflector without direct solar radiation is consistent with the simulated temperature trend of the corresponding points on the main reflector with the solar radiation.It is credible to calculate the temperature field of the main reflector through the finite element method.This work can provide valuable references for studying the thermal deformation and the surface accuracy of the main reflector of a large radio telescope.

Active sub-reflector research for a large radio telescope

This paper proposes an active sub-reflector suitable for large radio telescopes,which can compensate both of the deformation of the main reflector and sub-reflector position offsets.The mathematical formula of the main reflector deformation compensated by the sub-reflector is deduced based on Cassegrain and Gregory antenna structures.The position of the sub-reflector is adjustable to compensate for defocusing errors on high and low elevations,which are mainly caused by the deformation of the sub-reflector supporting legs.In this paper,the method of obtaining the optimum position of the sub-reflector from the aperture phase by the interferometric method is introduced.The actual measurement is verified on the Tianma 65 m radio telescope,which provides a new way to diagnose the position error of the sub-reflector.

A Millimeter-Wave Radio Telescope Project at Seoul National University

The Department of Astronomy at Seoul National University is carrying out a project to build a radio observatory, the Seoul Radio Astronomical Observatory (SRAO). The observatory will be constructed on our campus, which is located at sea level in Seoul, Korea, at (126°57.′3E, 37°27.′1N). The observatory will operate a 6 m millimeter radio telescope.

A Study of the Fitting Accuracy of the Active Reflector for a Large Spherical Radio Telescope

We propose a spatial three-degree-of-freedom (DOF) parallel mechanism combining two degrees of rotations and one degree of translation to support the active reflector units of a large spherical radio telescope. The kinematics, workspace and accuracy of the mechanism are analyzed. One-dimensional and two-dimensional fitting errors to the working region of active reflector are investigated. Dimensional parameters of the mechanism and active reflector unit are examined with respect to the requirement of fitting accuracy. The result of accuracy analysis shows the effectiveness and feasibility of the proposed mechanism, and gives a design rule to guarantee the highest working frequency required by large radio telescope.

Construction Finishes on World's Largest Single Dish Radio Telescope

After more than five years of construction,the world’s biggest single-dish radio telescope was finally ready to open its eye.On September 25,2016,the Fivehundred-meter Aperture Spherical radio Telescope(FAST)was officially put into use in a mountainous region of southwest China's Guizhou Province.With a total collecting area equivalent to the size of 30 soccer fields,FAST is expected to accomplish large scale

Man behind World's Largest Radio Telescope Passes Away at 72

NAN Rendong,a distinguished expert in radio astronomy who is known as the father of the world’s largest radio telescope,died from lung cancer in Boston on September 15,2017 at the age of 72.His untimely passing away was just ten days before his masterpiece,the Five-hundred-meter Aperture Spherical radio Telescope(FAST),which he spent over two decades conceiving and building for the next generation

IPS observation system for the Miyun 50m radio telescope and its commissioning observation

Ground-based observation of Interplanetary Scintillation （IPS） is an impor- tant approach for monitoring solar wind. A ground-based IPS observation system has been newly implemented on a 50 m radio telescope at Miyun station, managed by the National Astronomical Observatories, Chinese Academy of Sciences. This observa- tion system has been constructed for the purpose of observing solar wind speed and the associated scintillation index by using the normalized cross-spectrum of a simul- taneous dual-frequency IPS measurement. The system consists of a universal dual- frequency front-end and a dual-channel multi-function back-end specially designed for IPS. After careful calibration and testing, IPS observations on source 3C 273B and 3C 279 have been successfully carried out. The preliminary observation results show that this newly-developed observation system is capable of performing IPS observa- tion. The system＇s sensitivity for IPS observation can reach over 0.3 Jy in terms of an IPS polarization correlator with 4 MHz bandwidth and 2 s integration time.

The Qitai radio telescope

This study presents a general outline of the Qitai radio telescope(QTT)project.Qitai,the site of the telescope,is a county of Xinjiang Uygur Autonomous Region of China,located in the east Tianshan Mountains at an elevation of about 1800 m.The QTT is a fully steerable,Gregorian-type telescope with a standard parabolic main reflector of 110 m diameter.The QTT has adopted an umbrella support,homology-symmetric lightweight design.The main reflector is active so that the deformation caused by gravity can be corrected.The structural design aims to ultimately allow high-sensitivity observations from 150 MHz up to115 GHz.To satisfy the requirements for early scientific goals,the QTTwill be equipped with ultra-wideband receivers and large field-of-view multi-beam receivers.A multi-function signal-processing system based on RFSo C and GPU processor chips will be developed.These will enable the QTT to operate in pulsar,spectral line,continuum and Very Long Baseline Interferometer(VLBI)observing modes.Electromagnetic compatibility(EMC)and radio frequency interference(RFI)control techniques are adopted throughout the system design.The QTT will form a world-class observational platform for the detection of lowfrequency(nano Hertz)gravitational waves through pulsar timing array(PTA)techniques,pulsar surveys,the discovery of binary black-hole systems,and exploring dark matter and the origin of life in the universe.The QTT will also play an important role in improving the Chinese and international VLBI networks,allowing high-sensitivity and high-resolution observations of the nuclei of distant galaxies and gravitational lensing systems.Deep astrometric observations will also contribute to improving the accuracy of the celestial reference frame.Potentially,the QTT will be able to support future space activities such as planetary exploration in the solar system and to contribute to the search for extraterrestrial intelligence.

The Science of Radio Astronomy: An Investigation of Crab Nebula

The science of radio astronomy focuses on the observation and study of celestial objects by reading their radio waves. The 5 meter radio-telescope is able to observe different radio sources using a C-band LNB. This research was essentially focused on Crab Nebula, also known as Taurus A. The study led to interesting observations, which were validated numerically using various scientific computing software. The radio waves emitted by Taurus A are readable by the RTL-SDR, a software defined radio receiver. This device is capable of reading radio frequencies in the range of 0.5 MHZ to 1700 MHZ.

Back Frame Optimization of a Large Radio Telescope Based on Force Cone Method

A new research perspective is proposed to optimize the topology of truss structure by force cone method,which involves force cone drawing rules and growth rules.Through the comparison with the mature variable density topology optimization method,the effectiveness of force cone method is verified.This kind of new method is simple and easy to understand(no need to master complex structural optimization design theory).Besides,it is time-saving in finite element calculations,and can obtain an optimized truss layout easily.By drawing the force cone,its application on a large radio telescope’s back frame structure shows that,compared with the existing one in terms of structural stiffness,Root Mean Square(RMS)precision,and beam stress distribution,the optimized back frame using the force cone method has higher stiffness,better RMS,more uniform stress,and lighter weight.

Back Frame Section Size Optimization of Large Aperture Telescope

The back frame structure of a large radio telescope is an important component supporting the reflecting surface,which is directly related to the surface precision.Its optimal design is of key significance for ensuring the surface precision and reducing structural weight.Two methods are constructed to optimize the cross-section size of the telescope back frame in this paper,the criterion method and the first-order optimization method.The criterion method is based on the Lagrangian multiplier method and Kuhn-Tucker condition.This method first establishes the mathematical model by taking the inner and outer radiuses of the back frame beams as the design variables,the structural weight as the constraint condition,and the structural compliance as the objective function,then derives the optimization criterion.The first-order optimization method takes the inner and outer radiuses of the beams as the design variables,the back frame RMS as the objective function,and the structural weight as the constraint condition.Comparison of RMS,structural stress uniformity and optimization efficiency shows that both algorithms can effectively reduce structural deformation and improve RMS,but the criterion method has relatively better result than the first-order method.

The FAST Core Array

The Five-hundred-meter Aperture Spherical Radio Telescope(FAST)Core Array is a proposed extension of FAST,integrating 24 secondary 40-m antennas implanted within 5 km of the FAST site.This original array design will combine the unprecedented sensitivity of FAST with a high angular resolution(4.3"at a frequency of 1.4 GHz),thereby exceeding the capabilities at similar frequencies of next-generation arrays such as the Square Kilometre Array Phase 1 or the next-generation Very Large Array.This article presents the technical specifications of the FAST Core Array,evaluates its potential relatively to existing radio telescope arrays,and describes its expected scientific prospects.The proposed array will be equipped with technologically advanced backend devices,such as real-time signal processing systems.A phased array feed receiver will be mounted on FAST to improve the survey efficiency of the FAST Core Array,whose broad frequency coverage and large field of view(FOV)will be essential to study transient cosmic phenomena such as fast radio bursts and gravitational wave events,to conduct surveys and resolve structures in neutral hydrogen galaxies,to monitor or detect pulsars,and to investigate exoplanetary systems.Finally,the FAST Core Array can strengthen China's major role in the global radio astronomy community,owing to a wide range of potential scientific applications from cosmology to exoplanet science.

A Reverse-Design Strategy for the Track Error of the Qi Tai Telescope Based on Pointing Accuracy

The Qi Tai Telescope(QTT),which has a 110 m aperture,is planned to be the largest scale steerable tele-scope in the world.Ideally,the telescope’s repeated pointing accuracy error should be less than 2.5 arc seconds(arcsec);thus,the telescope structure must satisfy ultra-high precision requirements.In this pur-suit,the present research envisages a reverse-design method for the track surface to reduce the difficulty of the telescope’s design and manufacture.First,the distribution characteristics of the test data for the track error were verified using the skewness coefficient and kurtosis coefficient methods.According to the distribution characteristics,the azimuth track error was simulated by a two-scale model.The error of the long period and short amplitude was characterized as large-scale and described by a trigonometric function,while the short period and high amplitude error was characterized as small-scale and simulated by a fractal function.Based on the two-scale model,effect of the error on the pointing accuracy was deduced.Subsequently,the relationship between the root mean square(RMS)of the track error and the RMS of the pointing accuracy error of the telescope was deduced.Finally,the allowable RMS value of the track error was derived from the allowable pointing accuracy errors.To validate the effectiveness of the new design method,two typical radio telescopes(the Green Bank Telescope(GBT)and the Large Millimeter Telescope(LMT))were selected as experimental examples.Through comparison,the theoretical calculated values of the pointing accuracy of the telescope were consistent with the measured values,with a maximum error of less than 10%.

Upgrade Procedure for the Delingha 13.7-m Telescope

The 13.7-m millimeter-wave radio telescope of Purple Mountain Observatory operates at 3200-m above the sea level near Delingha, Qinghai Province, China. Equipped with a superconducting SIS receiver, the telescope is used in the millimeter-wave band ranging from 85 to 115 GHz. An upgrade procedure is reported here which includes a superconducting SIS receiver, a new phase-locked local oscillator, a dedicated multi-line backend system, and a new control system based on industrial computer with PCI bus. With the dedicated multi-line backend system, the CO and isotopic lines around 110 GHz are obtained simultaneously. In recent years, scientific activities with this telescope have been focused on studies of Galactic molecular clouds and star formation regions, including surveys of molecular lines from IRAS sources and large-scale map of molecular clouds. Other programs include studies of the circumstellar envelope of late-type stars and interaction of Galactic supernova remnants with dense molecular gas.

A 96-antenna radioheliograph

Here we briefly present some design approaches for a multifrequency 96-antenna radioheliograph. The configuration of the array antenna, transmission lines and digital receivers is the main focus of this work. The radioheliograph is a T-shaped centrally condensed radiointerferometer operating in the frequency range 4–8 GHz.The justification for the choice of such a configuration is discussed. The signals from antennas are transmitted to a workroom by analog optical links. The dynamic range and phase errors of the microwave-over-optical signal are considered. The signals after downconverting are processed by digital receivers for delay tracking and fringe stopping. The required step of delay tracking and data rates are considered. Two 3-bit data streams（I and Q） are transmitted to a correlator with the transceivers embedded in Field Programmed Gate Array chips and with PCI Express cables.