Studying solutions for the fatigue of the FAST cable-net structure caused by the process of changing shape

The Five-hundred-meter Aperture Spherical Radio Telescope(FAST) is supported by a cable-net structure,whose change in shape leads to a stress range of approximately 500 MPa.This stress range is more than twice the standard recommended value.The cable-net structure is thus the most critical and fragile part of the FAST reflector system.In this study,we first search for a more appropriate deformation strategy that reduces the stress amplitude generated by the process of changing shape.Second,we roughly estimate the tracking trajectory of the telescope during its service life,and conduct an extensive numerical investigation to assess the requirements for fatigue resistance.Finally,we develop a new type of steel cable system that satisfies the cable requirements for construction of FAST.     

Recognition of FAST reflector nodes based on Canny operator

The reflector system of Five-hundred-meter Aperture Spherical radio Telescope(FAST) is designed as 4450 rigid panels supported by a flexible cable-net structure. We use 10 total stations to measure2225 nodes of the cable-net and then control the shape of the reflectors. Every time, it takes at least 35 minutes to finish the calibration of the whole cable-net once. It is indeed far too inefficient. Thus, we developed a set of highly efficient instrument CRRS(CCD Rotation Ranging System). It is based on photogrammetry and can finish the measurement in 1 minute. However, the target we used in CRRS is active target, and it has serious electromagnetic interference problems to affect the use of FAST. Take the above reasons into consideration, we plan to identify the nodes by taking the gap between the reflector panels as the feature condition. The new method can take the place of active targets to finish the measuring task. The present work focuses on the following aspects. First, combined with the characteristics of FAST reflector images,the representative algorithms of image edge detection are discussed. Second, the process of node extraction is introduced in detail so that we know that it works. In addition, experimental results are given to draw a conclusion so that Canny algorithm was used for continuous research of reflector edge detection.     

FAST VLBI: current status and future plans

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the largest single-dish radio telescope in the world,and is now being commissioned after the first light in September 2016.Very long baseline interferometry(VLBI)is among the key science topics according to the original design.The FAST VLBI system has been established,and the first VLBI fringe has been successfully obtained.FAST will significantly improve the sensitivity of the existing VLBI networks in the future,and some science projects in need of high sensitivity will benefit from its participation.     

Five-hundred-meter Aperture Spherical Telescope project

A Five hundred meter Aperture Spherical Telescope (FAST) is proposed to be built in the unique karst area of southwest China, and will act, in a sense, as a prototype for the Square Kilometer Array (SKA). It will be over twice as large as the Arecibo telescope coupled with much wider sky coverage. Some results from site surveys for such a SKA concept are briefly reported. Technically, FAST is not simply a copy of the existing Arecibo telescope but has rather a number of innovations. Firstly, the proposed main spherical reflector, by conforming to a paraboloid of revolution in real time through actuated active control, enables the realization of both wide bandwidth and full polarization capability while using standard feed design. Secondly, a feed support system which integrates optical, mechanical and electronic technologies will effectively reduce the cost of the support structure and control system. Pre-research on FAST has become a key project in the CAS. This revised version was published online in July 2006 with corrections to the Cover Date.     

一种扩大FAST视场的方法

所有的大口径射电望远镜都存在这样一个问题：在其分辨率和灵敏度提高的同时，视场变小．而且口径越大，视场越小．这成为大口径望远镜不可回避的矛盾．要解决这个矛盾，可以在望远镜的焦平面上放置Ⅳ个分立馈源．让它们同时工作，这样可以看作把视场扩大了Ⅳ倍．望远镜的工作效率提高Ⅳ倍．但是这样做的缺点是——视场不连续．且馈源数目Ⅳ受到望远镜焦比(F／D)的限制．采用致密焦面阵(dense focal plane array)就可以很好地解决这个问题．致密焦面阵的单元不是喇叭口天线，而是无方向性的Vivaldi天线(Vivaldi antenna)．要把Vivaldi阵列应用到望远镜上，需要对单个Vivaldi天线和Vivaldi阵列的电性能有清楚的认识，并能根据需要来设计照明方向图．还要知道大望远镜的焦面上电磁场的分布情况，借此判断能否应用Vivaldi阵列，以及给出Vivaldi单元的分路赋权网络．主要给出了FAST的焦面场的分布情况．并说明应用Vivaldi阵列的可能性．     

Similarity model of feed support system for FAST

A new design of feed support system for Five hundred meter Aperture Spherical Telescope (FAST) is proposed in this paper. According to the similarity theory, a 1:15 scale model of feed support system has been built to make systemic research on the feasibility of the system. Then the control system and hardware structure of the feed support system are illustrated. A complete astronomical observation track is run by the scale model and the experiments results demonstrate that the new feed support system can satisfy the observation accuracy requirement of FAST.     

大射电望远镜FAST风环境数值模拟研究

500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical radio Telescope,FAST),整体结构处于复杂的喀斯特地貌上,反射面承受风载荷作用,需要进行抗风设计。建立了FAST反射面及其周边山地地形的计算流体动力学(Computational Fluid Dynamics,CFD)计算模型,计算域范围为40 km×10 km×5.5 km。确定了入口风速剖面的基准高度为海拔810 m。计算了不同风向下反射面风压系数分布特征,得出了不利风向。对挡风墙的研究结果表明,挡风墙高度选择的效果优于位置选择。该研究结果可为FAST工程提供抗风设计的初步参考。     

The role of FAST in pulsar timing arrays

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) will become one of the world-leading telescopes for pulsar timing array(PTA) research. The primary goals for PTAs are to detect(and subsequently study) ultra-low-frequency gravitational waves, to develop a pulsar-based time standard and to improve solar system planetary ephemerides. FAST will have the sensitivity to observe known pulsars with significantly improved signal-to-noise ratios and will discover a large number of currently unknown pulsars. We describe how FAST will contribute to PTA research and show that jitter-and timing-noise will be the limiting noise processes for FAST data sets. Jitter noise will limit the timing precision achievable over data spans of a few years while timing noise will limit the precision achievable over many years.     

Research on key technologies for installation and maintenance of reflector of FAST

The reflector of the Five-hundred-meter Aperture Spherical radio Telescope(FAST)consists of 4450 reflector units.Installation of the reflector faces the challenges of large span,complex terrain,serious interference,complex processes,high position and inability to use conventional equipment.The installation technology for the flexible reflector with a large span was specially studied and designed.Two half-span arc-moving cable cranes and two transfer trucks were jointly operated along a path that follows a circular beam.After installation of the reflector was completed,two half-span cable cranes were merged into a set of full-span cable cranes for maintenance of the reflector.Installation of the reflector combines features of unit and site topography of FAST.The installation technology follows scientific and reasonable practices,and is highly efficient and convenient.It represents a breakthrough in many key technologies in construction and maintenance techniques.It has promoted related technical progress in the construction and maintenance of complex projects.It has also provided an important reference for the construction and maintenance of similar projects,and has strong significance and applicability.     

Modeling of A Feed Support System for Fast

As an engineering demonstrator for SKA, the Five-hundred-meter Aperture Spherical Telescope (FAST) is proposed in China. This paper is focused on one of the most critical components of FAST, the feed support system. The engineering concept, the configuration and results from model experiments are presented. The mechanical characteristics of the structure are analyzed. The performance of the feedback control system of the model is described. The feasibility of the design is tentatively confirmed by the experiments described at the end of the report.     

Mechanical design of the solar telescope GREGOR

The mechanical structure of the GREGOR telescope was installed at the Observatorio del Teide, Tenerife, in 2004. New concepts for mounting and cooling of the 1.5‐meter primary mirror were introduced. GREGOR is an open telescope, therefore the dome is completely open during observations to allow for air flushing through the open, but stiff telescope structure. Backside cooling system of the primary mirror keeps the mirror surface close to ambient temperature to prevent mirror seeing. The large collecting area of the primary mirror results in high energy density at the field stop at the prime focus of the primary which needs to be removed. The optical elements are supported by precision alignment systems and should provide a stable solar image at the optical lab. The coudé train can be evacuated and serves as a natural barrier between the outer environmental conditions and the air‐conditioned optical laboratory with its sensitive scientific instrumentation. The telescope was successfully commissioned and will start its nominal operation during 2013 (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of central control system for FAST

FAST(The Five-Hundred-Meter Aperture Spherical Radio Telescope) is an under-building radio telescope which will be the largest single dish in the world. Through the study of the central control system, in accordance with the actual operation of the telescope and observation process, this article introduces the physical models for engineers and observers, the central control system architecture design, basic support modules and the necessary interfaces. We simulated observation control process and telescopes monitoring and control process, and took Active Reflector System as a subsystem example to complete the control system design and implementation using EPICS (Experimental Physics and Industrial Control System). The Central control system, with active reflector systems, feed supporting system has been taken to an integration test at Miyun model. In the case of the normal operation of the various sub-systems of the Miyun model by the central control system, a coordinated control is achieved.     

Experimental Research of First Feed-Support System of FAST

First feed support system, which is one of the key technologies of Five hundred meter Aperture Spherical Telescope (FAST) was discussed in this paper. A 1:30 scaled model (20 m × 20 m × 6 m) has been built to make systemic research on the feasibility of the system. The root mean square of pointing error of moving cable car was measured and the displacements of cable car within the wind speed of 8 m/s, which is the maximal wind speed of the place where the FAST will be located, were evaluated. Then the total maximal pointing error of cable car was computed. Experimental results demonstrate that the total pointing error of the cable car is less than 50 cm, the required pointing accuracy error of the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Suggested quasi-Cassegrain system for multi-beam observation of FAST

FAST, the largest single-dish radio telescope in the world, has a 500-meter diameter main reflector and a 300-meter diameter illuminated area. It has a main reflector that can vary its shape, which continuously changes the shape of the illuminated area in reflector into a paraboloid. In this article, we propose a quasiCassegrain system for FAST. The detailed design results are provided. Such a quasi-Cassegrain system only needs to add a 14.6-meter diameter secondary reflector, which is close to the size of the feed cabin. The distance from the secondary reflector to the focus is only 5.08 m, and it has excellent image quality. In this quasi-Cassegrain system, the shape of the illuminated area in the main reflector continuously changes into an optimized hyperboloid. Using this quasi-Cassegrain system from frequency 0.5 GHz to 8 GHz, the multi-beam system can include 7 to 217 feeds. If this system is used in combination with Phased Array Feed(PAF) technology, more multi-beam feeds or a higher working frequency can be used.     

The design of China Reconfigurable ANalog-digital backEnd for FAST

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)was launched on 2016 September 25.From early 2017,we began to use the FAST wideband receiver,which was designed,constructed and installed on the FAST in Guizhou,China.The front end of the receiver is composed an uncooled Quad Ridge Flared Horn feed(QRFH)with the frequency range of 270 to 1620 MHz,and a cryostat operating at 10 K.We have cooperated with the Institute of Automation of the Chinese Academy of Sciences to develop the China Reconfigurable ANalog-digital backEnd(CRANE).The system covers the 3 GHz operating band of FAST.The hardware part of the backend includes an Analog Front-end Board,a wideband high precision Analog Digital Converter,and a FAST Digital Back-end.Analog circuit boards,field programmable gate arrays,and control computers form a set of hardware,software,and firmware platforms to achieve flexible bandwidth requirements through parameter changes.It is also suitable for the versatility of different astronomical observations,and can meet specific requirements.This paper briefly introduces the hardware and software of CRANE,as well as some observations of the system.     

Preface:Planning the scientific applications of the Five-hundred-meter Aperture Spherical radio Telescope

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) is by far the largest telescope of any kind ever built. FAST produced its first light in September 2016 and it is now under commissioning, with normal operation to commence in late 2019. During testing and early science operation, FAST has started making astronomical discoveries, particularly pulsars of various kinds, including millisecond pulsars, binaries, gamma-ray pulsars, etc. The papers in this mini-volume propose ambitious observational projects to advance our knowledge of astronomy, astrophysics and fundamental physics in many ways.Although it may take FAST many years to achieve all the goals explained in these papers, taken together they define a powerful strategic vision for the next decade.     

FAST单元面板面型检测算法研究

500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical Radio Telescope,FAST)是一个超大口径的可动望远镜,有三项技术创新,一是选址,二是轻型馈源索支撑,三是主动反射面。在主动反射面上,单元面板的面型和面板的出厂加工精度对电磁波在反射面的汇聚有很大影响。FAST主反射面由4 600块三角形反射面板拼接而成,每块面板为边长11 m三角形,这对FAST反射面面板的测量技术提出了更高的要求。摄影测量直接在影像上进行量测,无需接触物体本身;所摄影像信息丰富,可以从中获得所研究物体的大量几何信息和物理信息;适用于大范围、多目标测量,效率高。目前世界上最大的射电望远镜,如GBT和ARECIBO都是采用摄影测量技术进行反射面面形检测。在对现有的面型检测技术调研并试验后,提出基于数字近景摄影测量的方法,对FAST反射面11 m单元面板的面型进行检测,数分钟完成反射面板面型的一次检测,测量精度达到2.5 mm,经过调整后的单元面板的面型精度达到了3.0 mm,结果表明摄影测量应用于FAST反射面单元面板面型检测是可行的。     

From KARST to FAST: The Conceptual Origin of FAST and Its Decision-making Process

In the era of big science, the construction of large science projects is becoming more complex. Designers have to comprehensively consider factors such as instrument performance, technical reserves, funding, risks, and the environment to make a reasonable decision. On the basis of domestic and international astronomy, this paper sorts out the process of the formation of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) concept and the decisions made by the FAST team, including the Chinese concept of the large telescope, the proposal of the prototype, and the adoption of the active reflector, etc. We also discuss the process of decision-making. FAST was born in the process of interaction and integration between Chinese and international astronomy development, and realized the transformation from following up to taking the lead. It can provide a reference for constructing future large science projects with limited foundations in terms of technology and funding.     

从KARST到FAST---中国天眼的概念起源与决策过程

在大科学时代,大科学工程的建设日益复杂,设计者需综合考虑设备性能、技术储备、经费、风险、环境等因素才能进行合理决策.在国内外天文学发展的背景中,梳理了500 m口径球面射电望远镜(Five-hundredmeter Aperture Spherical radio Telescope, FAST)概念形成的过程以及FAST团队在其中所做的决策,包括大望远镜中国方案的设想、先导单元的提出、主动反射面技术的采用等,并对决策过程进行了分析探讨. FAST诞生于我国与国际天文学发展的互动与融合进程,实现了从跟进到占据先机的转变,可为在相关基础薄弱的领域建设大科学工程提供参考.     

Preface: Key technologies for enhancing the performance of FAST

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)passed its national acceptance inspection on 2020 January 11.This special issue includes a total of 15 papers,which are selected to introduce the status of FAST’s performance and demonstrate the key technologies applied to FAST.The presented performance parameters can provide an important reference for scientists to propose observations with FAST.The key technologies presented in these papers include design and implementation in the measurement and control system,electromagnetic compatibility system,and receiver system.Finally,scientific achievements obtained by FAST during the commissioning phase are also reported.