Effect of the alidade thermal behavior on the pointing accuracy of a large radio telescope

The alidade’s non-uniform temperature field of a large radio telescope is very obvious under solar radiation.Estimating a radio telescope’s pointing errors,caused by the alidade deformation under solar radiation,is significant to improve the telescope’s pointing accuracy.To study the effect of the alidade thermal behavior on the pointing accuracy of a large radio telescope,a temperature experiment is first carried out in a 70-m radio telescope on a sunny day.According to the measured results,the temperature distribution rule of the alidade is summarized initially.In addition,the alidade’s temperature field is calculated by finite element thermal analysis.The simulated results are proved to be in good agreement with the experimental results.Finally,the alidade deformation under solar radiation is computed by finite element thermalstructure coupling analysis.The telescope’s pointing errors caused by alidade deformation are estimated via the alidade’s node displacements.The final results show that the effect of alidade thermal behavior on the telescope’s elevation pointing errorsΔε2+Δεr is much more than the effect on the telescope’s crosselevation pointing errorsΔε1.The maximum ofΔε2+Δεr is more than 45″,while the maximum ofΔε1 is less than 6″.This study can provide valuable references for improving the pointing accuracy of large radio telescopes.

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%.

Influence of chamber misalignment on cased telescoped(CT) ammunition accuracy

As part of a research program, it was desired to better understand the impact of the rotating chamber alignment with the barrel throat on the precision and accuracy of a novel cased telescoped(CT) ammunition firing rifle. In order to perform the study, a baseline CT ammunition chamber which was concentric with a Mann barrel bore was manufactured. Additionally, six chambers were manufactured with an offset relative to the barrel bore. These chambers were used to simulate a misaligned chamber relative to the bore axis. Precision and accuracy tests were then performed at 200 m in an indoor range under controlled conditions. For this project, 5.56 mm CT ammunition was used. As the chamber axis offset relative to the gun bore was increased, the mean point of impact was displaced away from the target center. The shift in the impact location is explained by the presence of in-bore yaw which results in lateral throw-off and aerodynamic jump components. The linear theory of ballistics is used to establish a relationship between the chamber misalignment and the resulting projectile mean point of impact for a rifle developed to fire CT ammunition. This relationship allows for the prediction of the mean point of impact given a chamber misalignment.

The Tianma 65 m radio telescope antenna

The Tianma 65 m radio telescope(TMRT)at Shanghai is a fully steerable single-dish radio telescope in China,operating at centimeter to millimeter wavelengths(1.25 GHz to 50 GHz).This paper presents details on the main specifications,design,performance analysis,testing,and construction of the telescope antenna.The measured total efficiency is better than 50%over the whole elevation angle range,first sidelobe levels are less than−20 dB,antenna system noise temperatures are less than 70 K at 30°elevation angle,and pointing accuracy is less than 3″.The measured and calculated results are in good agreement,verifying the effectiveness of the design and analysis.

The Tianma 65 m radio telescope at Shanghai

The Shanghai Tianma 65 m radio telescope(TMRT)is a large,fully rotatable radio telescope with multiple scientific purposes.The main body of the telescope and four low-frequency receiving systems,including L,C,and S/X bands,were completed between 2008 and 2012.From 2013 to 2017,four high-frequency receiving systems,including Ku,K,Ka,and Q bands,were constructed and their performance was comprehensively tested.There are three main innovations.(1)A fully movable large radio telescope system with advanced performance and complete functions has been built.(2)An advanced,reliable main reflector adjustment system has been completed,overcoming gravity deformation and creating a large antenna with a main reflective surface accuracy of 0.28 mm(root mean square)for any elevation.(3)Five innovative technologies have been developed to achieve high-precision pointing in any direction within 3″.The TMRT has made a crucial contribution to the orbital measurement and positioning of China’s lunar and deep space probes.Significantly enhancing China's ability to participate in international VLBI observations and radio astronomy,this has facilitated a series of achievements in observational radio astronomical research,in areas such as VLBI,spectral lines,and pulsars.

Hybrid position/force control strategy and experiment of the six-cable driven parallel manipulator for the forty-meter aperture radio telescope

This paper mainly analyzes a hybrid position/force control strategy and experiment of a six-cable driven parallel manipulator for a forty-meter aperture radio telescope. Through the establishments of a kinematic model, a catenary model and a cable-force characteristics model, a basic method is presented based on preventing the pseudo-drag problem of a flexible cable and realizing the hybrid position/force control for a six-cable driven parallel manipulator, and a hybrid position/force control system is developed. Some specific experiments in two typical velocities for astronomical observations are carried out. Experimental results show that the tracking accuracy is related to the speed of the movement. The desired tracking accuracy of the support system is achieved through an effective hybrid position/force control strategy, the cable forces are controlled effectively, and the pseudo-drag problem of flexible cable is solved. This study establishes the foundation of achieving the harmonious movement of the six-cable driven parallel manipulator, A-B rotating platform and the Stewart fine tuninz olatform.

Accuracy Analysis of Stewart Platform Based on Interval Analysis Method

A Stewart platform is introduced in thc 500 m aperture spherical radio telescope（FAST） as an accuracy adjustable mechanism for teed receivers. Accuracy analysis is the basis of accuracy design. However, a rapid and effective accuracy analysis method for parallel manipulator is still needed. In order to enhance solution efficiency, an interval analysis method（lA method） is introduced to solve the terminal error bound of the Stewart platform with detailed solution path. Taking a terminal pose of the Stewart platform in FAST as an example, the terminal error is solved by the Monte Carlo method（MC method） by 4 980 s, the stochastic mathematical method（SM method） by 0.078 s, and the IA method by 2.203 s. Compared with MC method, the terminal error by SM method leads a 20% underestimate while the IA method can envelop the real error bound of the Stewart platform. This indicates that the IA method outperforms the other two methods by providing quick calculations and enveloping the real error bound of the Stewart platform. According to the given structural error of the dimension parameters of the Stewart platform, the IA method gives a maximum position error of 19.91 mm and maximum orientation error of 0.534°, which suggests that the IA method can be used for accuracy design of the Stewart platfbnn in FAST. The 1A method presented is a rapid and effective accuracy analysis method for Stewart platform.

Establishment of the GPS Monitoring Network in North China, the Relation of Horizontal Crustal Movement to Stress Field and Seismicity

In the paper, the establishment, measurement, data-processing program and monitoring accuracy of the GPS seismic monitoring network in North China, especially in the Capital-Circle area, have been presented briefly. The relation of horizontal crustal deformation to tectonic movement, stress-field variation and seismicity has been analyzed in detail. The results indicate that the accuracy of GPS measurement has reached the order of 10-9 and the annual rate of horizontal crustal deformation in North China is about 4 ~5 mm. Horizontal crustal movement is a direct indication of the regional stress field. Therefore, by monitoring the time-sequence variation of horizontal crustal motion, it would be possible to investigate the change in the stress field, to analyze the tendency of seismicity and to determine the seismogenic zones.

大型高精度消像旋机构的设计与验证

在大口径望远镜巡天观测中,需要成像相机对指定天区长时间曝光,受地球自转的影响,长曝光图像会产生旋转现象。消像旋机构是为了抵消地球自转对成像质量的影响,使成像光斑在相机上位置稳定、能量集中。墨子巡天望远镜采用相机旋转的方式实现消像旋功能,消像旋机构要求具备承载能力≥250 kg、转速>20′/s和角定位精度≤2″。本文通过对影响消像旋机构承载能力、转动速度和定位精度的因素分析,采用高精度转台轴承结合轻量化转轴实现了高精度和高刚度轴系设计,轴系晃动为1.9″。传动系统采用谐波减速器结合圆柱直齿轮副两级传动,实现了低转速和高角分辨率。利用双读数头绝对式圆光栅测量转角误差并进行位置控制补偿,实现了角定位精度优于1.1″。墨子巡天望远镜成像图像在经过消像旋机构补偿后,光斑能量集中、无画圆,实现了高质量成像的目标。

上海天文馆双焦点可切换一米望远镜主焦点的天体测量精度评估

上海天文馆望舒天文台的双焦点可切换一米望远镜是目前国内建成的最大口径的科普天文望远镜。该望远镜采用人工切换主焦点和耐式焦点的双焦点设计方案,耐式焦点主要应用于大众科普的目视观测,主焦点配备了大靶面科学级CMOS终端,视场达到1.5°×1.1°。较大的观测视场除了适合开展重要的天象直播活动以外,还可以充分应用于新星和超新星巡天搜索、太阳系小天体和人造天体监测等科研课题的研究。基于实测资料,对该望远镜主焦点的天体测量精度进行分析评估,结果表明:对于信噪比大于5的星象,星象位置的重复测量精度优于0.1 pixel;当信噪比为30时,重复测量精度优于0.05 pixel。以高精度的Gaia DR3星表作为参考星表,分析得出该望远镜主焦点CMOS观测图像的非线性特征明显,归算时需要用到3阶(20参数)模型。对于测试观测资料,亮于15 mag的恒星观测精度约为0.05′′;观测精度随着星等变暗逐渐下降,17.5 mag的恒星观测精度约为0.1′′。

大型射电望远镜日照热误差及其补偿的仿真研究

射电望远镜广泛应用于射电天文、测控导航等领域,随着其工作频率的升高、口径的增大,日照引起的结构热变形对其性能的影响愈发严重;本文针对待建的新疆110 m口径射电望远镜,建立了其日照热力耦合模型,分析了天线在不同时刻、风速及姿态下的温度、变形情况,总结了结构日照温度场、变形场的时空分布特征,最后采用最佳吻合抛物面方法对反射面精度进行了评价,并通过副反射面位置补偿量的变化趋势揭示了天线热变形的共性规律及机理。结果表明:对于日照引起的天线热变形误差,风速越大,结构温度分布越均匀,其越接近等温膨胀变形,反射面形状精度越高;温差引起的结构不均匀变形是反射面精度下降的主要原因,温差越大结构的不均匀变形越大,反射面的形状精度越低;同一姿态不同风速下反射面热误差空间分布具有相似性,该分布与太阳直射点位置直接相关,且会跟随直射点位置发生变化,但由于日照强度、风速等因素的不同,其变形幅度不同。各种姿态下反射面精度变化规律相似,与风速的相关性均为反射面精度随风速上升而提高;采用副反射面位置补偿技术可明显缓解日照热误差影响。本文的分析方法与结论对大口径全可动射电望远镜的设计建造及其热误差控制具有一定参考价值。

公路隧道施工水平位移及收敛量测精度确定方法与衡量方法探讨

隧道施工监控量测是隧道工程专业与测绘工程专业的交叉领域,在精度要求方面,隧道专业和测绘专业的规范标准中都有相关的条文说明,但不同规范标准之间存在侧重和差异,这给使用者在参考时造成一定的困扰。为了明确公路隧道施工监控量测水平位移监测精度要求,通过分析现行的国家标准、行业标准中的相关规定,结合多本现行规范中关于精度要求的说明,给出一种以确定允许变形量→确定衡量标准(中误差)→确定最大允许误差(中误差限差)为思路的精度确定方法,和计算实测数据中误差→对比计算中误差与中误差限差→判断数据可信度的精度衡量方法,并通过实测数据论证其合理性。结果表明,文中提出的精度确定方法、精度衡量方法及仪器选用能满足公路隧道水平位移监测或收敛监测的工作需求。

复杂观测条件下长距离混凝土坝视准线观测的优化方法

为解决复杂观测条件下长距离混凝土坝视准线观测精度不满足规范要求的问题,提出基于高精度测量机器人和正倒垂监测数据的“分段对向小角度法”。通过试运行观测数据分析,各测点位移变幅符合大坝变形规律,且位移量与气温、水位的相关性强弱与监测点位置有关。观测精度分析表明:该方法能满足1mm的观测精度要求,故“全自动分段对向小角度法”为提高长距离混凝土坝视准线观测精度提供了有效途径。

飞机润滑工作对飞行安全性的影响分析——以“阿拉斯加空难事件”为例

针对MD-83飞机的水平尾翼平衡调节系统因润滑作业周期延长、润滑不足导致飞机坠毁的空难事件,介绍了润滑保养工作与飞行安全的关系、最佳的润滑作业周期确定方法、水平尾翼平衡调节系统组成及工作原理,阐述了空难事件发生过程,详细分析了空难事件产生原因。分析结果发现:阿拉斯加航空公司延长了伸缩螺杆润滑维修作业保养周期,违反润滑保养工作程序,是造成此次空难事件的主要原因,机长在应急处理中的人为差错是次要原因。最后,提出了四条预防措施,保证飞行安全。

基于历史建筑修缮与保护需求的地面三维激光扫描仪点距精度实验分析

为研究地面激光扫描技术对历史建筑修缮与保护的实用意义,满足对历史建筑修缮与保护的需要,本文采用Focus3D X330地面激光扫描仪(Terrestrial Laser Scanning,TLS)对扫描距离、水平入射角2个影响因素进行点距精度实验分析,以扫描仪内外符合精度作为站点布设依据,寻求扫描仪的最佳数据区间,得到符合精度要求的高质量测量数据。实验结果表明,扫描距离在5—15 m内,内外符合精度中误差均不超过4 mm,超过15 m后内外符合精度中误差急剧上升且波动较大;水平入射角为75°—90°时,内外符合精度中误差均不超过2 mm,在15°时中误差出现最大值且波动大。上述结果可为历史建筑的修缮与保护所需的数据采集提供参考依据。

水平定向钻技术在岩土工程勘察中的应用

针对岩土工程勘察问题,提出一种新的水平定向钻技术,其具有勘察精度高、适用范围广、环境友好等特点,解决了传统垂直定向钻中设备移动困难、费时费力的问题,实现了远距离的精准钻芯检测。工程实践应用表明,水平定向钻技术通过取芯测试、地应力测试、综合测井、CCTV检测等流程,不仅可准确记录钻进速度、深度等指标,还能借助地面接收器对孔内影像实时观测,自动存储全部影像资料。

捣固车道岔区起道作业效果提升方法

国内主流08-475型道岔捣固车在重型道岔捣固作业中存在起道力不足、起道后轨枕横向水平精度难以保证等问题。本文通过仿真计算分析了曲股第三轨起道点距直股第一轨、第二轨起道点的距离对道岔区起道能力及起道后轨枕横向水平精度的影响,起道点与后转向架中心的间距对起道效果的影响,起道后轨枕横向水平偏差对捣固效果的影响。研究结果表明:将曲股第三轨起道点距直股第一轨、第二轨起道点的距离由3根轨枕宽度调整至1根轨枕宽度,能有效提升捣固车起道能力和轨枕横向水平精度;增大起道点与后转向架中心的间距能有效提升起道能力;起道后轨枕横向水平偏差越大,捣固作业后枕下区域道床密实度越小。

BDS基准网处理技术在大坝安全监测中的应用

为准确了解大坝安全状态,减少传统大坝安全监测受气候、环境等因素的影响,基于BDS基准网处理技术实现了大坝安全监测自动化。在BDS基准网处理中,采用双差基线解算模型,并构建大气延迟修正算法,开发了BDS基准网处理软件。通过该软件在国内某大型水利大坝开展BDS安全监测应用测试,并将测试结果与商用软件TBC+COSA进行对比。结果表明,该软件在实验区域内的监测精度与商用软件相当,基于BDS-3和BDS-2/BDS-3两种模式下的水平定位精度均能达到±1 mm,说明该软件的解算成果可靠,也充分说明基于BDS-3的基准网处理技术可满足高精度自动化大坝安全监测的要求。

船行波对H-ADCP影响分析研究

作为当今世界上最先进的测流仪器,水平式声学多普勒流速剖面仪(Horizontal Acoustic Doppler Current Profiler,H-ADCP)因其精度高、速度快等突出优势在河流中的应用越来越广泛,但在航运业发达地区,由于受船行波的影响,很难得到稳定可靠的流速数据,阻碍了HADCP在平原河网地区的应用和推广。目前技术上很难做到完全消除船行波的影响,本文将HADCP应用在平原河网地区对流速进行测量,并分析了船行波对测量精度的影响。从H-ADCP设备选型、测量和安装方式、测量预处理、数据后处理等多方面入手,可以有效消减船行波对H-ADCP的影响,从而提高测流精度。同时,通过实验测量断面一天内平均流速变化情况,得到受船行波影响后的流速波形,然后采用数据处理手段,验证了所提方法的可行性。

山东地面气象观测站网布局评估

基于滚动需求评估的原则和结构函数,评估山东地面气象观测站网水平分辨率(平均站间距),研究山东国家级基准、基本及常规气象观测站气温、相对湿度、降水量的最佳布站方案和最佳布站距离。结果表明:(1)国家气象观测站和区域气象观测站各要素水平分辨率由小到大依次为降水量、气温、风向和风速、相对湿度、气压,国家级基准、基本及常规气象观测站各要素水平分辨率均相同,应用气象观测站气温与相对湿度要素的水平分辨率小于风向和风速及降水量。(2)除全球数值天气预报和海洋应用领域外,山东4类地面气象观测站各要素的水平分辨率相比观测系统能力分析和审查工具(Observation System Capability Analysis and Review,OSCAR)中各应用领域突破值尚有较大的差距。(3)山东国家级基准、基本及常规气象观测站的气温、相对湿度、降水量的四季结构函数整体上随距离的增加而增大。气温、相对湿度、降水量的线段内插、正三角形内插和正方形内插标准误差与距离均呈线性关系。在距离满足点值内插标准误差小于观测标准误差时,气温、相对湿度和降水量均为正三角形内插精度最高。(4)山东国家级基准、基本及常规气象观测站气温、相对湿度和降水量最佳的布站方案均为正三角形布设,其中气温、相对湿度、降水量的最佳布站距离应分别不超过43.6 km、63.4 km和40.3 km。