LAMOST反射施密特改正板风载分析

本文介绍LAMOST反射施密特改正板系统在风载下的变形及象质变化情况。文中建立了改正板系统的整体有限元模型 ,并计算分析了在技术要求规定的风载下的响应 ,计算结果表明反射施密特改正板支撑结构的设计是满足技术要求的     

LAMOST子镜镀膜研究进展

对大口径光学/红外天文望远镜而言,为保障其稳定高效运行,镜面镀膜是重要的维护环节之一.镀膜质量的好坏直接影响镜面光学反射率的高低,也严重影响到天文望远镜的成像质量、观测效率.国家重大科技基础设施—大天区面积多目标光纤光谱天文望远镜(Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST,又名郭守敬望远镜)自2009年6月通过国家竣工验收并逐步投入巡天观测,目前已进入第2个5 yr巡天计划阶段,取得近两千万的光谱产出和大批高显示度的科学成果. LAMOST共拥有24块施密特改正镜子镜和37块球面主镜子镜,为了确保在野外恶劣观测环境下镜面反射率维持在较高水平,每年要对大批子镜进行镀膜.主要介绍了镀膜需求、镀膜设备,并基于大量实验和多年的完善探索出一套可行的镀膜工艺流程,确保了LAMOST子镜极高的镀膜质量.镀膜后子镜平均反射率高达90%以上,满足了LAMOST光谱巡天的镜面反射率要求.     

LAMOST观测控制系统用户界面设计

位于国家天文台兴隆观测基地的大天区面积多目标光纤光谱天文望远镜(LAMOST)是世界上最大的、可操控的反射施密特望远镜。为了便于控制望远镜,提高观测效率,设计了观测控制系统图形用户界面。首先分析了LAMOST望远镜的控制软件体系结构,采用基于场景的以用户为中心的设计方法,对界面进行了分析和设计。使用Qt、CORBA、多线程技术和MVC模式,实现了用户界面,并对界面进行了测试。最后,用户界面得到了用户的认可,成功应用于LAMOST观测。     

由两块拼接反射镜组成的光学系统的衍射能量分布

LAMOST的光学系统由反射施密特改正板MA 和球面主镜MB 组成 ,MA 和MB 均为对角径 1 .1m的六角形子镜的拼镜面 .本文计算了星在子午圈上时望远镜观测不同的天区零视场和有视场时的光学系统衍射能量分布 ,还计算了MA 不变MB 改为整块的 6m镜以及MA 和MB 均为对角径 1 .5m的六角形子镜的拼镜面的衍射能量分布 .对这些计算结果进行分析 ,论证了六角形子镜尺寸选择的合理性     

高次非球面板补偿检验方法的研究

本文提出了检验高次非球面板的基本系统,并把五级球差应用于求补偿器的初始解,用网格法得到的初始解与优化结果符合．文章以口径为１５ｍ,视场为６°的施密特望远镜的消色差改正板为例,设计了两个补偿检验系统．被检面的面形残差均小于λ／１００．还以消色差施密特改正板一为例,对补偿系统在失调状态下的误差作了详细分析,同时结合实际加工情况,得出了较为宽松的公差要求．     

基于Keck方法的大型拼接镜面共面方法的研究

LAMOST是我国也是世界上唯一的同时应用薄镜面主动光学和拼接镜面主动光学的望远镜,但望远镜目前的设计要求还只是共焦,还没有很好地开展共面技术的研究和应用.Keck望远镜的共相方法已经得到了成功的应用.在红外波段得到了10m镜的衍射像.参照Keck的算法,开发了一套用于检测拼接子镜前后有一定平移误差时的模拟软件,在LAMOST及以后各大型望远镜的拼接镜面实验装置上应用.结果表明,这个方法是现实可行的.     

YNST光电导行镜机械设计

YNST(云南1m太阳望远镜)光电导行系统的作用除了获取足够清晰的太阳像用作光电导行外,还参与望远镜光轴的校正.介绍了YNST光电导行镜的光学要求、机械设计结果及镜体设计所采用的被动无热化技术.校核了导行镜在阳光辐照下的热变形,计算了导行镜镜筒的最大弯沉,结果表明,所采用的无热化设计是有效的,导行镜刚度满足导行系统要求...     

改进遗传算法在初始波长定标中的应用

在LAMOST和SDSS二维光谱数据处理的初始波长定标操作中,通常给定色散曲线的一组初始拟合系数,然后在其附近一定空间内进行搜索,以期找到一组最优的系数.这实际上是一个全局寻优的问题.LAMOST和SDSS目前使用的是枚举式搜索方式,但是由于缺乏全局最优解的先验知识,需要大量的时间遍历整个解空间才能得到全局最优解.遗传算法由于使用了启发式搜索方式,是一种高效的全局寻优算法.在标准遗传算法的框架上,通过使用有效的编码方式、适应度函数以及选择、交叉、变异等遗传算子,构造了一种能够用于初始波长定标的快速收敛的改进遗传算法.通过Shaffer's F6函数的测试,该改进遗传算法具有良好的全局收敛性.将该改进遗传算法引入到LAMOST初始波长定标的寻优操作中,实验表明该算法能够取得较好的效果.     

北京天文台施密特望远镜驱动系统的改进设计

介绍了北京天文台 60 0 / 90 0mm施密特望远镜驱动系统的改进设计 ,即用 2只步进电机 ,取代了原望远镜由 4只变速箱、 7只电机驱动的复杂的赤经 ,赤纬驱动系统 ,最终实现了计算机控制。     

LAMOST网络控制系统结构

LAMOST(大型多天体分光望远镜)建成后将成为世界上视场最大、光谱观测效率最高的4m级口径以上的光学望远镜。它将要同时高效地观测4000颗星的光谱,这对网络控制系统的设计是巨大的挑战。该文主要从LAMOST网络控制系统构建的角度介绍了系统如何在大数据量、多任务的情况下实现各子系统控制、环境监测、授时和无线远程监控等功能,叙述了在该系统中运用的实时分布式操作系统、实时数据库,全球定位系统(GPS)和全球移动通讯系统(GSM)等多项技术．     

SIESTA, a time domain, general purpose simulation program for the VIRGO experiment

In this paper we present the simulation program that has been developed for the VIRGO gravitational wave detection experiment. Although this program — SIESTA — is still evolving, it has reached a stage where the design requirements have been largely fulfilled. We first remind the needs and the choices which have steered the program design and led to the present structure. The contents of the program is then reviewed, the performances are discussed, and some typical applications are briefly described.     

Design and optimization of cross bow-tie dipole feed with cavity for FAST

A cross bow-tie dipole feed with cavity and symmetrical E and H plane pattern is presented for the Five hundred-meter Aperture Spherical radio Telescope(FAST).In this paper we describe the design,optimization and simulation results of a wide-band cross dipole feed with cavity covering the frequency range from 300 MHz to 600 MHz for FAST.The main goals of our design are to ensure that,(1)we cover the octave bandwidth,(2)the feed has symmetrical E and H plane pattern,and(3)the physical dimension is suitable for mounting it in the reserved position of the FAST feed cabin.The initial results indicate that we have met most of our design goals.This kind of feed had been equipped with the multi-beam receiver to carry out observation on the platform of FAST cabin.     

FAST望远镜两轴转向机构结构方案优化

FAST馈源支撑系统承载和驱动馈源运动,进行对天体的高精度跟踪观测.在实时的定位调整中,两轴转向机构起着辅助调整接收机姿态角的作用.为满足FAST两轴转向机构的重量及刚度要求,选择了一种空间刚架式的结构构型.提出了反映结构柔顺度及重量约束的目标函数,以各类杆件的截面面积以及整个结构的高度、半径等几何参数作为优化变量,采...     

Conceptual Design of the Aluminum Reflector Antenna for DATE5

DATE5,a 5 m telescope for terahertz exploration, was proposed for acquiring observations at Dome A, Antarctica. In order to observe the terahertz spectrum, it is necessary to maintain high surface accuracy in the the antenna when it is exposed to Antarctic weather conditions. Structural analysis shows that both machined aluminum and carbon fiber reinforced plastic(CFRP) panels can meet surface accuracy requirements. In this paper, one design concept based on aluminum panels is introduced. This includes panel layout, details on panel support, design of a CFRP backup structure, and detailed finite element analysis.Modal, gravity and thermal analysis are all performed and surface deformations of the main reflector are evaluated for all load cases. At the end of the paper, the manufacture of a prototype panel is also described.Based on these results, we found that using smaller aluminum reflector panels has the potential to meet the surface requirements in the harsh Dome A environment.     

The 3-D lattice theory of Flower Constellations

Flower Constellations (FCs) have been extensively studied for use in optimal constellation design. The Harmonic FCs (HFCs) subset, representing the symmetric configurations, have recently been reformulated into 2-D Lattice Flower Constellations (2D-LFCs), encompassing the complete set of HFCs. Elliptic orbits are generally avoided due to the deleterious effects of Earth’s oblateness on the constellation, but here we present a novel concept for avoiding this problem and enabling more effective global coverage utilizing elliptic orbits. This new 3D Lattice Flower Constellations (3D-LFCs) framework generalizes the 2D-LFCs, Walker constellations, elliptical Walker constellations, and many of Draim’s global coverage constellations. Previous studies have shown FCs can provide improved performance in global navigation over existing Global Navigation Satellite Systems (GNSS). We found a 3D-LFC design that improved the average positioning accuracy by 3.5 % while reducing launch $\varDelta v$ Δ v requirements when compared to the existing Galileo GNSS constellation.     

System Optimisation Of Multi-Beam Aperture Synthesis Arrays For Survey Performance

Investigating the requirements for an aperture synthesis array that optimise the performance for surveying shows that, next to collecting area and system temperature, the field-of-view (FoV) is key parameter. However, the effective sensitivity not only depends on bandwidth and integration time but could be seriously limited by side lobe confusion and by gain errors that determine the effective dynamic range. From the basic sensitivity equation for a radiometric system we derive an optimum cost ratio between collecting area and processing electronics, where the latter should be less than a third of the total cost. For an instrument that has to cover a fraction of sky larger than its field-of-view, the FoV enters the equation for survey sensitivity and we identify the number of independent feed systems per unit collecting area as a key parameter. Then the optimum cost distribution allows the electronics to account for up to half the total cost. Further analysis of the sensitivity formula shows that there is an optimum design frequency for a survey instrument below 1 GHz. We discuss the impact of station size and array configuration on self-calibration, side lobe confusion and effective sensitivity and conclude that a minimum station size of 20 m diameter is required at 0.3 GHz as long as multi-patch self-calibration procedures need, per baseline, a signal-to-noise ratio of more than two for each ionospheric coherence patch.     

Performance of the Nuclear Compton Telescope

On 1 June 2005, the prototype Nuclear Compton Telescope (NCT) flew on a high altitude balloon from Fort Sumner, New Mexico. NCT is a balloon-borne soft γ-ray (0.2–10 MeV) telescope for studying astrophysical sources of nuclear line emission and γ-ray polarization. Our program is designed to develop and test technologies and analysis techniques crucial for the Advanced Compton Telescope; however, our detector design and configuration is also well matched to the focal plane requirements for focusing Laue lenses. The NCT prototype utilizes two, 3D imaging germanium detectors (GeDs) in a novel, ultra-compact design optimized for nuclear line emission in the 0.5–2 MeV range. Our prototype flight provides a critical test of the novel detector technologies, analysis techniques, and background rejection procedures developed for high resolution Compton telescopes.     

Effect of altered Arctic sea ice and Greenland ice sheet cover on the climate of the GENESIS general circulation model

Previous studies have examined the effect of reduced Arctic sea ice cover on the circulation of climate models. Generally, the response is restricted to high northern latitudes. Here we examine a variant on those simulations, specifying both reduced Arctic sea ice cover and no Greenland ice sheet. The GENESIS general circulation model is used in these experiments. As in earlier studies, we find the effect limited primarily to the high latitudes of the northern hemisphere, being greater in winter than in summer. New results reported herein involve: (1) in winter reduced Arctic ice cover has a significantly greater effect than reduced Greenland ice cover; (2) reduced ice cover had little effect on location of the winter freezing line over North America and Eurasia; (3) removal of ice caused a 30–50% increase in precipitation in high northern latitudes; however there were no significant effects elsewhere. This result does not support the hypothesis that past changes in Arctic ice cover were responsible for significant changes in area of tropical rainforests; (4) there is a peculiar surface pressure anomaly that extends into the high latitudes of the southern hemisphere. This anomaly may be a spurious artifact of the effect of the removed Greenland ice sheet on the spherical harmonic expansion terms in the model. These sensitivity experiments should serve as a useful frame of reference for future Pliocene simulations with a more complete set of altered boundary conditions.     

How to build a continental scale fireball camera network

The expansion of the Australian Desert Fireball Network has been enabled by the development of a new digital fireball observatory based around a consumer digital camera. The observatories are more practical and much more cost effective than previous solutions whilst retaining high imaging performance. This was made possible through a flexible concurrent design approach, a careful focus on design for manufacture and assembly, and by considering installation and maintenance early in the design process. A new timing technique for long exposure fireball observatories was also developed to remove the need for a separate timing subsystem and data integration from multiple instruments. A liquid crystal shutter is used to modulate light transmittance during the long exposure which embeds a timecode into the fireball images for determining fireball arrival times and velocities. Using these observatories, the Desert Fireball Network has expanded to cover approximately 2.5 million square kilometres (around one third of Australia). The observatory and network design has been validated via the recovery of the Murrili Meteorite in South Australia through a systematic search at the end of 2015 and the calculation of a pre-atmospheric entry orbit. This article presents an overview of the design, implementation and performance of the new fireball observatories.     

Mechanical structure of JNLT

The Japanese National Large Telescope (JNLT) requires mechanical performance of high tracking accuracy to achieve good image quality and a mechanical configuration to provide several kinds of focus modes. Under these requirements, a conceptual design for the JNLT mechanical structure has been performed. This paper presents the results of the conceptual design currently under consideration.Paper presented at the symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.