Research on the principle of space high-precision temperature control system of liquid crystals based Stokes polarimeter

The magnetic field is one of the most important parameters in solar physics,and a polarimeter is the key device to measure the solar magnetic field.Liquid crystals based Stokes polarimeter is a novel technology,and will be applied for magnetic field measurement in the first space-based solar observatory satellite developed by China,Advanced Space-based Solar Observatory.However,the liquid crystals based Stokes polarimeter in space is not a mature technology.Therefore,it is of great scientific significance to study the control method and characteristics of the device.The retardation produced by a liquid crystal variable retarder is sensitive to the temperature,and the retardation changes 0.09°per 0.10℃.The error in polarization measurement caused by this change is 0.016,which affects the accuracy of magnetic field measurement.In order to ensure the stability of its performance,this paper proposes a high-precision temperature control system for liquid crystals based Stokes polarimeter in space.In order to optimize the structure design and temperature control system,the temperature field of liquid crystals based Stokes polarimeter is analyzed by the finite element method,and the influence of light on the temperature field of the liquid crystal variable retarder is analyzed theoretically.By analyzing the principle of highprecision temperature measurement in space,a high-precision temperature measurement circuit based on integrated operational amplifier,programmable amplifier and 12 bit A/D is designed,and a high-precision space temperature control system is developed by applying the integral separation PI temperature control algorithm and PWM driving heating films.The experimental results show that the effect of temperature control is accurate and stable,whenever the liquid crystals based Stokes polarimeter is either in the air or vacuum.The temperature stability is within±0.0150℃,which demonstrates greatly improved stability for the liquid crystals based Stokes polarimeter.     

Comparison of three filters in asteroid-based autonomousnavigation

At present, optical autonomous navigation has become a key technologyin deep space exploration programs. Recent studies focus on the problem of orbit de-termination using autonomous navigation, and the choice of filter is one of the mainissues. To prepare for a possible exploration mission to Mars, the primary emphasisof this paper is to evaluate the capability of three filters, the extended Kalman filter（EKF）, unscented Kalman filter （UKF） and weighted least-squares （WLS） algorithm,which have different initial states during the cruise phase. One initial state is assumedto have high accuracy with the support of ground tracking when autonomous navi-gation is operating; for the other state, errors are set to be large without this support.In addition, the method of selecting asteroids that can be used for navigation fromknown lists of asteroids to form a sequence is also presented in this study. The simula-tion results show that WLS and UKF should be the first choice for optical autonomousnavigation during the cruise phase to Mars.     

镜面材料

结合实际加工过的镜面,回顾了用于反射镜面材料的发展历程、性质和加工方法,叙述了材料的现状及存在的问题,为今后的发展指出了方向.最后对常用的反射镜面材料性能进行归纳,对被广泛看好的新材料一碳化硅的应用及加工做了简要叙述.     

Instructions for authors

<正>Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).     

Blazar喷流节点运动视速度的统计研究

VLBI观测表明,TeV伽马射线Blazar(耀变体)的喷流运动视速度远小于MeV/GeV伽马射线Blazar,然而TeV伽马射线辐射流量的快速变化却要求这些Blazar的相对论喷流速度与MeV/GeV Blazar的相当.对于这一矛盾,目前有多种解释.为了检验这些模型,我们收集了VLBI对Blazar喷流运动的监测数据,样本包括86个FSRQs(平谱射电类星体)、22个BL Lac天体,共108个Blazar;从统计上研究了,该样本中各Blazar最大视速度喷流节点的位置与射电光度相关关系.结果表明,Blazar最大视速度喷流节点的位置与射电光度有较强的相关关系,随着Blazar射电光度的减小,喷流中最大视速度VLBI节点的位置到VLBI核的距离逐渐变小.这意味着,TeV伽马源(低光度Blazar)的喷流减速区距离VLBI核较近,喷流从高能辐射区到VLBI可分辨尺度已经减速,支持减速喷流模型对TeV伽马射线Blazar上述矛盾的解释.     

波片相位延迟的光强测量法研究

通过Mueller矩阵运算,推导出采用接收光强的方法计算波片相位延迟的唯一表达式,并由此总结归纳出4种测试波片延迟的方法,发现目前发表的多种光强测量法都可归纳为该4种中的一种.文中给出了这4种方法的测试原理,并对各方法中方位角误差带来的测量误差进行了分析及比对,给出不同方法所适宜的测试对象.     

征稿启事

《中国科学院上海天文台年刊》第33期(2012年)开始征稿。欢迎台内外科技工作者,把您们的科研成果、阶段性成果、观测数据分析、仪器研制、课题研究的有关软件编制、工作报告等在此期上发表。来稿要求观点明确、论据充足、论述简练、资料数据反映的情况务求核实准确。     

诗意的星河——古诗中的五星

古人对行星的称谓 古人很早就发现,在满天的繁星中,有5颗星非常与众不同：第一,它们不象其他星星那样“恒定”（保持着相对不动的位置）,而是在众星中游动;第二,它们都很亮,多数情况下亮度都超过或仅暗于天狼星,而且亮度不断发生变化。随着社会的进步,文明的发展,我们的先辈为这5颗特别的星星起了名字,大约在商、周时期,这5颗星分别被称作辰星、太白、荧惑、岁星、镇星（填星）,这就是今天肉眼可见的五星：水星、金星、火星、木星、土星。     

和全世界一起数星星

2010年10月29日至11月12日,这个秋天,和其他成千上万的学生、家庭成员、科学家们共同加入“了不起的全球恒星计数”活动中,一起来数星星吧!美国地球科学教师协会（National Earth Science Teachers Association）正在通过他们支持的“宇宙之窗”网站（www．windows2universe．org）向全世界的人们发出邀请。“了不起的全球恒星计数”活动,     

丝路之旅逐日影—赴甘肃观日全食散记

今年8月1日的日全食带开始于加拿大北部,经过格陵兰岛,穿过北极圈,掠过俄罗斯的新西伯利亚,北京时间18时59分日全食经阿尔泰山入境,途径新疆、甘肃、内蒙古、宁夏、陕西、山西,在北京时间19时21分结束于河南海里漯河附近,全食的持续时间约2分钟。这是进入21世纪之后在我国境内第一次观察日全食的好时机,笔者有幸福在甘肃金塔目睹了这大自然的壮观。     

大漠·峡谷·荧惑——记首届“中美太空少年”（CYSA）·火星学生拍摄项目（MSIP）

农历大年三十,清晨六点,美国亚利桑那州凤凰城机场。一行十五名中国学生挥泪告别亚利桑那大学的教授。再见,亲爱的Wendy,再见,可爱的Ferdane,再见,宜人的亚利桑那。站在机场的玻璃幕墙前远眺亮黄的朝阳跃出沙丘,我在心中祈祷,能再次造访这片点缀着仙人掌与棕榈树的神奇土地……     

诗意的月球（七）——月亮与海潮

潮汐是大海特有的一种现象,久存海边的人会发现：海水每天都有规律地上升和下降,仿佛人的呼吸一般（如上图所示）。海水这种奇特的运动,经常成为诗人歌咏的对象,有时特殊的地理环境会造成壮观的大潮（如钱塘江大潮）,成为特别的景观,也留下许多诗词佳作。     

2014年3月日、月及行星动态

水星晨星。日出时位于东南方天空。3月上甸,水星与太阳的角距逐渐增大,升起的时间也逐日提前,日出时水星的地平高度约为11°,可以观测。3月14日水星到达西大距,与太阳的最大角距离为28°,日出时地平高度约1O°,亮度约＋O．1等,由于水星地平高度不高,因此此次大距过后,水星又缓缓向太阳靠拢,日出时水星的地平高度进—步降低,不易观测。22日20时水星合海王星,水星位于海王星之南1°。29日13时水星合月,水星位于月亮之南6°。     

Spacecraft Doppler tracking with possible violations of LLI andLPI： a theoretical modeling

Currently two-way and three-way spacecraft Doppler tracking techniquesare widely used and play important roles in control and navigation of deep space mis-sions. Starting from a one-way Doppler model, we extend the theory to two-way andthree-way Doppler models by making them include possible violations of the localLorentz invariance （LLI） and the local position invariance （LPI） in order to test theEinstein equivalence principle, which is the cornerstone of general relativity and allother metric theories of gravity. After taking the finite speed of light into account,which is the so-called light time solution （LTS）, we make these models depend on thetime of reception of the signal only for practical convenience. We find that possibleviolations of LLI and LPI cannot affect two-way Doppler tracking under a linear ap-proximation of LTS, although this approximation is sufficiently good for most cases inthe solar system. We also show that, in three-way Doppler tracking, possible violationsof LLI and LPI are only associated with two stations, which suggests that it is betterto set the stations at places with significant differences in velocities and gravitationalpotentials to obtain a high level of sensitivity for the tests.     

宇宙画廊

变化多端的极光,很难预期它会给我们带来怎样的惊喜,一位天文摄影师居然在阿拉斯加看极光时,捕捉到星空中奔跑着的一只“小狗”。看,这只小狗尖耳朵,翘尾巴,前后小腿儿都腾空而起,背上驮着北斗七星,后腿还蹬着火星。     

天文学与其他科学--天文学PK物理学（下）

现在恐怕不知道雷达的人已不会太多了。因为在第二次世界大战中,它为反法西斯战争建立了赫赫功勋。从实力而言,当年英国空军远非希特勒的对手,正如丘吉尔所言：“在人类战争史上,如此以强凌弱,而强者反而遭到如此惨败的先例恐怕是从来没有过的。”英国所以会取胜的因素固然不少,但不可否认,1940年发明的雷达是重要因素之一。     

9月星空看点

火土西垂心宿随 几千年来,人类一直观测星空,试图了解宇宙的秘密。古人认为,宇宙就是由地球、太阳、月亮和星星组成的。其中5颗亮星特别引人注目,它们总在群星间移动,像是夜空流浪者,于是,古人把它们称为行星。这5颗肉眼可见的行星就是水星、金星、火星、木星和土星。     

2015年1月行星出没图（北纬40°）

左图显示每日日落到次日日出之间的五颗行星出没状态及观测备件,包括晨昏蒙影时刻,水星与金星的出没时刻,火星、木星与土星的出没及中天时刻,以及月亮出没状态,横坐标为地方平时,纵坐标为日期。     

月球的起源

月亮是夜空中最为明显的天体,自人类文明之初,它就在世界各地的文化中占据着特殊的地位。大多数古代文明都相信,月亮是由神放置在天空中的。随着现代天文学的发展,人们以更现实的方式考察月球的起源。今天最广为接受的理论认为,地球在年轻时曾与一颗火星大小的天体相撞,而月球正晕场大冲撞溅出的碎片凝聚形成的。