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。     

2020年2月重要天象预告

本月的天象看点以肉眼可见的几颗大行星为主。水星将在本月10日到达今年的第一次东大距,也是今年第一次观测它的好时机;金星在本月将一直处于良好的观测状态,每天日落后都能看见它闪耀在西方天空。火星、木星和土星已经运行到太阳的西侧,在日出前可以看到三星连线的现象。     

为什么恒星有不同的颜色?

问天狼星是白色的,心宿二是红色的老人星是黄色的……为什么恒星有不同的颜色?答夜空中闪烁的星光,有的像心宿二—样呈现出红色,有的像老人星一样泛着黄色的光芒,还有的像天狼星一样发出白色的光……其实,恒星的颜色主要跟恒星表面温度密切相关。这种颜色与温度间的关系不单存在于遥远的太空中,在我们日常生活中也随处可见。     

氢原子频标的小型化

小型化是目前氢钟的发展方向之一，氢钟的小型化主要是谐振腔的改进，它的结构尺寸决定了氢钟的最小尺寸和重量，目前要用的小型腔主要有电极负载腔，磁控管腔，介质负载腔和TE111腔，新型的谐振腔虽然减小了体积减轻的重量，但量由于它本身已经很难满中立起振条件，所以在伺服电路上也不同于主动型氢钟，根据电路原理的不同，将小型化的氢钟分为反馈振荡型和被动型，反馈振荡型氢钟使激射器工作在反馈振荡状态，通过正反馈维持激射器振荡，被动型氢钟的激射器工作在振荡阈值之下，其作用与揩振放大器相似。     

SOHM-4型氢原子钟的设计改进与初步性能

氢原子钟是一种最稳定的 (除极短测量时间间隔之外 )频率标准 ,但是环境温度变化及微波谐振腔老化会引起原子钟输出频率的变化 ,从而导致氢原子钟长期性能变差。为了减小这些影响 ,可借助一种自动调谐器来确保谐振腔的频率始终工作在所需的频率上 ,并采用新的温度控制系统来改善氢原子钟的长期性能。针对这些年来许多氢钟出现的有关问题 ,上海天文台在借鉴国外氢钟实验室经验的基础之上 ,对原有氢钟进行了技术改造 ,并为国家授时中心研制了SOHM - 4型氢原子钟。对该型氢原子钟技术改造特点作了介绍 ,并给出了期望的性能指标及初步的测试结果     

被动型氢钟流量变化对长期频率稳定度的影响分析

为提高系统的长期频率稳定度(它是被动型氢钟的一个重要指标),设计了一种实验,用以分析在不同微波腔谐振频率下,氢气流量变化对输出频率的影响。通过实验发现微波腔的控制电压存在一个调谐点,在调谐点附近,流量变化对输出频率的影响变小。但是对于单频系统,如何将微波腔锁定在调谐点附近以及如何减小流量的影响和提高系统的长期频率稳定度还需要进一步探索。     

Solar-wind interactions: Nature and composition of lunar atmosphere

The solar wind interacts directly with the lunar surface material resulting in an essentially complete absorption of the corpuscles producing no upstream bowshock but a cavity downstream from the Moon. The main source of most neutral species of the atmosphere, except probably⁴⁰Ar, is the solar-wind interaction products. The other sources which appear to be minor contributors to the atmosphere are the interaction products of cosmic rays, planetary degassing, effects of meteorite impacts and radioactive decays. Most of the hydrogen atoms derived from the solar-wind protons contribute to the atmosphere as hydrogen molecules rather than atoms. Only on the basis of the solar-wind protons, alpha particles and ions of oxygen and carbon, the atmospheric species concentration (cm^–3) near the lunar surface at 300K are as follows: H₂ 3.3 to 9.9 × 10³; He 2.4 to 4.7 × 10³; H 3.7; OH 0.25; H₂O 0.24; and O₂, O, CO, CO₂ and CH₄ in concentrations smaller than H₂. Whatever the source, the OH and H₂O concentrations in the atmosphere are about the same. The calculated concentrations are in good agreement with the observations by the Apollo 17 lunar surface mass spectrometer and the Apollo 17 orbital UV spectrometer. At the time of sample collection from the Moon, the hydrogen content in the trapped gas layer of the lunar surface material was partly as hydrogen atoms and partly as hydrogen molecules, but at the time of sample analysis hydrogen was mostly in molecular form. The H₂O content at the time of sample analysis was only a few parts per million by weight.Paper presented at the Conference on Interactions of the Interplanetary Plasma with the Modern and Ancient Moon, sponsored by the Lunar Science Institute, Houston, Texas and held at the Lake Geneva Campus of George Williams College, Wisconsin, between September 30 and October 4, 1974.     

Hydrodynamic simulations of molecular outflows driven by slow-precessing protostellar jets

We present hydrodynamic simulations of molecular outflows driven by jets with a long period of precession, motivated by observations of arc-like features and S-symmetry in outflows associated with young stars. We simulate images of not only H₂ vibrational and CO rotational emission lines, but also of atomic emission. The density cross-section displays a jaw-like cavity, independent of precession rate. In molecular hydrogen, however, we find ordered chains of bow shocks and meandering streamers which contrast with the chaotic structure produced by jets in rapid precession. A feature particularly dominant in atomic emission is a stagnant point in the flow that remains near the inlet and alters shape and brightness as the jet skims by. Under the present conditions, slow jet precession yields a relatively high fraction of mass accelerated to high speeds, as also attested to in simulated CO line profiles. Many outflow structures, characterized by HH 222 (continuous ribbon), HH 240 (asymmetric chains of bow shocks) and RNO 43N (protruding cavities), are probably related to the slow-precession model.     

氢原子钟蓝宝石谐振腔的设计和实验表现

为了设计主动型氢原子钟蓝宝石谐振腔的结构尺寸,对根据TE011模式下蓝宝石谐振腔的麦克斯韦尔方程组推出的超越方程进行了求解,利用电磁场有限元分析软件对蓝宝石腔进行了仿真分析。通过计算S参数,确认了所设计的氢原子钟蓝宝石谐振腔实现氢脉泽自激振荡的现实性。利用SOHM-4型氢钟机架作为实验床,在离子泵电流1.1 mA时,得到了强度为-102.93 dbm的脉泽振荡信号。此信号强度与标准的主动型氢原子钟在相同的离子泵电流下的信号强度相仿。     

参考腔模式匹配及其在激光稳频中的应用

窄线宽激光器是光钟的核心部件,也是原子光精密测量的关键仪器。利用参考腔的功率反射率和功率透射率与损耗的关系给出了窄线宽激光器系统稳频中腔镜损耗的理论表达式。对腔镜的实际反射率与损耗进行了实验测量和计算。实验结果表明,优化模式匹配效率,可以进一步减小腔镜损耗。更重要的是,腔镜损耗的优化有助于提高稳频的锁定质量。     

Whistler wave amplitude oscillation and frequency modulation in the magnetospheric cavity

A magnetospheric cavity model is presented to explain self-pulsing and frequency modulation of ducted whistler waves associated with triggered emissions. Partial reflection of these waves at the ends of the duct suggests such a magnetospheric cavity analogous to a laser cavity.     

Laboratory Experiment of Plasma Flow Around Magnetic Sail

To propel a spacecraft in the direction leaving the Sun, a magnetic sail (MagSail) blocks the hypersonic solar wind plasma flow by an artificial magnetic field. In order to simulate the interaction between the solar wind and the artificially deployed magnetic field produced around a magnetic sail spacecraft, a laboratory simulator was designed and constructed inside a space chamber. As a solar wind simulator, a high-power magnetoplasmadynamic arcjet is operated in a quasisteady mode of 0.8 ms duration. It can generate a simulated solar wind that is a high-speed (above 20 km/s), high-density (10¹⁸ m⁻³) hydrogen plasma plume of ∼0.7 m in diameter. A small coil (2 cm in diameter), which is to simulate a magnetic sail spacecraft and can obtain 1.9-T magnetic field strength at its center, was immersed inside the simulated solar wind. Using these devices, the formation of a magnetic cavity (∼8 cm in radius) was observed around the coil, which indicates successful simulation of the plasma flow of a MagSail in the laboratory.     

Hydromagnetic wave coupling in the magnetosphere—Plasmapause effects on impulse-excited resonances

Recent analytical and numerical modelling has demonstrated the possibility that impulsively-stimulated compressional hydromagnetic cavity resonances can drive local field-line resonances in the magnetosphere. This paper extends the modelling to include axisymmetric plasmapause structures with realistic radial variation in the magnetospheric cavity. The results show that: (a) the plasmapause plays an important rôle in determining which cavity resonances are dominant; (b) when the wave fields are significantly non-axisymmetric, additional cavity resonances are evident which are at least partly trapped within the plasmasphere; (c) the position of the plasmapause determines where (and whether) cavity resonances couple significantly to field-line resonances; (d) for the small “azimuthal” wavenumber chosen, there is no evidence of a compressional surface wave on the plasmapause.