Status of the T2L2/Jason2 Experiment

The T2L2 (Time Transfer by Laser Link) project, developed by CNES and OCA will permit the synchronization of remote ultra stable clocks and the determination of their performances over intercontinental distances. The principle of the experiment derives from Satellite Laser Ranging (SLR) technology with dedicated space equipment. T2L2 was accepted in 2005 to be on board the Jason2 altimetry satellite. The payload consists of both event timer and photo detection modules. The system uses the ultra-stable quartz oscillator of DORIS as on-board reference clock on one hand, and the Laser Reflector Array, making T2L2 a real two-way time transfer system on the other hand. The expected time stability of the T2L2 instrument (detection and timing), referenced by the DORIS oscillator and including all internal error sources should be at the level of 10–12 ps at 1 s and <1 ps at 1000 s. The metrological specifications of T2L2 should permit to maintain a precision of 1 to a few ps when measuring the phase of a clock during around 1000 seconds.     

Comparison of ionospheric F2 peak parameters foF2 and hmF2 with IRI2001 at Hainan

Monthly median values of foF2, hmF2 and M(3000)F2 parameters, with quarter-hourly time interval resolution for the diurnal variation, obtained with DPS4 digisonde at Hainan (19.5°N, 109.1°E; Geomagnetic coordinates: 178.95°E, 8.1°N) are used to investigate the low-latitude ionospheric variations and comparisons with the International Reference Ionosphere (IRI) model predictions. The data used for the present study covers the period from February 2002 to April 2007, which is characterized by a wide range of solar activity, ranging from high solar activity (2002) to low solar activity (2007). The results show that (1) Generally, IRI predictions follow well the diurnal and seasonal variation patterns of the experimental values of foF2, especially in the summer of 2002. However, there are systematic deviation between experimental values and IRI predictions with either CCIR or URSI coefficients. Generally IRI model greatly underestimate the values of foF2 from about noon to sunrise of next day, especially in the afternoon, and slightly overestimate them from sunrise to about noon. It seems that there are bigger deviations between IRI Model predictions and the experimental observations for the moderate solar activity. (2) Generally the IRI-predicted hmF2 values using CCIR M(3000)F2 option shows a poor agreement with the experimental results, but there is a relatively good agreement in summer at low solar activity. The deviation between the IRI-predicted hmF2 using CCIR M(3000)F2 and observed hmF2 is bigger from noon to sunset and around sunrise especially at high solar activity. The occurrence time of hmF2 peak (about 1200 LT) of the IRI model predictions is earlier than that of observations (around 1500 LT). The agreement between the IRI hmF2 obtained with the measured M(3000)F2 and the observed hmF2 is very good except that IRI overestimates slightly hmF2 in the daytime in summer at high solar activity and underestimates it in the nighttime with lower values near sunrise at low solar activity.     

Satellite capture as a restricted 2 + 2 body problem

A restricted 2?+?2 body problem is proposed as a possible mechanism to explain the capture of small bodies by a planet. In particular, we consider two primaries revolving in a circular mutual orbit and two small bodies of equal mass, neither of which affects the motion of the primaries. If the small bodies are temporarily captured in the Hill sphere of the smaller primary, they may get close enough to each other to exchange energy in such a way that one of them becomes permanently captured. Numerical simulations show that capture is possible for both prograde and retrograde orbits.     

Amino acid synthesis from CO-N2 and CO-N2-H2 gas mixtures via complex organic compounds.

Reaction among hydrogen cyanide (HCN), formaldehyde (H2CO) and ammonia (NH3) are generally considered an important reaction in amino acid synthesis by electric discharge. Precursors of glycine and aspartic acid were, however, synthesized by adding water to metastable complex compounds produced by quenching a CO-N2 high-temperature plasma. In order to investigate effects of water remaining in an experimental vacuum chamber, optical emission spectroscopic and mass spectrometric measurements were conducted with CO-N2 and CO-N2-H2 gas mixtures. Although residual hydrogen atoms were detected in the CO-N2 experiment, the amount of them was much less than that in the CO-N2-H2 experiment.     

Impact of Jason-2/T2L2 Ultra-Stable-Oscillator Frequency Model on DORIS stations coordinates and Earth Orientation Parameters

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) is a tracking technique based on a one-way ground to space Doppler link. For Low Earth Orbit (LEO) satellites, DORIS shows a robust capability in terms of data coverage and availability, due to a wide and well-distributed ground network, where data are made available by the International Doris Service (IDS). However, systematic errors remain in the DORIS data, such as instabilities of the on-board clock due to radiation encountered in space, which limit the accurate determination of station positions.The DORIS on-board clock frequency stability is degraded by the increased radiation found in the region of the South Atlantic Anomaly (SAA) and has been shown to degrade station position estimation. This paper introduces a new model correction to the DORIS data for the frequency of the Jason-2 Ultra Stable Oscillator (USO), derived from the Time Transfer by Laser Link (T2L2) experiment (Belli and Exertier, 2018). We show that a multi-satellite DORIS solution including this T2L2-corrected data applied to the frequency modelling for The DORIS data, improves the estimation of station coordinates. We show the tie residuals with respect to collocated GPS stations are improved by several millimeters. We also demonstrate that the 117-day (Jason-2) draconitic signal in the geophysical parameters is reduced, implying that the origin of this signal is not just solar radiation pressure mis-modeling, but also radiation-induced clock perturbations on the Jason-2 DORIS Ultra-Stable-Oscillator (USO). Finally we demonstrate through comparisons with the International Earth Rotations and Reference Systems Service (IERS) C04 series for Earth Orientation Parameters (EOP), that the estimation of EOP is improved in both a Jason-2 DORIS-only and a multi-satellite DORIS solution for EOP.     

“嫦娥二号”卫星L2点角动量管理

对“嫦娥二号”(CE-2)卫星进入环绕日地拉格朗日L2点的李萨如轨道后卫星喷气卸载所产生的影响进行了研究.提出了一种利用光压力矩辅助卫星太阳电池翼角度调整进行角动量管理的方法.在轨试验表明,太阳光压强度足够对飞行在L2点环绕轨道上的CE-2卫星进行角动量管理,可以大幅度减少动量轮在轨喷气卸载的次数,有利于CE-2卫星的轨道维持.     

二维H2/O2混合和流动的直接数值模拟

用高阶精度的紧致差分方法,对低速的随时间发展的二维可压缩H-2/O-2混合层流动编制了直接数值模拟的计算机程序,对雷诺数Re为400、来流马赫数Ma分别为0.4(上部的H₂)和1.57(下部的O₂)的H₂/O₂亚跨超声速混合层流动进行了计算,得到了相应的计算结果,并对结果进行了分析和研究.     

Ionospheric behavior of the F2 peak parameters foF2 and hmF2 at Hainan and comparisons with IRI model predictions

Monthly median values of foF2, hmF2 and M(3000)F2 parameters, with hourly time interval resolution for the diurnal variation, obtained with DPS-4 digisonde observations at Hainan (19.4°N, 109.0°E) are used to study the low latitude ionospheric variation behavior. The observational results are compared with the International Reference Ionospheric Model (IRI) predictions. The time period coverage of the data used for the present study is from March 2002 to February 2005. Our present study showed that: (1) In general, IRI predictions using CCIR and URSI coefficients follow well the diurnal and seasonal variation patterns of the experimental values of foF2. However, CCIR foF2 and URSI foF2 IRI predictions systematically underestimate the observed results during most time period of the day, with the percentage difference ΔfoF2 (%) values changing between about −5% and −25%, whereas for a few hours around pre-sunrise, the IRI predictions generally overestimate the observational ones with ΔfoF2 (%) sometimes reaching as large as ∼30%. The agreement between the IRI results and the observational ones is better for the year 2002 than for the other years. The best agreement between the IRI results and the observational ones is obtained in summer when using URSI coefficients, with the seasonal average values of ΔfoF2 (%) being within the limits of ±10%. (2) In general, the IRI predicted hmF2 values using CCIR M(3000)F2 option shows a poor agreement with the observational results. However, when using the measured M(3000)F2 as input, the diurnal variation pattern of hmF2 given by IRI2001 has a much better agreement with the observational one with the detailed fine structures including the pre-sunrise and post-sunset peaks reproduced reasonably well. The agreement between the IRI predicted hmF2 values using CCIR M(30,000)F2 option and the observational ones is worst for the afternoon to post-midnight hours for the high solar activity year 2002. During daytime hours the agreement between the hmF2 values obtained with CCIR M(30,000)F2 option and the observational ones is best for summer season. The discrepancy between the observational hmF2 and that obtained with CCIR M(30,000)F2 option stem from the CCIR M(3000)F2 model, which does not produce the small scale structures observed in the measured M(3000)F2.     

2-D differential interferometer

A new type of differential interferometer based on holographic optical elements is developed, which allows the exact determination of a refractive index gradient field in two orthogonal directions. This interferometer will be used in TEXUS experiments to determine the temperature field in a convective liquid cell in which the temperature may be known at only one point.     

新型2-2PRUR并联机构运动学分析及工作空间优化

基于工业生产线实际需求,设计了新型2-2PRUR并联机构,进行运动学分析的同时基于散点图对工作空间进行了优化。提出了通过拆分动平台为两部分并加装行星轮系以解决四自由度并联机构过约束及增大转动自由度转角的方法;运用坐标法写出机构约束方程并求解位置正反解;利用位置反解方程解的散点画出机构工作空间,同时以散点数最大为原则运用遗传算法对工作空间进行优化,获得了合理的结构参数。为此类并联机构的研究和应用奠定了基础。     

Options for mapping foF2

Available long-term and near-real time global and regional maps of foF2 are examined in relation to telecommunication and aeronomy requirements and recommendations are made for the best present-day maps to adopt. In particular, it is shown that current CCIR maps do not meet all requirements and should not necessarily be regarded as standards against which other mappings should be compared.     

8mm波段二维综合孔径微波辐射计(BHU-2D)

介绍了二维综合孔径微波辐射计BHU-2D成像原理、系统构成及性能指标、校正方法、部分成像实验及其成像结果.BHU-2D工作在8mm波段,共有10个接收单元,天线阵列为T形结构,接收机为二次变频超外差结构,I/Q解调及相关运算采用了数字方式并通过软件实现,采用点辐射源校正方法及背景对消反演算法校正系统通道间不一致、相关偏置及混叠误差.目前,BHU-2D已经研制完成,并进行了系统测试及成像实验,得到了室内人工场景及人物场景的辐射亮温分布图像.     

委内瑞拉遥感卫星-2成功发射

正2017年10月9日12时13分,委内瑞拉遥感卫星-2(VRSS-2,又名"苏克雷"卫星)由长征-2D(CZ-2D)运载火箭在中国酒泉卫星发射中心发射升空。该星是继委内瑞拉通信卫星-1(Venesat-1)、委内瑞拉遥感卫星-1(VRSS-1)之后,中国和委内瑞拉在航天领域合作的第3颗卫星,也是委内瑞拉拥有的第2颗遥感卫星,主要应用于委内瑞拉国土资源普查、环境保护、灾害监测和管理、农作物估产和城市规划等领域,对     

放飞希望的希望-2卫星群

<正>2015年9月20日,长征-6运载火箭以"一箭二十星"的方式成功将20颗微小卫星送入太空,其中的希望一2卫星(包括希望-2A、2B、2C、2D、2E和2F)由中国航天科技集团公司下属航天东方红卫星有限公司(以下简称"航天东方红公司")抓总研制。希望-2卫星的成功发射,对我国皮纳卫星技术发展具有重要意义。希望-2卫星由6颗卫星构成,其中,希望-2A质量为28.5 kg,希望-2 B、2 C、2 D质量均为9.7kg,希望-2E、2F(由希望-2B发射的子卫星)质量均为1.3kg,希望-2卫星拥有大气密度探测     

新型大转角2T2R并联机构的设计与分析

针对大尺寸细长结构部件的加工需求，提出了一种新型五自由度混联机器人，并对机器人中新型大转角2T2R并联机构模块进行了研究分析。首先，应用螺旋理论计算出了2-UPS&（2-RPR）R并联机构的自由度，并应用修正的G-K公式进行了验证；其次，应用封闭矢量方程对机构进行了运动学分析，建立了运动学正反解模型，并计算出了雅可比矩阵；然后，利用机构的约束条件，绘制了机构的工作空间；然后，应用线速度各向同性指标和角速度各向同性指标对机构的灵巧性进行了分析；最后，通过给定轨迹进行运动学仿真。通过分析，验证了该机构的可行性和实用价值，为新型五自由度混联机器人的应用奠定了基础。      

Plasma chemical reactions in C2H2/N2, C2H4/N2, and C2H6/N2 gas mixtures of a laboratory dielectric barrier discharge

Plasma chemical reactions in C₂H₂/N₂, C₂H₄/N₂, and C₂H₆/N₂ gas mixtures have been studied by means of mass spectrometry at a medium pressure of 300 mbar in a laboratory dielectric barrier discharge. A major reaction scheme is production of larger hydrocarbons like C_nH_m with n up to 12 including formation of functional CN groups.     

Jason-2 DORIS phase measurement processing

The DORIS instrument on Jason-2 is the first of a new generation. The satellite receivers have now seven simultaneous measurement channels, with synchronous dual frequency phase and pseudo-range measurements. These measurements are now described in a similar manner as GPS measurements and an extension of the RINEX 3.0 format has been defined for DORIS. Data are available to users with a shorter latency.     

H2O对空间站5A分子筛CO2去除性能影响

为进一步研究分子筛CO2去除系统应用于空间站的工作可靠性和鲁棒性,针对空间站4床分子筛(4-BMS)系统中可能出现的湿度失效保护问题展开了实验研究.测试了两种载人航天分子筛材料TC-5A与PSA-5A,研究了不同相对湿度对CO2吸附性能的影响;比较了相同湿度条件下,进口气体CO2浓度、粒径及吸附温度的变化对分子筛吸附CO2性能的影响,采用不同实验方法探究了H2O和CO2在两种分子筛材料中的竞争吸附关系.结果表明:PSA-5A吸附CO2性能优于TC-5A,但对H2O的吸附率略低于TC-5A.H2O的存在对分子筛吸附CO2影响非常大,空气中相对湿度达到60%时,分子筛基本失去了吸附CO2的能力.此外,温度升高会造成CO2的吸附量显著下降,但对H2O的吸附量影响相对较小,尤其是当相对湿度较高时.这对中国未来长期运行的空间站分子筛CO2去除系统工作有效性与工作鲁棒性的评价具有指导意义.