地月拉格朗日L2点中继星轨道分析与设计

地月L2点位于地月连线的延长线上,在地月L2点运行的卫星可以连续观测月球背面,解决月球背面与地球之间的通讯问题,在月球背面着陆探测任务中起着至关重要的作用。对从地球出发、利用月球引力辅助变轨、形成地月L2点的轨道进行了研究,分析了发射窗口、地月转移时间、近月点高度、近月点倾角、轨道振幅等多项因素对转移轨道和使命轨道特性的影响,寻求满足地月L2点中继任务需求的飞行轨道。通过分析研究,文章明确了转移和使命轨道的相关特性,可为中继星任务轨道的参数设计和优化提供有益参考。     

J2轨道模型对月地激光通信预瞄准精度影响研究

基于J_2轨道预测模型,设计了不同倾角和轨道高度圆轨道月球卫星,通过将J_2轨道预测模型预瞄准仿真结果与直接积分RKF7(8)法仿真结果相对比,研究了不同类型月球卫星轨道对-Y面卫星舱板激光通信终端瞄准精度的影响。仿真结果表明,J_2轨道预测模型可以满足月球极地卫星月地激光通信要求,当轨道高度为1 000 km和2 000 km的时候,10 min方位角偏差不超过40μrad,而俯仰角偏差仅为7μrad时,在一定程度上J2轨道预测模型可以满足月地激光通信预瞄准要求。     

一种小卫星绕飞编队的运动学设计新方法研究

在用运动学方法进行小卫星绕飞编队的相对运动分析和轨道设计时，一般假设环绕卫星和参考卫星的升交点赤经差、轨道倾角差和纬度幅角差均为小量，从而对相对运动方程进行近似和简化．但是当参考卫星的轨道倾角等于零或较小时，环绕卫星和参考卫星的升交点赤经差和纬度幅角差并不是小量，此时由于假设条件不成立而无法得到合理的轨道设计结果．针对这种情况，本文提出了一种小卫星绕飞编队的运动学设计新方法．首先对零轨道倾角卫星编队的卫星相对运动方程进行近似简化，得到了以轨道根数差为参数的相对运动方程和卫星编队设计方法，然后通过转移矩阵变换来进行任意轨道倾角的卫星绕飞编队设计，最后通过实例验证了方法的正确性．     

“嫦娥一号”卫星的调相轨道设计

中国第一颗月球探测卫星"嫦娥一号"的飞行轨道的设计中采用了调相轨道,在"长征三号甲"运载火箭提供的超地球同步转移轨道与地月转移轨道之间增加了一段由周期为24h和48h轨道构成的环绕地球飞行的调相轨道。为了将几条不同的轨道精确地拼接起来,必须考虑地球引力场对轨道的摄动影响。克服这个难点的做法是基于经典的轨道摄动理论,先将整段调相轨道设计为考虑地球引力场J2项影响的平轨道,在与运载的发射轨道拼接时,先将运载的包括短周期摄动的瞬时轨道转换为平轨道,在与地月转移轨道拼接时将调相轨道转换成拼接点的瞬时轨道。由于采用了平轨道的处理方法使得轨道控制策略的表述十分简明并易于操作。     

地月L2点周期轨道的月球背面覆盖分析

地月L2点附近轨道具备独特的动力学和运动学特性,是月球背面探测任务的中继卫星首选布设位置。面向未来月球背面探测任务的中继通信需求,分析并研究了地月L2点周期轨道(halo轨道)对月球背面的覆盖。在圆型限制性三体问题模型下,研究并给出了halo轨道族延拓计算方法,基于延拓法设计了地月系大范围南北halo轨道族;给出了中继卫星的月球背面覆盖计算模型,定义了相应的时间覆盖因子;数值仿真了地月系南北halo轨道族的月球背面覆盖情况。研究结果表明:地月L2点周期轨道幅值和类型决定其对月面的覆盖性,幅值较小的轨道的月面整体覆盖性较好,幅值较大的轨道对月球南北极覆盖较好,南北族轨道分别有利于月球南北半球的覆盖。文章研究可为我国"嫦娥4号"月球背面探测任务的中继星轨道设计提供有益参考和借鉴。     

全方向长期伴飞卫星集群轨道设计与仿真

主要研究在J2摄动的影响下,在中心卫星周围全方向上部署长期相对有界伴飞卫星的轨道设计方法。首先,利用J2不变的条件,由已知中心卫星轨道根数建立伴飞卫星的半长轴、偏心率及轨道倾角之间关系。然后,通过对伴飞卫星和中心卫星之间初始相对位置及轨道根数之间关系的分析,得到伴飞卫星的全部初始轨道根数,使其能够部署到中心卫星周围的任意方向上,从而能实现卫星集群在中心卫星的周围全方向长期有界伴飞。最后,通过轨道仿真验证了该方法的有效性。     

载人月球极地探测定点返回轨道设计

针对载人月球极地探测任务,对定点返回轨道优化设计问题进行了研究。根据月球极地轨道的特性,介绍了三种返回轨道机动方案。结合三脉冲变轨方案,采用了从初步计算到精确计算的串行求解策略,对定点返回轨道进行优化设计。初步计算阶段,建立了基于近月点伪参数的三段二体拼接模型,将三脉冲机动段与月球逃逸段解耦,求解轨道初值;精确计算阶段,提出了两段拼接方法,分别进行逆向和正向高精度数值积分。经过仿真测试,验证了该策略求解的有效性和准确性。最后,通过大量的仿真计算,分析了定点返回轨道的特性。研究结论对未来载人月球极地探测定点返回轨道方案的设计具有重要的参考价值。     

单自由度太阳帆板极月轨道月球卫星的初步热分析与热设计

对国外极月轨道月球卫星的热设计进行了概述,并以一个极月轨道月球卫星为例,介绍了采用单自由度太阳帆板技术的某极月轨道月球卫星.针对该卫星,对其奔月飞行和在极月轨道上环月运行时的外热流与空间散热问题进行分析,根据分析结果,初步提出了该卫星的热设计方案,重点对有效载荷热控问题, ±y侧仪器设备的热控问题,以及热控百叶窗的应用技术等进行了描述.     

两种J_2摄动模型下卫星编队相对位置误差分析

为了研究一个轨道周期内卫星和卫星编队的运动规律,在J2摄动理论基础之上,采用摄动加速度分析方法,给出了J2瞬时摄动模型。以近地太阳同步轨道卫星和双星编队为例,与只考虑J2一阶长期项的平均摄动模型比较,仿真分析结果表明,对卫星而言,一个轨道周期内,卫星半长轴相对平均半长轴漂移达到18km,偏心率相对平均偏心率漂移达到10-3量级,轨道倾角相对平均轨道倾角漂移达到0.01°,即由于J2瞬时摄动的影响,卫星运动发生了摄动;对双星编队而言,一个轨道周期内,两星相对位置的径向误差达到5km,沿迹向误差达到19km,法向误差相对较小,在10-2量级上,相对距离的误差达到了19km,随着时间的推移,误差会越来越大。     

嫦娥-1的奔月之路

中国已经发射过各种轨道的人造地球卫星,但是还没有发射过人造月球卫星.从地球到月球不但距离遥远,将近4×105km,而且月球自身还在围绕地球进行公转,平均运动速度为1.023km/s.因此,如何让嫦娥-1月球探测卫星与运动着的月球精确交会,并按绕月的工作轨道运行是非常困难的事情.在世界探月历史上,曾多次发生探测器距离月球很远飞过,与月球"失之交臂",也曾发生过探测器未能进入环月轨道而撞到月球表面上"粉身碎骨".由此可见,嫦娥-1飞行轨道的设计是整个工程中一项必须突破的关键技术.     

Stochastic particle acceleration by the forced interaction of relativistic current sheets

We address the problem of interacting relativistic current sheets in self-consistent kinetic plasma simulations within the framework of the Particle-In-Cell model. The interaction is enforced in head-on collisions of up to 10 current sheets at relativistic bulk speeds. The simulations are motivated by the general problem of Poynting flux dissipation in ‘striped wind’ configurations presumably governing the relativistic outflows pervasive in pulsar winds and gamma-ray bursts. We identify the generation of non-thermal particles and formation of a stable power-law shape in the particle energy distributions f(γ) dγ ∝ γ^−s dγ. In 1D, a spectral index s ∼ 2 is observed and attributed to a stochastic Fermi-type acceleration mechanism. In 2D, the generic index of s ∼ 3–4 is retained as in previous simulations of individual current sheets. Whereas in 2D the high energy cut-off is constrained by the limited dissipation of magnetic energy, in 1D the process converts the bulk motion of current sheets towards directed particle momentum of an exclusive class of non-thermal particles.     

基于LuGre模型的电液加载系统摩擦补偿

为了提高电液加载系统控制精度,针对摩擦问题提出了基于LuGre摩擦模型的前馈补偿方法.建立了用于摩擦仿真分析和补偿器设计的电液加载系统数学模型;通过实验获取并分析了相关的摩擦数据;基于实验数据进行LuGre模型参数辨识,把LuGre模型和辨识结果引入电液加载系统数学模型,并进行仿真结果与实际摩擦数据的对照,证明了LuGre摩擦模型的准确性.设计前馈补偿器,进行了实验对比,实验结果表明前馈补偿器可将摩擦产生的控制误差有效地降至未补偿时的30%左右.      

CoRoT and Kepler results: Solar-like oscillators

The space-borne observatories CoRoT (Convection Rotation and planetary Transits) and Kepler have provided photometric time series data of unprecedented precision for large numbers of stars. These data have revolutionized the fields of transiting exoplanets and asteroseismology. In this review some important asteroseismic results obtained using data from the CoRoT and Kepler space missions concerning stars that show solar-like oscillations are discussed. These results comprise, among others, measurements of the location of the base of the convection zone and helium second-ionization zone in main-sequence stars, the presence (or not) of core-helium burning in red-giant stars, as well as differential rotation in these stars.     

Radioactivity of the Moon and planets

In this report the main results of the study of radioactivity of the solar sistem bodies are considered. The radioactivity of the Moon and planets was measured by means of vehicles in situ. The radioactivity of the lunar samples, brought to the Earth was studied with laboratory equipment.     

清镇陨石（EH3）中陨硫钙石的REE微量元素及成因意义

本文运用INAA分析了14个清镇陨石中陨硫钙石单矿物颗粒的难熔元素(La、Ce、Sm、Eu、Yb、Lu、Ca、Sc、Hf和Th),挥发性元素(Na、Cr、Zn、Se、Br等)和亲铁元素(Fe、Ni、Co、Ir、Au、As)含量。结果表明陨硫钙石高度富集难熔亲石元素,是顽火辉石陨石中REE的主要载体,携带了约80％的全岩REE总量。相对于HREE,LREE有更大的富集程度,而且早期凝聚的颗粒较晚期凝聚的颗粒更富集REE,同时陨硫钙石富集挥发性元素Se、Br等。清镇陨硫钙石的微量元素特征揭示了它来自于太阳星云的高温凝聚特征和成因。     

柔性航天器IPACS建模与动力学分析

利用拟坐标下的拉格朗日方程和动量矩定理,建立了带变速控制力矩陀螺群(VSCMGs,Variable Speed Control Moment Gyroscopes)的柔性航天器的能量/姿态一体化控制系统(IPACS, Integrated Power/Attitude Control System)的动力学模型,该模型适合于姿态控制律设计及VSCMGs操纵律设计.采用动量管理和VSCMGs构型选取相结合的方法,有效地避免了VSCMGs设计时可能出现的奇异问题.分析了采用VSCMGs的柔性航天器IPACS中的动力学耦合问题,并以某大型航天器为例进行了数值仿真.分析和仿真结果显示出,当VSCMGs的力矩轴接近(或陷入)奇异或进行储/放能切换时,VSCMGs都会对柔性附件造成显著影响.      

Progress in tropospheric ammonia retrieval from the MIPAS satellite instrument

The Michelson Interferometer for Passive Atmospheric Sounding is a polar orbiting high resolution mid-infrared emission limb sounder with a nominal vertical resolution of 3 km. Work to extend the list of routinely retrieved species led to the examination of ammonia, NH₃. In this paper, we explore the feasibility of upper tropospheric retrievals around 6-km altitude, discussing appropriate methods. We demonstrate a weak north to south gradient outside the error bars, using co-addition to improve signal-to-noise and compare these first results with a model.     

Monitoring spatio-temporal variations in aerosols and aerosol–cloud interactions over Pakistan using MODIS data

Clouds are important elements in climatic processes and interactions between aerosols and clouds are therefore a hot topic for scientific research. Aerosols show both spatial and temporal variations, which can lead to variations in the microphysics of clouds. In this research, we have examined the spatial and temporal variations in aerosol particles over Pakistan and the impact of these variations on various optical properties of clouds, using Moderate Resolution Imaging Spectroradiometer (MODIS) data from the Terra satellite. We used the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model for trajectory analysis to reveal the origins of air masses, with the aim of understanding these spatial and temporal variabilities in aerosol concentrations. We also documented seasonal variations in patterns of aerosol optical depth (AOD) over Pakistan, for which the highest values occur during the monsoon season (June–August). We then analyzed the relationships between AOD and four other cloud parameters, namely water vapour (WV), cloud fraction (CF), cloud top temperature (CTT) and cloud top pressure (CTP). Regional correlation maps and time series plots for aerosol (AOD) and cloud parameters were produced to provide a better understanding of aerosol–cloud interaction. The analyses showed strong positive correlations between AOD and WV for all of the eight cities investigated. The correlation between AOD and CF was positive for those cities where the air masses were predominantly humid, but negative for those cities where the air masses were relatively dry and carried a low aerosol abundance. These correlations were clearly dependent on the meteorological conditions for all of the eight cities investigated. Because of the observed AOD–CF relationship, the co-variation of AOD with CTP and CTT may be attributable to large-scale meteorological variations: AOD showed a positive correlation with CTP and CTT in northern regions of Pakistan and a negative correlation in southern regions.     

Technology development for a long duration,mid-cloud level Venus balloon

This paper describes the results of ongoing technology development activities for a Venus spherical superpressure balloon capable of flying for long durations (30 days) in the middle cloud layer at an altitude of 55.5 km. Data is presented from a successful aerial deployment and inflation flight experiment on a 5.5 m diameter prototype balloon conducted at a 2.5 km altitude above the Earth. Although the balloon in that test was not released for free flight, all other steps in the deployment and inflation process were successfully executed. Experimental and computational results are also presented from an investigation of the stress concentration phenomenon at the junction of the metal end fitting and fabric end cap of the prototype Venus balloon. Good agreement was found between the simulation and experimental results and a stress concentration factor of 1.55 determined for this end cap design compared to the expectations of thin membrane theory. Finally, results are presented for a new, second-generation Venus balloon material utilizing Aclar™ film instead of Teflon. Optical property and sulfuric acid tolerance data are presented for this material based on laboratory testing of samples.     

An all-sky survey at 230 GHz by MLS on Aura

The Microwave Limb Sounder (MLS) instrument is a small satellite-borne radio telescope. Its purpose is to make limb-scanning measurements of atmospheric composition. One of the gases to which it is sensitive is carbon monoxide (CO), detected via the J = 2 → 1 rotational transition at 230 GHz. CO is present in molecular gas clouds in the Milky Way. Although it was not designed for the purpose, MLS can detect emissions from galactic CO, allowing a map of the 230 GHz radio sky to be constructed. We report the MLS measurements of galactic radio emission and discuss their effect on the atmospheric mission of MLS. The region of the Milky Way with emissions strong enough to significantly affect MLS observations of atmospheric CO is identified. Ground-based radio astronomers have been mapping the sky using CO emission for many years. However, the MLS data are the first such survey to be carried out from space. The MLS survey covers a larger area of the sky than any other 230 GHz survey, but no previously unknown gas clouds are observed.