基于双目视觉的自动空中加油近距导航方法

为解决插头锥管式自动空中加油中的近距精确导航问题,提出了一种基于双目视觉的近距导航方法.该方法使用受油机上的两个摄像机拍摄加油锥管端面上光学标记的图像,采用轮廓跟踪法检测图像中的光斑区域,并将其灰度重心作为光学标记的像点,根据对极几何约束完成像点的匹配,利用空间圆形拟合法计算加油锥管的位置和姿态.建立了空中加油的三维虚拟场景对该导航方法进行仿真验证,仿真结果表明,该方法在近距离加油对接时具有很高的位置和姿态测量精度,可以满足自动空中加油的需要.     

一种小天体旋转参数估计方法

小天体旋转参数是科学数据，也是小天体测绘，着陆导航的基础数据.研究一种在小天体探测接近段过程中使用的基于图像上特征点跟踪和扩展卡尔曼滤波器的小天体旋转参数估计方法.该方法首先建立小天体旋转关系模型，表示小天体在相机坐标系中的姿态变化；然后定义小天体旋转的状态方程，推到了扩展卡尔曼滤波器的计算过程.通过对观测图像序列上的特征点跟踪，利用扩展卡尔曼滤波器方法得到小天体旋转轴指向和自转角速度估计.实验中，在仿真相机与小天体相机100 km距离上，分析了相机坐标系小天体坐标系之间的四元数初值，图像上特征点跟踪精度，相机的观测指向等因素对小天体旋转参数估计精度的影响.实验结果表明，提出的基于图像特征点跟踪和扩展卡尔曼滤波器的小天体旋转参数估计方法能够得到具有较高精度的估计结果.     

基于视觉原理的运动物体空间姿态测量技术研究

针对物体运动姿态的测量问题，以提高姿态求解方法的便捷性和准确性为目的，研究了一种基于双目视觉相机高速摄影测量物体姿态的测试技术。为实现该测量，使用高速相机获取同步影像，利用特征点间的几何约束关系，通过姿态优化算法确定被测物体空间姿态。试验结果表明：该方法正确、可靠，测量频率达到100帧/s，姿态角测量误差小于0.04°。     

基于粒子群算法的航天器姿态机动路径规划

研究航天器在星载设备受多种几何约束情况下,大角度姿态机动时的姿态路径规划问题.采用罗德里格斯参数描述姿态,将姿态机动路径规划问题转化为点机器人的三维路径规划问题.基于粒子群优化技术设计了航天器复杂约束下大角度姿态机动的路径规划算法.数值仿真结果表明,该方法对于复杂约束下航天器姿态机动的运动规划是有效的.     

聚焦光场成像三维粒子场重建方法

层析重建是层析粒子图像测速(Tomo-PIV)技术实现三维粒子位置和强度信息(三维粒子场)重构的核心步骤。相比于多相机的Tomo-PIV技术,单聚焦光场相机通过一次成像能够同时采集示踪粒子的散射光的方向和位置信息。因此,提出一种单聚焦光场相机的层析重建技术用于重构流场中的三维粒子场信息。为了验证本文方法的可行性及准确性,利用几何光学建立了示踪粒子的光场成像模型,利用光线追迹技术计算了粒子在聚焦光场相机中的成像,对比了被测流场中位于不同深度位置的粒子在聚焦光场相机中的成像差异;建立了基于单聚焦光场相机的层析重建数学模型,利用乘法代数重构技术(MART)对模拟所得的光场图像进行反演计算,实现了三维粒子场的重构,并利用归一化互相关系数来表征粒子的重建质量。结果表明,单个粒子在Z轴方向上的位置精度为±0.35 mm,初步证明了基于聚焦光场成像理论的三维粒子场重建方法的可行性。     

小行星三维地形模型几何重建方法

DOI： 10.3969/j.issn.1674 1579.2020.01.008小行星三维地形模型几何重建方法刘兴潭，武延鹏，吴奋陟，顾营迎，郑然，梁潇摘要： 小行星全球测绘对深空探测定点着陆具有重要意义.通过对绕飞段光学敏感器拍摄的序列图像进行几何立体重建方法的研究，可以实现探测器位姿信息未知情况下的三维地形建模.综合小行星表面特性、小行星运行特点与探测器飞行需求，首先通过全局的运动恢复结构完成小行星稀疏点云重建，再利用多视角场景重建对点云进行稠密化得到致密均匀的网格.然后采用隼鸟号探测器绕飞阶段实测影像，对小行星糸川(25143 Itokawa)的三维地形进行仿真重建，分辨率为0.36 m；并在光学实验室对3D打印的小行星比例模型进行模拟观测实验，得到重建分辨率为0.67 m.最后通过点云配准，进一步验证方法的有效性.结果表明，本方法稳定性较强，在分辨率要求在米级范围内的情况下，能够较好地针对小行星表面地形进行三维重建.     

结合轮廓及骨架序列编码的二维形状识别

二维形状识别是物体识别中的一个基本问题，被广泛地应用于商标检索、指纹识别、物体定位、图像检索等多个领域。其中，基于生物信息学的二维形状识别是近期一个新的研究方向，基本思想是把二维形状的轮廓转化为生物信息序列，借助标准的生物信息序列分析工具来进行二维形状的匹配和识别。不过，利用轮廓进行信息序列编码存在编码冗余和编码准确性不高的问题，本文提出了一种新型的结合形状轮廓和骨架的序列编码方法。该方法利用骨架表示形状的细长分支，减少编码的冗余；并分别对轮廓和骨架进行不同类型的编码，具备编码简洁、后续匹配准确性高等优点。最后，本文在三个公开数据集上进行大量的形状识别实验，并与多种通用形状识别方法进行了比较。实验表明，本文方法在多个实验中均取得了较高的识别准确率，相比基本的形状特征描述方法，准确率提高了近5%。      

基于视频的三维人体姿态估计

已有的三维人体姿态估计方法侧重于通过单帧图像来估计人体的三维姿态，忽略了视频中前后帧之间的相关性，因此，通过挖掘视频在时间维度上的信息可以进一步提高三维人体姿态估计的准确率。基于此，设计了一种可以充分提取视频时序信息的卷积神经网络结构，在获得高精度的同时也具有消耗计算资源小的优点，仅仅使用二维关节点的坐标为输入即可恢复完整的三维人体姿态。然后提出了一种新的损失函数利用相邻帧间人体姿态的连续性，来改进视频序列中三维姿态估计的平滑性，同时也解决了因缺少帧间信息而导致准确率下降的问题。通过在公开数据集Human3.6M上进行测试，实验结果表明本文方法相比目前的基准三维姿态估计算法的平均测试误差降低了1.2 mm，对于视频序列的三维人体姿态估计有着较高的准确率。      

HELIO: The Heliophysics Integrated Observatory

Heliophysics is a new research field that explores the Sun–Solar System Connection; it requires the joint exploitation of solar, heliospheric, magnetospheric and ionospheric observations.     

Scaling analysis and model estimation of solar corona index

A monthly average solar green coronal index time series for the period from January 1939 to December 2008 collected from NOAA (The National Oceanic and Atmospheric Administration) has been analysed in this paper in perspective of scaling analysis and modelling. Smoothed and de-noising have been done using suitable mother wavelet as a pre-requisite. The Finite Variance Scaling Method (FVSM), Higuchi method, rescaled range (R/S) and a generalized method have been applied to calculate the scaling exponents and fractal dimensions of the time series. Autocorrelation function (ACF) is used to find autoregressive (AR) process and Partial autocorrelation function (PACF) has been used to get the order of AR model. Finally a best fit model has been proposed using Yule-Walker Method with supporting results of goodness of fit and wavelet spectrum. The results reveal an anti-persistent, Short Range Dependent (SRD), self-similar property with signatures of non-causality, non-stationarity and nonlinearity in the data series. The model shows the best fit to the data under observation.     

Development of a gas chromatography compatible Sample Processing System (SPS) for the in-situ analysis of refractory organic matter in martian soil: preliminary results

In the frame of the 2009 Mars Science Laboratory (MSL) mission a new sample preparation system (SPS) compatible with gas chromatography–mass spectrometry (GC–MS) has been developed for the in situ analysis of complex organic molecules in the Martian soil. The goal is to detect, if they exist, some of the key compounds that play an important role in life on Earth including carboxylic acids, amino acids and nucleobases.     

绳驱动并联机器人张力约束工作空间分析

绳驱动三自由度机器人可以实现空间的自由转动.由于绳索只可拉伸不可压缩的单向特性,研究驱动绳索张力对机器人的控制具有重要意义.运用几何和矩阵的方法可以分析绳索的张力分配情况;在存在张力约束的条件下,提出张力系数作为评价张力分配优劣状况的指标,通过计算可以得到张力系数分布图,从而对机器人工作空间有直观的认识,进而提出有效的张力优化算法;通过对最小预紧力影响因素及选取方法的讨论,可以得到动态最小预紧力实时计算公式,保证绳索时刻处于张紧状态;通过样机的力检测系统张力反馈的实验可以验证理论推导.通过对以上几部分的分析和研究,可以对四绳驱动三自由度机器人的张力问题有综合全面的认识.     

火卫二地形地貌探测综述

火卫二（Deimos）是火星自然卫星之一，研究人员利用火星探测器对其地形地貌开展了大量研究。首先对火卫二的基本参数及起源假说进行了介绍，进而全面梳理了与火卫二相关的航天探测活动，重点对地形地貌探测活动进行了详细介绍，并对围绕火卫二地形地貌的研究成果进行了归纳分析，结果表明火卫二表面分布有撞击坑、风化层、明亮的反射物质及块状物，并存在物质移动。最后针对火卫二探测不全面的情况，给出了中国关于火卫二探测的建议。     

测试有效性对软件可靠性验证测试量的影响

针对传统软件可靠性验证测试方法均不考虑软件测试性可能会对验证测试用例数量产生影响的现状,提出一种引入测试有效性对软件可靠性验证测试最小量进行改进的方法.分析了软件测试性的定义及其对软件可靠性测试集合的影响,提出软件测试有效性的概念.比较了考虑测试有效性前后软件可靠性验证测试集合在数量上的差异,证明经典统计方法和无先验知识的Bayesian统计推断方法确定的均为假定测试有效性为零情况下的保守估计.提出结合测试有效性的验证测试量的量化表示模型和验证测试方案的改进方法,基于统计故障注入的原理,提出测试有效性的定量评估方法,最后通过示例给出定量评估过程和方法.     

H2 and H∞ control options for the combined attitude and thermal control system (CATCS)

The combined attitude and thermal control system (CATCS) combines the conventional attitude control and thermal control subsystems. Its principle is based on circulating a heat conducting fluid inside a closed duct wielding the excess onboard heat in order to produce the attitude control torques. Previously only the proportional-integral (PI) controller has been tested for CATCS. In this paper two other control options for CATCS were designed based on the H₂ and H_∞ control methods to improve the attitude control performance of a small satellite. The control gain matrix with the minimum cost function is obtained by solving the Riccati equation and fed back to the system in order to achieve the system’s performance. The designed controllers can efficiently control the roll, pitch and yaw satellite attitudes. Simulations for the two techniques were carried out using Matlab and Simulink for ideal and non-ideal system models. Results show that the H₂ controller has a better attitude control performance over the H_∞ controller and PI controller itself.     

From Titan’s tholins to Titan’s aerosols: Isotopic study and chemical evolution at Titan’s surface

In the present work, we focused on the possible isotopic fractionation of carbon during the processes involved in the formation of Titan’s tholins. We present the first results obtained on the ¹²C/¹³C isotopic ratios measured on Titan’s tholins synthesized in laboratory with cold plasma discharges. Measurements of isotopic ratio ¹²C/¹³C, done both on tholins and on the initial gas mixture (N₂:CH₄ (98:2)) used to produce them, do not show any evident deficit or enrichment in ¹³C relatively to ¹²C in the synthesized tholins, compared to the initial gas mixture. This observation allows to go further in the analyses of the ACP experiment data, including part of the Cassini–Huygens mission.     

Hemisphere-coupled modeling of nighttime medium-scale traveling ionospheric disturbances

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs), which have tilted frontal structures in the midlatitude ionosphere, are investigated by the midlatitude ionosphere electrodynamics coupling (MIECO) model in this study. It has been proposed that the electrodynamic coupling between the E and F regions plays an important role in generating MSTIDs within a few hours. An intriguing aspect of MSTIDs is that they were simultaneously observed at magnetic conjugate locations in the Northern and Southern Hemispheres. In order to study the hemisphere-coupled electrodynamics, the MIECO model has been upgraded to consist of two simulation domains for both hemispheres in which the electrostatic potential is solved by considering electrodynamics in both hemispheres. The simultaneous occurrence of MSTIDs at the magnetic conjugate stations has clearly been reproduced when the F-region neutral wind satisfies the unstable condition in both hemispheres and a sporadic-E layer is given only at the Northern (summer) Hemisphere. Even if the unstable condition is satisfied in the summer hemisphere, an unfavorable F-region neutral wind in the winter hemisphere largely suppresses the growth of MSTIDs in both hemispheres.     

Return to Europa: Overview of the Jupiter Europa orbiter mission

Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, the Galileo spacecraft supplied fascinating new insights into this satellite of Jupiter. Now, an international team is proposing a return to the Jupiter system and Europa with the Europa Jupiter System Mission (EJSM). Currently, NASA and ESA are designing two orbiters that would explore the Jovian system and then each would settle into orbit around one of Jupiter’s icy satellites, Europa and Ganymede. In addition, the Japanese Aerospace eXploration Agency (JAXA) is considering a Jupiter magnetospheric orbiter and the Russian Space Agency is investigating a Europa lander.