一种空间非合作目标的稀疏点云配准算法

点云数据配准是三维重构的关键技术之一,为了提高空间非合作目标的稀疏扫描点云数据配准的速度和精度,提出一种改进的基于四点算法的全局配准算法进行初始配准,再使用迭代最近点算法精确配准.针对直接扫描所得到点云数据量大的问题,本文提出一种基于KD Tree点云均匀采样简化算法,并且对传统基于四点算法中的阈值参数进行了统一,确定了各误差阈值参数和点云密度之间的关系.仿真结果表明,该方法能够快速、有效地实现卫星稀疏点云的配准,改进的四点算法配准耗时仅为几何哈希算法的42.49%.     

基于激光扫描技术的大型船舶舱容量计量技术研究

介绍了一种应用三维激光扫描技术,采集获取船舱三维点云数据,对点云数据进行配准、修补,完成船舱内部构件精细建模,快速高精度的重建大型船舱三维模型,实现大型船舱容量快速计算的方法。运用三维激光扫描技术完成158000吨大型油轮液货舱容量计量,通过与传统容量计量方法进行比对分析,解决了单点数据采集模式弊端,达到了大型船舶舱容量快速、精准计量效果。     

The feasibility of using an L1 positioned dust cloud as a method of space-based geoengineering

In this paper a method of geoengineering is proposed involving clouds of dust placed in the vicinity of the L₁ point as an alternative to the use of thin film reflectors. The aim of this scheme is to reduce the manufacturing requirement for space-based geoengineering. It has been concluded that the mass requirement for a cloud placed at the classical L₁ point, to create an average solar insolation reduction of 1.7%, is 7.60 × 10¹⁰ kg yr⁻¹ whilst a cloud placed at a displaced equilibrium point created by the inclusion of the effect of solar radiation pressure is 1.87 × 10¹⁰ kg yr⁻¹. These mass ejection rates are considerably less than the mass required in other unprocessed dust cloud methods proposed and are comparable to thin film reflector geoengineering requirements. Importantly, unprocessed dust sourced in-situ is seen as an attractive scheme compared to highly engineered thin film reflectors. It is envisaged that the required mass of dust can be extracted from captured near Earth asteroids, whilst stabilised in the required position using the impulse provided by solar collectors or mass drivers used to eject material from the asteroid surface.     

空间非合作目标的多视角点云配准算法研究

为了提高相邻视角间稀疏扫描点云数据配准的速度和精度,实现多视角点云精确配准,提出一种基于KD Tree点云均匀采样简化算法,并且对传统四点算法（4 PointsCongruentSetsAlgorithm,4PCS）中的阈值参数进行了统一,确定了各误差阈值参数和点云密度之间的关系,通过基于姿态校正的方法有效解决了对称视角点云引起的误配准问题。仿真结果表明,该方法能够快速、有效地实现卫星稀疏点云的配准。     

Microscopic approach to analyze solar-sail space-environment effects

Near-sun space-environment effects on metallic thin films solar sails as well as hollow-body sails with inflation fill gas are considered. Analysis of the interaction of the solar radiation with the solar-sail materials is presented. This analysis evaluates worst-case solar radiation effects during solar-radiation-pressure acceleration. The dependence of the thickness of solar sail on temperature and on wavelength of the electromagnetic spectrum of solar radiation is investigated. Physical processes of the interactions of photons, electrons, protons and α-particles with sail material atoms and nuclei, and inflation fill gas molecules are analyzed. Calculations utilized conservative assumptions with the highest values for the available cross sections for interactions of solar photons, electrons and protons with atoms, nuclei and hydrogen molecules. It is shown that for high-energy photons, electrons and protons the beryllium sail is mostly transparent. Sail material will be partially ionized by solar UV and low-energy solar electrons. For a hollow-body photon sail effects including hydrogen diffusion through the solar-sail walls, and electrostatic pressure is considered. Electrostatic pressure caused by the electrically charged sail’s electric field may require mitigation since sail material tensile strength decreases with elevated temperature. It also can substitute inflation-gas pressure loss due to gas diffusion and perforation by micrometeoroids impact to keep the sail inflated.     

Economic assessment of high-thrust and solar-sail propulsion for near-earth asteroid mining

Asteroid mining has the potential to greatly reduce the cost of in-space manufacturing, production of propellant for space transportation and consumables for crewed spacecraft, compared to launching the required resources from the Earth’s deep gravity well. This paper discusses the top-level mission architecture and trajectory design for these resource-return missions, comparing high-thrust trajectories with continuous low-thrust solar-sail trajectories. The paper focuses on maximizing the economic Net Present Value, which takes the time-cost of finance into account and therefore balances the returned resource mass and mission duration. The different propulsion methods are compared in terms of maximum economic return and sets of attainable target asteroids. Results for transporting resources to geostationary orbit show that the orbital parameter hyperspace of suitable target asteroids is considerably larger for solar sails, allowing for more flexibility in selecting potential target asteroids. Also, results show that the Net Present Value that can be realized is larger when employing solar sailing instead of chemical propulsion. In addition, it is demonstrated that a higher Net Present Value can be realized when transporting volatiles to the Lunar Gateway instead of geostationary orbit. The paper provides one more step towards making commercial asteroid mining an economically viable reality by integrating trajectory design, propulsion technology and economic modelling.     

车身逆向设计中点云多视拼合技术

针对整车车身点云空间尺寸较大,数据量庞大,还原精度要求高等特点,提出基于骨架点的点云拼合算法,算法的基本思想是构造整车模型的骨架点和分块点云的mark点,由全等三角形法则搜索骨架点与mark点的映射关系,应用加速迭代的改进ICP(Iterative Closest Point)算法拼合整车点云.某厂轻卡整车点云的拼合实例证明,该算法拼合精度高,运算速度快,是拼合整车点云行之有效的方法.      

The absorption of solar energy and the heating rate in the atmosphere of Venus

The Solar Flux Radiometer (LSFR) experiment on the large probe of the Pioneer Venus (PV) mission made detailed measurements of the vertical profile of the upward and downward broadband flux of sunlight at a solar zenith angle of 65.7°. These data have been combined with cloud particle size distribution measurements on the PV mission to produce a forward-scattering model of the Venus clouds. The distribution of clouds at high altitudes is constrained by measurements from the PV orbiter. Below the clouds the visible spectrum and flux levels are consistent with Venera measurements at other solar zenith angles. The variations in the optical parameters with height and with wavelength are summarized in several figures. The model is used to evaluate the solar heating rate at cloud levels as a function of altitude, solar longitude, and latitude for use in dynamical studies.     

Atmospheric dynamics on Venus and Mars

New results from Pioneer Orbiter observations indicate a continued vortex organization of the cloud level atmosphere in either hemisphere, centered over respective poles. Significant changes in the magnitude of the cloud level zonal circulation over a period of several years have been detected. A strong signature of the solar tidal circulation has been detected in the atmospheric circulation with the lowest speeds occurring in equatorial latitudes about 20° upstream of the sub-solar point. Finally, a solar-locked persistent spatial structure has been discovered in the variance of the ultraviolet brightness measured from brightness normalized images of Venus. Vega balloons (drifting at about 53 km altitude near 7°N and 7°S latitudes) have also provided some unique observations of atmospheric circulation, significant among them being the strong vertical motions, the zonality of their drift speeds as well as a significant temperature difference between the two balloons. The temperature difference which amounts to 6.5°K on average is currently being interpreted as a temperature variation with longitude or time.

Diagnostic modelling efforts towards simulating the atmospheric circulation on Venus are continuing and have provided some clues about the processes that maintain them but have not yet been successful in explaining the superrotation of the atmosphere.

Knowledge of the Martian atmospheric dynamics on the other hand is still limited by lack of adequate observations. Numerical modelling of the Martian atmosphere continues to provide most of the information about the atmospheric circulation. The situation regarding the paucity of observations should improve with the completion of the proposed Mars Observer mission. The low circular polar orbit planned provides an excellent opportunity to study the Martian atmosphere.     

一种基于层次聚类的空间非合作目标重构方法

由于激光传感器内在的缺陷,获得的非合作目标原始点云数据往往处于一个分布不均匀的状态,这就对后续的高质量非合作目标表面重构带来了很大的挑战.提出了一种基于全局约束的局部层次聚类方法来提升非合作目标点云分布的连续性.该方法主要可分为两步：1.基于全局约束的自适应八叉树三维空间分解,2.基于全局约束的层次聚类.第一步的主要目的是为了降低算法的复杂度,第二步则将分布不均匀的点集转化为均匀分布的状态.本文在三个非合作目标模型上进行了实验.实验的可视化结果与定量计算结果均验证了该方法的有效性.     

Modeling of the outer heliosphere with the realistic solar cycle

Time-dependent kinetic-continuum model of the solar wind interaction with the two-component local interstellar cloud (LIC) has been developed recently [Izmodenov, V., Malama, Y.G., Ruderman, M.S. Solar cycle influence on the interaction of the solar wind with local interstellar cloud. Astron. Astrophys. 429, 1069–1080, 2005a.]. Here, we adopted this model to the realistic solar cycle, when the solar wind parameters at the Earth’s orbit are taken from space data. This paper focuses on the results related to the termination shock (TS) excursion with the solar cycle that may help to understand Voyager 1 data obtained at and after the crossing of the termination shock and to predict the time of the TS crossing by Voyager 2.     

正态云模型雾化性质统计分析

对于超熵较大情况下的正态云模型,说明了云模型雾化过程.通过统计分析云滴离散的整体趋势,说明超熵增大过程中,云滴整体趋于离散.通过分析各论域区间内云滴离散趋势,说明靠近概念核心的云滴的离散速度相对缓慢.归纳云模型雾化性质:在超熵取值持续增大的过程中(HeEn/3),正态云表示的概念的论域范围持续增大,呈雾化状态,但靠近概念核心的论域区间内的云滴不失数量优势.雾化性质适用于建模偏离正态分布、缺乏共识的定量数据,期望表示概念语义值核心,熵描述概念语义的离散程度,超熵表示各种语义的共识程度,扩展了云模型知识表示的应用范围.     

基于姿态标准化的线特征点云提取方法

从零件三维点云中提取棱边等线特征所对应的点云是零件模型重构的关键,也是点云数据处理的基本操作.基于曲率的线特征点云提取方法易受点云初始姿态以及曲率估计方法的影响,曲面拟合及曲率估计误差较大.提出了一种基于点云姿态标准化的线特征点云提取方法:首先计算点云主方向并将其同z轴对准实现点云姿态的标准化,然后进行曲面拟合并以最大主曲率绝对值作为曲率估计值,最后对曲率值取阈值提取出线特征点云.用不同类型的点云数据进行了实验,结果表明所提方法有较高的提取效率和良好的适用性.     

基于起爆概率的无线电引信抗箔条干扰能力的量化表征方法

针对现有量化无线电引信抗箔条干扰方法的缺少,以防空导弹引信为例,结合箔条云运动轨迹模型和概率统计手段,提出基于起爆概率的无线电引信抗箔条干扰能力的量化表征方法。首先,在对单根箔条丝的螺旋下降运动进行分析的基础上,结合6-DOF非线性差分方程迭代计算得到箔条云的运动轨迹。其次,通过拟蒙特卡罗算法推导出箔条云的动态体密度函数,以箔条云的运动模型和动态体密度函数分别计算引信在箔条云近区干扰和远区干扰2种干扰作用下的不起爆概率。基于MATLAB构建箔条云轨迹模型,详细分析后得到箔条云动态的点分布模型,在此基础上利用拟蒙特卡罗方法得到箔条云的动态体密度函数,利用八叉树算法及最小二乘曲面法得到箔条云体积。最后,根据概率定义公式计算出箔条云干扰引信起爆概率。结果表明:所提方法客观、合理,为今后设计无线电引信抗箔条云干扰算法的启动条件提供了理论依据。      

基于卫星云图的大区域云层预测方法

云层覆盖是影响对地观测卫星成像的一个重要问题,如果遥感图像中云层比例太高,或者特定目标不可见,则遥感图像就会失效。对地观测卫星能够根据云层预测信息,在多个观测目标之间进行选择。面向对地观测卫星任务规划的应用,设计了大区域范围的短期云层预测方法,首先通过光流法获取云运动矢量,然后依据云运动矢量外推获得预测的云层图像,同时引入拉普拉斯算子刻画云层运动过程中的扩散现象,利用风云二号卫星的真实云图序列数据,通过神经网络的反向传播算法优化扩散因子,以提升云层预测的效果。通过对结果进行分析,引入的拉普拉斯算子方法能够提高云层预测的精度,80%分位数的云层覆盖率误差约为11.7%,该精度的云层预测可以用于指导对地观测卫星任务规划。     

卫星太阳电池阵的刚-柔耦合动力学

研究了卫星太阳电池阵在多点撞击过程中的刚-柔耦合动力学问题．基于Jourdain速度变分原理和单向递推组集方法，建立了柔性多体系统的动力学模型．用Hertz撞击法则建立了撞击力和撞击处的局部变形关系，分别用刚体模型和柔性体模型仿真计算了太阳电池阵的撞击力、撞击时间，揭示了变形运动和大范围运动的相互耦合作用．     

磁云边界层与间断的观测研究

利用WIND飞船的磁场和等离子体观测数据,分析了1995年2月至2003年8月之间82个磁云中的边界层事件.我们认为(1)磁云边界层中方向间断DD(Directional Discontinuity)类型中RD(Rotational Discontinuity),TD(Tangential Discontinuity),ED(Either Discontinuity),ND(NeitherDiscontinuity)的分布为37:18:44:1(%),与背景太阳风中的分布51:12:35:2(%)不同;主要区别在于RD与TD的比例变化. (2)磁云边界层的内外边界切向间断的比例很高,占总数的20%,而且两侧的密度和温度平均相对变化分别为|△N/N|=0.24和|△T/T|=0.19,大于边界层内部的平均值,显示了更多的切向间断特征;此外,磁云边界层中方向间断的出现频次约为太阳风中的1.87倍. (3)磁云边界层中方向间断的法向分布在θ-φ平面中不是随机分布,而是以θ=-24.90°,φ=217.49°为几何中心,主要是指向远离太阳的方向,而不是简单的各向同性分布.初步结果表明,间断是磁云边界层中的重要结构,它有着不同于背景太阳风间断类型比,为诊断磁云边界层的形成机理提供了依据.      

项目工程风险评估云判别模型设计

针对工程项目的特点和项目风险定量评估任务,提出了基于云判别模型的风险评估方法.云理论是一种用于处理不确定性和含糊性知识的数学工具,可实现概念与数据之间的相互转换.在云理论的基础上,建立了综合能力模型以及风险评估云模型,提出了基于云理论项目工程风险评估的方法,解决了风险评估中定性语言到定量的转化问题.该方法通过分析项目生命周期中的具体风险与风险因素之间的因果关系,建立项目工程风险评价模型,拓展了在国内经济转轨时期项目工程风险模型的研究思路,并结合应用实例评价该方法对建立工程内部风险评价体系的应用价值.      

基于三维点云重建的助推器位姿估计

助推器分离是运载火箭发射过程中的关键动作之一,常用的激光雷达姿态测量技术在助推器分离阶段受外界干扰严重,难以准确获得位姿。基于视觉的助推器位姿变化测量技术具有优秀的抗干扰能力,通过搭建三维点云重建网络,以图像为输入,三维点云为输出,在构建的助推器分离过程的图像 点云数据上进行了训练和测试,对测试重建的助推器点云使用主成分分析的方法完成了位姿的估算。测试结果表明,所建立的三维点云重建网络可以根据仿真图像数据,精确测量助推器分离阶段的位姿变化,在R2score指标下,对三维坐标的预测分数均在0.98以上,姿态角平均误差约为21°,预测分数则均在0.80以上。     

Orbit-attitude-vibration coupled dynamics of tethered solar power satellite

A new orbit-attitude-vibration coupled dynamic model of the tethered solar power satellite (Tethered SPS) is established based on absolute nodal coordinate formulation. The Hamilton’s equation of the system is derived by introducing generalized momentum through Legendre transformation. The correctness of the proposed model is verified by an example. The dynamic characteristics of the Tethered SPS are studied using the symplectic Runge-Kutta method. Simulation results show that the orbital radius and the total energy of the system are well preserved. The attitude of the system is unstable when the mass of the bus system is small. However, the attitude stability is dependent on some other parameters of the system, which requires further studies. It is also found that the average tether force/deformation can be roughly estimated by simplifying the solar panel as a particle. The proposed model can be used to study the orbit-attitude-vibration coupled dynamics and control problems.