The Success of the 2014 Nuclear Security Summit and its Contribution to the Nonproliferation Regime

The 2014 Nuclear Security Summit (NSS) in The Hague was a resounding success, both in organizational terms and in terms of substance. The new substance can be found in the Communiqué, as well as in innovative joint statements by participants, all of which may be considered as implementation of actions decided upon in the Final Document of the 2010 Review Conference of the Treaty on the Non-Proliferation of Nuclear Weapons. The next two years in the NSS process cannot be business as usual. This viewpoint makes some suggestions for NSS states to undertake between now and the final summit in 2016, including preparations for winding down the NSS process as we know it.     

基于改进遗传算法的天基光学监视平台轨道优化

针对地球遮挡、地影、太阳光干扰、月光干扰、空间目标相对观测平台的角速度等约束对空间目标可见性的影响问题,基于已编目空间目标双行轨道根数,研究以太阳同步晨昏圆轨道作为观测平台轨道,采用改进多变异位自适应遗传算法对单星观测平台轨道进行优化设计。仿真结果表明,改进的多变异位自适应遗传算法有效地解决了多变异位自适应遗传算法不能保证收敛到所有种群中最优个体的问题,且随机抽取10%左右的目标样本可以达到与采用所有目标相当的性能,计算效率提高约一个量级。     

椭圆轨道上空间飞行器的编队飞行轨道设计

针对椭圆轨道上空间飞行器的编队飞行,基于开普勒轨道方程推导了一组新的相对运动方程,该方程组采用轨道要素表示,可直接用于编队的轨道设计。分析了一些典型的相对运动轨迹及编队轨道的精度,在此基础上,设计了线性编队和垂直圆编队。仿真结果验证了这种方法是有效的。     

测控站布局对区域卫星导航系统的影响

建立区域卫星导航系统的测控网是卫星导航系统要解决的关键问题之一。讨论国内测控站的布设问题,采用网格计算方法分析国内测控站对导航星座的可观测性。引入位置精度衰减因子PDOP和定轨中的法矩阵条件数,分析测控网对导航星座的观测几何结构强度以及测站位置分布对轨道确定精度的影响,仿真结果表明,利用我国有限的国土跨度和航天测控资源可以确保对导航卫星的测控任务的完成。对在国外布设测控站进行讨论和仿真,结果说明位于国外的测控站(如可在澳大利亚的珀斯设站)的加入能明显改善观测的几何结构强度、提高导航卫星的轨道精度。     

大椭圆轨道航天器四面体编队运动分析与设计

若干正处于计划或实施中的空间物理测量任务较多采用运行于大椭圆轨道上的四面体航天器编队协同完成任务轨道段内地球磁层结构和动力学现象的分布式测量与分析。采用基于轨道根数的相对运动模型,分析了参考轨道根数对四面体性能指标——质量因子和平均边长的影响;假设某一航天器运行于参考轨道,提出了以其他三个航天器的15个相对轨道根数为设计变量,目标函数兼顾质量因子和平均边长的四面体优化设计方案,并将其应用于第一阶段MMS任务的四面体构形设计中。仿真结果表明,在不考虑摄动和控制的前提下,通过优化可以得到任务轨道段内四面体性能保持较优的轨道设计方案。     

基于Hill方程的编队卫星群运动分析与轨道设计

从Hill方程出发 ,研究了绕飞轨道的性质及编队卫星群的轨道设计方法。从三方面对绕飞轨道进行了描述 :坐标平面投影 ,与坐标平面的夹角 ,绕飞轨道根数。编队卫星群的轨道设计分两步进行 :先求基本环绕卫星的轨道根数 ;再求其它环绕卫星的轨道根数。仿真结果表明 ,此方法适用于编队飞行的初步设计     

Satellite constellation design for forest fire monitoring via a stochastic programing approach

There is significant value in the data collected by satellites during and after a natural disaster. The current operating paradigm in practice is for satellites to passively collect data when they happen to fly over a disaster location. Conversely, this article considers the alternative approach of actively maneuvering satellites to fly directly overhead of the disaster site on a routine basis. Toward this end, we seek to compute a satellite constellation design that minimizes the expected maneuver costs for monitoring an unknown forest fire. In this article, we present a 2‐stage stochastic programing model for this problem as well as a accelerated L‐shaped decomposition approach. A comparison between our approach and the current operating paradigm indicates that our solution provides longer duration data collections and a greater number of data collections. Analysis also shows that our proposed solution is robust over a wide array of scenarios.     

地月转移轨道的天基测向初轨确定研究

研究了利用天基测向数据对地月转移轨道的初轨确定。天基平台分别考虑采用单颗卫星和星座卫星,研究了观测数据的噪声平滑,分析了观测弧段长度和观测几何对两种平台的定轨精度的影响,基于数值分析结果,研究了初定轨中系统差的消除。研究结果表明,星座双星同步定轨比较适用于地月转移轨道的天基测向初定轨。     

双二体几何切面法及天梯地月转移轨道分析

双二体模型是求解地月转移轨道的重要基础。与传统的采用月球影响球入口点经纬度的描述方式不同,本文提出一种基于飞行轨道面参数来描述地月转移轨道的双二体模型几何表达方式,结合一维非线性方程求根算法Brent算法和Lambert原理,将原始三维球面搜索算法降维成为二维圆上的搜索算法,可以高效求解地月转移轨道的形状参数。为避免重复计算,将转移轨道窗口计算的轨道多变量搜索问题解耦分解成两个子问题——转移轨道形状参数求解问题和转移轨道面空间定向问题,降低了问题的求解维度。形成两级并行计算算法,充分发挥多核计算机算力,加速计算过程。仿真结果表明,基于提出的并行圆锥曲线几何切面法,可以成功应用于计算天梯地月转移轨道分析。     

NUCLEAR TERRORISM AND THE GLOBAL POLITICS OF CIVILIAN HEU ELIMINATION

An increasing number of countries recognize the special risks of nuclear terrorism associated with the civilian use and storage of and commerce in highly enriched uranium (HEU). They are especially concerned that non-state actors might gain access to HEU and use it to build and detonate improvised nuclear devices. The risk is aggravated by the very large global stocks of HEU, some of which are inadequately protected. Although HEU has few commercial uses, and most experts believe it is technically feasible to substitute low-enriched uranium for HEU in nearly all civilian applications, efforts to reduce HEU stocks have been impeded by a variety of economic, political, and strategic considerations. This article analyzes the nature of these impediments and discusses what is required to overcome them.