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61.
在英译汉训练中,加强英文单词的辨析和理解,提高英语的分析能力是表达原著内容的基础;只有了解英语文化背景,掌握常用的翻译技巧,才能提高汉语水平使译文达意通顺。 相似文献
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《中国航空学报》2016,(6):1730-1739
This paper derives a distance-based formation control method to maintain the desired formation shape for spacecraft in a gravitational potential field. The method is an analogy of a vir-tual spring-damper mesh. Spacecraft are connected virtually by spring-damper pairs. Convergence analysis is performed using the energy method. Approximate expressions for the distance errors and control accelerations at steady state are derived by using algebraic graph representations and results of graph rigidity. Analytical results indicate that if the underlying graph of the mesh is rigid, the convergence to a static shape is assured, and higher formation control precision can be achieved by increasing the elastic coefficient without increasing the control accelerations. A numerical exam-ple of spacecraft formation in low Earth orbit confirms the theoretical analysis and shows that the desired formation shape can be well achieved using the presented method, whereas the orientation of the formation can be kept pointing to the center of the Earth by the gravity gradient. The method is decentralized, and uses only relative measurement information. Constructing a distributed virtual structure in space can be the general application area. The proposed method can serve as an active shape control law for the spacecraft formations using propellantless internal forces. 相似文献
64.
Madjid Tavana Faramak Zandi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Sending man to Mars has been a long-held dream of humankind. NASA plans human planetary explorations using approaches that are technically feasible, have reasonable risks and have relatively low costs. This study presents a novel Multi-Attribute Decision Making (MADM) model for evaluating a range of potential mission scenarios for the human exploration of Mars. The three alternatives identified by the Mission Operations Directorate (MOD) at the Johnson Space Center (JSC) include split mission, combo lander and dual scenarios. The proposed framework subsumes the following key methods: first, the conjunction method is used to minimize the number of alternative mission scenarios; second, the Fuzzy Risk Failure Mode and Effects Analysis (RFMEA) is used to analyze the potential failure of the alternative scenarios; third, the fuzzy group Real Option Analysis (ROA) is used to estimate the expected costs and benefits of the alternative scenarios; and fourth, the fuzzy group permutation approach is used to select the optimal mission scenario. We present the results of a case study at NASA’s Johnson Space center to demonstrate: (1) the complexity of mission scenario selection involving subjective and objective judgments provided by multiple space exploration experts; and (2) a systematic and structured method for aggregating quantitative and qualitative data concerning a large number of competing and conflicting mission events. 相似文献
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D. Koc-San B.T. San V. Bakis M. Helvaci Z. Eker 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Astronomical observatory site selection is a complex problem that involves evaluation of multiple factors from different sources. The aim of this study is to select the best possible candidates for astronomical observations sites using Multi-Criteria Decision Analysis integrated with Geographical Information Systems and remote sensing technologies. The study was implemented in the Antalya province of Turkey, which is convenient for astronomical site observatory facilities with its appropriate climate properties and weather conditions. Eleven factors (cloud cover, precipitable water, earthquake zones, geology, landslide inventory, active fault lines, Digital Elevation Model, city lights, mining activities, settlement areas, roads) were determined, splitting into three categories; meteorological, geographical and anthropogenic criteria. These factors were evaluated using Analytical Hierarchy Process method and the weights of criteria layers were determined. As a result, the most suitable areas were located extensively in western and eastern part of Antalya. This study offers a robust, accurate, cost and time effective procedure for preliminary site selection for astronomical observatory. However, for a final decision of the best location of astronomical observatory, site testing measurements and atmospheric seeing observations will be further required in these preliminary areas. 相似文献
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建立了基于双星定位系统距离和观测数据的近地卫星联合定轨模型,设计了相应的数值融合联合定轨算法;为进一步提高近地卫星定轨精度,考虑融合双星及备份星距离和观测数据,建立了基于双星和备份星的近地卫星联合定轨模型及实现算法,并针对不同仿真条件进行了联合定轨仿真实验。仿真计算结果表明,联合定轨方式较传统近地卫星精密定轨方式可以更好地抑制双星星历误差对近地卫星定轨精度的影响,近地卫星和双星的定轨精度均得到了一定程度的提高;同时,融合备份星观测数据的近地卫星联合定轨精度得到进一步改善,达到5.17m。 相似文献
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以制定数控技术专业双证书认证试点方案为目的,结合市场需求,采用职业岗位能力分析的方法,将职业资格证书认证体系嵌入学历教育,构建了核心课程体系,设计了培养该专业学生核心职业能力的学习包,并设计了相对应的职业资格证书体系,从而制定了该专业双证书认证试点方案,通过实施,取得了好的效果。 相似文献
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船体变形对航天测量船外弹道测量的影响 总被引:9,自引:2,他引:7
简要介绍了航天测量船船体变形测量系统的基本构成、测量原理和测量元素,分析了变形测量数据的基本特性,给出了船载外测数据船体变形修正的方法和计算公式;重点考察研究了船体变形数据对航天测量船外测数据和外测定轨的影响。 相似文献
70.
航天测量船外测数据的复杂误差特性 总被引:3,自引:2,他引:1
使用三次样条最小二乘拟合残差法研究了航天测量船外测数据误差的统计特性,分析了其误差的相关特性,建立了时序模型。研究结果表明,航天测量船外测数据误差具有强自相关性、非正态性、时变方差性和分段平稳性,其特性可以用高阶AR模型描述。 相似文献