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881.
马文坡 《运载火箭与返回技术》2007,28(4):23-27
介绍了卫星光学遥图像获取与图像处理一体化优化设计的思路;运用通用像质方程(GIQE)对于利用小相对孔径光学系统和调制传递函数补偿(MTFC)方法得到的图像的品质与利用相对较大相对孔径光学系统得到的图像的品质进行了对比分析。 相似文献
882.
Optimal guidance based on receding horizon control for low-thrust transfer to libration point orbits
Haijun Peng Qiang Gao Zhigang Wu Wanxie Zhong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper addresses the design and computation of a guidance law for a transfer mission from an orbit near the Earth to a halo orbit around the libration point L2 in the Sun–Earth system. The guidance law, which is designed based on receding horizon control and compensates for launch velocity errors that are introduced by inaccuracies of the launch vehicle, is solved using the generating function method. During the design of the closed-loop guidance law, the entire transfer mission, which is considered a nonlinear optimal control problem, is evaluated to obtain a nominal reference trajectory. Using the launch velocity errors and the uncertainty of the model, a spacecraft controlled by the proposed guidance law tracks the reference trajectory. Furthermore, the original Riccati differential equation in the receding horizon control algorithm is replaced by an equivalent convenient form of the Riccati differential equation that is based on the generating function. The high-efficiency solution of the equivalent equation avoids the online direct integration of the original Riccati differential equation, which significantly increases the computational efficiency for the receding horizon control problem. Numerical simulations using a nonlinear bicircular four-body model demonstrate the capabilities of the proposed receding horizon guidance law for the transfer mission. In addition, the generating function method improves the computational efficiency by at least one order of magnitude over the backward sweep method in solving the receding horizon control problem. 相似文献
883.
气动发动机多参数多目标寻优方法 总被引:1,自引:0,他引:1
气动发动机设计需要考虑多个参数间的耦合对性能优化的影响,且对理想功率、工作效率等多个性能指标难以建立客观的综合评价函数.为此以发动机进气压力和进排气机构部分控制参数为设计变量进行正交设计,利用灰色关联度分析法计算贴合期望指标组合的最优参数组合,并结合参数指标趋势图,依据计算结果对参数区间进行调整,通过有限次循环得到最优设计参数.经测试该算法快速有效,且设计参数与性能指标数量可扩展,对气动发动机的样机设计和实验具有重要的理论和工程意义. 相似文献
884.
Government organizations have to justify high expenditure during periods of financial crisis such as the one we are experiencing today. Space agencies have attempted to increase the returns on their investments in space missions by encouraging the commercial use of advanced technologies. This paper describes two technology transfer (TT) cases promoted by JAXA, in order to identify the organizational models and determinants of TT. The development of a TT process from space to Earth not only benefits the aerospace industry but also the network of national companies. The aim of the paper is to investigate who the actors are and the nature of their role, as well as the determinants of the TT process in the Japanese space sector. The case studies confirm the typical path of transfer as ‘Earth–space–Earth’. 相似文献
885.
886.
887.
U.M. Leloglu E. Kocaoglan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Although it is generally agreed that the outer space should be used for the benefit of all mankind, only a fraction of the countries have the necessary technological base for accessing space. Space technology, with its implications on science, economy and well-being of citizens, is mostly chosen as one of the priority areas for technological development by developing countries. However, there is already an over-capacity in global space industry and there are doubts on necessity of additional capacity establishment by developing countries. In this study, the importance and benefits of capacity-building in these countries are emphasized and the advantages and disadvantages that developing countries have in the framework of space technology acquisition are briefly presented. The feasibility of certain levels of space technology is discussed and the necessity of combining existing indigenous capabilities with technology obtained from foreign sources in the optimal way is stressed. We have also mentioned various general mechanisms of technology transfer and argued the importance of licensing in catching-up developed countries. After considering the necessary conditions of efficiency of technology, such as establishment of regional centers of space science and technology education by United Nations, joint development of space systems, complete technology transfer packages, cooperative space projects within regional organizations, coordinated constellations and special agreements with large space agencies, which are specific mechanisms already in use, are reviewed. Some typical examples of mechanisms are also given with special emphasize on small satellite technology that makes access to space affordable for many countries. Through sharing and analyzing the experience of developing countries in their odyssey of space capacity-building, the difficulties can be negotiated and the vicious circles can be broken. This study, in our view, is a step to incite a general discussion of obstacles and opportunities for developing countries, that could help them in using their limited resources effectively, hence, enable them to offer better conditions to their citizens and to contribute space science to a larger extend. 相似文献
888.
Oleg Polovnikov 《Aerospace Science and Technology》2000,4(8):567
At present, various radio navigation systems are employed during the automated approach of a transport vehicle to a space station. Experience has shown that emergency situations can occur in which it is necessary to revert to manual override of the automatic approach.Such situations have indeed occurred during flight operations of the space station Mir. The crews of the transport vehicles and the Mir used manual steering more than 30 times for successful docking, and four times for approach to the station.Successful manual steering demands absolute understanding of the relative orbit parameters. The decisive task of the crew is to determine these relative parameters. This is possible using visual observations from either the transport vehicle or the station using simple and reliable instruments. This article explains the algorithm for determining the relative orbits from visual crew observations, based on similarities of relative orbit families. 相似文献
889.
The convection of heat-generating fluid in a rotating horizontal cylinder is experimentally investigated. The threshold of convection excitation, the structure of convective flows and the heat transfer in the cylinder depending on the heat release capacity, liquid viscosity and aspect ratio of the cavity are studied. It is found that the average convection is excited by the thermovibrational mechanism —the gravity force, rotating in the cavity frame, produces the oscillations of non-isothermal fluid relative to the wall, which in turn result in excitation of mean convective flows. It is shown that the structure of convective flows depends on the dimensionless velocity of rotation. At relatively low rotation velocity the convection develops in the form of a periodic system of vortices regularly distributed along the cylinder axis. The threshold of excitation (critical value of vibration parameter) of three-dimensional vortex structures grows with rotation velocity. Above some definite rotation velocity the convection develops as two-dimensional rolls parallel to the axis of rotation. The threshold of two-dimensional structures excitation does not depend on the rotation velocity. Besides the structure of thermal convective flows the analysis of the relatively weak currents generated by the inertial waves below the threshold of convection is performed. 相似文献
890.
简要概述了光学采样成像系统组成及调制传递函数补偿(MTFC)概念;采用计算机仿真的方法模拟成像链路,MTFC是成像链路的一个重要环节,通过改变成像链路中的参数,研究链路中的混叠、光学遥感器噪声、量化、有损压缩对MTFC的影响。 相似文献