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101.
In 1994-1995 Lavochkin Association (Russia) together with the other enterprises in accordance with technical requirements of the Russian Space agency, developed a new Russian communication satellite of a small class that will operate in both the geostationary (GSO) and high-elliptical (HEO) orbits. This satellite may be injected into operational orbits using a SOYUZ-2 launch vehicle (LV) and a FREGAT upper stage (US) from Plesetsk and Baykonur space launch sites (SLS).The main reason for creating such a satellite was to decrease the cost of the support and development of the Russian communication geostationary satellites group.Russian satellites Horizont, Express, Ekran and Gals, which operate in GSO, are the basis of the space segment for communications, radio and TV broadcasting. All of these satellites are injected into GSO by the PROTON LV. PROTON is a launch vehicle of a heavy class. The use of a middle class LV instead of a heavy class will allow to reduce considerably the launch cost. The change of a heavy class LV to a LV of middle class determined one economic reason for this project. Besides, the opportunity to launch S/C into GSO from Russian Plesetsk SLS increases the independence of Russia in the domain of space communications, despite the presence of the contract with Kazachstan about the rent of Baykonur SLS. Finally, use of small satellites with a rather small number of transponders is more effective than the use of big satellites. It will allow also to increase a satellite group (by the launch of additional satellites) precisely in accordance to the development of the ground segment. 相似文献
102.
103.
This paper summarizes the final report of the Earth Observation and Data Policy and Europe (EOPOLE) fixed-term project, set up to review national research on the subject and to make recommendations for its improvement within an EU-wide context. It identifies the major issues to have emerged from the areas of user perspectives, pricing policy, the impact of new technologies on data policy, archiving policy and legal regulation and suggests ways of dealing with them. These include orienting data policies towards specific uses rather than users themselves; presenting a common European voice over the trade and exchange of geo-information via new communication means; and establishing a European-scale think-tank able to provide independent assessments of the economic, legal and international relations questions affecting Earth observation. 相似文献
104.
For Space Transportation System (i.e. Space Shuttle) launched satellites destined for a Geosynchronous Earth Orbit (GEO), there is a need for cost-effective, versatile propulsion systems to provide the perigee burn, i.e. to boost the satellite from Low Earth Orbit (LEO) to Geosynchronous Transfer Orbit (GTO). Surveys of commercial spacecraft activities and future GEO satellite requirements indicate that a spacecraft propulsion system that will provide the perigee burn for a broad range of future commercial satellites would have an excellent market potential.Parametric studies to investigate and define attractive perigee-burn upper propulsion systems (i.e. an Upper Propulsion Stage, or a UPS) are presented. The feasibility and payload capacilities that could be provided by a UPS assembled from essentially off-the-shelf components and subsystems, and the benefits that could be achieved by using major subsystems specifically tailored for the application are presented. The results indicate that attractive UPS configurations can be defined using either off-the-shelf or optimized major subsystems. 相似文献
105.
Attitude control techniques for the pointing and stabilization of very large, inherently flexible spacecraft systems are investigated. The attitude dynamics and control of a long, homogeneous flexible beam whose center of mass is assumed to follow a circular orbit is analyzed. In this study, first order effects of gravity-gradient are included, whereas external perturbations and related orbital station keeping maneuvers are neglected. A mathematical model which describes the system deflections within the orbital plane has been developed by treating the beam as having a maximum of three discretized mass particles connected by massless, elastic structural elements. The uncontrolled dynamics of this system are simulated and, in addition, the effects of the control devices are considered. The concept of distributed modal control, which provides a means for controlling a system mode independently of all other modes, is examined. The effect of varying the number of modes in the model as well as the number and location of the control devices are also considered. 相似文献
106.
智能天线结构模糊自适应变形控制实验研究 总被引:2,自引:1,他引:2
基于dSPACE半物理仿真系统和所研制的压电作动器,设计并构建了智能天线结构实验平台,进行了结构变形控制实验研究。实验中采用常规PID作为基本控制方法,并在此基础上设计了一种模糊自适应PID控制器,将两种方法对应的不同控制效果进行了对比。结果表明:在所给的实验条件下,基于压电材料可实现对智能天线结构变形的控制,作动器控制变形量最大可达166μm;两种控制方法均可对结构变形进行控制,模糊自适应方法的绝对位置控制精度达到±0.5μm;应用模糊自适应PID控制方法对结构进行变形控制,较之常规PID控制方法能够降低系统响应的超调量,缩短稳定时间,提高控制精度,得到更好的控制过程。 相似文献
107.
108.
概述了机载雷达技术发展的基本情况,总结出有源相控阵雷达相对于传统的机械雷达所具有的独特优势,指出有源相控阵雷达是未来机载雷达的一个发展方向。 相似文献
109.
通过分析返回舱在着陆时所具有的水平速度也可能对着陆安全构成威胁的事实,论述了为返回舱增加横向缓冲装置的必要性,由此提出亟需解决的问题——在返回舱着陆下降过程中测量其水平运动速度。提出了全新概念的以视觉图像为唯一信息来源的返回舱水平速度测量方法,仅以双目摄像机系统作为传感器,避免了对返回舱原有传感器系统的改造。通过对着陆区域地面图像的采集和在线处理,利用双目交会测量原理得到返回舱当前的大地坐标和姿态。仿真实验证明,方法简单易行,测量结果可靠。 相似文献
110.
L. M. Zelenyi M. S. Dolgonosov A. A. Bykov V. Yu. Popov Kh. V. Malova 《Cosmic Research》2002,40(4):357-366
Using both analytical and numerical models of the collisionless anisotropic current sheet generated by the impinging flows of transient ions, we have studied the self-consistent solutions taking the plasma trapped in the sheet into account. It is demonstrated that there exists a limited window in the space of system parameters where self-consistent solutions can exist. When the density of the quasi-trapped plasma is sufficiently large, a redistribution of the total current can be a cause of the sheet decay, when the local current of the trapped particles compensate (totally or in part) the main current in the center and at the edges of the sheet, while the total current generated by ions on the trapped trajectories vanishes. 相似文献