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研究了扰动后的电离层对不同波段的电磁波传播的影响,并探讨了该项技术在通信对抗上的具体应用。结果表明:受扰电离层可以引导VLF波进行"哨声模式"传播,进而实现对潜通信;可以使得HF波传播轨迹发生偏转、逃逸、聚焦和散焦,进而实现短波干扰;可以降低卫星通信频率,进而利用新波段实现卫星保密通信,同时还能产生透镜效应,对实现卫星通信的VHF电波产生额外增益,增强通信效果。 相似文献
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针对巡航飞行器非线性模型具有快时变、强耦合和高度非线性的特点,在考虑飞行过程中可能存在的气动参数以及大气密度不确定性情况下,提出了一种高精确、强鲁棒控制方法。通过将扰动观测器与指数时变滑模控制方法结合,构造了一种基于扰动观测器的巡航飞行器指数时变滑模控制设计方法,并利用Lyapunov理论分析了采用该控制律后整个闭环系统的稳定性。该方法能够有效地减小采用边界层方法来处理滑模抖振问题时所引入跟踪稳态误差,提高系统控制精度。最后,通过仿真验证了所提出方法的有效性。 相似文献
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为了解决弹道导弹扰动引力计算精度与速度的矛盾,利用模糊控制的特点,通过对模糊控制器的改进,成功将模糊控制运用于扰动引力的计算。从计算思路、基本点扰动引力的计算、分级模糊控制规则的具体改进等方面进行了详细分析,仿真结果表明:运用所提出的模糊控制方法计算得到的扰动引力与真值误差很小,而计算速度远快于分层点质量法等常规方法。 相似文献
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利用有限元方法逼近飞行器轨道主动段扰动引力 总被引:9,自引:2,他引:9
为了克服引力位系数模型计算飞行器轨道主动段扰动引力所存在的计算量大,并且难以进行实时计算的缺点,提出利用有限元内插的方法对主动段扰动引力进行逼近。根据有限元分析中区域剖分插值的原理,采用了对飞行器轨道周围有限范围的空间区域进行有限元剖分的方式,计算出各剖分单元每个顶点处的扰动引力,然后利用剖分单元各顶点的扰动引力分量内插出飞行器轨道点对应的扰动引力分量值。计算过程和结果表明,这种方法能够快速、精确可靠地逼近飞行器轨道主动段扰动引力,满足了有关文献中所提出的要求。 相似文献
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文章针对动静隔离式双超敏捷卫星载荷舱存在活动部件时,载荷舱指向精度下降的问题,依据双超敏捷卫星的特点,对双超敏捷卫星载荷舱进行了扰动补偿研究。首先,建立了载荷舱活动部件扰动模型以及双超敏捷卫星模型,扰动包括反作用飞轮小幅值高频随机扰动和摆镜扫描大幅值规律性扰动;然后,在采用飞轮扰动被动隔振和摆镜扫描主动补偿的基础上,利用双超敏捷卫星磁浮机构带宽高的特点进行二次主动隔振。仿真结果表明:在进行飞轮扰动被动隔振以及摆镜扫描扰动主动补偿后,载荷舱的指向精度提高到6×10-3(deg);磁浮机构进行二次主动隔振后,载荷舱的指向精度提高到2×10-4(deg)。该方法为双超敏捷卫星载荷舱受扰时指向精度下降问题提供解决思路。利用磁浮机构不仅可以隔离平台舱的扰动,而且可以提供高带宽主动控制力来抑制载荷舱的扰动。但在具体实施过程中还需考虑载荷舱与平台舱之间的碰撞问题。 相似文献
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为实现参数不确定和扰动下运载火箭大偏航入轨过程高精度姿态稳定控制,提出了一种双回路扰动观测补偿有限时间收敛滑模控制方法。首先基于运载火箭飞行动力学方程构建了面向控制的姿态模型;然后分析模型中存在的复合扰动,构建双回路扰动观测补偿滑模控制框架;通过引入有限时间收敛微分器、观测器和滑模控制器,实现了运载火箭姿态控制回路对姿态指令的高精度快速响应。该方法能够有效观测并补偿同时存在的匹配和非匹配扰动项,提高运载火箭姿态控制系统对参数不确定的适应性。通过对比传统PID控制方法,充分验证了双回路扰动观测补偿有限时间收敛滑模控制方法的良好性能。 相似文献
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In the framework of the approximation of geometric optics, the peculiarities of VLF-wave propagation in the Earth’s ionosphere and magnetosphere during the creation of large-scale artificial plasma irregularities by heating facilities such as HAARP and “Sura” in the ionosphere are studied. For calculation of ray trajectories, the profile of the concentration and ion composition of plasma is taken by calculating the SAMI2 ionospheric model, which was modified to take the influence on the ionosphere of the HF emissions of heating facilities into account. As a result of the influence of the heating facilities on the ionosphere, a region could occur with an increased plasma concentration that is stretched out along the geomagnetic field (up to heights on the order of the Earth’s radius) with small dimensions across the field (~1°). The ray trajectories of waves that propagate from heights of about 100 km from different initial points in the region where such a disturbance has been created with different initial inclination angles of the wave normal are studied in this paper. Both lightning discharges and modulated HF heating of the ionosphere could be the sources of such waves. It is shown on the basis of the performed analysis that the presence of such disturbances in density can lead to a substantial changes in wave-propagation trajectories, in particular, to efficient channeling of VLF waves in the disturbance region and an increase in the interval of the initial propagation angles of waves, which can reach the ionosphere in the opposite hemisphere. 相似文献
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The spatial dimensions and temporal dynamics of large scale disturbances of electron density in the ionospheric F-region during the preparatory phase of destructive earthquakes are estimated. The most appropriate data (as far as the moments of satellite passages are concerned) were selected out of more than 300 investigated cases. In order to demonstrate effects at different latitudes, the cases of high-latitude (Alaska), mid-latitude (Central Italy), and low-latitude (New Zealand) earthquakes were considered. Using the data of external vertical sounding of the ionosphere performed by the Alouette-1 and Interkosmos-19 satellites together with the data of vertical sounding of the ionosphere by ground-based instruments, we get for the first time with reasonable accuracy the spatial characteristics of precursors in the ionosphere. It is shown that seismic ionospheric disturbances are strongly time-dependent before the beginning of the main shock. Seismic ionospheric disturbances are generated weakly several days before the first shock, but at that moment the disturbed region is located not above the epicenter, but rather a little displaced from it. As the moment of the earthquake approaches, the disturbance covers more and more space; moreover, its value also increases. Several hours after the shock the disturbance migrates in the reverse order. Under some conditions, the disturbances may appear not only above epicenter regions. They can be transferred along the magnetic field lines into conjugate regions in the opposite hemisphere. 相似文献
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L. F. Chernogor 《Cosmic Research》2011,49(4):292-307
Results of radiophysical and magnetometric observations of dynamical processes in the ionosphere and geomagnetic field that
followed launches of four rockets of different power and made from different launching sites are analyzed. It is found that
the rocket launches were accompanied by an intensification of wave activity in the ionosphere and geomagnetic field. The medium
reactions from various sources (various rockets) were overlapping, which made their identification more difficult. Both ionospheric
and geomagnetic disturbances have, most probably, two groups of propagation velocities: about 1.2–1.7 km s−1 and 440–760 m s−1. Slow MHD waves and internal gravity waves corresponded to these velocities. 相似文献
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Ya. A. Ilyushin 《Cosmic Research》2010,48(2):157-164
The problem of deep sounding of planet interior using ultra wide band radar with synthesized aperture is considered for the
case when anisotropic fluctuations of the ionosphere plasma density take place. Modeling is performed for a number of values
of the medium and radar characteristic parameters. The degree of influence of mutual orientation of the anisotropy direction
of ionospheric fluctuations and of the spacecraft flight trajectory is estimated. It is demonstrated that widening of radar
pulses is determined by characteristic spatial scale of ionosphere plasma disturbances in the transverse direction relative
to the spacecraft flight trajectory. On the other hand, attenuation of the peak power of the pulses is shown to be determined
basically by the longitudinal scale of disturbance correlations. 相似文献
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We present the results of spectral analysis of a signal of oblique sounding of the ionosphere. This signal was received at the Doppler phase-angle measuring facility of Kazan University during the geomagnetic storm on October 29–31, 2003. On various short-wave (SW) radio paths, intense variations of Doppler frequency shift were observed. These variations exceeded variations observed on days without geomagnetic disturbances by an order of magnitude (and by two orders of magnitude during some short periods). Relatively short periods (1–3.5 min) are predominant on these days in variations of the Doppler frequency shift. It should be noted that, while for weak geomagnetic disturbances the response in the form of distortions of SW signal parameters was observed, as a rule, only for the paths coming from high-latitude regions, in the given case the effect was observed for all radio paths.Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 6, 2004, pp. 640–644.Original Russian Text Copyright © 2004 by Bochkarev, Petrova, Teplov. 相似文献
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Bezrukikh V. V. Kotova G. A. Lezhen L. A. Lemaire J. Pierrard V. Venediktov Yu. I. 《Cosmic Research》2003,41(4):392-402
We present the results of temperature and density measurement of plasmaspheric protons under quiet and disturbed conditions in the night and dayside sectors of the plasmasphere obtained with the Auroral Probe/Alpha-3 instrument during September 1996 and January 1997. According to the experimental data, the proton temperature in the night sector of the plasmasphere depends on the level of geomagnetic disturbance: it is found that at night hours the values of temperatures inside the plasmasphere at 2.4 < L < 3.5 decreased considerably after the commencement of a geomagnetic storm. The temperature decrease, as a rule, was accompanied by the formation of a flat plateau on the density distribution n(L) at 2.4 < L < 3.5. The above experimental facts (decreasing proton temperature and formation of a flat part on the n(L) distribution) allow us to conclude that the decrease in the proton temperature in the night sector of the plasmasphere connected with magnetic disturbances is caused by the filling of field tubes (depleted after the commencement of the storm) with colder ionospheric plasma. The proton temperature in the dayside sector of the plasmasphere virtually does not depend on the level of the geomagnetic disturbance. 相似文献
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We consider the influence of harmonics generated by an internal gravity wave (IGW) on the formation of nonlinear disturbances in the ionospheric E region. It is shown that the response of the lower ionosphere to the IGW propagation should be less efficient than the action of the IGW on the ionospheric F region. Nevertheless, if there are some thin layers (e.g., sporadic E layers) in the lower ionosphere, the response can be amplified; its amplitude is determined by the sharpness of the density gradient as compared with the characteristic scale of the atmosphere. 相似文献
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E. S. Andreeva M. B. Gokhberg V. E. Kunitsyn E. D. Tereshchenko B. Z. Khudukon S. L. Shalimov 《Cosmic Research》2001,39(1):10-14
Long-lived local disturbances of the ionospheric density over the site of ground industrial explosions were detected by the ionosphere radiotomography method. It is assumed that the density anomalies arise because of the initiation of vortex motion in a neutral component after acoustic impulse passage. 相似文献