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71.
卫星通信与卫星定位系统的应用发展,对终端设备天线的性能提出了更高的应用需求。为实现宽频带宽波束圆极化天线的设计,采用正交移相馈电网络对含有背腔的交叉偶极子天线馈电,实现了宽带圆极化单向辐射特性,同时利用磁电偶极子对交叉偶极子进行加载,展宽了天线的波束宽度,促使天线在50.7%的相对带宽内S11<-10dB,在1.3~1.75GHz的频带内轴比小于3dB,轴比小于3dB的圆极化波束宽度可达180°,增益不小于6.6dB。经实测验证,所设计的天线具有宽频带宽波束特性,同时具有结构紧凑、性能稳定的优点,适用于卫星通信与导航终端系统。 相似文献
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航天器的发电能力与太阳电池阵有效发电面积成正比。针对圆柱形载人航天器,提出了一种体装太阳电池阵有效发电面积计算方法。首先,将太阳电池阵沿圆周方向划分为多个子阵,通过坐标变换,计算太阳矢量与每个子阵法线的夹角(即太阳入射角);然后,将每个子阵面积与对应太阳入射角的余弦相乘并求和,得到体装太阳电池阵的有效发电面积。对不同轨道日照角、不同飞行姿态下体装太阳电池阵有效发电面积进行仿真分析,仿真结果表明:三轴对地姿态下平均有效发电面积为安装面积的25%~32%,通过固定角度偏航可将有效发电面积提高至安装面积的30%~44%。 相似文献
73.
V.?A.?Afanas’ev G.?L.?Degtyarev A.?S.?MeshchanovEmail author 《Russian Aeronautics (Iz VUZ)》2018,61(1):23-31
Real values of parameters for a space vehicle and its steering devices are specified by using the motion parameters measured in flight based on solving the differential equations of motion. 相似文献
74.
Asteroids and comets are the remnants of the swarm of planetesimals from which the planets ultimately formed, and they retain records of processes that operated prior to and during planet formation. They are also likely the sources of most of the water and other volatiles accreted by Earth. In this review, we discuss the nature and probable origins of asteroids and comets based on data from remote observations, in situ measurements by spacecraft, and laboratory analyses of meteorites derived from asteroids. The asteroidal parent bodies of meteorites formed \(\leq 4\) Ma after Solar System formation while there was still a gas disk present. It seems increasingly likely that the parent bodies of meteorites spectroscopically linked with the E-, S-, M- and V-type asteroids formed sunward of Jupiter’s orbit, while those associated with C- and, possibly, D-type asteroids formed further out, beyond Jupiter but probably not beyond Saturn’s orbit. Comets formed further from the Sun than any of the meteorite parent bodies, and retain much higher abundances of interstellar material. CI and CM group meteorites are probably related to the most common C-type asteroids, and based on isotopic evidence they, rather than comets, are the most likely sources of the H and N accreted by the terrestrial planets. However, comets may have been major sources of the noble gases accreted by Earth and Venus. Possible constraints that these observations can place on models of giant planet formation and migration are explored. 相似文献
75.
In order to make the power level angle (PLA) have the same bijection relationship with the thrust when the environment changes before operational limit exceedance, and ensure the pilots ability of unrestricted throttle movement as well as the safety of the engine, a method used to design a constant thrust power schedule was proposed. The research was based on a simulink turbofan engine model and the results were organized as look-up tables in different structures with limitations. Simulation was done to confirm the validity and demonstrate the effectiveness of the schedule obtained with the approach. The constant thrust takeoff schedule, constant thrust idle schedule and constant thrust part power schedule with the present constant thrust control (CTC) method were proved to be valid. The results can be applied to this specific engine but the method can be applied to any areoengine and can be even extended to the unmanned plane. 相似文献
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Diffusive shock acceleration is the theory of particle acceleration through multiple shock crossings. In order for this process to proceed at a rate that can be reconciled with observations of high-energy electrons in the vicinity of the shock, and for cosmic rays protons to be accelerated to energies up to observed galactic values, significant magnetic field amplification is required. In this review we will discuss various theories on how magnetic field amplification can proceed in the presence of a cosmic ray population. On both short and long length scales, cosmic ray streaming can induce instabilities that act to amplify the magnetic field. Developments in this area that have occurred over the past decade are the main focus of this paper. 相似文献