近地空间飞艇发展现状与趋势

近地空间飞艇今天不但在军事上得到了应用,就是在民用中也得到各领域的关注。因此,近年来各国竟相发展,使得飞艇在军事上成为近地空间的首选装备。文章针对国外飞艇发展现状与发展趋势进行论述,旨在阐述飞艇在未来军事领域中的应用与地位。     

一种X频段双圆极化器的设计

介绍了一种X频段双圆极化器的设计。设计实例采用方波导和圆波导两种形式,具有结构紧凑、功率容量大、极化轴比小、频带宽和适于星载使用等特点。仿真结果表明：设计出的双圆极化器,隔离度大于29dB,电压驻波比小于1.2,轴比小于0.5dB。该极化器的设计方法可应用于星载X频段双圆极化数传天线的设计。     

基于GA-PSO的低轨星座传感器资源优化调度方法

针对低轨星座目标跟踪传感器资源调度,基于函数优化和组合优化理论,建立了传感器资源优化调度模型,并设计了基于遗传算法-粒子群优化(GA-PSO)的优化调度算法。仿真结果表明,与现有的构造优化调度算法相比,该算法的性能更优,但运算量有所增加。     

遥感图像去雾算法研究

针对现有的去雾算法对彩色图像处理后会出现色彩畸变的问题,提出了基于Retinex算法和色度比的去雾算法,该算法在用Retinex算法进行图像恢复的过程中引入了原图像的色彩信息,改善了处理后的图像的色彩。     

低等级进口元器件卫星使用存在问题及风险评估方法探索

文章针对近年来卫星使用的低等级元器件的特点和存在的问题进行了分析,对低等级元器件的卫星使用策略及风险评估方法进行了研究和总结。     

FM接收机中频滤波器的设计

介绍了一种基于双极技术的中心频率、带宽、增益可控的Gm-C型多相滤波器。分析了滤波器的基本原理,推导出其电路结构形式,并对其中关键的Gm单元进行了优化设计,实现了一个六级带通滤波器。该滤波器应用于低功耗FM低中频接收机中频滤波器的设计,镜像抑制比高达66 dB,总功耗仅为3.75 mW。     

中等后掠机翼平面参数设计与实验研究

采用Euler数值计算方法,对60多种中等后掠角及展弦比的切尖菱形机翼、双三角机翼纵向气动力特性进行了计算、分析和比较,从中筛选出16种切尖菱形机翼、14种双三角机翼进行了全机高速风洞实验研究,给出了机翼的展弦比、前缘后掠角、根梢比(后缘前掠角)及几何扭转变化对全机升力、阻力及俯仰力矩的影响曲线和数据分析,在此基础上提出了用于定量估算两类机翼纵向气动力特性的关系式及修正因子。本文研究结果为建立战斗机机翼气动力设计数据库及飞机气动布局设计提供了实用的数据和设计参考。     

Analysis of the orbit lifetime of CubeSats in low Earth orbits including periodic variation in drag due to attitude motion

It is estimated that more than 22,300 human-made objects are in orbit around the Earth, with a total mass above 8,400,000 kg. Around 89% of these objects are non-operational and without control, which makes them to be considered orbital debris. These numbers consider only objects with dimensions larger than 10 cm. Besides those numbers, there are also about 2000 operational satellites in orbit nowadays. The space debris represents a hazard to operational satellites and to the space operations. A major concern is that this number is growing, due to new launches and particles generated by collisions. Another important point is that the development of CubeSats has increased exponentially in the last years, increasing the number of objects in space, mainly in the Low Earth Orbits (LEO). Due to the short operational time, CubeSats boost the debris population. One of the requirements for space debris mitigation in LEO is the limitation of the orbital lifetime of the satellites, which needs to be lower than 25 years. However, there are space debris with longer estimated decay time. In LEÓs, the influence of the atmospheric drag is the main orbital perturbation, and is used in maneuvers to increment the losses in the satellite orbital energy, to locate satellites in constellations and to accelerate the decay.The goal of the present research is to study the influence of aerodynamic rotational maneuver in the CubeSat?s orbital lifetime. The rotational axis is orthogonal to the orbital plane of the CubeSat, which generates variations in the ballistic coefficient along the trajectory. The maneuver is proposed to accelerate the decay and to mitigate orbital debris generated by non-operational CubeSats. The panel method is selected to determine the drag coefficient as a function of the flow incident angle and the spinning rate. The pressure distribution is integrated from the satellite faces at hypersonic rarefied flow to calculate the drag coefficient. The mathematical model considers the gravitational potential of the Earth and the deceleration due to drag. To analyze the effects of the rotation during the decay, multiple trajectories were propagated, comparing the results obtained assuming a constant drag coefficient with trajectories where the drag coefficient changes periodically. The initial perigees selected were lower than 400 km of altitude with eccentricities ranging from 0.00 to 0.02. Six values for the angular velocity were applied in the maneuver. The technique of rotating the spacecraft is an interesting solution to increase the orbit decay of a CubeSat without implementing additional de-orbit devices. Significant changes in the decay time are presented due to the increase of the mean drag coefficient calculated by the panel method, when the maneuver is applied, reducing the orbital lifetime, however the results are independent of the angular velocity of the satellite.     

A deformation model of flexible,HAMR objects for accurate propagation under perturbations and the self-shadowing effects

A new type of space debris in near geosynchronous orbit (GEO) was recently discovered and later identified as exhibiting unique characteristics associated with high area-to-mass ratio (HAMR) objects, such as high rotation rates and high reflection properties. Observations have shown that this debris type is very sensitive to environmental disturbances, particularly solar radiation pressure, due to the fact that its motion depends on the actual effective area, orientation of that effective area, reflection properties and the area-to-mass ratio of the object is not stable over time. Previous investigations have modelled this type of debris as rigid bodies (constant area-to-mass ratios) or discrete deformed body; however, these simplifications will lead to inaccurate long term orbital predictions. This paper proposes a simple yet reliable model of a thin, deformable membrane based on multibody dynamics. The membrane is modelled as a series of flat plates, connected through joints, representing the flexibility of the membrane itself. The mass of the membrane, albeit low, is taken into account through lump masses at the joints. The attitude and orbital motion of this flexible membrane model is then propagated near GEO to predict its orbital evolution under the perturbations of solar radiation pressure, Earth’s gravity field (J₂), third body gravitational fields (the Sun and Moon) and self-shadowing. These results are then compared to those obtained for two rigid body models (cannonball and flat rigid plate). In addition, Monte Carlo simulations of the flexible model by varying initial attitude and deformation angle (different shape) are investigated and compared with the two rigid models (cannonball and flat rigid plate) over a period of 100?days. The numerical results demonstrate that cannonball and rigid flat plate are not appropriate to capture the true dynamical evolution of these objects, at the cost of increased computational time.     

Characterization of the low latitude plasma density irregularities observed using C/NOFS and SCINDA data

Complex electrodynamic processes over the low latitude region often result in post sunset plasma density irregularities which degrade satellite communication and navigation. In order to forecast the density irregularities, their occurrence time, duration and location need to be quantified. Data from the Communication/Navigation Outage Forecasting System (C/NOFS) satellite was used to characterize the low latitude ion density irregularities from 2011 to 2013. This was supported by ground based data from the SCIntillation Network Decision Aid (SCINDA) receivers at Makerere (Geographic coordinate 32.6°E, 0.3°N, and dip latitude ?9.3°N) and Nairobi (Geographic coordinate 36.8°E, ?1.3°N, and dip latitude ?10.8°N). The results show that irregularities in ion density have a daily pattern with peaks from 20:00 to 24:00 Local Time (LT). Scintillation activity at L band and VHF over East Africa peaked in 2011 and 2012 from 20:00 to 24:00 LT, though in many cases scintillation at VHF persisted longer than that at L band. A longitudinal pattern in ion density irregularity occurrence was observed with peaks over 135–180°E and 270–300°E. The likelihood of ion density irregularity occurrence decreased with increasing altitude. Analysis of C/NOFS zonal ion drift velocities showed that the largest nighttime and daytime drifts were in 270–300°E and 300–330°E longitude regions respectively. Zonal irregularity drift velocities over East Africa were for the first time estimated from L-band scintillation indices. The results show that the velocity of plasma density irregularities in 2011 and 2012 varied daily, and hourly in the range of 50–150 m s^?1. The zonal drift velocity estimates from the L-band scintillation indices had good positive correlation with the zonal drift velocities derived from VHF receivers by the spaced receiver technique.