Solar-photon sail hovering orbits about single and binary asteroids

Solar-photon sails can be useful for missions towards and about asteroids. Indeed, for the interplanetary transfer phase, missions to asteroids often require a large variation in inclination and solar-photon sails perform very well for such high energy missions. In the same way, solar-photon sails are also expected to perform well in the phase about the asteroid. This paper studies single and binary asteroids’ hovering regions by using a sailcraft. In order to consider a sailcraft with its own mass and shape, the mutual polyhedral method (usually used to study asteroid dynamics) is used; therefore, the sailcraft is designed by means of tetrahedra. The procedure to obtain the hovering regions about a single asteroid is presented and an accurate analysis of the control variables is carried out. Moreover, control torques required to maintain hovering orbits are obtained by considering the gravitational torques acting on the sailcraft due to the asteroid. In the end, the theory for hovering orbits is extended to binary-asteroid systems and applied to the binary system 1999 KW4.     

Guidance law with impact time and impact angle constraints

A novel closed-form guidance law with impact time and impact angle constraints is pro- posed for salvo attack of anti-ship missiles, which employs missile’s normal acceleration (not jerk) as the control command directly. Firstly, the impact time control problem is formulated as tracking the designated time-to-go (the difference between the designated impact time and the current flight time) for the actual time-to-go of missile, and the impact angle control problem is formulated as tracking the designated heading angle for the actual heading angle of missile. Secondly, a biased proportional navigation guidance (BPNG) law with designated heading angle constraint is constructed, and the actual time-to-go estimation for this BPNG is derived analytically by solving the system differential equations. Thirdly, by adding a feedback control to this constructed BPNG to eliminate the time-to-go errorthe difference between the standard time-to-go and the actual time-to-go, a guidance law with adjustable coefficients to control the impact time and impact angle simultaneously is developed. Finally, simulation results demonstrate the performance and feasibility of the proposed approach.     

弱太阳闪烁中深空探测信道的自适应控制

为提高探测器发射机功率利用率,在探测器和地球间建立可靠的传输链路,弱太阳闪烁中的深空信道的自适应控制十分重要。根据CCSDS规范,提出了一种基于连续功率控制和离散速率控制策略的深空信道自适应控制方法。数学分析和计算机仿真表明,(1) 太阳闪烁越强,自适应功率控制效果越明显;(2) 当太阳闪烁引起的信号衰减不大,小于9.4dB时,MPSK自适应控制信道容量高于非自适应控制信道容量。
     

低(负)仰角跟踪的综合平滑算法

分析多径测角误差的形成机理，阐明在多信息源的跟踪系统中，对跟踪数据作综合平滑算法的原理、计算方法及实现，以及由这种软件控制的跟踪系统的外场实验结果。     

复合材料螺旋桨扭转变形对推力脉动影响研究

本文基于面元法和有限元法,采用Fortran和Python语言混合编程,开发了求解复合材料螺旋桨稳态流固耦合的自迭代算法,并以某碳纤维桨为对象开展了静态加载变形试验和水动力性能试验,对自迭代算法有限元计算精度和水动力计算精度进行了试验验证。在此基础之上以大侧斜的4383复合材料螺旋桨为研究对象,采用该算法对4383复合材料螺旋桨在设计工况下的螺距角变化量和推力系数差值之间的对应规律进行了研究,结果表明大侧斜的4383复合材料螺旋桨能够有效降低推力脉动。     

某离心式喷嘴雾化特性及优化设计研究

喷嘴结构参数、喷油压降和燃油物性对喷嘴雾化特性具有重要影响。采用数值计算和试验手段研究某离心式喷嘴航空煤油和0#柴油雾化特性及差异性,并讨论喷嘴内部流动和喷嘴结构参数对雾化特性的影响。结果表明:数值计算与试验值存在差异,但雾化锥角、流量系数等随压力变化的趋势一致,验证了流体体积函数(VOF)追踪油气两相界面的正确性;喷嘴内部气、液相的涡是内部流动不稳定和气液面波动的原因;几何结构参数对喷嘴雾化特性影响明显;优化后的喷嘴结构,流量系数和雾化锥角分别增大了0.15和0.16倍,而喷嘴出口液膜厚度减小了0.53倍,明显改善了该喷嘴的雾化质量。     

核磁共振陀螺信号仿真及噪声分析

核磁共振陀螺具有体积小、精度高、功耗低等优势,有望成为下一代惯性导航系统的核心部件,目前正受到人们的广泛关注。比较全面的介绍了核磁共振陀螺的基本理论,在此基础上利用时间离散化方法推导并建立了能够充分考虑核磁共振陀螺系统动态特性的仿真模型。利用该模型研究分析了锁相环相位、磁场、温度以及探测光强在1×10-5均方根幅度下均匀白噪声对陀螺信号的影响,发现它们对角随机游走、零偏不稳定性影响依次减小,且都具有自身独特的频率响应特性。其中,锁相环相位噪声引起的角随机游走与零偏不稳定性分别为5.1985×102(°)/h1/2、3.4593×103(°)/h,而探测光强噪声引起的角随机游走与零偏不稳定性分别为3.1623×10-1(°)/h1/2、4.7603×10-1(°)/h。该研究对深入分析核磁共振陀螺动力学机理、寻找主要噪声来源、提高陀螺性能具有重要意义。     

CBERS地面接收系统G/T值测量

利用宇宙射电源测量地面接收系统品质因数Ｇ／Ｔ值是大多数地球站普遍采用的测量方法。本文针对中国科学院遥感卫星地面站ＣＢＥＲＳ接收系统给出系统Ｇ／Ｔ值测量需要的射电源流量密度和修正系数计算公式以及测量误差分析。最后，根据ＣＢＥＲＳ系统工厂验收测试遇到的问题，对不同天线仰角间的Ｇ／Ｔ值换算进行分析。分析表明：不同天线仰角间的Ｇ／Ｔ值可以换算，ΔＧ／Ｔ等于不同天线仰角下测量的背景冷空噪声功率之差。     

第24太阳活动周地球附近磁云与非磁云事件的统计分析

为研究第24太阳活动周中磁云（Magnetic Clouds,MC）与非磁云（Non-Magnetic Clouds,non-MC）的等离子体性质及其对空间天气的影响,使用1AU处的观测数据对2008-2015年168个ICME事件进行统计与分析,其中认证出磁云事件68个,占总数的40.48%.通过分析磁云与非磁云等离子体参数对空间天气环境的影响及与太阳活动的关系,整体性质的对比及在第23和24太阳活动周中性质的对比,可以发现：在第24太阳周中,磁云引起的磁暴强度普遍大于非磁云,南北向磁场分量是引起磁暴的重要参数;磁云数和太阳黑子数有很好的相关性,非磁云数与行星际日冕物质抛射总数及黑子数的相关性稍弱,磁云数在太阳周的不同阶段表现出不同的分布特性;磁云的磁场强度和南向磁场分量整体强于非磁云,两者质子温度、密度等参数差异不大.第24周磁云事件引起的地磁效应整体上弱于第23周磁云事件,这与第24周磁云事件最大南向磁场分量、传播速度以及质子温度整体小于第23周磁云事件有关.     

Estimation of Galactic Cosmic Ray exposure inside and outside the Earth’s magnetosphere during the recent solar minimum between solar cycles 23 and 24

The evidently low solar activity observed between solar cycles 23 and 24 during the years 2008–2010 led to a substantial increase in the Galactic Cosmic Ray (GCR) intensity in comparison with preceding solar minima. As the GCRs consist of highly-ionizing charged particles having the potential to cause biological damage, they are a subject of concern for manned missions to space. With the enhanced particle fluxes observed between 2008 and 2010, it is reasonable to assume that the radiation exposure from GCR must have also increased to unusually high levels. In this paper, the GCR exposure outside and inside the Earth’s magnetosphere is numerically calculated for time periods starting from 1970 to the end of 2011 in order to investigate the increase in dose levels during the years 2008–2010 in comparison with the last three solar minima. The dose rates were calculated in a water sphere, used as a surrogate for the human body, either unshielded or surrounded by aluminium shielding of 0.3, 10 or 40 g/cm².