Feasibility study of creep feed grinding of 300M steel with zirconium corundum wheel

The ultrahigh strength 300M steel has been commonly used in the manufacture of aircraft landing gear and rotor shaft parts due to its excellent mechanical properties. Creep feed grinding is one of the essential operations during the whole component manufacturing processes. In this work, the feasibility of creep feed grinding of 300M steel by using the hard zirconium corundum wheel was theoretically and experimentally evaluated. A variety of responses including grinding forces, temperature fields...     

径向两星库仑编队队形保持自适应控制研究

研究地球同步轨道处径向两星库仑编队队形保持的自适应控制问题.建立了双星库仑编队在地球同步轨道处径向两星库仑编队动力学模型.基于建立的非线性化动力学模型,同时考虑到外部扰动和动力学模型误差等因素,设计径向两星库仑编队在地球同步轨道处的构型保持自适应控制律,并利用Lyapnuov稳定性理论证明系统的闭环稳定性.最后进行数值仿真,并与传统PID控制进行了比较.仿真结果表明提出的自适应控制律响应速度快,稳定性好,编队构型能够收敛到期望值,控制性能明显优于PID控制.     

航天器分布式有限时间编队方法

以二阶积分环节作为单体航天器动力学模型,在固定通信拓扑的基础上,假设每个航天器仅获取相邻航天器的速度位置信息,设计了分布式有限时间跟踪控制算法,并证明了算法的有效性。在该算法的基础上,采用了虚拟结构和阶级控制方法,使第一阶级航天器接受虚拟领队形成的虚拟结构信息,次级航天器接受上一级航天器信息,给出了有限时间编队方法,并通过数值仿真验证了该编队算法。     

超低轨航天器气动力分析与减阻设计

轨道降低,航天器受到的气动力增大,气动力对航天器影响显著。考虑自由分子流态 下的超低轨航天器,利用分割法把简单外形的航天器分割为几部分,分别计算各部分的气动 力,然后相加获得总的气动力效果;通过对平面的气动力进行计算分析,提出了超低 轨航天器的减阻设计方法;结果表明：当轨道高度降低到250 km左右时,航天器受到的气动 阻力比500 km高出约2个数量级;一般情况下,超低轨航天器应采用细长体构型,减小迎风 面积;侧面积引起的航天器阻力已经不可忽略,应采用侧面光滑技术,减少侧面阻力;当超 低轨航天器长细比超过一定限度后,随着长细比增大,大气阻力升高。
     

编队卫星碰撞规避方法研究

对编队卫星碰撞规避方法进行了研究。通过递推编队卫星的初始状态协方差阵,将碰撞概率密度函数在危险区域积分获得编队卫星的碰撞概率。当碰撞概率大于安全阈值时,向卫星施加最小脉冲速度修正量Δv,在垂直于终止时刻相对速度的平面机动一定距离以降低碰撞概率。仿真结果表明:用计算的碰撞概率能较好地预测编队卫星的潜在碰撞危险,所选机动策略有效。     

航天器编队飞行和空间演示验证技术——有人照料空间实验室与平动-转动物理仿真器

航天器编队飞行是近年来国内外航天领域研究的热点问题,同时也是空间技术今后一个重要发展方向。为此文章首先讨论航天器编队飞行特点;其次研究编队飞行今后能否获得顺利成功应用,有关它的各种算法和软件空间飞行演示验证技术和方法;最后介绍了美国麻省理工学院空间系统实验室（MITSSL）对航天器编队飞行算法软件空间演示验证的方法和实验。     

大展弦比飞翼构型的横航向操纵特性

大展弦比飞翼构型取消了垂尾和方向舵,通常采用开裂式方向舵和多组升降副翼组合来实现滚转和偏航操纵.通过与常规的侧力类方向舵对比,揭示了阻力类开裂式方向舵的操纵机理,包括偏航和滚转力矩产生原理以及操纵效能等.对大展弦比飞翼构型的横航向配平能力和协调机动能力进行了分析,并与常规飞机进行了对比,研究结果表明单发失效对偏航操纵效能要求最高,需要适当地增加开裂式方向舵的舵容量或对现有布局进行改进设计.      

DOA estimation for attitude determination on communication satellites

In order to determine an appropriate attitude of three-axis stabilized communication satellites, this paper describes a novel attitude determination method using direction of arrival （DOA） estimation of a ground signal source. It differs from optical measurement, magnetic field measurement, inertial measurement, and global positioning system （GPS） attitude determination. The proposed method is characterized by taking the ground signal source as the attitude reference and acquiring attitude information from DOA estimation. Firstly, an attitude measurement equation with DOA estimation is derived in detail. Then, the error of the measurement equation is analyzed. Finally, an attitude determination algorithm is presented using a dynamic model, the attitude measurement equation, and measurement errors. A developing low Earth orbit （LEO） satellite which tests mobile communication technology with smart antennas can be stabilized in three axes by corporately using a magnetometer, reaction wheels, and three-axis magnetorquer rods. Based on the communication satellite, simulation results demonstrate the effectiveness of the method. The method could be a backup of attitude determination to prevent a system failure on the satellite. Its precision depends on the number of snapshots and the input signal-to-noise ratio （SNR） with DOA estimation.     

Simultaneous ISAR imaging of group targets flying in formation

This paper proposes a novel inverse synthetic aperture radar(ISAR) imaging method based on second-order keystone transform(KT) and Sandglass transform for group targets flying in a formation with constant accelerated rectilinear motion in the same radar beam. First, range curvature and range walk of each sub-target among group targets are corrected by the second-order KT combined with the quadratic phase term compensation. After range alignment, the signals in each range frequency cell can be modelled as multiple chirp signals and then the Sandglass transform is utilized to cross-range imaging, which transforms the time–frequency distribution of the signals in each range frequency cell into beelines parallel to the slow time axis simultaneously. Finally, cross-range profiles of group targets in each range frequency cell are obtained via a projection of the perk of every scatterer in the two-dimensional accumulation plane onto the frequency axis. The advantage of the proposed method is that it can align range profiles of each sub-target simultaneously and image cross-range profiles directly without separating the returned signals, which simplifies the operation procedure. Simulation results are used to demonstrate the effectiveness of the proposed method.     

两栖攻击舰编队火力支援作战能力综合评估分析

在建立两栖攻击舰编队火力作战能力评估指标体系的基础上,构建了以战场感知能力、指挥系统控制能力、对岸火力打击能力和火力支援综合保障能力为二级指标的多层次评估指标体系,并将二级指标细化为51个具体指标,运用AHP和熵权法得到评价指标的综合权重,通过模糊综合评判得出综合评判总分。所得结果对两栖攻击舰编队火力支援作战能力的评估具有实际应用价值。