Two-maneuver indirect contingency return from a low lunar orbit

The problem of contingency return from the low lunar orbit is studied. A novel two-maneuver indirect return strategy is proposed. By effectively using the Earth’s gravity to change the orbital plane of the transfer orbit, the second maneuver in the well-known three-maneuver return strategy can be removed, so the total delta-v is reduced. Compared with the single-maneuver direct return, our strategy has the advantage in that the re-entry epoch for the minimum delta-v cost can be advanced in time, with a minimum delta-v value similar to that of the direct return. The most obvious difference between our strategy and the traditional single- or multiple- maneuver strategies is that the complete transfer orbit is a patch between a two-body conic orbit and a three-body orbit instead of two conic orbits. Our strategy can serve as a useful option for contingency return from a low lunar orbit, especially when the delta-v constraint is stringent for a direct return and the contingency epoch is far away from the return window.     

适用于长时间烧蚀防热的蜂窝增强低密度材料

针对长时间烧蚀防热对防热材料的需求,研制了两种蜂窝增强低密度烧蚀防热材料,采用电弧风
洞加热设备对其防热性能进行了考核,并对其力学及热物理性能进行了研究。结果表明,在两种长时间(1 000
s 左右)热环境的考核下,蜂窝增强低密度材料烧蚀后背面温度均低于200℃,表面碳层均匀、完整,无明显烧蚀
量,显示了优异的隔热性能和良好的抗气流冲刷能力。     

Very low thrust station-keeping for low Earth orbiting satellites

Traditional station-keeping for Earth observation satellites with chemical thrusters generally involves maneuvers every couple months that are able to change significantly the semi-major axis and the inclination. These strategies do not scale down to very low thrust level (a few hundreds of μN) electrical thrusters. This paper presents both in-plane and out-of-plane strategies that spread corrections over very long arcs and discretize them to tiny maneuvers every couple orbits, taking into account mission-constraints on maneuvers locations. These strategies scale up to medium thrust strategies, filling the gap between propulsion technologies. The out-of-plane strategy although features a new no-deadband property and controls the full orbital momentum. All strategies allow control very close to the reference (a few hundreds meters in osculating parameters) and very low cost.     

Improving the low orbit satellite tracking ability using nonlinear model predictive controller and Genetic Algorithm

The satellite motion on the reference orbit (RO) with less energy consumption has always persuaded researchers to design optimal control systems. The nonlinear nature and time-varying equations of motion make this quest more challenging. The present study proposes a novel control system for satellite motion on the RO by considering a comprehensive model of its dynamics in orbit and a Nonlinear Model Predictive Controller (NMPC). The NMPC calculates the sub-optimal control inputs of satellite motion reference on the elliptic orbit by minimizing a convex cost function at each stage. Moreover, all weighting parameters of the cost function are optimized by the Genetic Algorithm (GA) to produce less perturbation and guarantee the best NMPC performance. Finally, the implemented NMPC has been compared to a Linear MPC (LMPC). The results show that not only can the NMPC resist against larger errors and perturbations, but it can also compensate for those errors by returning the satellite to its main orbit and maintaining it.     

基于LEO辅助的北斗B1C高灵敏快速捕获算法

随着低轨(LEO)卫星数量的不断增加,利用LEO星座辅助增强GNSS导航性能已经成为一种新的趋势.针对低信噪比环境下B1C信号难以捕获的问题,提出了一种基于LEO辅助的B1C信号高灵敏快速捕获算法.首先对提升接收机捕获灵敏度进行了分析,对比了相干积分与非相干积分对于信号处理增益的影响,得出在低轨导航增强信号的辅助下采用增加相干积分时间的捕获算法对低信噪比条件下B1C信号的捕获更有效.然后提出了一种基于LEO辅助的B1C高灵敏快速捕获算法,从理论分析和实验仿真两方面,对比验证了在LEO辅助下可以显著提高B1C信号的捕获灵敏度,缩短捕获时间,提高捕获效率.     

低冲击火工分离装置优化设计研究

对低冲击火工分离装置在分离过程中产生的冲击进行了研究,分析其分离冲击产生的机理,并以某低冲击火工分离装置为典型,从冲击产生源、结构设计、冲击的阻断与吸收3个环节深入开展了降冲击优化设计研究和试验验证。结果表明,采用的降冲击优化设计方法能够有效降低火工分离装置的分离冲击,可为后续同类装置的方案设计提供参考。     

一种低数据传输的多机器人实时视觉SLAM

针对多机器人视觉SLAM在实际应用中带宽受限的问题,设计了一种低数据传输的多机器人实时视觉SLAM系统.系统中引入了NetVLAD神经网络模型,通过改进NetVLAD降低了多机器人回环检测的计算资源占用,提高了回环检测的实时性.提出了一种针对描述子缺失情况下的特征匹配算法,提高了回环检测与相对量测的鲁棒性,并提出了一种增量式多机器人位姿图共享和优化方法.最后,通过在KITTI数据集进行测试,验证了该SLAM系统能有效减少多机器人通信过程中的数据传输,具有与单机器人SLAM相当的定位精度和实时性.     

嵌银丝低易损推进剂增速比和综合燃速试验研究

针对嵌银丝端羟基聚醚（HTPE）低易损推进剂的复杂燃烧过程，采用水下声发射法对增速比和综合燃速随基础燃速、压强、银丝直径及温度的变化规律开展试验研究。结果显示，低压下推进剂的综合燃速随基础燃速的增大整体呈上升趋势，而增速比呈下降趋势；综合燃速随压强的增大呈上升趋势，增速比高压段低于低压段，平均值相差24%；推进剂增速比随银丝直径增大先增大后减小，存在一个最佳银丝直径为0.25mm，使得增速比最大；综合燃速和增速比随推进剂的温度增加呈上升趋势。     

基于边界层燃烧方法的宽速域飞行器内流道减阻研究

为了降低宽速域飞行器的内流阻力，基于边界层燃烧方法，分析了系列进口马赫数条件下二维扩散段总阻力中摩阻和压阻的特性，研究了不同进口马赫数下摩阻和压阻分量对总减阻的贡献、燃烧影响区域和壁面热流密度，探讨了喷射参数对减阻效果的影响，探索了边界层燃烧方法在典型混压式进气道中的减阻应用。结果表明，随着进口马赫数的增加，总阻力中摩阻分量随之增加；边界层燃烧对摩阻和压阻减阻的机理有所不同，壁面附近流场特性变化使得摩擦系数减小，燃烧局部增压对壁面产生的增推效果使得压力系数减小；从总内阻减阻百分比看，在相同燃料/空气当量比下，低马赫数工况下边界层燃烧减阻效果不如高马赫数工况，且在低马赫数工况下，喷嘴附近壁面热流密度会显著增加；在本文所研究的参数范围内，摩阻和压阻对当量油气比更为敏感，而对喷射方向和喷射速度不敏感。     

低功率霍尔推力器束流发散和推力矢量偏心特性研究

为了准确掌握不同工况下混合励磁模式低功率霍尔推力器束流发散和推力矢量偏心特性，凭借自主设计和改进的一套快速评估霍尔推力器束流发散角和推力矢量偏角原位集成诊断装置，系统研究了推力器在不同阳极质量流率、磁场、电场下束流分布和推力矢量偏心特性的变化规律。结果表明，束流发散角随阳极质量流率（0.65mg/s~0.95mg/s）和磁场强度（112Gs~142Gs）的变化呈现负相关的特性。当阳极质量流率0.95mg/s，束流发散角降到29.1°（＜30°）。推力矢量偏角随阳极质量流率和磁场强度的变化分别存在极大值（1.19°）和极小值（0.91°）。束流发散角、推力矢量偏角在250V~330V放电电压范围内基本保持不变。