直扩测控系统抗多址能力分析与验证

为了防止多址干扰造成接收机出现误捕和假锁,改善直接序列扩频测控系统抗多址干扰性能,在Gold码特性和扩频接收机性能分析的基础上,结合最大似然原理,对采用扩频体制测控系统的抗干扰能力进行了分析。为契合工程应用,采用仿真遍历结合理论分析的方式,对Gold码的互相关抑制能力理论值进行了工程修正。在分析捕获阶段的抗干扰捕获门限后,还分析了载噪比估计结果在正常锁定和假锁两种状态下的差异,给出了接收机对假锁状态的判决方法和门限。根据分析和仿真的结果,给出了系统设计约束条件和优化的接收机设计流程,作为测控系统和接收机设计的参考。     

用户星中继终端在轨应用策略

在介绍在轨用户星中继终端的分类、功能和使用现状的基础上,重点对用户星中继终端多约束条件进行了梳理分析。为缓解常态化应急测控带来的资源紧张矛盾,提出了用户星中继终端在轨应用策略,即Ka/S模式下影随测控,小S模式下定时捕获。针对Ka+小S模式下实现影随测控的可行性问题,利用STK(Satellite Tool Kit,卫星开发工具包)软件进行了仿真计算分析,结果表明:为实现影随测控,满足测控快速响应需要,要求星载S频段中继测控天线对中继卫星的覆盖范围,应大于星载中继数传天线对中继卫星的覆盖范围。     

Energetic Hydrogen and Oxygen Atoms Observed on the Nightside of Mars

We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet. We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach 10⁵ cm⁻² sr⁻¹ s⁻¹, but no oxygen ENA signals above the detection threshold of 10⁴ cm⁻² sr⁻¹ s⁻¹ are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed. Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 10¹⁰ m⁻³ and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 10¹² m⁻³ and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss rate of hydrogen and oxygen due to the production of ENAs.     

航天航空中急性缺氧条件下功效改变的研究

受试者为84名男性青年和实验工作人员,在低压舱1500、2500、3000、4000、5000和6000米高度上停留60分钟。每次实验一个高度,总共133人次。实验中,记录了数字记忆、听觉警觉和跟踪操作等多项功效指标。应用统计和模型方法对结果进行了分析,并试用模糊集理论对五种基本功效进行综合评定,得到了急性缺氧下功效改变有意义的结果。这些结果可为飞行员执行飞行任务,航天员在船舱内或穿着航天服在舱外执行任务及制订医学保证方案提供了科学依据。     

Study of the rheological properties of water and Martian soil simulant mixtures for engineering applications on the red planet

The rheological properties of mixtures of water and the Martian soil simulant JSC-Mars-1A are investigated by preparing and testing samples at various solids concentrations. The results indicate that the dispersion is viscoelastic and, at small timescales (～0.1?s), reacts to sudden strain as an elastic solid. At longer timescales the dispersion behaves like a Bingham fluid and exhibits a yield stress. Hysteresis loops show that rapid step-changes (2?s duration) of shear-rate result in thixotropic behaviour, but slower changes (>10?s duration) can result in rheopexy. These observations are explained with the breakdown and recovery of the packing structure under stress. The rheological information is used to generate practical tools, such as the system curve and the Moody chart that can be used for designing piping systems, and calculating pump sizes and pressure requirements.     

Load distribution strategy for multi-lift system with helicopters based on power consumption and robust adaptive game control

It is of great significance to reasonably distribute the slung load to each helicopter while considering difference in power consumption, relative position and interaction comprehensively. Therefore, the load distribution strategy based on power consumption and robust adaptive game control is proposed in this paper. The study is on a “2-lead” multi-lift system of four tandem helicopters carrying a load cooperatively. First, based on the hierarchical control, the load distribution problem is divided into two parts: the calculation of expected cable force and the calculation of the anti-disturbance cable force. Then, aimed at minimizing the maximum equivalent power of helicopter, an optimization problem is set up to calculate the expected cable force. Specially, the agent power model is trained by BP neural network, the safe distance constraint between helicopters is set to 2.5 rotor diameters to reduce aerodynamic interference, and the helicopters with different performance can be considered by introducing the equivalent power factor into the objective function. Next, considering the difference and interaction between helicopters, the robust adaptive differential game control is proposed to calculate the anti-disturbance cable force. Particularly, to solve the coupled Hamiltonian equations, an adaptive solving method for value function is proposed, and its stability is proved in the sense of Lyapunov. The simulation results indicate that the proposed load distribution method based on power consumption is applicable to the entire flight trajectory even there are differences between helicopters. The game control can consider interaction between helicopters, can deal with different objective functions, and has strong robustness and small steady-state error. Based on the entire strategy, the cable force can be reasonably allocated so as to resist disturbance and improve the flight performance of the whole system.     

差分 GPS 鉴定地基雷达测量系统精度的方法研究

提出了利用差分ＧＰＳ分析地面雷测系统跟踪误差的思想,详细分析了各种误差源,建立了一组简洁的差分ＧＰＳ模型,构造了测量数据的比对分析算法以及具有良好抗野值能力的误差偏差最优统计算法,并利用模拟数据进行了仿真计算     

Unscented Kalman滤波在空间飞行器被动测距中的应用

介绍了Unscented Kalman滤波及其空间飞行器被动测距中的应用。Unscented Kalman滤波通过设计少量的sigma(抽样)点,计算这些点经过非线性函数的传播,获得滤波值基于非线性方程的更新。Unscented Kalman滤波避免了广义Kalman滤波等线性化方法的缺点,并提高了滤波精度。     

新一代GNSS接收机的智能跟踪状态评估技术

新一代全球导航卫星系统的接收机需要根据用户所处环境,自适应地调整接收机内部参数以达到最稳健的导航效果。这就要求接收机在运行过程中通过评估跟踪状态去检测和分析用户场景。基于对传统接收机控制系统缺陷的分析,提出了智能接收机的概念、特点及系统框架;在此基础上设计、分析接收机的智能跟踪状态评估算法;最后通过仿真验证了所设计的算法可以有效地识别场景及场景间的切换。     

带有跟踪微分器的导弹增量动态逆控制律设计

针对基本动态逆控制鲁棒性差的特点,设计了一种带有跟踪微分器的导弹增量动态逆过载控制律。首先建立了快慢两个回路的导弹过载控制模型,然后通过状态速率反馈,对快慢回路分别设计了增量式动态逆控制律,并进行了鲁棒性分析。最后通过引入快速跟踪微分器解决增量动态逆控制律中所需状态速率无法量测的问题。仿真结果表明,所设计的带有跟踪微分器的导弹增量动态逆控制律具有强鲁棒性。