Design and experiment of onboard laser time transfer in Chinese Beidou navigation satellites

High-precision time synchronization between satellites and ground stations plays the vital role in satellite navigation system. Laser time transfer (LTT) technology is widely recognized as the highest accuracy way to achieve time synchronization derived from satellite laser ranging (SLR) technology. Onboard LTT payload has been designed and developed by Shanghai Astronomical Observatory, and successfully applied to Chinese Beidou navigation satellites. By using the SLR system, with strictly controlling laser firing time and developing LTT data processing system on ground, the high precise onboard laser time transfer experiment has been first performed for satellite navigation system in the world. The clock difference and relative frequency difference between the ground hydrogen maser and space rubidium clocks have been obtained, with the precision of approximately 300 ps and relative frequency stability of 10E−14. This article describes the development of onboard LTT payload, introduces the principle, system composition, applications and LTT measuring results for Chinese satellite navigation system.     

A real-time ionospheric model based on GNSS Precise Point Positioning

This paper proposes a method of real-time monitoring and modeling the ionospheric Total Electron Content (TEC) by Precise Point Positioning (PPP). Firstly, the ionospheric TEC and receiver’s Differential Code Biases (DCB) are estimated with the undifferenced raw observation in real-time, then the ionospheric TEC model is established based on the Single Layer Model (SLM) assumption and the recovered ionospheric TEC. In this study, phase observations with high precision are directly used instead of phase smoothed code observations. In addition, the DCB estimation is separated from the establishment of the ionospheric model which will limit the impacts of the SLM assumption impacts. The ionospheric model is established at every epoch for real time application. The method is validated with three different GNSS networks on a local, regional, and global basis. The results show that the method is feasible and effective, the real-time ionosphere and DCB results are very consistent with the IGS final products, with a bias of 1–2 TECU and 0.4 ns respectively.     

X-ray pulsar-based navigation system with the errors in the planetary ephemerides for Earth-orbiting satellite

The objective of this paper is to investigate and reduce the impact of the errors in the planetary ephemerides on X-ray pulsar-based navigation system for Earth-orbiting satellite. Expressions of the system biases caused by the errors in the planetary ephemerides are derived. The result of investigation has shown that the impact of the error in Earth’s ephemeris is must greater than the errors in the other ephemerides and would greatly degrade the performance of X-ray pulsar-based navigation system. Moreover, the system bias is modeled as a slowly time-varying process, and is handled by including it as a part of navigation state vector. It has been demonstrated that the proposed navigation system is completely observable, and some simulations are performed to verify its feasibility.     

高轨飞行器主动段双向测控陆基导航方案

高轨飞行器主动段飞行过程中,倒置GPS导航等传统陆基导航方案存在资源需求高、导航精度差等问题。研究了地天地双向测控(TTC)陆基导航方案和天地天双向测控陆基导航方案,建立了时序分析模型,阐述了天地天双向测控陆基导航方案的定位数据使用延迟约为地天地双向测控陆基导航方案的1/2。通过理论分析推导和仿真验证,对比了不同陆基导航方案的资源需求、导航精度及位置速度准确度。结果表明:双向测控陆基导航方案相比传统陆基导航方案对地面站资源需求少,导航精度高,且天地天双向测控陆基导航方案的位置速度准确度更高。     

相控阵雷达导引头技术现状及发展趋势

相控阵雷达导引头具有反隐身和抗干扰等方面的突出优势,是当前国内外精确制导技术研究的重点和热点,且向着高集成度、超宽带、多功能、智能化的方向快速发展。本文结合当今相控阵雷达导引头的研究动态,阐述了相控阵雷达导引头的发展历程和世界各国相控阵雷达导引头的研究现状,从多个角度分析了相控阵雷达导引头的技术特点和技术优势,展望了相控阵雷达导引头在多频段/宽带、共形、多通道阵列、智能化等方面的发展方向和应用前景。随着相控阵制导技术的普及和应用,必将带动精确制导武器性能的大幅提升。     

Individual Differences in Representational Precision Predict Spatial Working Memory Span

Perhaps the signature feature of working memory is that it is limited. In the same subjects, we used two different retrieval tasks to independently measure two different limits of spatial memory. Precision was measured by asking participants to localize a missing target item among a field of other targets and distracters. Capacity was measured with a similar task where participants identified, rather than localized, a set of remembered targets from within a larger set of identical items. Across participants, the precision of localization was positively correlated with the number of successfully retrieved items. These data suggest that an individual's representational capacity may ultimately be constrained by their ability to form precise representations of space.     

天地环境差异对航天器设备安装精度影响分析

文章分析了地面重力环境和在轨内压环境对不同位置和状态下的载人航天器陀螺组件及姿轨控敏感器设备安装精度的影响,并进行了试验验证,分析结果与试验数据一致性较好。研究结果显示:设备布局位置不同,其安装精度受环境差异的影响程度也不同;航天器在空载、垂直停放状态下,设备安装精度受地面重力环境影响较小;陀螺组件和姿轨控敏感器A的安装精度受在轨内压环境影响较小,在地面常压环境下的精测结果能够真实反映其在轨状态,而姿轨控敏感器B的安装精度受压力环境影响明显。以上结果可为航天器设备布局及精度测量工作提供借鉴。     

系绳卫星体制高精度INSAR系统设计

针对现有分布式干涉系统难以实现更高比例尺高效率地形测绘的问题,提出了一种基于系绳卫星体制的InSAR系统。首先,结合系绳卫星动力学仿真,给出了系绳干涉系统的几何模型,提出了系绳干涉系统的工作模式,然后研究了系绳卫星SAR载荷的具体工程实现途径,提出了基于系绳电缆解决实现同步和相位同步的方法。首次建立了系绳长度及面内角等参数与模糊高度的关系,对SAR载荷的工作频段、发射峰值功率、天线口径、入射角范围等进行了优化设计。对系绳InSAR系统的关键性能指标进行仿真分析,仿真结果表明该系统可以实现0.5m测高精度等核心指标。该研究提出了一种1:5000比例尺的高精度测绘SAR系统,相对测高精度比德国的Tandem-X系统提升了4倍,可为我国后续开展高精度星载InSAR工程研制提供参考。     

超精密磨削中的砂轮在线动平衡技术的研究

介绍了作者研制的一种新型砂轮在线动平衡系统。该系统以单片机为核心,通过检测砂轮旋转时不平衡量引起的振动信号并进行数据处理,以确定不平衡量的大小,然后控制跟随砂轮高速旋转的平衡头内的平衡块移动对不平衡量进行补偿。经过初步实验表明,该系统显著降低了砂轮不平衡量引起的振动,获得了良好的平衡效果。     

HOI延迟对LEO卫星简化动力学POD的影响

通常使用无电离层(IF)线性组合(LC)消除低地球轨道(LEO)卫星简化动力学精密定轨(POD)一阶电离层延迟误差,忽略了高阶电离层(HOI)延迟误差。随着LEO卫星POD技术的发展,计算不同轨道高度的HOI延迟并探索其变化已成为进一步提高POD精度的重要手段。首先,使用国际参考电离层-2016(IRI-2016)和国际地磁参考场第13代(IGRF-13)模型,计算电离层穿刺点(IPP)位置和地磁场强度。其次,使用平滑星载GNSS数据计算电离层斜路径总电子含量(STEC)。然后,分别计算GOCE、GRACE-A和SWARM-A/B卫星的二阶和三阶电离层延迟。最后,评估了HOI延迟对LEO卫星重叠轨道分析、卫星激光测距(SLR)检核和精密科学轨道(PSO)比较结果的影响。实验结果表明：HOI延迟对LEO卫星简化动力学POD的影响大约在毫米至厘米的数量级上;HOI延迟对LEO卫星简化动力学POD外符合精度的影响分别达到0.92,0.22,0.21和0.18 mm;随着LEO卫星轨道高度的增加,HOI延迟对LEO卫星简化动力学POD的影响减小。