Proposal for a realtime Einstein-synchronization-defined satellite virtual clock

Realization of high performance satellite onboard clock is vital for various positioning, navigation, and timing applications. For further improvement of the synchronization-based satellite time and frequency references, we propose a geosynchronous(GEO) satellite virtual clock concept based on ground–satellite synchronization and present a beacon transponder structure for its implementation(scheduled for launch in 2025), which does not require atomic clocks to be mounted on the satellite. Its high performance relies only on minor modifications to the existing transponder structure of GEO satellites. We carefully model the carrier phase link and analyze the factors causing link asymmetry within the special relativity. Considering that performance of such synchronization-based satellite clocks is primarily limited by the link's random phase noise, which cannot be adequately modeled, we design a closed-loop experiment based on commercial GEO satellites for pre-evaluation. This experiment aims at extracting the zero-means random part of the ground-satellite Ku-band carrier phase via a feedback loop. Ultimately, we obtain a 1σ value of 0.633 ps(two-way link), following the Gaussian distribution. From this result, we conclude that the proposed real-time Einstein-synchronization-defined satellite virtual clock can achieve picosecond-level replication of onboard time and frequency.

Shift control method for the local time at descendi ngnode based on sun-synchronous orbit satellite

This article analyzes the shift factors of the descending node local time for sun-synchronous satellites and proposes a shift control method to keep the local time shift within an allowance range. It is found that the satellite orbit design and the orbit injection deviation are the causes for the initial shift velocity, whereas the atmospheric drag and the sun gravitational perturbation produce the shift acceleration. To deal with these shift factors, a shift control method is put forward, through such methods as orbit variation design, orbit altitude, and inclination keeping control. The simulation experiment and practical application have proved the effectiveness of this control method.

Method of Time-Delay Calculating and Correcting to Control Spin-Stabilized Satellite Synchronously

The key to control Spin-Stabilized Satellites Synchronously is to determine the models for calculating and correcting of time-delay at the different situations. Based on the principle of Synchronous-Control mode, the methods of determining the models of calculating and correcting of time-delay are proposed. The methods have been proved to be effective in real satellite control engineering.

Approach to inter-satellite time synchronization for micro-satellite cluster

Micro-satellite cluster enables a whole new class of missions for communications, remote sensing, and scientific research for both civilian and military purposes. Synchronizing the time of the satellites in a cluster is important for both cluster sensing capabilities and its autonomous operating. However, the existing time synchronization methods are not suitable for microsatellite cluster, because it requires too many human interventions and occupies too much ground control resource. Although, data post-process may realize the equivalent time synchronization, it requires processing time and powerful computing ability on the ground, which cannot be implemented by cluster itself. In order to autonomously establish and maintain the time benchmark in a cluster, we propose a compact time difference compensation system（TDCS）, which is a kind of time control loop that dynamically adjusts the satellite reference frequency according to the time difference. Consequently, the time synchronization in the cluster can be autonomously achieved on-orbit by synchronizing the clock of other satellites to a chosen one＇s. The experimental result shows that the standard deviation of time synchronization is about 102 ps when the carrier to noise ratio（CNR） is 95 d BHz, and the standard deviation of corresponding frequency difference is approximately0.36 Hz.

Neighborhood Awareness and Stock Return Synchronicity:Evidence from Satellite Nighttime Light Data

This paper examines the impact on stock return synchronicity of information provided by people who neighbor firms.Neighboring people have inherent advantages in acquiring and interpreting information.We employed novel satellite nighttime light data as a proxy for information held by neighboring people.Our analyses confirmed that brighter nighttime light was related to greater and better-quality information production.Using a sample of 18,963 firm-year observations over the 2000-2013 period,we found that information from nearby people facilitated the incorporation of firm-specific information into stock prices,resulting in lower stock return synchronicity.The results were robust when using the slope as an instrumental variable and were supported by various sensitivity checks.The effect of nighttime light intensity was more pronounced for firms operating across multiple geographic regions or diverse industries,those situated near more parks and shopping malls,and those with fewer institutional investors and less media coverage.

Integrated method for measuring distance and time difference between small satellites

The advancement of small satellites is promoting the development of distributed satellite systems,and for the latter,it is essential to coordinate the spatial and temporal relations between mutually visible satellites.By now,dual one-way ranging(DOWR)and two-way time transfer(TWTT)are generally integrated in the same software and hardware system to meet the limitations of small satellites in terms of size,weight and power(SWaP)consumption.However,studies show that pseudo-noise regenerative ranging(PNRR)performs better than DOWR if some advanced implementation technologies are employed.Besides,PNRR has no requirement on time synchronization.To apply PNRR to small satellites,and meanwhile,meet the demand for time difference measurement,we propose the round-way time difference measurement,which can be combined with PNRR to form a new integrated system without exceeding the limits of SWaP.The new integrated system can provide distributed small satellite systems with on-orbit high-accuracy and high-precision distance measurement and time difference measurement in real time.Experimental results show that the precision of ranging is about 1.94 cm,and that of time difference measurement is about 78.4 ps,at the signal to noise ratio of 80 dBHz.

Synchronous anorectal melanoma

Anorectal melanoma is a very rare tumor with poor prognosis. Rectal bleeding is the most frequent symptom and surgical treatment ranges from local excision to radical abdominoperineal resection. We report a case of a 75-years-old male patient who presented with a history of recurrent rectal bleeding, and whose histopathological diagnosis was melanoma. Macroscopically, we found two distinct tumors in anorectal region, 0.5 cm and 1.5 cm from dentate line. The first one was pedunculated, on a thin stalk, measuring 1 cm in greatest diameter, and the second one was sessile and nodular measuring up to 2.8 cm in largest diameter. Microscopic examination and immunohistochemical analysis of both tumors confirmed the diagnosis of melanoma. This case represents multiple synchronous primary melanoma of the anorectal region, with a possibility that one of the lesions is primary melanoma and the second one is a satellite lesion.

Protected Fair Secret Sharing Based Bivariate Asymmetric Polynomials in Satellite Network

Verifiable secret sharing mainly solves the cheating behavior between malicious participants and the ground control center in the satellite network.The verification stage can verify the effectiveness of secret shares issued by the ground control center to each participant and verify the effectiveness of secret shares shown by participants.We use a lot of difficult assumptions based on mathematical problems in the verification stage,such as solving the difficult problem of the discrete logarithm,large integer prime factorization,and so on.Compared with other verifiable secret sharing schemes designed for difficult problems under the same security,the verifiable secret sharing scheme based on the Elliptic Curve Cryptography(ECC)system has the advantages of less computational overhead and shorter key.At present,the binary polynomial is a single secret scheme and cannot provide effective verification.Therefore,based on a Protected Verifiable Synchronous Multi Secret Sharing(PVS-MSS)scheme,this paper is designed based on bivariate asymmetric polynomials.The advanced verifiable attribute is introduced into the Protected Secret Sharing(PSS)scheme.This paper extends the protected synchronous multi-secret sharing scheme based on bivariate polynomial design.The ECC system constructs the security channel between the ground control center and participants and constructs the verification algorithm.Through the verification algorithm,any participant can verify the consistency and effectiveness of the secret shadow and secret share received from other participants or presented by the secret distribution center.Therefore,no additional key agreement protocol is required;participants do not need to negotiate the session key for encryption;the secret share polynomial can generate the session key between participants and speed up the secret reconstruction process.The verification stage has lower computational complexity than the verifiable scheme constructed by Rivest Shamir Adleman (RSA) and other encryption methods. Chinese Remainder Theorem (CRT)is used to update the secret shadow. The secret shadow does not need to beupdated with the change of the scheme shared secret, and the public valueupdate efficiency is higher. Reduce the complexity of sharing secret updatesin a synchronous multi-secret sharing scheme.

A 5M Synchronization Mechanism for Digital Twin Shop-Floor

In recent years,as a promising way to realize digital transformation,digital twin shop-floor(DTS)plays an impor-tant role in smart manufacturing.The core feature of DTS is the synchronization.How to implement and maintain the synchronization is critical for DTS.However,there is still a lack of a common definition for synchronization in DTS.Besides,a systematic synchronization mechanism for DTS is strongly needed.This paper first summarizes the defi-nition and requirements of synchronization in DTS,to clarify the understanding of synchronization in DTS.Then,a 5M synchronization mechanism for DTS is proposed,where 5M refers to multi-system data,multi-fidelity model,multi-resource state,multi-level state,and multi-stage operation.As a bottom-up synchronization mechanism,5M synchronization mechanism for DTS has the potential to support DTS to achieve and maintain physical-virtual state synchronization,and to realize operation synchronization of DTS.The implementation methods of 5M synchronization mechanism for DTS are also introduced.Finally,the proposed synchronization mechanism is validated in a digital twin satellite assembly shop-floor,which proves the effectiveness and feasibility of the mechanism.

一种天基双基地InSAR系统的相位同步方法及验证情况

以德国的TanDEM-X双星编队干涉合成孔径雷达(InSAR)卫星系统为背景,提出了基于点频连续波同步信号双向对传,实现编队卫星InSAR系统相位同步的方法。文中给出了该同步方法实现的框架,对该相位同步方法的原理进行了理论推导,得出了补偿相位差的表达式,并对影响同步精度的因素进行了初步的分析。该方法可用于天基双/多基地合成孔径雷达系统相位同步链路的设计,仿真分析的结果验证了该方法的理论可行性。此外,通过搭建实物系统对系统的工程可实现精度进行了验证,结果表明获取的载波频率相位同步精度与倍频器件的频率精度和一致性密切相关。该相位同步方法为与TanDEM-X相近InSAR系统的设计提供参考。

太阳同步轨道遥感卫星快速目标访问计算方法

目标访问计算是指根据遥感卫星轨道和待观测目标的位置,计算遥感卫星对目标观测的时刻和姿态,是遥感卫星任务管控领域的重要基础技术之一。高效的目标访问计算方法可大幅提升卫星任务管控的时效性,对后续大规模遥感星座任务管控具有重要意义。利用太阳同步轨道卫星交点地方时不变的特点,快速估算出卫星经过目标的较短时间窗口,对时间窗口内的星历进行逐点计算,获取卫星对目标进行访问的最佳时刻。试验结果证明,该方法可大幅提升目标访问时间的计算效率。

基于卫星双向时间比对的无中心站间时间同步

针对多站分布式协同站间高精度时间同步关键问题,在详细介绍卫星双向时间比对的基本原理和精度分析基础上,设计了一种无中心多站卫星双向比对逻辑架构和多站时间同步处理算法,充分考虑硬件资源约束,并提供时差测量数据冗余,避免了因某个站故障造成的全系统时间同步功能失效,提高系统时间同步的鲁棒性和灵活性。基于精密单点定位技术进行了异地远程卫星双向时间同步精度验证,试验结果表明时间同步精度优于6 ns。

敦煌戈壁地表反射率光谱的旋翼无人机测量及定标评估

利用敦煌中国遥感卫星辐射校正场的星地同步观测试验,实现对我国在轨气象、海洋、陆地资源、环境减灾、测绘地震、高分、军事等系列卫星光学成像载荷太阳反射波段的绝对辐射定标,是目前的重要手段之一。然而,中国遥感卫星辐射校正场传统的地表反射率光谱星地同步测量方法是基于汽车跑场观测,不仅耗费较大的人力物力、容易造成场地破坏,而且获取的测量数据缺乏区域代表性。鉴于此,自2016年起,在敦煌星地同步观测试验中以旋翼无人机低空同步测量为主,跑场测量为辅,完成从航线设计、航高选择、仪器参数配置、采样策略、航空数据处理的全链路摸底测试。多次飞行试验表明,采用多旋翼无人机低空飞行来代替汽车跑场同步测量,不仅提高了地表反射特性测量的空间一致性和代表性,还提高了地表反射率光谱的测量效率,也对宝贵的中国遥感卫星辐射校正场敦煌戈壁场区地表进行了有效保护,极大的节约了人力物力成本。通过传统跑场测量和航飞测量的地表反射率光谱数据对比分析,发现多次测量数据的均值一致性较好,并且航飞测量的数据标准差更小。利用TERRA MODIS的同步观测来对无人机测量数据开展辐射定标评估,结果表明航飞数据的相对偏差均在5%以内,可以代替跑场数据完成定标,精度满足要求。随着无人机性能的进一步优化和提高,在不久的将来必将得到更加广泛和深入的应用,在外场定标试验领域也将发挥更大更重要的作用。

高动态跳频信号时钟同步设计与实现

由于跳频信号各跳之间的符号速率和符号数量不一致,特别是低速跳只含少量符号,导致时钟误差提取困难。针对高动态下的跳频信号时钟同步难题,提出基于频偏估计的钟偏反馈调整方法。该方法通过同步序列进行频率估计和钟偏估计,并结合反馈方法调整钟偏和时钟跟踪,实现了高精度时钟同步。仿真结果表明:该方法适应飞行速度7.9 km/s、加速度0.2 km/s2的超高动态,定时同步性能优越,定时精度满足高速跳频信号解调要求,且解调损失小于0.1 dB。

基于最大似然估计的低轨通信星座分布式时间同步方法研究

随着低轨巨型星座的快速部署和卫星互联网的快速发展,由大规模低地球轨道卫星组成的分布式卫星系统是空天地一体化的重要特点。在卫星网络中,低成本、高精度的时间同步技术是其中的核心技术之一。针对低轨卫星高动态、拓扑结构时变特性因素影响下的低轨通信星座的分布式时间同步问题,考虑低轨卫星场景下的通信时延特性,同时为解决现有方法在动态网络拓扑下同步精度和收敛速度方面的不足,提出了一种基于最大似然估计的低轨卫星时间同步方法,能有效解决分布式动态网络中的通信时延随机不可预测以及星间距离不对称的问题。仿真结果表明,低轨卫星动态场景和拓扑结构变化下,本文提出的基于最大似然估计的时间同步方法同步误差均小于5ns。

GPS欺骗信号对变电站时间同步装置的干扰分析与测试

当前无人机诱骗设备发射的GPS欺骗信号对变电站自动化系统的安全问题尚未明晰。为此提出了一种全球定位系统(global positioning system,GPS)欺骗信号对变电站时间同步装置的干扰评测方法,理论分析了GPS欺骗信号对变电站时间同步装置的影响。测量了无人机诱骗设备在不同发射功率下的欺骗信号功率强度及电场强度空间分布,实验验证了GPS欺骗信号对时间同步装置接收卫星质量与授时精度的影响,分析了无人机诱骗设备的发射功率以及其与时间同步装置GPS/北斗卫星导航系统(Bei-Dou system BDS)接收天线间的距离对授时精度的影响规律。结果表明:时间同步装置天线距离无人机诱骗设备10 m以外,GPS诱骗信号不会使时间同步装置进入守时状态;时间同步装置天线距离无人机诱骗设备60 m以上,GPS诱骗信号对时间同步装置的影响可忽略不计,为变电站安全稳定运行提供了参考依据。

相对论体系下卫星原时及星间钟差机理建模

面向新一代导航卫星对高精度自主时间基准的需求,针对皮秒级星间钟差机理不清晰问题,在广义相对论体系下提出一种卫星原时以及星间皮秒钟差模型,该模型可基于卫星状态计算星载原子钟相对参考时钟的偏差以及星间钟差。首先从地心参考坐标系的度规张量出发,利用广义相对论建立了卫星的运动模型;然后,根据时空间隔的不变性,提出考虑地球非球形J2摄动项的卫星原时模型,并进一步给出了包含J2项修正的星间钟差模型。最后以北斗卫星导航系统和GPS为研究对象对建立的模型进行了仿真分析,为新一代导航系统的时间校准和同步提供了一种可行的建模方法。仿真结果表明,卫星原时模型与星间钟差模型的精度都在皮秒量级,能够准确地计算星载原子钟在引力场中的原时偏差以及星间钟差。

星链Ⅲ期回归共地面轨迹星座构型与覆盖分析

基于轨道同步进动特性分析了星链卫星系统Ⅰ期、Ⅱ期星座演化趋势,揭示了多Walker-δ子星座构型存在的问题,研究了星链Ⅲ期拟采用的回归共地面轨迹星座构型的实现机理,并对其覆盖特性进行了仿真分析。结果表明:不同倾角的回归共地面轨迹卫星链可以在轨道高度差异很小的情况下实现同步进动,相对于多Walker-δ子星座的构型具有构型更稳定、覆盖性能更优的明显优势,特别适合巨型低轨互联网卫星系统。该研究可为加速推进我国同类卫星系统建设提供借鉴。

基于信号同步注入的多源配网阻抗测量防孤岛保护方法

分布式电源(distributed generator,DG)并网运行需配备防孤岛保护,以避免电网停电产生非计划孤岛。阻抗测量法相比于过/欠压(over/under-voltage, OUV)和过/欠频(over/under-frequency,OUF)等被动式防孤岛保护,具有检测盲区小,不易误动等优势。但现有信号注入策略及孤岛保护判据无法应对多DG系统中信号干扰引起的保护失效问题。为此提出利用外部同步信号实现检测信号同步注入的阻抗测量方法。在分析孤岛前后DG测量阻抗特征的基础上,确定基于阻抗角的孤岛保护方案,并依据对线路参数,电网谐波及注入信号频率的分析,提出保护判据。最后,结合DG控制策略给出保护的信号注入及检测方法。基于RTDS的仿真验证表明,该文方法可有效辨识电网扰动及孤岛运行状态,并且避免了OUV、OUF的拒动及误动问题。

一种适用于北斗三号星间扩展用户的定轨算法

针对北斗卫星导航系统星间链路网络扩展服务航天器的精密轨道确定及时间同步需求,提出了基于多项式轨道拟合方法的轨道确定与时间同步算法,克服了传统算法中使用北斗星间链路双向测量数据必须具备初始轨道和钟差等先验信息的约束,可有效拓宽北斗星间链路使用场景。该算法以多项式表达航天器一段时间的轨道和钟差,并使用星间双向测量数据基于最小二乘算法迭代估计多项式系数,从而完成航天器轨道和钟差解算。利用北斗三号星间链路在轨实测数据的试验表明定轨和时间同步精度均在0.12 m以内,有效验证了该算法的正确性。