全球巨型低轨星座通信网络发展、特征与思考

正低轨宽带通信卫星星座的大容量、高速率、全球覆盖特点,要求其星座规模相比低轨移动通信卫星星座的卫星数量呈数量级增长,卫星星座巨型化特征显著。而近年来,以巨型低轨道通信卫星星座为基础的空间宽带通信网络发展进入新的高潮。本文从国际主流巨型低轨星座通信网络的发展入手,阐述了巨型空间互联网系统发展的特征及系统建设面临的挑战,并就我国同类系统未来的方向进行思考。     

星下点轨迹恒定的低轨星座构型设计方法

为探寻适用于低轨巨型星座的构型设计方法,提供了一种所有卫星共星下点轨迹,且该轨迹固定不变的低轨恒定轨迹星座构型解析设计方法。该构型用回归因子、卫星总数两个参数进行编码。首先,利用平均轨道根数思想,建立了地球非球形摄动带谐项阶数为J₄条件下的回归轨道设计解析模型。其次,根据卫星与地球相对运动规律,确立了满足共星下点轨迹条件的解析式。最后,结合回归轨道设计与共星下点轨迹设计思想,建立低轨恒定轨迹星座构型设计模型。最终仿真结果表明,该构型设计方法符合所有卫星共星下点轨迹、且轨迹固定不变的设计预期,验证了本构型设计方法的有效性。本星座构型具有形式简易、构型易维持、覆盖范围广的特点,确保了空间系统与地面系统的方位一致性,极大程度降低了星地系统协同的复杂度。     

低轨Walker星座构型偏置维持控制方法分析

针对低轨（low earth orbit,LEO）Walker星座构型稳定性维持问题，分析了低轨卫星的轨道摄动和星座构型稳定性的影响因素。通过分析低轨Walker星座的轨道摄动和相对漂移特点，提出了两次偏置策略。首先，依据未偏置时星座相对漂移量拟合得出第一次偏置时的偏置量。然后利用第一次偏置后的相对漂移量拟合得出第二次偏置量，消除残余项影响。两次偏置量叠加，使相对漂移大大降低。结果表明，低轨Walker星座中各卫星的初始参数偏差造成了升交点赤经和沿迹角相对漂移的发散，两次偏置策略可将两种星座的相对漂移量降至0.1°以下，证明了策略的有效性，提高了星座构型稳定性。     

基于GDE 3算法的红外低轨星座设计

针对红外低轨系统,综合考虑定位精度、空间覆盖以及星座成本等因素,提出了红外低轨星座的设计准则,并定义星座性能的度量指标.然后,引入GDE 3算法用于红外低轨星座设计,该方法基于Pareto最优概念,能够得到多个最优解,适于多目标优化设计.通过星座建模和目标函数设计,进行了仿真实验.最后验证了设计得到的星座在多项性能指标上均优于已有文献中的星座.     

基于QoS保障的低轨卫星星座设计

低轨卫星星座设计是部署低轨卫星网络的前提和关键。然而，不均匀的地面用户分布和不合理的卫星资源配置对卫星网络的服务质量提出了重大挑战。针对以上问题，通过构建服务质量(QoS)指标体系，提出了一种基于QoS保障的低轨卫星星座设计方法。首先，建立了低轨卫星网络模型和星座覆盖模型，通过星间链路的建链准则来定义星座抗毁性指标。其次，通过建立用户链路以及定义用户匹配度来分析星座对目标区域用户的资源匹配情况。接着，建立了以QoS指标为约束最大化效费比的低轨卫星星座设计优化问题，定义的QoS指标包括信噪比、误码率、抗毁性以及星座覆盖率和用户匹配度。此外，通过遗传禁忌智能算法求得了所设计的低轨卫星星座的轨道参数。仿真结果表明，提出的低轨卫星星座设计方案在满足指定QoS约束的同时具有最大星座效费比。     

面向低轨巨型星座的载荷托管技术发展趋势及展望

<正>低轨巨型卫星星座具有全球网络覆盖、通信低时延等优势，被视为改变卫星行业发展的重要技术。随着该技术的不断发展和普及，载荷托管技术以为各种应用提供高速、大容量和低延迟的通信服务脱颖而出，为各个行业提供了新的技术选择。本文首先对天基载荷托管技术的发展现状进行阐述，并分析了面向低轨巨型星座的载荷托管发展挑战，从3个设计角度对面向低轨巨型星座的载荷托管技术方向进行了分析，最后，对该技术发展趋势及研究现状进行了总结展望。     

低轨大规模卫星星座内部防碰撞安全性分析

针对低轨大规模星座卫星间碰撞安全问题，对星座构型的最大漂移量开展了研究。基于球面三角形理论计算了卫星轨道平面的最小相位差；采用控制变量法对星座构型参数进行研究，分析不同构型参数对星座卫星最小相位差的影响，以及升交点赤经漂移量与最小相位差的关系，提出了基于最小相位差的星座构型参数协同设计方法；基于相对相位分析方法，建立升交点赤经漂移量与相位漂移量随时间变化的函数关系；最后，以Starlink第一期星座为参考对象进行仿真，验证了构型参数协同设计方法的合理性。     

星间链路联合磁测约束的低轨星座自主导航

为解决星座仅依靠星间链路测量进行自主导航时的整体旋转和漂移问题,提出一种星间链路联合磁测约束的低轨星座自主导航方法.通过星间观测相机和磁强计,获得同轨道相邻卫星视线矢量与地磁场方向之间的角距和地磁场模值,为低轨星座引入空间基准信息.在非秩亏性分析的基础上,分别建立状态方程和量测方程,利用扩展卡尔曼滤波方法进行整星座的最优状态估计.仿真结果表明,星座卫星自主导航位置精度优于20m,速度精度优于0.05m·s-1,自主导航运行时间维持180天,能够满足低轨卫星星座自主导航的应用需求.      

红外低轨星座突发任务多重策略调度方法

面向红外低轨星座的突发任务规划与资源调度问题，结合红外低轨星座的空间与时间分布特性，提出一种基于多重策略的红外低轨星座任务应急调度方法。所提方法结合红外低轨星座的设计特点，从星座全球分布的均匀性、结构的对称性及星座内卫星运动的周期性分析作为输入，提出一种以地理分区为长期值守分组策略与事件触发下基于相对运动分析的动态快速分组策略相结合的多重策略。在所提策略指导下完成任务分组，开展工作窗口调度。经仿真分析可得:所提策略可有效应对不同区域的目标触发，并实时完成分组及工作窗口规划调度，较好解决了任务突发情况下的系统响应，由于采用优先分组的策略，降低了全局优化的复杂度，具有创新性，且具备较好的应用价值。      

基于TLE的Starlink星座第一阶段部署情况分析

近年来,随着卫星技术的快速发展和低轨（low earth orbit,LEO）卫星宽带互联网建设需求的不断增加,低轨大规模星座发展日新月异。针对Starlink星座初始化部署问题,首先论述了“星链”（Starlink）星座现状,分析在轨卫星高度变化。然后利用公开的两行轨道根数（two-line element,TLE）,从卫星发射入轨、轨道面分布两个方面,简要分析了Starlink星座的部署情况,给出升交点的变化规律;同时仿真分析了Starlink星座对地面的覆盖性能。最后,给出星座轨道面和相位分布、故障卫星处置以及可见卫星数量。所分析的结果以期为中国未来部署大规模LEO星座的建设提供借鉴。     

Low Earth orbit constellation design using a multi-objective genetic algorithm for GNSS reflectometry missions

Spaceborne global navigation satellite system reflectometry (GNSS-R) is an innovative bistatic radar remote sensing technique utilizing low Earth orbit (LEO) based GNSS-R instruments to acquire GNSS L-band opportunistic signals for measuring geophysical parameters. A GNSS-R LEO constellation with an optimization design for its specialized missions is very significant and necessary. However, the constellation design involves multi-parameter and multi-objective optimization, and the classical analytic solution is not capable of such a complicated issue. This study proposes a multi-objective LEO constellation design method with a genetic algorithm (GA) and presents a framework for designing two GNSS-R LEO constellations, termed “lower-latitude constellation” for typhoons and hurricanes observation in the tropics and “global constellation” for global geophysical parameter measurements. Then, the observation capability of both designed constellations is evaluated in terms of the number of reflection points, spatial coverage density, and revisit time to verify the GA efficiency in LEO constellation design. Results show that the two designed LEO constellations with high fitness function values possess optimal orbit parameter set configuration and outperform the existing CyGNSS constellations in observation performance. Compared with CyGNSS, the number of reflection points observed by the lower-latitude constellation and the global constellation increases by 38% and 45%, as well as the spatial coverage density increases by 28% and 36%. The revisit time for the lower-latitude constellation is reduced by 0.29 h, whereas the revisit time for the global constellation increases by one hour.     

Assessing and minimizing collisions in satellite mega-constellations

We aim to provide satellite operators and researchers with an efficient means for evaluating and mitigating collision risk during the design process of mega-constellations. We first introduce a novel algorithm for conjunction prediction that relies on large-scale numerical simulations and uses a sequence of filters to greatly reduce its computational expense. We then use this brute-force algorithm to establish baselines of endogenous (intra-constellation), or self-induced, conjunction events for the FCC-reported designs of the OneWeb LEO and SpaceX Starlink mega-constellations. We demonstrate how these deterministic results can be used to validate more computationally efficient, stochastic techniques for close-encounter prediction by adopting a new probabilistic approach from Solar-System dynamics as a simple test case. Finally, we show how our methodology can be applied during the design phase of large constellations by investigating Minimum Space Occupancy (MiSO) orbits, a generalization of classical frozen orbits that holistically account for the perturbed-Keplerian dynamics of the Earth-satellite-Moon-Sun system. The results indicate that the adoption of MiSO orbital configurations of the proposed mega-constellations can significantly reduce the risk of endogenous collisions with nearly indistinguishable adjustments to the nominal orbital elements of the constellation satellites.     

大规模卫星星群域管控策略设计

针对大规模卫星星群单节点管控带来的系统通联性差、地面资源依赖度高等问题,提出了分层管理、域内自治、动态维护的卫星星群分布式域管控策略。首先,设计了衡量卫星节点管控能力的静态指数及动态指数,并提出了多因素加权的星群簇首选择方法。其次,提出了通过逐层择优的方式进行域结构初始化的算法流程。最后,根据星群变化情形,提出了基于事件触发的动态时间片域管控方法,保证了大规模星群在全任务周期内能维持相对稳定的管控构型。仿真结果表明,所提出的域管控策略能够有效完成对目标星群的簇首选择、域初始化及动态维护过程,并保持域结构的稳定。实现了目标星群在空间中的域结构划分管理,使地面直接参与管理的卫星节点数目降至原管理模式的14%,有效解决了星群管控严重依赖地面资源的相关问题。     

Towards the automated operations of large distributed satellite systems. Part 2: Classifications and tools

Recent developments have seen a trend towards larger constellations of spacecraft, with some proposals featuring constellations of more than 10.000 satellites. While similar concepts for large constellations already existed in the past, traditional satellite deployments hardly ever feature groups of more than 100 satellites. This trend towards considerably larger satellite numbers originates from non-traditional design and operations of spacecraft by non-traditional space companies. The evolution in the space sector, precipitated by new players, is often referred to as “Space 4.0” or “New Space”. It necessitates a rethinking of the way satellites and satellite constellations are planned, designed, and operated. New operational paradigms are needed to enable automatic, optimal task definition, and scheduling in a holistic approach.This is the second of two companion papers that investigate the operations of distributed satellite systems. This second article investigates the classification of distributed satellite systems and evaluates commercial tools for automated spacecraft operations, whereas the first article performed a survey of conventional and “new space”operations of spacecraft constellations.Classification metrics for constellations are derived and evaluated with respect to their informative value concerning the operation, the automation, and the scalability of the constellation. The proposed classification system is applied to the Dove and RapidEye constellation and allows for a comparison between the presented automation approaches. Commercial tools for automated spacecraft operations are evaluated for several mission task elements, such as orbit control, orbit maintenance, and collision avoidance. Subsequently, the trends, benefits, and standardization needs for operational automation are identified.     

Assessment of the close approach frequency and collision probability for satellites in different configurations of large constellations

The Earth orbital environment is drastically changing due to an intensification of the space activities. In particular, several projects of large constellations, proposed for the next years for communications purpose like global internet access, Internet of Things, or for Earth observations, will lead to the deployment of several thousands of new satellites at an unprecedented rate. It is a crucial challenge for space traffic management, which will deal with a great number of satellite conjunctions, potentially causing a collision with damaging consequences for the constellation itself and the space environment sustainability.In this paper, we investigate the close approach frequency and the cumulative collision probability for each referenced constellation. For this purpose, we compute the orbital evolution of satellites in different constellations during the lifecycle, from the deployment to the decommissioning, and we apply the CUBE algorithm and the Foster method to assess the collision probability with the background space debris population assuming a constant uncertainty in position. We show the variation of risk defined by the close approach frequency and the cumulative collision probability as a function of the proposed configuration. In particular, satellites of the Iridium and Kuiper constellation, but also satellite of the Telesat constellation on polar orbits are the most exposed at a collision. Moreover, the decommissioning phase contribute for a major part to the final cumulative collision probability.     

Iridium/ORBCOMM机会信号融合定位技术

在全球导航卫星系统(GNSS)不可用情况下，低地球轨道(LEO)卫星机会信号(SOP)定位技术是一种有效的导航定位解决方案。单LEO星座机会信号定位技术面临星座构型不足或可见卫星偏少等问题，多LEO星座机会信号融合定位技术可有效解决该问题。通过分析瞬时多普勒定位原理，建立了Iridium/ORBCOMM机会信号融合定位模型，引入基于Helmert方差估计的加权最小二乘算法进一步提高定位精度。实测数据表明:基于Helmert方差估计的Iridium/ORBCOMM机会信号融合定位精度优于70 m，验证了多LEO星座机会信号融合定位的可行性和有效性。