导航星座自主导航的时间同步技术

导航星座自主导航能够有效地减少地面测控站的布设数量,减少地面站至卫星的信息注入次数,降低系统维持费用,实时监测导航信息的完好性,增强系统的生存能力。卫星时间同步是实现导航星座自主导航的关键技术之一,而星载原子时钟的频率稳定性能直接影响着卫星时间同步精度。本文基于星载原子时钟频率稳定性的Allan方差表达,建立系统状态方程,并以星间双向测量伪距差作为基本观测量,组成系统测量方程。从而,可以设计适用于导航星座卫星时间同步的Kalman滤波算法。系统仿真结果表明:通过滤波处理星间双向测距数据,不断地更新卫星时钟参数,能够实现星座卫星自主高精度时间同步。     

基于STK的GPS卫星可见性仿真分析

GPS卫星在现代信息化战争中的作用日趋重要。针对GPS的观测应用需求,以目前在轨的31颗GPS卫星为研究对象,分析GPS卫星轨道的特征,研究GPS卫星对地面系统的可见性。结合STK和Matlab软件进行仿真分析,为地面GPS观测系统的天线波束宽度、波束个数设计提供参考。     

长期在轨运行卫星的轨道维持技术

本文研究近地轨道卫星长期在轨运行的轨道维持问题。轨道维持的任务是将卫星的星下点轨迹保持在设计的参考轨迹附近。近地轨道卫星所受的摄动力包括地球引力摄动、日月摄动、大气阻力摄动和光压摄动等,而影响卫星轨道星下点漂移的主要因素是大气阻力摄动。本文给出了一种新的卫星轨道维持策略,数学仿真表明了其有效性。     

基于TMS320C6701的程序冗余加载设计方法

为满足航天产品高可靠性、高安全性的要求,用户对软件存储和加载方式也提出了更多的需求,如程序三区冗余备份、在轨重构等。TMS320C6701是一款高精度浮点数字信号处理芯片,其运算速度快、实时性高,近年来广泛应用于电机控制、轨道运算等宇航软件产品中。TMS320C6701内部程序区和数据区独立,设计师需要编写二次引导程序实现代码和数据的先后加载。根据TMS320C6701的加载特性,将二次引导与重构功能结合,设计了一个引导系统。引导系统对应用软件进行三取二判决,将判决结果加载至RAM中运行,并通过总线实现应用软件的更新。实验证明,该系统可以通过总线通信对应用软件重构升级,大大提高了软件的可靠性和可维护性,且缩短了单机研制周期和维护成本。     

卫星星座整网轨道确定分析与仿真

编队飞行的卫星或卫星星座对轨道确定自主性和精度提出了较高要求。针对这个问题,通过建立星座的轨道动力学模型和星间观测的测量模型,将星座中的星间观测数据和地面观测数据融合起来,将待估的卫星轨道参数和部分动力学参数进行适当的分类,研究卫星星座整网轨道确定的新方法,并在理论上分析了整网定轨方法能提高定轨精度的原因;最后采用自主开发的卫星星座整网轨道确定软件进行了仿真计算。计算表明,该方法能有效地减少对地面站的依赖,并较大幅度提高定轨时卫星绝对位置和相对位置精度。
     

Design of meo constellations for galileo: towards a “design to cost” approach

GALILEO aims at involving Europe in a new generation of satellite navigation services. In the context of the phase A of this programme, many system options are still widely open: detailed requirements, constraints and hypotheses are not yet fully stabilised.In order to design a satellite constellation satisfying civil aviation and other users needs in this early stage of the system definition, it is necessary not only to take into account classical performance aspects, such as accuracy and availability of accuracy, but also cost constraints. The paper describes the design and dimensioning method which has led ALCATEL to propose a set of MEO constellations in the frame of the GALILEO project for ESA. It especially places emphasis upon the sensitivity of the system design to numerous parameters as well as its sensitivity to performance requirements.Potential candidate constellations obviously need to meet given performance specifications which are determined by operational aspects such as: satellite reliability, maintenance strategy (spare in orbit, launch on schedule, launch on need), deployment strategy (launcher choice, etc.). The estimated cost of a potential solution is mainly derived from the number of satellites and the deployment/maintenance strategy, but it is representative of the whole life-cycle of the constellation. Furthermore, the exhibited solution shall be “as robust as” possible to requirement or assumption changes. So, it should be a baseline solution that could be easily updated in order to take into account small upgrades.This has led to the performance of some trend analyses to understand the actual influence of some constraints or requirements on the system design, and to see how initial requirements can be efficiently relaxed in order to obtain the maximum system cost diminution for a minimum constraint relaxation. This will be very useful, if cost reduction is necessary, to quickly propose alternative or sub-solutions to the baseline one.     

带有控制增益自校正的甚低轨道卫星自主轨道维持方法

为实现甚低轨道的长期稳定运行,分析了甚低轨道的摄动特性,设计了一种带有轨控增益校正的自主轨道维持方法。该方法可通过前一次轨控的结果对轨控增益进行校正,提高轨控算法对卫星质量、推力大小等不确定因素的鲁棒性,逐渐提高轨道控制的精度。对轨道控制的频率、每次轨控的时间长度及对偏心率的影响进行了分析,仿真结果表明:自主轨道维持方法能实现甚低轨道高度维持控制,在参数不确定的情况下,与传统算法相比可大幅提高轨道控制的精度,确保平均偏心率矢量收敛,满足甚低轨道卫星的长寿命要求。所设计的算法结构简单,运算量小,可由目前的星载计算机实现。     

单站多普勒跟踪定轨的优化算法

由于低轨道小卫星应用的日益广泛，在轨卫星数目的迅速膨胀，对传统的多个地面站相互协调管理卫星领域模式提出了挑战。小卫星的低成本特性必然要求存在与之相应的地面站设施降低复杂性、降低成本。本文针对当前已提出的单站多普勒定轨方案，进一步研究了多普勒定轨的有关方法，提出和建立了多普勒定轨的优化算法与模型，最后进行了仿真分析与模型的有效性验证。     

Comparative economics of very high capacity communications satellites

Technology advances expected by the late 1980 or early 1990 time period will allow the construction of powerful and complex communications satellites with large multibeam antennas and very many transponders, and their operation and maintenance in geostationary orbit. The high sensitivity and effective radiated power of such satellites will enable the Earth stations using them to shrink dramatically in size and cost, thus becoming readily available to very large numbers of users as well as making possible new kinds and levels of communications services simply not possible with smaller satellites. This paper briefly describes three such new designs, concerning electronic mail transmission, educational TV distribution, and mass personal communications; it compares the users' service costs with those of terrestrial networks designed for the same performance.     

Reconfigurable dual feed antenna for direct broadcast satellites

Direct Broadcast Satellites covering large countries such as Canada, require more than one spacecraft, located at different orbital positions, as well as the use of multiple shaped beams. This would minimize eclipse requirements over several time zones, provide increased capacity by frequency reuse and permit the use of cost effective ground receivers.Two such satellites are envisaged, one covering Eastern Canada, the other Western Canada, using two different sets of three highly shaped beams. This paper is the result of a feasibility study of a satellite antenna designed such that while at either orbital location it can be reconfigured in orbit, by ground command and hence can save the cost of one additional spare spacecraft.An offset parabolic reflector is proposed for the 12 GHz downlink, with a switched “dual feed” structure, consisting of two separate but contiguous sets of pyramidal horns and their associated beam forming networks (BFN). Only one BFN set is used at any one orbital location. Detailed radiation patterns demonstrate good beamshaping capabilities, with coverage efficiencies of the order of 94%. Other considerations such as the effect of orbital locations, gain equalization and TWTA standardization are discussed.It is concluded that a satellite, reconfigurable in orbit with a “dual feed” antenna, is feasible and cost effective, for a DBS spare as well as for the main spacecraft.     

Rapid model-based inter-disciplinary design of a CubeSat mission

With an increase in the use of small, modular, resource-limited satellites for Earth orbiting applications, the benefit to be had from a model-based architecture that rapidly searches the mission trade-space and identifies near-optimal designs is greater than ever. This work presents an architecture that identifies trends between conflicting objectives (e.g. lifecycle cost and performance) and decision variables (e.g. orbit altitude and inclination) such that informed assessment can be made as to which design/s to take on for further analysis. The models within the architecture exploit analytic methods where possible, in order avoid computationally expensive numerical propagation, and achieve rapid convergence. Two mission cases are studied; the first is an Earth observation satellite and presents a trade-off between ground sample distance and revisit time over a ground target, given altitude as the decision variable. The second is a satellite with a generic scientific payload and shows a more involved trade-off, between data return to a ground station and cost of the mission, given variations in the orbit altitude, inclination and ground station latitude. Results of each case are presented graphically and it is clear that non-intuitive results are captured that would typically be missed using traditional, point-design methods, where only discrete scenarios are examined.     

一种提高导航卫星星座自主定轨精度的方法研究

针对近地导航卫星仅利用星间测距进行自主定轨时,因无法消除星座整体旋转误差而导致长期自主定轨精度不高的问题,提出了利用拉格朗日导航卫星星座与近地导航卫星星座联合仅利用星间测距进行自主定轨的方法。建立了拉格朗日轨道导航卫星星座和近地导航卫星星座联合仅利用星间测距进行自主定轨的动力学模型和观测模型。利用扩展Kalman滤波（EKF）算法和星间测距信息实现了拉格朗日轨道导航星座与近地导航星座的长期自主定轨。以4颗拉格朗日卫星组成的导航星座与12颗GPS卫星组成的近地导航星座作为仿真对象进行了仿真分析,仿真结果表明本文仅利用星间测距的联合自主定轨方法可以有效提高导航卫星星座的长期自主定轨精度。
     

一种新型卫星携气瓶推力器喷气时长计算方法

卫星自主编队保持通常采用开环控制模式,需要星载计算机(AOCC)根据推进系统的工作状态实时计算喷气时长。由于AOCC计算能力有限,在携气瓶推力器仿真测试过程中采用的速度增量关机方式不适用于在轨喷气时长的计算。为减小AOCC运算量,提高控制精度,开展了携气瓶推力器的动力学建模仿真,进行了寿命期间的性能分析。针对该时变推力模型,设计了AOCC喷气时长计算方法。通过推力的状态传递和推力预测,构造了以喷气时长为变量的代数方程,并将该方法应用到一组多次喷气情况下的喷气时长计算。仿真结果显示:与以往基于单点测量的推力器喷气时长的计算方法相比,采用该方法计算的喷气时长更接近理论值,能够有效提高卫星自主编队保持的控制精度。     

高低轨双星时频差无源定位精度

高低轨卫星联合定位是提高地面辐射源无源定位精度的有效方法。从时差基线、速度差增加方面分析了高低轨双星定位精度相对同轨卫星定位精度高的原因,推导出高低轨双星时频差定位误差分布表达式,分析了高低轨联合定位适用的时频差测量方法及其测量精度。仿真分析结果表明:在低轨卫星星下点附近较大范围内,定位精度达到百米量级。验证了双星相对位置变化、时频差测量误差、高低轨卫星自身位置速度测量误差等因素对高低轨双星定位精度的影响。     

基于地面图像的卫星自主定轨方法可观测性及定轨性能分析

卫星自主定轨是航天发展趋势之一。近年来,高分辨率遥感卫星不断发展,为利用光学遥感图像进行自主定轨提供了可能。在此背景下,提出了一种基于地面特征点图像的自主定轨方法。通过构造局部可观测矩阵分析了该定轨系统的可观测性,并用局部可观测矩阵的条件数表征可观测度,估计系统的定轨性能。通过Monte-Carlo仿真实验评估了系统的定轨表现,结果表明:该定轨方法与多点定位方法相比可以得到更高的定轨精度。     

北斗系统地固系自主定轨算法

为避免传统惯性系自主定轨算法中的多次坐标转换,针对地固系分布式自主定轨算法原理及其中的关键技术开展研究。给出在地固系中进行自主星历生成的总体框图,推导了地固系自主定轨算法的基本方程,提出一种新的以地固系位置速度为状态量的状态转移矩阵解析计算方法并分析其计算量,证明了地固系自主定轨算法可以进一步降低定轨算法复杂度,且无需上注地球定向参数进行坐标转换。使用仿真数据和真实在轨测量数据的测试结果表明,提出的地固系分布式自主定轨算法与传统算法定轨精度相当,说明了所提算法的可行性,验证了星载自主定轨原型软件的有效性。     

一种基于时间调制的弹性化SAR卫星系统

星载合成孔径雷达(SAR)系统能全天时、全天候观测,在地震、洪涝、台风等自然灾害监测中具有重要作用。双基、多基SAR卫星更具有极高的经济、科学、安全价值。然而,目前在轨的大型星载SAR卫星造价昂贵,且双基SAR卫星需数颗同等规模的卫星。双基SAR卫星系统存在星间同步链路,因此卫星可扩展性不强。提出了一种基于时间调制的低成本弹性化Ka波段调频连续波(FMCW)SAR小卫星星座系统。该系统基于一组独立、模块化的发射卫星和接收卫星。采用Ka FMCW SAR体制和时间调制天线(TMA)技术,可减轻接收星2/3以上的质量。该系统采用自主任务规划技术,具备多样化的工作模式,为单发多收、多发多收等应用需求提供了一种弹性化的解决方案。     

一种同轨区域集中的北斗卫星自主导航算法

基于北斗三号卫星配置规划,提出了一种同轨区域集中的北斗卫星自主导航算法。利用Ka星间链路指向切换灵活特性与激光链路高速通信特性,并克服激光终端异轨面通信困难,指向切换不便等缺陷,算法设计将轨道面内各卫星采集的Ka双向测距信息利用激光星间链路传入轨道面主卫星中,从而将测距信息集中处理并完成轨道面内各卫星的轨道信息更新。并且,本文还搭建了星内模拟仿真环境,对算法精度及性能进行验证。仿真结果表明,同轨道区域集中自主导航算法可在星内仿真环境中稳定运行,且其导航精度远优于分布式自主导航精度。     

Tracking and data relay satellite system: NASA's new spacecraft data acquisition system

The growth in NASA's ground network complexity and cost triggered a search for an alternative. Through a lease service contract, Western Union will provide to NASA 10 years of space communications services with a Tracking and Data Relay Satellite System (TDRSS). A constellation of four operating satellites in geostationary orbit and a single ground terminal will provide complete tracking, telemetry and command service for all of NASA's Earth orbital satellites below an altitude of 12,000 km. The system is shared: two satellites will be dedicated to NASA service; a third will provide backup as a shared spare; the fourth satellite will be dedicated to Western Union's Advanced Westar commercial service. Western Union will operate the ground terminal and provide operational satellite control. NASA's Network Control Center will provide the focal point for scheduling user services and controlling the interface between TDRSS and the rest of the NASA communications network, project control centers and data processing facilities. TDRSS single access user spacecraft data systems should be designed for efficient time shared data relay support. Reimbursement policy and rate structure for non-NASA users are currently being developed.     

MEO卫星氢镍蓄电池组自主充电管理方法

MEO卫星运行轨道存在不可测控弧段,每年有长光照期和两个地影季,为此对星上充电管理的自主能力提出了较高要求。文章介绍了我国首颗在轨飞行的MEO卫星的氢镍蓄电池组的在轨自主管理方法,包括地影季的电压-温度（V-T）控制与电量计结合的充电管理方法和长光照期控制电池压力的涓流管理方法,并给出了在轨飞行的实际效果,可作为后续卫...