分布式单星转发的定位测速模型及其应用

在城市峡谷中通过接收导航卫星信号以实现连续的定位与测速一直是卫星导航应用中的一个难题。针对此问题,借鉴卫星导航对抗中转发式欺骗干扰的定位控制基本原理,提出了通过分布式单星转发来解决城市峡谷中实现连续卫星导航的新方法,并构建了分布式单星转发的定位测速模型。在此基础上详细讨论了转发器天线对被遮挡卫星的指向跟踪、转发器相关参数的获取、转发器收发之间的有效隔离、直达信号与转发信号的同时利用等应用性问题。所提出方法的可行性得到了仿真试验的有效验证,从而为城市峡谷中的卫星导航应用提供了新的参考。     

Communication Subsystem Design Trends for the Defense Satellite Communications Program

The Initial Defense Communication Satellite Program (IDCSP) hasbeen implemented successfully and is handling unique and vital militaryary communications. Tradeoff studies now being made are intended todefine the characteristics of the next phases of the Defense Satellite Communications Program (DSCP). This paper discusses briefly thecommunication subsystem design of the IDCSP for backgroundfor-information, and then discusses the design trends for future phases of the DSCP.The communication subsystem for the IDCSP is characterized bya single hard-limiting, low-power repeater with a toroidal patternantenna. Future trends in design will be toward multiple beams andmultiple repeaters with very wide bandwidths, high-powerquasilinear operation, and highly directive antennas. Several alternatetransponder configurations are evaluated in this paper, and an illustrativeive example is shown. Although long life is essential to future systems,as it was to the IDCSP, the trend will be to adding more complexity inthe satellite to increase the system capacity, while at the same timerequiring less complexity in earth terminals.     

INMARSAT integrity channels for global navigation satellite systems

The transmission of integrity information using a signal format compatible with the Global Positioning System (GPS) and relayed through a geostationary satellite repeater, which will be critical in achieving high integrity and availability of global navigation by satellite is discussed. The inclusion of navigation repeaters designed to fulfil this function, the next generation of INMARSAT spacecraft, INMARSAT-3 is examined. The global navigation satellite system (GNSS) integrity channel (GIC) will employ pseudorandom codes in the same family as, but distinct from, the codes reserved by GPS. The data format of the basic integrity channel is designed to convey user range error information for 24 to 40 satellites. A closed-loop timing compensation technique will be used at the uplinking Earth station, to make the signal's clock and carrier Doppler variations identical to those that would result from an onboard signal source. Therefore, the INMARSAT-3 satellites will increase the number of useful navigation satellites available to any user, and can also function as sources of precise timing. There is also a possibility that wide area differential corrections can be carried on the same signal     

Packet Radio Monitoring Via Repeater-On-Packets

The packet radio network (PRNET) is a store-and-forward packet switching system consisting of switching nodes which share a single radio communication channel. Recent studies have shown that PRNETs can easily be saturated and become unstable unless efficient routing and flow control algorithms are used. To enable point-to-point packet transportation, network stations assign a code (label) to each repeater; the process of assigning such labels is referred to as "network initialization." The initialization procedure assumes that the network topology is now known a priori and is changing with time. Thus the initialization procedure involves mapping of network topology, determining network structure (labels for repeaters), and transmitting labels to the repeaters. Although many authors have developed analytical models to study channel access schemes, no one has yet addressed the initialization issue. We present a Markov chain model which enables one to obtain in close form the optimal rates at which repeaters and station must transmit repeater-on-packets (ROPs) and label packets (LLPs) to minimize the network initialization time in a one-hop network, finite buffer station. Our most important result is that the network initialization time is relatively insensitive to the station transmission rate, but the repeater transmission rate must be carefully chosen to achieve rapid initialization.     

A Kilowatt Rotary Power Transformer

Many future satellite configurations will require the transfer of signals and power across rotating interfaces. Satellite systems are particularly cost effective for both commercial and military communications applications if their useful lifetime can be demonstrated to be greater than five years. The rotary transformer has the desireable characteristics of high reliability and low noise which qualify it as a potential replacement for slip rings. This paper describes the development of a rotary transformer for typical spacecraft applications. The transformer is built in modular sections, each capable of transferring 500 watts across a gap at efficiencies greater than 88 percent, dc to dc. The design effort included a study of pertinent electrical characteristics required for typical spacecraft configurations, electrical design and analyses of the overall dc-dc converter, mechanical design of the transformer cores and their assembly, and a study of transformer core and winding characteristics. Breadboard test results have demonstrated the desired level of efficiency, satisfactory operation over temperature, and satisfactory electrical characteristics.     

Cross-Correlation Interference Effects in Multiaccess Optical Communications

The effects of the cross correlation between user codes in an opticalcode-division multiple-access communication system are investigated. The system model is a multiaccess satellite repeater in which the uplink and downlink channels are direct-detection, optical-polarization modulation links. The error probability is derived in terms of the cross correlation between the intended and interfering user codes. It is shown that the system error rate can be minimized by using code sequences in which the normalized second moment of the cross correlation between codes is small. The signalto- noise ratio (SNR) on the uplink is shown to be proportional to 1/K while the SNR on the downlink is proportional to 1/K1/2, where K is the number of users which are simultaneously accessing the system.     

Low-cost TDRSS communications for NASA's long duration balloonproject

A transponder and RF ground support equipment that are making tracking and data relay satellite system (TDRSS) communications available to lower budget NASA projects are discussed. The Goddard Space Flight Center (GSFC)/Wallops Flight Facility's long duration balloon project (LDBP) will be the first to take advantage of this TDRSS user hardware for communications through the TDRSS S-band multiple access system during their around-the-world scientific balloon flight campaigns. The transponder is one tenth the cost of the current generation space-qualified transponder, and the TDRSS user RF test set (TURFTS) is less than one half the cost of the currently available transponder test equipment     

A data transmission scheduling algorithm for rapid-response earth-observing operations

With the development of rapid-response Earth-observing techniques, the demand for reducing a requirements-tasking-effects cycle from 1 day to hours grows rapidly. For instance, a satellite user always wants to receive requested data in near real-time to support their urgent mis- sions, such as dealing with wildfires, volcanoes, flooding events, etc. In this paper, we try to reduce data transmission time for achieving this goal. The new feature of a responsive satellite is that users can receive signals from it directly. Therefore, the traditional satellite control and operational tech- niques need to be improved to accommodate these changes in user needs and technical upgrading. With that in mind, a data transmission topological model is constructed. Based on this model, we can deal with the satellite data transmission problem as a multi-constraint and multi-objective path- scheduling problem. However, there are many optional data transmission paths for each target based on this model, and the shortest path is preferred. In addition, satellites represent scarce resources that must be carefully scheduled in order to satisfy as many consumer requests as possible. To efficiently balance response time and resource utilization, a K-shortest path genetic algorithm is proposed for solving the data transmission problem. Simulations and analysis show the feasibility and the adaptability of the proposed approach.     

下一代数据中继卫星系统发展思考

通过系统阐述中继卫星系统的发展过程,给出了主要国家和组织的中继卫星系统技术体制和现状.再结合卫星、载人航天器和深空探索的未来发展趋势,分析了下一代中继卫星系统的发展需求.在此基础上,从体系结构、卫星平台、链路调制体制、网络协议等方面,探讨并给出了下一代中继卫星系统的发展趋势和技术途径.为满足未来近地、深空航天任务,以及临近、低空快速移动用户的不同要求,节约系统成本,下一代中继卫星系统将向专业化和与其他系统融合的方向发展:星间链路将增加激光链路,数据速率可达到10 Gbit/s以上;多址业务成为主用,同时支持用户数能力将极大提高;对于链路调制体制,在采用CR(Cognitive Radio,认知无线电)和SDR(Software Defined Radio,软件定义无线电)技术的基础上,可实现实时自适应调整和根据需求加载配置;数据传输将采用网络化方式,天地间构成一体化DTN(Delay Tolerant Network,容延迟网络).     

北斗空间信号误差统计特征及描述方法研究

通过对比北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)广播星历与事后精密星历,提取了轨道和卫星时钟误差。基于北斗轨道误差及北斗卫星时钟误差统计特征分析,构建区别于全球定位系统(Global Positioning System,GPS)的BDS空间信号用户测距误差(Signal-In-Space User Range Error,SISRE)描述方法,对BDS广播星历中用户测距精度(User Range Accuracy,URA)进行了验证。6个月的北斗数据测试结果表明,北斗GEO、IGSO和MEO卫星的URA分别为3.0m、1.9m和1.6m。     

Space power systems requirements and issues: the next decade

Some of the more important space power technology issues, requirements, and challenges of the 1990s are described, and the impact of new component technology on the overall performance of space power systems is assessed. Advanced component, subsystem and system technologies that will significantly affect the performance, reliability, and survivability of next-generation baseload and burst mode space power systems are emphasized. Technology disciplines related to power sources (solar/nuclear and chemical), power conversion, energy storage, power conditioning/distribution and control, and waste-heat acquisition, transport, and rejection are primarily addressed. For some of them, performance trends that can be used as the basis for projecting future advanced power-system performance are developed. Performance capabilities for several different types of space power system for both baseload and burst mode applications are postulated on the basis of evolving technology and point designs that incorporate projections of advanced component capabilities     

卫星定位系统与飞行力学

概述了卫星定位系统的发展和应用，重点论述了它与飞行力学的关系，在ＧＰＳ卫星星座布置，地面站测控和用户应用中，飞行力学及其相关学科作为应用基础起到了重要的作用，成为卫星定位这门新兴交叉学科的一部分，最后提出了作为ＧＰＳ高级应用专题的飞行力学若干研究课题。     

基于联合映射的高速数传发射机设计及其查找表法实现

根据高速数传发射机的要求,提出基于联合映射的高速卫星发射机设计及基于查找表的FPGA(F ieldProgramm ab le Gate Array,现场可编程门阵列)硬件实现方案。该方法将发射机中数字部分的TCM编码和成形滤波一起设计,将多个卷积相乘项相加后再量化,减少了量化次数,提高了量化信噪比。并根据FPGA芯片内部结构设计硬件实现方案,符合SOC(System of Ch ip)的趋势。用片内的BLOCKRAM精心设计查找表,在X ILINX公司25万门芯片VIRTEX2-250中就能实现此方案。MODELSIM的时序仿真结果表明可支持高达200Mb it/s的数据。文章结尾针对未来更高速率的高速数传发射机给出了一种通用硬件实现方法。     

航空涡轴发动机发展趋势

基于国际上典型航空涡轴发动机的发展历程,概括了航空涡轴发动机产业发展趋势,其所呈现的系列化、军民两用化和国际合作化特点十分鲜明,国家层面实施的发展计划对航空涡轴发动机的发展起到了重要引领作用。基于统计分析,展望了航空涡轴发动机结构布局和性能发展趋势。研究表明:在结构布局方面,航空涡轴发动机朝着结构紧凑化方向发展,压气机和涡轮级数呈现不断减少的趋势。1 500 kW级以下的航空涡轴发动机将更普遍地采用单级/双级离心压气机和单级涡轮,1 500 kW以上的航空涡轴发动机将更普遍地采用轴流+离心组合压气机和双级涡轮,同心轴前输出功率型式成为主流功率输出型式。在性能方面,未来先进航空涡轴发动机的压比将达到30,涡轮前温度将达到1 900 K,油耗将低至0.20 kg/(kW·h),单位功率将达到400 kW/(kg/s),功质比将达到14 kW/kg。      

Satellite inclination effects on UHF Satcom operation

The cause, magnitude, and time variance of satellite inclination are examined in light of the effects on military UHF SATCOM operation. The effects on required demodulator acquisition range, earth coverage footprint, and user terminal antenna pointing accuracy are considered. It is shown that the allowable satellite inclination to maximize on-orbit lifetime is not based on earth-terminal antenna pointing accuracy, but on allowable loss of high-latitude satellite coverage area. Worst-case Doppler shift for a UHF military satellite is 85-Hz uplink and 67-Hz downlink for a 5° SATCOM user elevation angle and 10° of satellite inclination. This amount of inclination is a reasonable allowance for station-keeping, to minimize thruster fuel and thus maximize satellite life. It is also shown that uplink Doppler frequency shift due to satellite inclination may be corrected based on satellite ephemeris data and rough user terminal location data     

基于ISM参数偏差阶梯式变化的ARAIM可用性

针对双频多星座全球卫星导航系统提供垂直引导服务的先进接收机端完好性监测技术(ARAIM)是当前完好性研究的重要热点之一,完好性支持信息(ISM)是实现ARAIM可用性的核心内容。为了探讨ARAIM可用性对ISM参数偏差的敏感度,在梳理ISM各参数和ARAIM性能关系的基础上,研究了基于阶梯式变化的ISM参数偏差对ARAIM可用性的影响情况。研究结果表明,ARAIM算法的四种可用性判据对ISM参数偏差表现出不同的耐受性,ISM各参数偏差对ARAIM可用性影响差异较大,且ISM参数中的用户测距精度(URA)对ARAIM可用性的影响最为明显,可造成大于10%的严重影响。     

基于非合作低轨卫星的测向交叉定位技术

根据非合作低轨卫星的特点，可以被动测量多颗卫星信号的来向，通过测向交叉的方式进行定位。但是通过星历解算出的卫星位置位于地心地固坐标系，用户测量的方位角和俯仰角基于站心坐标系。针对非合作低轨卫星测向交叉定位时目标用户角度信息与卫星位置基于不同坐标系的问题，提出了一种迭代最小二乘定位算法，通过迭代的方式不断收敛定位结果，能够在目标用户角度信息与卫星位置基于不同坐标系的情况下，解决非合作低轨卫星的测向交叉定位问题。仿真结果表明，基于迭代最小二乘定位算法能够实现非合作低轨卫星仅利用角度定位，并分析了测角精度、卫星轨道高度、参与定位卫星数与定位误差之间的关系。针对迭代的计算方法，分析了迭代过程中不同收敛条件下迭代次数与定位误差之间的关系。在保证定位精度的情况下，将迭代收敛范围设置为8~30 km，可以降低2~3次迭代次数。     

Recent development of casing treatments for aero-engine compressors

Casing treatment is a mature stabilization technique which has been widely applied on aero-engines for modern aircrafts and turbo-chargers for automobiles. After the investigations of half century since the 1960s, this technique has been well developed for various configurations with different effectiveness. From the perspective of stabilization mechanism, this paper roughly categorizes the configurations of casing treatment into two types: traditional ones which work by affecting the flow structure of blade tip region; a novel one named as Stall Precursor-Suppressed (SPS) casing treatment. The effectiveness of both types will be demonstrated for their applications on axial compressors and centrifugal compressors with uniform or distorted inlet. And the stabilization mechanism of casing treatments for regular types and SPS one will also be explained respectively. In addition, this review will summarize the methodologies of casing treatments with the numerical simulations for regular grooved configurations and the eigenvalue approach for SPS casing treatment. Looking forward to the future of compressor stabilization, casing treatment technique will still exist as a general and inexpensive option, and the exploration for its effectiveness and mechanism will be deeper with the development of computational fluid dynamics and advanced measurement techniques.