The impact of satellite altitude on the performance of LEOS based communication systems

Low earth orbit satellite (LEOS) systems promise to provide global communication, including voice and data services from Iridium and high capacity broadband services from Teledesic. In design of LEOS systems, the choice of satellite altitude is an important consideration, which has a significant impact on system performance. Among the factors affected by satellite altitude choice are system capacity, user‐to‐user delay, power system design and communication services that can be offered. This paper analyzes the effects of satellite altitude on quality of service, frequency reusability and power system sizing. It is found that a choice of low altitude has a positive impact on system capacity and power system requirements. As a consequence, satellite mass and launch cost can be reduced for satellites in lower orbits due to the lower power requirements. In terms of user‐to‐user delay, the results are in favor of medium altitudes, while very high altitudes are not a good choice relative to these measures. This revised version was published online in June 2006 with corrections to the Cover Date.     

可展开空间光学望远镜技术发展及展望

为了获得更高的角分辨率,空间光学望远镜的口径越来越大,口径超过4 m的空间望远镜将难以突破现有运载火箭整流罩有效包络的限制。另一方面,在研制周期及成本等方面拥有较大优势的微纳光学遥感卫星也对提高空间分辨率和集光面积有广泛的需求,需要在较小的发射体积里容纳下较大的光机系统,以降低发射成本。可展开空间光学望远镜将成为解决发射尺寸受限的可行方式。从大口径空间天文望远镜、分块式可展开对地观测望远镜和光轴方向可展开微纳卫星光学望远镜等方面对国内外可展开空间光学望远镜的研究现状进行了综述。对可展开空间光学望远镜涉及到的一些关键技术和发展趋势进行了阐述和归纳。     

Design,Implementation, and Validation of KOMPSAT‐2 Software Simulator

In this paper, we present design features, implementation, and validation of a satellite simulator subsystem for the Korea Multi‐Purpose Satellite‐2 (KOMPSAT‐2). The satellite simulator subsystem is implemented on a personal computer to minimize costs and trouble on embedding onboard flight software into the simulator. An object‐oriented design methodology is employed to maximize software reusability. Also, instead of a high‐cost commercial database, XML is used for the manipulation of spacecraft characteristics data, telecommand, telemetry, and simulation data. The KOMPSAT‐2 satellite simulator subsystem is validated by various simulations for autonomous onboard launch and early orbit phase operations, anomaly operation, and science fine mode operation. It is also officially verified by successfully passing various tests such as the satellite simulator subsystem test, mission control element system integration test, interface test, site installation test, and acceptance test.     

Calibration strategy for the Earth Observing System (EOS)-AM1platform

The Earth Observing System (EOS) is an international, 18-year program in global remote sensing of the Earth comprising multiple instruments flown on several satellite platforms. The first EOS platform, AM1, scheduled for launch in 1998, includes five instruments designed to make radiometric and reflectance measurements of the Earth over a wavelength range extending from the visible to the thermal infrared. The goal of the EOS-AM1 platform and instruments is to advance the scientific understanding of the Earth in the areas of clouds, aerosols, radiative balance, terrestrial and oceanic characterization, and the carbon cycle. In order to achieve this goal, the EOS-AM1 instruments must produce state-of-the-art accurate, precise, and consistent radiance and reflectance measurements over their five-year lifetimes. In addition, the production of continuous remote-sensing data from multiple instruments on several platforms requires that the remote-sensing measurements of the AM1 platform be radiometrically tied to the measurements made by instruments on successive platforms. This is achieved through careful prelaunch and postlaunch instrument calibration, cross-calibration, and level 1B data validation (i.e. vicarious calibration). This paper presents an overview of the calibration, cross-calibration, and level 1B data validation strategy for the AM1 platform     

Ion propulsion-a technology for improving the cost-effectiveness oflarge communications satellites

The overall launch mass of a communications satellite has a major influence on its economic performance. If this mass can be reduced substantially, the launch cost will be lower, or more revenue can be generated by carrying a larger payload or extending the operational lifetime. Since an ion propulsion system provides an exhaust velocity at least an order of magnitude higher than that of chemical thrusters, the propellant mass required for north-south station-keeping can be reduced by hundreds of kilogrammes, thereby gaining these benefits. This application of ion propulsion is discussed and quantified in the paper, for the Intelsat VII spacecraft and the UK-10 ion propulsion system     

RCA satellite networks: High technology and low user cost

Channel demands on the RCA Americom domestic satellite communications system have continued to increase rapidly since the first launch in 1975. After deploying four of the first-generation 24-channel spacecraft, Americom introduced an advanced, all-solid-state design in 1982 which has more than twice the traffic capacity of the original series. To supplement the operational network of six C-band satellites, K-band satellites will be introduced in 1985 to serve the "small master-antenna TV market and digital satellite networks. Accompanying the continuous incorporation of state-of-the-art technology into successive satellites to achieve increased traffic capacity and longer life, new terrestrial equipment and efficient signal processing/modulation techniques are being exploited to continue the competitive reduction of cost per satellite Circuit per year.     

NGSO遥感卫星监测方法

遥感卫星具有技术要求低、成本低、发射简单、无轨位限制等特点,可广泛应用于各种领域,目前我国已建成陆地观测、海洋观测和大气观测等多领域的遥感观测。遥感卫星大部分属于非静止轨道(NGSO)卫星,数量庞大的NGSO遥感卫星不断涌现和部署,对卫星业务及频率轨道资源的监管带来严峻挑战,为促进无线电频率轨道资源的有效使用,开展NGSO遥感卫星的监测迫在眉睫。     

COMETS experiments for advanced mobile satellite communications and advanced satellite broadcasting

The Communications and Broadcasting Engineering Test Satellite (COMETS) was developed to evaluate Ka‐band (31/21GHz) and millimetre‐wave (47/44 GHz) advanced mobile satellite communications systems, 21GHz advanced satellite broadcasting systems, and S‐band and Ka‐band inter‐orbit satellite communications systems. COMETS was launched because it was to become the new ‘bridge’ toward advanced satellite communications technologies in the next century, but the launch on 21 February 1998 regretfully failed due to premature shut down of the second stage engine of the H‐II launch rocket. After this accident, the initial low elliptic orbit of COMETS was improved by the apogee engine to a larger elliptic orbit with an apogee altitude of 17711km, a perigee altitude of 473 km, an inclination of 30.1°, and an orbital period of 319 min. Original and modified COMETS experimental plans, countermeasures in earth stations for the orbiting satellite, as well as an overview of the COMETS satellite and ground terminals are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

Lightning-induced voltages in a satellite launch-pad protection system

Modern satellite launch pads are provided with lightning protection systems to take care of direct lightning strike to the satellite launch vehicle during the launch preparation period. This paper presents the results of the study on induced voltage on the conductors interlinking the towers of such a protection system due to a nearby lightning strike. The variation in the induced voltages with lightning-strike distances as well as ground conductivities are studied and the results presented in the paper. It has been seen that the waveshape of the induced voltage depends on conductor height and striking distance, whereas the ground conductivity has negligible effect on the induced voltage.     

Geoid undulation accuracy

For use in oceanographic applications the geoid is ideally needed to a high accuracy and to a high resolution. In 1979 the cumulative geoid undulation error to spherical harmonic degree 20 was ±1.4 m for the GEM10 potential coefficient model. Today the corresponding value has been reduced to ±25 cm for GEM-T3 or ±11 cm for the OSU91A model. Similar improvements are noted in harmonic degree (wavelength) and in resolution. The accuracy of the determination of the geoid is discussed from several points of views. Some comparisons are made with information available 12 years ago and that now available in the time framework of the TOPEX launch. It is noted that the accuracies described are subject to constant improvement. This is especially true as new satellite tracking data (e.g. DORIS data) are used in the potential coefficient models and more satellite altimeter data become available from the ERS-1 and TOPEX/Poseidon missions     

The new space race: satellite mobile communications

The how and why of LEO satellite communications are considered from technical and economic viewpoints; the market forecast for large systems of this nature is pessimistic. Particulars of six major services planned for launch within the next 10 years are tabulated     

场地自动化定标技术进展

场地自动化替代定标是光学遥感卫星定标发展的新方向。自动化定标通过在场地布设无人值守的全自动观测仪器获取地面和大气光学参数,实施对卫星遥感器的高频次定标,从而提升定标精度。论文分析了自动化定标的方法和技术发展现状,针对自动定标的应用需求,提出了自动化定标设备的设计方案和关键技术,讨论了自动化定标的未来发展前景。     

地球同步轨道随动可展开异形遮光罩技术研究

对于地球同步轨道空间遥感器的成像系统,太阳入侵引起的杂散光和热流量问题是影响系统成像质量的重要因素。目前,解决这个问题的一个有效办法是在通光口径处安装一个外遮光罩。对于未来大口径高分辨率成像系统,其遮光罩尺寸受到了火箭整流罩空间包络的限制。针对地球同步轨道遥感器的高分辨率大口径成像系统,研究了一种随动可展开的异形遮光罩技术,提出一种收缩发射、在轨展开的设计方案,可以优化遮光罩与卫星的空间接口关系;同时,随动技术可以让遮光罩具备相对于太阳入射角度的转动功能,对日形成遮蔽,更加有效地解决太阳引起的杂散光和热流量问题。     

基于遗传算法的低轨天基雷达星座设计

从目标监视性能的角度出发,分析了低轨天基雷达星座的卫星总数、能量需求以及星座发射费用等优化目标。综合考虑了Walker星座的碰撞等约束问题,建立了低轨天基雷达星座设计的优化目标。提出了一种基于遗传算法的低轨天基雷达星座设计方法。根据天基雷达星座的特点,该算法在进化过程中使用了非可行解修正和约束分级等约束处理方法,有效提高了算法的运算效率。通过仿真实验验证了该方法能够有效的同时优化低轨天基雷达星座的构形和卫星参数。     

Stability Control in Polygon Based Topology Formation and Information Gathering in Satellite Based Wireless Sensor Network

The Space today has considerable surge in distributed network of small satellites to meet the imperative demand of both commercial and scientific applications (Selva and Krejci in Acta Astronaut 74:50–68, 2012). As the complexity of the design and launch of large satellites is high , the need of distributed networking is gaining lot of interest in space domain as well. Thus single large satellite is replaced by many, small satellite that collaboratively work to perform the same functionality of single large satellite forming Space Based Wireless Sensor Network (SBWSN). The SBWSN are dynamically decoupled network as each satellite, orbits in its own path and the positioned with considerable distance between them. Stability of network with respect to formation flying to accomplish the task by collaboration is quite essential. In this paper, we develop the stability criteria in small satellite network using graph theory, covariant derivatives and linear algebra to ensure distributed processing and communication, required to accomplish the mission task.

     

TMS 32020单片信号处理器在测控系统中的应用

在卫星地面测控系统中,要求在低信噪比(如-20分贝)条件下提取目标的多普勒频率信息,以引导接收机锁相环捕获信号并锁定。模拟式频率引导采用经典的晶体滤波器组,其数量大、成本高、重量体积大。数字式频率引导采用对接收信号采样序列进行FFT运算处理实现对目标的频率捕获,具有显著的优越性。作者等人以8086微机实现的数字频率引导设备已成功地应用于同步通讯卫星测控站中。为了进一步提高处理速度,采用了TMS32020单片信号处理器研制出频率引导快速处理机,使频率引导处理时间提高15倍以上。该成果的硬件设备可适应不同的实时数字信号处理要求,应用于雷达、通讯、遥控、仪器、语音、智能等各种场合。     

Architectural Decisions for Communications Satellite Constellations to Maintain Profitability While Serving Uncovered and Underserved Communities

The rise of the commercial space industry has resulted in the development of mega-constellations that promise to provide global broadband. These constellations capitalize on advancements in technology, improved modeling capabilities, and reductions in launch cost. One of the significant open questions is whether these constellations will significantly increase access for uncovered and underserved communities, in addition to serving existing markets. This paper analyzes which constellation characteristics provide the best global coverage at the lowest operational cost. First, we present the demand model that assesses the number of under-served and uncovered users in a given region. Then, we present a genetic algorithm used to identify potential constellations. Finally, we conclude by identifying which characteristics are the most promising for broadband constellations, as well as predictions of how the market will develop in the coming years. Our analysis has found that geostationary (GEO) and medium Earth orbit (MEO) satellite constellations have the highest likelihood of profitability. LEO networks are on average 27% more expensive, but if designed wisely, they can be competitive. Our work shows that there are diminishing returns with large constellations, and that it is more cost effective to have a small number of highly capable satellites, rather than many low complexity satellites. Key technologies like high frequency bands and miniaturization of components can lead to further cost reductions and increase the competitiveness of LEO constellations.     

Coalignment and synchronization of the AIRS instrument suite

Previous multispectral sounders have consisted of infrared and microwave instruments operated asynchronously, with the data interpolated during ground processing to common fields of view (FOVs) for geophysical retrieval processing. To help achieve the high retrieval accuracy required for the Atmospheric Infrared Sounder (AIRS) system, the four instruments making up the AIRS suite are aligned and synchronized in such a way as to achieve common FOVs without interpolation. We describe the system, how the alignment is accomplished, and the plans to verify performance after launch and compensate for misalignments that might be revealed then.     

简缩极化SAR数据处理与应用研究进展

极化信息能丰富合成孔径雷达(SAR)数据的信息量,在农业、环境、海洋、森林、军事等领域取得了广泛的应用,但同时也面临分辨率较低、幅宽较小的问题,带来较高的应用成本。简缩极化SAR(CP SAR)作为一种能同时获取较为丰富的地表信息并实现较大幅宽观测的极化SAR模式,在过去十余年中引起了科研人员的广泛关注。随着印度RISAT-1卫星的成功发射,简缩极化SAR在一系列应用研究中取得了新进展。该文简要介绍了简缩极化SAR的经典数据处理方法,总结了近十余年来简缩极化SAR在农业和海洋应用领域的主要研究成果,最后对其发展方向进行了分析与展望。      

Satellite-Systems Cost Estimation

Cost-Estimate Relations (CER's) are derived for launch/orbit insertion, payload/satellite(s), and the total satellite system. These CER's are expressed in terms of orbit altitude (or apogee), orbit type (circular or elliptical), and payload weight. The CER's are also presented briefly in terms of number of rings, number of satellites per ring, and satellite weight. They are applicable only to recurring (production) costs and include an 80percent "learning-curve rate." Satellite-subsystem percent weights are also discussed for single-axis and three-axis stabilized satellites, and guidance is developed for estimating total satellite weight given the required RF power.