Galileo系统在空间飞行器定位中的应用

欧洲的Galileo系统将在2008年建成，届时它将与美国的GPS系统相互补充。在对Galileo系统导航星座轨道和信号结构分析的基础上，结合各种不同轨道高度的空间飞行器用户的动态特点，推导了用户卫星接收天线的可见可用性模型，建立了基于Galileo坐标系统(ITRF-96)的高动态定位算法模型，针对实际航天工程任务的LEO和GEO卫星进行了定位仿真，为Galileo系统在空间领域的实际应用打下了基础。     

Developing the next phase in NASAs satellite communications program

NASAs early efforts in satellite communications development brought confidence in space technology use for improved telecommunications. New, worldwide satellite communications systems have resulted, and are now on a commercial, self-sustaining operational basis. Since 1973, NASA has conducted hundreds of user experiments and demonstrated newer technology using ATS-1, -3, -6 and CTS. Now, projections show that the commercial demand will continue to increase, soon exceeding the current technology's capacity.As a result, U.S. Space Policy affirmed in 1978 that NASA should embark again on a research and development program for satellite communications with specific, characterized goals. The resulting plan's elements include $\text{30}\text{20}\text{GHz}$ Ka-band technology, extending the current work in advanced multi-beam antennas; a narrowband system and technology study that could lead to mobile and transportable communications developments; and studies of future uses of technology in communications. The program plan and its evolution are described, followed by a report of current progress and future expectations.     

Application of a Multiple Hypothesis Filter to near GEO high area-to-mass ratio space objects state estimation

Optical surveys have identified a class of high area-to-mass ratio (HAMR) objects in the vicinity of the Geostationary Earth Orbit (GEO) regime. The nature of these objects is not well known, though their proximity to the GEO belt implies origins from space objects (SOs) near GEO. These HAMR objects pose a collision hazard as they transit through the vicinity of active GEO satellites. Due to their high area-to-mass ratios (AMRs), ranging from 0.1 to 20 m²/kg and higher, the effective solar radiation pressure perturbs their orbits significantly. Improvements in detection sensitivity will result in large numbers of uncorrelated tracks from surveys. A Multiple Hypothesis Filter (MHF) approach to the initial state estimation and track association provides a potentially automated and efficient approach to the processing of multiple un-correlated tracks.The availability of long-term optical angles data collected for a set of near GEO HAMR objects provides the means for testing candidate estimation processes such as the MHF. A baseline orbit determination (OD) process uses an Extended Kalman Filter/Smoother to manually estimate the 6 orbital elements and the effective area-to-mass ratio (AMR) which drives the solar radiation pressure perturbations on the orbital trajectories. In addition to allowing the characterization of the long-term behavior of the AMR, this process establishes a pseudo-truth trajectory to which the MHF analysis can be compared. An Unscented Kalman Filter (UKF) is applied in the MHF estimation process to estimate the 6 orbital elements and AMR, with no a priori state assumptions, and the results are compared to the pseudo-truth results for validation.The work to be presented summarizes the UKF/MHF process and assesses state estimation performance based on selected data for selected near GEO HAMR objects having a range of AMR value and variations. The prediction accuracy is also assessed by comparing predictions derived from filter updates to segments of the pseudo-truth trajectory determined from data not included in the updates.     

Application of a Multiple Hypothesis Filter to near GEO high area-to-mass ratio space objects state estimation

Optical surveys have identified a class of high area-to-mass ratio (HAMR) objects in the vicinity of the Geostationary Earth Orbit (GEO) regime. The nature of these objects is not well known, though their proximity to the GEO belt implies origins from space objects (SOs) near GEO. These HAMR objects pose a collision hazard as they transit through the vicinity of active GEO satellites. Due to their high area-to-mass ratios (AMRs), ranging from 0.1 to 20 m²/kg and higher, the effective solar radiation pressure perturbs their orbits significantly. Improvements in detection sensitivity will result in large numbers of uncorrelated tracks from surveys. A Multiple Hypothesis Filter (MHF) approach to the initial state estimation and track association provides a potentially automated and efficient approach to the processing of multiple un-correlated tracks.The availability of long-term optical angles data collected for a set of near GEO HAMR objects provides the means for testing candidate estimation processes such as the MHF. A baseline orbit determination (OD) process uses an Extended Kalman Filter/Smoother to manually estimate the 6 orbital elements and the effective area-to-mass ratio (AMR) which drives the solar radiation pressure perturbations on the orbital trajectories. In addition to allowing the characterization of the long-term behavior of the AMR, this process establishes a pseudo-truth trajectory to which the MHF analysis can be compared. An Unscented Kalman Filter (UKF) is applied in the MHF estimation process to estimate the 6 orbital elements and AMR, with no a priori state assumptions, and the results are compared to the pseudo-truth results for validation.The work to be presented summarizes the UKF/MHF process and assesses state estimation performance based on selected data for selected near GEO HAMR objects having a range of AMR value and variations. The prediction accuracy is also assessed by comparing predictions derived from filter updates to segments of the pseudo-truth trajectory determined from data not included in the updates.     

Further analysis of infrared spectrophotometric observations of high area to mass ratio (HAMR) objects in GEO

Optical surveys have identified a class of high area-to-mass ratio (HAMR) objects in the vicinity of the Geostationary Earth Orbit (GEO) ring^. The exact origin and nature of these objects are not well known, although their proximity to the GEO belt poses a hazard to active GEO satellites. The prevalent conjecture is that many of these objects may be thermal materials shed from derelict spacecraft in ‘graveyard’ orbits above the GEO ring. Due to their high area-to-mass ratios and unknown attitude dynamics and material characteristics, solar radiation pressure (SRP) perturbs their orbits in ways that makes it difficult to predict their orbital trajectories over periods of time exceeding a week or less. To better understand and track these objects and infer their origins, we have made observations that allow us to determine physical characteristics that will improve the non-conservative force modeling used for orbit determination (OD) and prediction. Information on their temperatures, areas, emissivities, and albedos may be obtained from thermal infrared and visible measurements. Simultaneous observations in the thermal infrared and visible wavelengths may allow disentangling of projected area, albedo, and object emissivity.Further analysis and modeling of observational data on certain of the HAMR objects collected at the AMOS observatory 3.6 m AEOS telescope are presented. The thermal-IR spectra of these geosynchronous orbit objects acquired by the Broadband Array Spectrograph System (BASS) span wavelengths 3 to 13 μm and constitute a unique data set, providing a means of measuring object fluxes in the infrared and visible wavelengths. These, in turn, allow temperatures and emissivity-area products to be calculated, and in some cases provide information on rotation rates. We compare our observational results with the outputs of simple models, in terms of visible and infrared flux and orbital characteristics. The resulting temperatures and rotation rates are used in SRP acceleration models to demonstrate improvements in OD and prediction performance relative to models which assume default ambient temperature and static attitude dynamics. Additionally, we have the capability and plans to measure material properties with the same instrument in the lab as used at the telescope to facilitate direct comparisons.     

全球导航星座星间链路技术发展建议

美国全球定位系统（GPS）的Block IIR和Block IIF系列导航卫星安装了UHF频段的星间链路收发设备,未来的GPS Ⅲ系列导航卫星将用Ka频段星间链路替代UHF频段星间链路,提高星间数据通信容量,增强抗干扰能力;俄罗斯全球导航卫星系统（GLONASS）的新一代GLONASS-K系列导航卫星开始安装S频段星间链路收发设备;欧洲的伽利略（Galileo）卫星导航系统也在规划全球导航星座的星间链路体系;我国北斗（Compass）卫星导航系统正处在由区域覆盖向全球覆盖的过渡阶段,全球星座的星间链路正处在多种系统体制的抉择中。文章在对国外各种星间链路研究的基础上,从导航星座星间链路需求和特点出发,提出建议：1）建设高频段星间链路;2）加强星间天线与卫星总体的联合设计;3）星间网络协议要具有灵活性;4）尽可能保持每颗卫星的星间链路设备状态一致。文章考虑了现有国内技术储备和国外未来技术发展方向,提出的观点可以作为我国全球卫星导航系统对星间链路选择的参考,对我国Compass系统建设技术先进的星间链路有一定的指导意义。     

European Sail Tower SPS concept

Based on a DLR-study in 1998/99 on behalf of ESA/ESTEC called “System Concepts, Architectures and Technologies for Space Exploration and Utilization (SE&U)” a new design for an Earth-orbiting Solar Power Satellite (SPS) has been developed. The design is called “European Sail Tower SPS” and consists mainly of deployable sail-like structures derived from the ongoing DLR/ESA solar sail technology development activity. Such a SPS satellite features an extremely light-weight and large tower-like orbital system and could supply Europe with significant amounts of electrical power generated by photovoltaic cells and subsequently transmitted to Earth via microwaves. In order to build up the sail tower, 60 units - each consisting of a pair of square-shaped sails - are moved from LEO to GEO with electric propulsion and successively assembled in GEO robotically on a central strut. Each single sail has dimensions of 150m × 150 m and is automatically deployed, using four diagonal light-weight carbon fiber (CFRP) booms which are initially rolled up on a central hub. The electric thrusters for the transport to GEO could also be used for orbit and attitude control of the assembled tower which has a total length of about 15 km and would be mainly gravity gradient stabilized. Employing thin film solar cell technology, each sail is used as a solar array and produces an electric power in orbit of about 3.7 MW_e. A microwave antenna with a diameter of 1 km transmits the power to a 10 km rectenna on the ground. The total mass of this 450 MW SPS is about 2100 tons. First estimates indicate that the costs for one kWh delivered in this way could compete with present day energy costs, if launch costs would decrease by two orders of magnitude. Furthermore, mass production and large numbers of installed SPS systems must be assumed in order to lower significantly the production costs and to reduce the influence of the expensive technology development. The paper presents the technical concept and an economic assessment as well as results of a recent solar sail deployment ground demonstration at DLR's facilities in Cologne.     

Prospects for commercial satellite services at Q- and V-bands

Some 16 proposed new satellite systems operating at 36 to 46 GHz (Q-band) and 46 to 56 GHz (V-band) have been proposed to the U.S. Federal Communications Commission by U.S. companies. Of these. 14 are intended to provide global, or nearly global, service. One is intended for U.S. domestic service, and one is a package to provide additional store-and-forward capability on an earlier proposed “Little LEO” system. This paper provides a brief summary of the 14 global systems, which for the most part are designed to exploit the wide band of frequencies available for services such as multimedia distribution and Internet access.

Systems are proposed that would use geostationary orbit, medium earth orbit, low earth orbit, and Molniya orbit satellites, and in some cases combinations of two of these orbits. Most of the new systems propose to employ new technologies such as multiple narrow spot-beam antennas, onboard demodulation and routing of traffic between beams, intersatellite links, and in some cases scanning beams to continuously illuminate the service area as the satellite flies by.

Some of the difficulties involved in fielding systems at these high frequencies arise from the propagation impairments that can be expected and the high cost of solid-state power devices for user terminals, which will drive up costs. It is concluded that, while the large amount of bandwidth (3 GHz) proposed by the FCC for these systems is attractive, few if any are likely to be built while spectrum remains available at Ka-band.     

GEO移动通信卫星合成多波束天线仿真分析

针对地球静止轨道（GEO）移动通信卫星星上多波束天线波束成形技术,研究了合成多波束对地覆盖、点波束天线增益以及波束间干扰抑制技术。利用仿真分析软件进行多波束天线的波束成形仿真分析,优化了天线系统的设计参数,改善了波束间的隔离度指标,提高了系统通信性能和局部地区的信道容量,完成了地球静止轨道移动通信卫星系统合成多波束天线的设计。     

Q/V频段甚高通量卫星(VHTS)地面应用系统设计（英文）

Over the next decade,Very High-Throughput Satellite(VHTS) will bring enough capacity to serve high speed internet and in-flight connectivity markets at scale, offering fiber-like services both in terms of price and speed. In this context, a generic VHTS mission utilizing Q/V-band feeder links and Ka-band user links is described. However, the rain attenuation on the feeder links becomes a limiting issue because of the higher frequencies. Toward this, an exploitation of multiple gateways(GWs) as a transmit diversity measure for overcoming severe propagation effects are being considered. Ground Application System(GAS) design of VHTS is illustrated including N+P GWs(N active and P redundant GWs) diversity, frequency plan, link budget and system capacity.     

Ka-band high-rate telemetry system upgrade for the NASA deep space network

The NASA Deep Space Network (DSN) has a new requirement to support high-data-rate Category A (Cat A) missions (within 2 million kilometers of the Earth) with simultaneous S-band uplink, S-band downlink and Ka-band downlink. The S-band links are required for traditional telemetry, tracking & command (TT&C) support to the spacecraft, while the Ka-band link is intended for high-data-rate science returns. The new Ka-band system combines the use of proven DSN cryogenic designs, for low system temperature, and high-data-rate capability using commercial telemetry receivers. The initial Cat A support is required for the James Webb Space Telescope (JWST) in 2014 and possibly other missions. The upgrade has been implemented into 3 different 34-meter Beam Waveguide (BWG) antennas in the DSN, one at each of the complexes in Canberra (Australia), Goldstone (California) and Madrid (Spain). System test data are presented to show that the requirements were met and the DSN is ready for Cat A Ka-band operational support.     

A parametric study of space transfer/upper propulsion stages

For Space Transportation System (i.e. Space Shuttle) launched satellites destined for a Geosynchronous Earth Orbit (GEO), there is a need for cost-effective, versatile propulsion systems to provide the perigee burn, i.e. to boost the satellite from Low Earth Orbit (LEO) to Geosynchronous Transfer Orbit (GTO). Surveys of commercial spacecraft activities and future GEO satellite requirements indicate that a spacecraft propulsion system that will provide the perigee burn for a broad range of future commercial satellites would have an excellent market potential.Parametric studies to investigate and define attractive perigee-burn upper propulsion systems (i.e. an Upper Propulsion Stage, or a UPS) are presented. The feasibility and payload capacilities that could be provided by a UPS assembled from essentially off-the-shelf components and subsystems, and the benefits that could be achieved by using major subsystems specifically tailored for the application are presented. The results indicate that attractive UPS configurations can be defined using either off-the-shelf or optimized major subsystems.     

Design of a 40/50 GHz satellite ground station for fade mitigation experiments

Due to the increasing demand in satellite capacity, driven by applications such as high-definition television (HDTV), 3D-TV and interactive broadband services, higher frequency bands will have to be exploited. The capacity on Ku-band is already becoming scarce and Ka-band systems are more commonly used. It can be expected that 40 and 50 GHz (Q and V band) will have to be used in the future. At these frequencies the wave propagation effects have a significant impact on the performance. The traditional approach of implementing large fade margins in the system design is not suitable as it leads to expensive ground terminals. Fade mitigation by adaptive coding and modulation (ACM) is a cost-efficient method. To investigate the Q/V-band for future commercial exploitation, ESA's ALPHASAT satellite will provide experimental payloads for communications and wave propagation experiments. In Graz a Q/V-band ground station is currently under development. It will be equipped with a 3 m tracking antenna, a 50 W Klystron amplifier and a 290 K LNA. Fade mitigation experiments will be conducted, initially using DVB-S2 modems which allow to vary the modulation scheme, the Forward Error Correction code and the symbol rate under control of the ACM computer. In addition, uplink power control can be combined with the ACM methods. A specially developed signal analyser provides precise measurement of the signal/noise ratio. In addition, propagation data will be available from a beacon receiver, also developed by Joanneum Research. Important goals of the experiment are to investigate the reliability of links under realistic operating conditions using ACM and to develop efficient ACM and signal/noise ratio measurement algorithms which can be later implemented in optimised modems for Q/V-band.The paper describes the ground station design and addresses the planned fade mitigation experiments.     

Ground assisted rendezvous with geosynchronous satellites for the disposal of space debris by means of Earth-oriented tethers

Previous studies have shown that extended length Earth-oriented tethers in the geosynchronous (GEO) region can be used to re-orbit satellites to disposal orbits. One such approach involves the extension of a GEO based tether, collection of a debris object, and retraction of the tether, which transfers the retracted configuration to a higher energy orbit for debris disposal. The re-extension of the tether after debris disposal returns the configuration to the near-GEO altitude. The practical feasibility of such a system depends on the ability to collect GEO debris objects, attach them to a deployed tether system, and retract the tethers for transfer to the disposal orbits.This study addresses the collection and delivery of debris objects to the deployed tether system in GEO. The investigation considers the number, type and the characteristics of the debris objects as well as the collection tug that can be ground controlled to detect, rendezvous and dock with the debris objects for their delivery to the tethers system.A total of more than 400 objects are in drift orbits crossing all longitudes either below or above the geostationary radius. More than 130 objects are also known to librate around the stable points in GEO with periods of libration up to five or more years. A characterization of the position and velocity of the debris objects relative to the collection tug is investigated. Typical rendezvous performance requirements for uncooperative GEO satellites are examined, and the similarities with other approaches such as the ESA's CX-OLEV commercial mission proposal to extend the life of geostationary telecommunication satellites are noted.     

频率偏置对Ka频段圆极化频率复用数传链路的影响

采用国际电信联盟(ITU)的星地链路计算模型,仿真分析Ka频段双圆极化频率复用(简称"圆极化复用")链路可用情况随2个正交射频通道载波中心频率偏置量变化的关系,得出特定链路可用率下频率偏置量与临界接收仰角的定量关系。在此基础上,为了综合衡量频谱利用情况,提出有效频带利用率指标,并依据此指标对地面站的利用方案进行尝试性设计,以达到优化利用频谱资源的效果。研究结果表明:中心频率偏置量与有效频带利用率是对立统一体。增大中心频率偏置量,在特定链路可用率下可增长数传弧段,进而改善链路可用情况,但无法获取最大有效频带利用率。当载波中心频率偏置量为零时,通过选择合适的链路可用率可实现最大有效频带利用率。文章采用的分析方法和提出的有效频带利用率指标,可推广到其他频段的星地数传链路分析中,为Ka频段星地数传系统设计提供参考。     

W波段FMCW SAR系统实现与试验

与C波段、X波段和Ka波段相比,W波段的调频连续波(FMCW)合成孔径雷达(SAR)系统因具有更高的分辨率,更易实现低功耗与小型化而备受关注。W波段波长短,因此该波段的FMCW SAR更适用于短距离成像。提出一种W波段FMCW SAR系统的设计方案,根据提出的系统方案与指标,实现W波段FMCW轨道SAR系统的样机研制。该系统分辨率可达5 cm。系统样机试验在上海交通大学的多功能船模拖拽水池完成。设置不同目标进行成像试验,最终得到多组有效试验数据,并基于改进的RD算法进行数据处理,得到理想的SAR图像。经分析可知,系统实际分辨率优于5 cm。试验结果证明了W波段FMCW SAR系统的可行性与有效性。     

美国AEHF军事通信卫星推进系统及其在首发星上的应用

美国先进极高频（AEHF）项目将采用4颗运行于地球同步轨道（GEO）的AE—HF军事通信卫星。AEHF卫星的推进系统由远地点发动机、姿态控制发动机组和双模式霍尔电推进子系统组成。首发星AEHF-1是世界上首个采用霍尔电推进系统执行发射后轨道提升任夯的GEO卫星。AEHF-1卫星星箭分离后,远地点发动机未能正常工作,因此...     

静止轨道卫星在轨延寿技术研究进展

随着星上设备及元器件可靠性的提高,推进剂耗尽将成为未来静止轨道卫星的主要失效
模式。静止轨道卫星在轨延寿技术可通过发射延寿飞行器与失效卫星对接,采用辅助控制或燃料加注方式,进一步延长卫星在轨工作寿命。本文首先对近年来静止轨道失效卫星进行了统计和分析,随后介绍了静止轨道卫星在轨延寿技术的基本概念和任务特点,在国外典型项目调研的基础上,对在轨延寿任务所涉及的交会轨迹规划与控制、视觉测量与导航等关键技术进行了分析。在轨延寿技术的发展必将对未来静止轨道卫星的设计及运营模式产生重要的影响。     

空间红外点目标遥感探测系统在轨辐射定标

空间红外点目标遥感探测系统由于其任务与技术等方面的特殊性,其在轨辐射定标方法同一般对地观测遥感器相比较存在诸多差别。文章在广泛调研成功在轨运行的此类系统在轨辐射定标方法与技术基础之上,对其在轨辐射定标方法进行了分析与总结。为中国此类系统在轨辐射定标技术的深入研究提供参考。     

Local debris congestion in the geosynchronous environment with population augmentation

Forecasting of localized debris congestion in the geostationary (GEO) regime is performed to investigate how frequently near-miss events occur for each of the longitude slots in the GEO ring. The present-day resident space object (RSO) population at GEO is propagated forward in time to determine current debris congestion conditions, and new probability density functions that describe where GEO satellites are inserted into operational orbits are harnessed to assess longitude-dependent congestion in “business-as-usual” launch traffic, with and without re-orbiting at end-of-life. Congestion forecasting for a 50-year period is presented to illustrate the need for appropriately executed mitigation measures in the GEO ring. Results indicate that localized debris congestion will double within 50 years under current 80% re-orbiting success rates.