Small satellites and the 2000s

Over the last 20 years we have seen the development of many initiatives around the concept of small satellites for low cost missions using the available or expected low cost launch opportunities. What are the main lines of the French Space Agency's policy for the coming years?     

A survey of the outer planets Jupiter,Saturn, Uranus,Neptune, Pluto,and their satellites

A survey of current knowledge about Jupiter, Saturn, Uranus, Neptune, Pluto, and their satellites is presented. The best available numerical values are given for physical parameters, including orbital and body properties, atmospheric composition and structure, and photometric parameters. The more acceptable current theories of these bodies are outlined with thorough referencing offering access to the details. The survey attempts to cover the literature through May 1, 1972. Prepared Under Contract No. NAS7-100 National Aeronautics and Space Administration.     

多状态空间信息网络拓扑生成优化算法

依据空间信息网络（SIN）高动态性的特点,并考虑卫星工作的多状态特性,兼顾星间通信时延和拓扑抗毁性的要求,研究了多状态下空间信息网络拓扑生成及动态优化的问题。根据卫星星座的周期性,建立了一种卫星网络的拓扑周期表。综合卫星的可视性和连接度等约束条件,以网络平均和最大时延作为通信性能的优化目标,建立拓扑的多目标优化模型。提出一种改进的多目标模拟退火（IMOSA）算法,求解全局时延最优的卫星拓扑,并在考虑多状态情况下对链路进行优化,以满足网络高动态性。最后基于具有66颗低轨（LEO）的铱星星座进行仿真,研究表明：针对多状态条件下的铱星星座,该算法最大化减小了通信时延,得到抗毁性良好的拓扑结构,通信性能较之原有静态拓扑明显得到改善。     

共信道干扰环境下星基ADS-B系统监视性能

星基广播式自动相关监视系统（星基ADS-B）是实现广域范围内航空器监视的主要技术手段。为揭示星基ADS-B系统共信道干扰对系统监视性能的影响，提出了星基ADS-B系统监视容量的计算方法。首先给出了星基ADS-B系统模型，随后理论分析给出消息正确接收概率、位置消息更新间隔及位置报告更新间隔的计算公式，以此为基础给出了星基ADS-B系统监视容量的计算公式，最后基于SNS软件构建了星基ADS-B仿真系统，仿真验证了理论结果的正确性。研究表明：星基ADS-B系统的监视容量由ADS-B应用子系统所要求的航空器位置报告更新间隔、航空器-卫星链路的误码率、星-地面站链路的误码率及卫星数目联合确定。     

Overview of multiple satellite communication networks

Recently interest in packet communications has stimulated an interest in constellations of low altitude satellites. Such a configuration would have less propagation delay and be cheaper to launch than satellites at higher or geosynchronous altitude. However, many more satellites are necessary at low altitude to achieve reasonable coverage of the earth and insure availability of the resource. Further, the geometry of such a constellation would be dynamic with communication links of short duration as the satellites speed past each other or a ground site. The most difficult design issue in these systems is a stable method of routing messages that will sustain a reasonable level of traffic. This paper explores the problems of routing and switching messages through a constellation of low altitude satellites and examines some of the related demands on technology. The dynamic nature of crosslinks, uplinks, and downlinks requires a very agile antenna system, and the volume of information for routing of traffic is overwhelming. Use of some type of facetted phased array antenna is advocated to solve the former problem, but the latter problem is more subtle. Since the volume of ephemeris and constellation data as well as the rate of update is unmanageable, schemes relying on some form of broadcast or random access may be considered. It is concluded that none of the known or examined approaches to routing and switching is completely satisfactory     

电动力缆绳离轨系统中绳索建模研究

 空间碎片对在轨运行航天器的安全构成重大威胁,使废弃卫星脱离原轨道进入大气层烧毁是减少空间碎片的有效途径。利用导电缆绳与地磁场相互作用产生的洛仑兹力使卫星特别是低地球轨道卫星的轨道高度快速衰减是一种很有应用前景的离轨方式。在研究电动力缆绳离轨的刚性杆模型基础上,建立了更符合电动力缆绳特性的柔索模型,并对刚性杆模型和柔索模型进行仿真。结果表明柔索模型能更精确地体现电动力缆绳的性质。     

编队卫星星间相对状态测量的国外研究现状

空间状态测量是编队卫星应用需要解决的关键问题之一。针对国外几种典型的编队卫星星间状态测量方案,详细地分析了它们的设计特点、测量原理及测量精度,最后得出2个结论,对编队卫星的状态测量具有非常重要的参考价值。     

Galileo卫星星钟故障前后信号质量分析

星载原子钟是卫星导航系统的核心器件,是影响导航信号质量的重要因素。2016年11月,Galileo系统利用一箭四星发射升空4颗新一代Galileo卫星。根据观测显示,截至2017年7月,仅能接收到其中1颗卫星发射的导航信号。在2017年1月,欧洲航天局通告称多颗卫星原子钟大规模故障。针对此,40m 大口径高增益天线系统设备对不同批次和星钟故障情况的3颗Galileo卫星E5频点信号进行了数据采集处理,对各信号分量的功率谱、星座图、码片波形、相关损失、相关峰、S曲线偏差等信号质量指标进行了分析评估。结果表明,此次星载原子钟的大面积故障并未影响Galileo卫星信号的可用性,足够的星载备份钟避免了信号质量的严重恶化。     

OPPORTUNITIES FOR MAGNETOSPHERIC RESEARCH WITH COORDINATED CLUSTER AND GROUND-BASED OBSERVATIONS

ESA's first multi-satellite mission Cluster is unique in its concept of 4 satellites orbiting in controlled formations. This will give an unprecedented opportunity to study structure and dynamics of the magnetosphere. In this paper we discuss ways in which ground-based remote-sensing observations of the ionosphere can be used to support the multipoint in-situ satellite measurements. There are a very large number of potentially useful configurations between the satellites and any one ground-based observatory; however, the number of ideal occurrences for any one configuration is low. Many of the ground-based instruments cannot operate continuously and Cluster will take data only for a part of each orbit, depending on how much high-resolution (burst-mode') data are acquired. In addition, there are a great many instrument modes and the formation, size and shape of the cluster of the four satellites to consider. These circumstances create a clear and pressing need for careful planning to ensure that the scientific return from Cluster is maximised by additional coordinated ground-based observations. For this reason, the European Space Agency (ESA) established a working group to coordinate the observations on the ground with Cluster. We will give a number of examples how the combined spacecraft and ground-based observations can address outstanding questions in magnetospheric physics. An online computer tool has been prepared to allow for the planning of conjunctions and advantageous constellations between the Cluster spacecraft and individual or combined ground-based systems. During the mission a ground-based database containing index and summary data will help to identify interesting datasets and allow to select intervals for coordinated studies. We illustrate the philosophy of our approach, using a few important examples of the many possible configurations between the satellite and the ground-based instruments.     

The Juno Gravity Science Instrument

The Juno mission’s primary science objectives include the investigation of Jupiter interior structure via the determination of its gravitational field. Juno will provide more accurate determination of Jupiter’s gravity harmonics that will provide new constraints on interior structure models. Juno will also measure the gravitational response from tides raised on Jupiter by Galilean satellites. This is accomplished by utilizing Gravity Science instrumentation to support measurements of the Doppler shift of the Juno radio signal by NASA’s Deep Space Network at two radio frequencies. The Doppler data measure the changes in the spacecraft velocity in the direction to Earth caused by the Jupiter gravity field. Doppler measurements at X-band (\(\sim 8\) GHz) are supported by the spacecraft telecommunications subsystem for command and telemetry and are used for spacecraft navigation as well as Gravity Science. The spacecraft also includes a Ka-band (\(\sim 32\) GHz) translator and amplifier specifically for the Gravity Science investigation contributed by the Italian Space Agency. The use of two radio frequencies allows for improved accuracy by removal of noise due to charged particles along the radio signal path.     

THEMIS Operations

THEMIS—a five-spacecraft constellation to study magnetospheric events leading to auroral outbursts—launched on February 17, 2007. All aspects of operations are conducted at the Mission Operations Center at the University of California at Berkeley. Activities of the multi-mission operations team include mission and science operations, flight dynamics and ground station operations. Communications with the constellation are primarily established via the Berkeley Ground Station, while NASA’s Ground Network provides secondary pass coverage. In addition, NASA’s Space Network supports maneuver operations near perigee. Following a successful launch campaign, the operations team performed on-orbit probe bus and instrument check-out and commissioning tasks, and placed the constellation initially into a coast phase orbit configuration to control orbit dispersion and conduct initial science operations during the summer of 2007. Mission orbit placement was completed in the fall of 2007, in time for the first winter observing season in the Earth’s magnetospheric tail. Over the course of the first 18 months of on-orbit constellation operations, procedures for instrument configuration, science data acquisition and navigation were refined, and software systems were enhanced. Overall, the implemented ground systems at the Mission Operations Center proved to be very successful and completely adequate to support reliable and efficient constellation operations. A high degree of systems automation is employed to support lights-out operations during off-hours.     

Next generation GOES satellite power subsystem

Hughes space and communications was awarded a contract in January 1998 from NASA's Goddard Space Flight Center for the design, manufacture, integration and launch of two next generation geostationary operational environmental satellites (GOES) and options for two additional satellites. The satellites measure weather phenomena as the primary mission and X-rays and charged particles as the secondary missions. This paper describes the GOES electrical power subsystem (EPS) requirements, architecture, hardware and energy balance analysis. As of this writing, the design of the EPS has completed the critical design review phase and the hardware has entered the manufacturing phase     

CLUSTER MISSION OPERATIONS

The Cluster ground segment design and mission operations concept have been defined according to the basic mission requirements, namely, to allow the transfer of the four spacecraft from the initial geostationary transfer orbit achieved at separation from the launcher into the final highly elliptical polar orbits, such that in the areas of scientific interest along their orbits, the four spacecraft will form a tetrahedral configuration with pre-defined separation distances, to be changed every six months during the mission. The Cluster mission operations will be carried out by ESA from its European Space Operations Centre; the task of merging the Principal Investigators' requests into coordinated, regular scientific mission planning inputs to ESOC will be undertaken by the Joint Science Operations Centre. The mission products will be distributed to the scientific community regularly in form of CD-ROMs. Principal Investigators will also have access to quick-look science, housekeeping telemetry and auxiliary data via an electronic network.     

MEO/LEO双层卫星网络中层间链路的连接度分析

作为未来卫星移动通信系统的一个重要的研究方向,提出了一种由MEO卫星和LEO卫星共同组成的双层卫星网络(Double-Layer Satellite Network,DLSN),以更好为用户提供多媒体服务.作为多层卫星网络的一个重要的研究内容,连接不同高度上卫星的层间链路(Inter-Orbit-Links,IOLs)的特性对于整个DLSN网络的性能会有很大的影响.根据所设计的多层卫星网络的星座参数,通过对层间链路几何特性的研究,分析了多层卫星网络中MEO卫星与LEO卫星的连接度性能.采用计算机仿真的方法,给出了层间链路连接度的特性.结果表明,为了提高网络性能,在多层卫星网络中应按照一定参数有选择的建立层间链路,而不是简单的采用视距可见原则建立层间链路.     

Chemical Composition of Icy Satellite Surfaces

Much of our knowledge of planetary surface composition is derived from remote sensing over the ultraviolet through infrared wavelength ranges. Telescopic observations and, in the past few decades, spacecraft mission observations have led to the discovery of many surface materials, from rock-forming minerals to water ice to exotic volatiles and organic compounds. Identifying surface materials and mapping their distributions allows us to constrain interior processes such as cryovolcanism and aqueous geochemistry. The recent progress in understanding of icy satellite surface composition has been aided by the evolving capabilities of spacecraft missions, advances in detector technology, and laboratory studies of candidate surface compounds. Pioneers 10 and 11, Voyagers I and II, Galileo, Cassini and the New Horizons mission have all made significant contributions. Dalton (Space Sci. Rev., 2010, this issue) summarizes the major constituents found or inferred to exist on the surfaces of the icy satellites (cf. Table 1 from Dalton, Space Sci. Rev., 2010, this issue), and the spectral coverage and resolution of many of the spacecraft instruments that have revolutionized our understanding (cf. Table 2 from Dalton, Space Sci. Rev., 2010, this issue). While much has been gained from these missions, telescopic observations also continue to provide important constraints on surface compositions, especially for those bodies that have not yet been visited by spacecraft, such as Kuiper Belt Objects (KBOs), trans-Neptunian Objects (TNOs), Centaurs, the classical planet Pluto and its moon, Charon. In this chapter, we will discuss the major satellites of the outer solar system, the materials believed to make up their surfaces, and the history of some of these discoveries. Formation scenarios and subsequent evolution will be described, with particular attention to the processes that drive surface chemistry and exchange with interiors. Major similarities and differences between the satellites are discussed, with an eye toward elucidating processes operating throughout the outer solar system. Finally we discuss the outermost satellites and other bodies, and summarize knowledge of their composition. Much of this review is likely to change in the near future with ongoing and planned outer planet missions, adding to the sense of excitement and discovery associated with our exploration of our planetary neighborhood.     

高能电子对地球同步轨道卫星的影响分析

为了厘清在轨GEO(Geosynchronous Earth Orbit,地球同步轨道)卫星不时出现异常的原因,提高卫星执行任务的可靠性,首先从机理上介绍了空间环境中的地球辐射带及高能电子的情况,引出GEO卫星所处恶劣空间环境的现实;其次基于我国SEPC(Space Environment Prediction Center,国家空间环境预报中心)以及NSMC(National Satellite Meteorological Center,国家卫星气象中心)的空间环境月报资料,结合某GEO环境业务卫星故障的实际数据,经统计归纳,分析得出了地球辐射带中的高能电子是导致GEO卫星发生故障的主要原因;最后按照事例技术分析、常规按需预报和特殊情况下的实时预报等3个层次对高能电子预报方法进行了初步探讨。通过分析可以看出,为提高卫星完成任务的可靠性、降低长期管理风险,需要加强GEO卫星所处空间环境高能电子的预报工作。     

Balloon Position Determination on Venus

A position determination technique for balloons floating in the Venusian atmosphere is described. Measurements are all made using a single station of the NASA Deep Space Network. One coordinate of the fix is derived from a ranging measurement, and the other coordinate is derived from observation on earth of the polarization of a signal radiated from a linearly polarized antenna on the balloon, aligned to vertical by balloon local gravity.     

The Indian Space Program

The Indian Space Program is described. The main objectives of the program are to provide operation space services to the nation, especially in the fields of communications and remote sensing, and to use modern space technology for the benefit of the Indian people. Some applications of the Indian Space Program are remote sensing, imagery, communications, broadcasting, and surveys of natural resources for water, crop, forest, land, minerals, and ocean. The emphasis is on the development and operation of indigenous satellites and launch vehicles for providing these space services     

EUMETSAT

EUMETSAT is an intergovernmental organisation of 17 European States. Its primary objective is to establish, maintain and exploit European systems of operational meteorological satellites. EUMETSAT's initial system is based on the Meteosat satellite developed by the European Space Agency (ESA).