第一章航天器通信概述

DevelopmentandApplicationofSpacecraftCommunication（航天器通信的发展和应用）LLIUXLiuXinReferenceBooks2王建萍，刘涛，邓忠礼，郑雪峰

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周贤伟

编丛书名：现代通信高技术丛书----深空通信国防工业出版社Overview（绪论）3SpacecraftsandCommunications4Whenthespacecraftroams(漫游)intheexpansive(浩瀚)space,thestaffonthegroundwillneedtogetintouchwiththespacecrafttimelyandeffectively,inthiscase,thespacecraft‘scommunicationsystemwillplayahugerole(发挥巨大作用).Byspacecraftcommunicationsystem,peoplecanlearntheintuitive(直观)flightconditions,andformannedspacecraft,agoodcommunicationsystemcandisplaythedetailedstatusoftheastronauts（宇航员）inthespacetothegroundstaff.5ClockonthespacecraftAfterthespacecraftgoesintoorbit（轨道）,thegroundmonitoringstations(地面监测站)willalwaysobservethespacecraft'sactivities.Forthesatellitesandthemannedspacecraft,theaccuracyofthetimeisparticularlyimportant,whichrelateswiththereturnofthespacecraft,andevenaffectsthelivesoftheastronauts（宇航员）.Therefore,itisveryimportantthattheclocksonthegroundandthespacecraftbecomesextremelyaccurateandconsistent（一致）.6AccordingtotheEinstein’srelativitytheory（爱因斯坦相对论）,theclockinaweakgravitationalfield(弱重力场)goesfasterthanthatinthestronggravitationalfield;inthevicinity（附近）oftheEarth'ssurface,theclockfrequencywillincreasesomebyincreasingonemeter,however,thiseffectisnotobvious.Thefrequencyoftheclockontheearthwilldecreasesomebytheaffectionoftheearth’sorbitmovementaroundthesunandthesun‘sgravity（引力）;iftheclockisveryfarfromtheground,theacceleration（加速）effectofthetimeismoreobvious.Thus,itisinevitable（不可避免）thattheclockonthespacecraftmovinginthespaceorbitrunsfasterrelatively.7Clockonthespacecraft8

WorldTimeTheworldtimingmethodwasproposedbefore1960.DuetotheEarth’srotation（旋转）,thesunwillgooveraplaceoftheearthperiodically,andtheaveragetimeintervalthatthesunpassesthroughthemeridian（子午线）twiceiscalledameansolarday（平均太阳日）.thetimereferencingthemeansolardayiscalledthemeansolartime;themeansolartimestartingfromtheBritainGreenwichMeridian（格林威治子午线）iscalledtheworldtime.9Atomictime（原子时）StartfromZeroo’clockoftheworldtimein1thJanuary1958.Asthefrequencyoftheelectromagneticwave（电磁波）emitted（发射）andabsorbedbythechangedatomisextremelystable（稳定）,theatomictimingismoreuniformthanthetimingsystembasedontheEarthrotation,thereforetheatomicclockiswidelyusedinthespacecraftcommunications.10Inordertomaketherunningvelocities（速度）oftheclocksonthespacecraftandtheterrene（陆地）tobeconsistent,thescientistsslowtherunningvelocityoftheclockonthespacecraft,inthiscase,thetimedisplayedbytheclockonthespacecraftisthesameasthatdisplayedbytheclockontheterrene,whichgivesaverybighelptothesatellitecommunicationandpositioning.Receptionandtransmissionoftimecommandbythespacecraft11SpacecraftCommunicationsSpacecraftcommunicationsystemreferstoacquireandtransmitthevisual,dataandaudio（视频音频）informationbetweenthespacecraftandtheterreneincludingtheenvironmentalimagesinsideandoutsidethemannedspacecraftcabin（载人飞船仓）thelivingimagesoftheastronautsthevoicebetweentheastronautsandthestaffschargingthegroundstationthedatainformationordatacommandbetweenthespacecraftandtheterrene.Voicecommunicationisabasicrequirementofthemannedspacecraft.Voicecommunicationsestablishthemutual（相互）contactbetweentheterrestrial-communicationstaffsandtheastronauts,andsometimesitcanbeconverted（转接）directlytotheflightcontrolcenter.Byvoicecommunications,thecontrolcentercanreceivetheastronauts’currentsituationstimely,andsendthemactiveinstructions（活动指令）tocompletethespaceflightmissions.1213Informationreceptionandtransmissionontheterrene14Theearlyspacecraftssuchasthe“Oriental”（东方号）spacecraftoftheformerSovietUnion（前苏联）andtheAmerica‘s“Gemini（双子座）”spaceship,transfertheimagesusingtheanalogsignals(模拟信号).Althoughthetransfertechniqueoftheanalogimageisverysimple,thetransferqualityoftheimageisnotgood.Withthedevelopmentofthespacetechnology,theimage’squalityrequirementsareincreasing,andcurrentlymostofthemannedspacecraftstransmitthedigitalimage(数字图像),whichhashigherqualityandcanbetransmittedbysharingthechannelwithotherspacecraftcommunications.15Throughtransmittingthetelevisionimagesfromthespacecrafttotheground,theastronauts’statecanbedirectlymonitoredbythegroundstations.Whentherendezvous（交汇）anddocking（对接）isimplemented,theTVimagescanmaketheastronautsandthegroundstationstointuitively（直观）understandtherelativemotionbetweenthespacecraftandthetarget,inordertocontrolthespacecrafteffectively.TVcanalsobeusedforpublicity（宣传）,unexpectedeventmonitoringandflightliteraturecompilation（飞行文献的编集）etc.16InformationTransmissionandreceptionofthespacecraft17SpacecraftPowerTomakethespacecraftexplore(探索)thespace,thegreatpowerisneeded,thereforethescientistsattach（绑缚）avarietyofpowerequipmentsonthespacecraftforitsnormalwork.Therocketengine（火箭发动机）isthesolepowersourcetosendthespacecraftintothespace,andafterenteringthespace,thespacecraftwilluseitsowncarryingfuel（携带燃料）topushitselftothetarget.Somespacecraftsalsohavesmallrocketenginesonthem,andmaycarrysomefuel.However,therocketengineonthesatellitehavetobeusedrepeatedly,sothatthesatellitecanchangesitsorbitslowly.18Theenergyclassificationusedbythespacecraftpropulsion（推进）includeschemicalpower,airpower,electricpower,solarsailpower（太阳帆动力）,nuclearpower（核动力）andlaserpower（激光动力）.Thepropulsionsusedinthemannedspacecraftarebasicallythechemicalrocketengines,mostofwhichareliquid（液态）rocketengines.Thesolid（固态）engineisonlyusedinthesituationforstartingonce,forexample,theescapinglife-saving（逃逸求生）engineandthebrake（制动）engine.19Liquidhydrogen-fueledrocketengine液氢燃料发动机Ionengine离子发动机20Thepropulsionsystemofthe“Union（联盟）”TMspacecrafthasatotalof35rocketengines,including1brakeengine,14bigattitudecontrol(大姿态控制)engines,12smallattitudecontrolengines,and8returning-capsule(返回舱)attitudecontrolengine.The“Apollo（阿婆罗）”spacecraftisequippedwith50engines,andsevenpropulsionsubsystemsincludingthelaunchescape(发射救生)system,theservicepropulsion(服务推进)system,thedecliningpropulsion(倾斜推进)system,therisingpropulsion（上升推进）system,theserving-capsulereactedcontrol（服务舱反作用控制系统）system,thelunar-capsulereactedcontrolsystems（登月舱反作用控制系统）andcommanding-capsulereactedcontrolsystem（指挥舱反作用控制系统）21"Viking"5Crocketengine22Thespacecraftdoesn’tonlysendthepayload（载荷）ontotheEarthorbitorbacktotheEarth,butalsostaysontheorbit,takingadvantageofavarietyoftestinginstrumentsandequipmentstocarryoutvariousexperimentsandstudies.Toaccomplishthesetasks,thespacecraftdoestheentering-orbitflight（入轨飞行）,andperformsorbitalmaneuvers(轨道机动),aswellaschangesandmaintainsacertainflightattitudewiththepropulsionsystem.Thus,thespacecraftrequiresthreekindsofpropulsiondevices,thatisthemainengine,themaneuvering(机动)engineandtheattitudecontrolengine.23Enginesonthespacecraft24ReturntotheEarthSomespacecraftsdon’tonlybeartheburdenofexploringthemysterious（神秘）space,butalsoreturntotheearthaftercompletingthespacemissions.Sincethespeedofthespacecraftisveryhigh,howtoensurethesafereturningandlandingofthespacecraftisveryimportant.25Stepone:orbitalchange（轨道改变）BeforereturningtotheEarth,thespacecraftautomaticallyadjusts（调整）thespaceorbitattitudetothereturningattitudeaccurately,andaftertheadjustment,thespacecraftmaintainsastablerunninginthisattitude.Thenbystartingthebrakerocketengineandgeneratingareversepushforce(反相推力),therunningspeedofthespacecraftisreduced,andthespacecraftisforcedtobeawayfromtheoriginalorbitandenterthepresetreturningorbit(预先返回轨道).26Steptwo:throughtheblackarea黑障区Whenthespacecraftgoesdowntotheheightofabout40kilometersawayfromtheground,thegas（气体）andthespacecraft’ssurfacematerialintheseveral-thousand-degreehigh-temperatureareaformedaroundthespacecraft’ssurface,aredecomposed（分解）andionized（电离）intoalargenumberofmolecules（分子）.Thesemoleculesformaplasmasheath（等离子鞘）outsidethespacecraft.Theplasmasheathcanabsorbandreflecttheelectromagneticwaves,andmaketheradiocommunicationsbetweenthespacecraftandtheoutsideworldinterrupted（中断）.Thisphenomenonbecomestheblackbarrier,andtheareayieldingtheblackbarrieriscalledtheblackbarrierarea.27Step3:SoftlandingThespacecraft’ssoftlandingisthatthespacecraftlandedsafelybythedeceleration（减速）meanssuchasbrakerocketandparachute(降落伞).Toensurethespacecraft’ssafereturntotheground,itisnecessarytodevelopareliableparachutesystemthatallowsthespacecrafttolandatlowspeedbyparachutedecelerationinlowaltitudeclosetotheground,sothatthespacecraftcanbeensuredtoreturntothegroundintactly(完好).28PositioningandSearchingIftheabovekeytechnologiesaresuccessfullyresolved,thespacecraftwillbeabletoreturnsafelytotheground.Butonthevast（辽阔）andcomplexland,wheretofindthespacecraftbackfromthespace?Thisrequiresthatthepositionofthelandingspacecraftcanbeforecasted（预测）andmeasuredtimelyandaccurately,andthestaffintherecoveryarea（回收区）canfindthelandingspacecraftassoonaspossible.29303132ImportanceofpositioningandcommunicationwhenlandingWhentheRussia“Union”TMAlmannedspacecraftreturntothelandonMay4,2003,itdeviates（偏离）460kmfromapredeterminedlandingsite,andoncelosesthecontactwiththegroundcontrolcenterinMoscowforuptotwohours.Fortunately,thethreeastronautsonthespacecraftaresafe.Thisisthefirstmannedspacecraftreturningfromthespace,sincethewreck（失事）oftheUnitedStates“Columbia（哥伦比亚）”spaceshuttle（航天飞机）inFebruary2003.

33LandingfieldselectionAtfirstglance,thelandingfieldhasnodifferencefromthegeneralgrassland（草原）andsea,whichseemstobechosenveryrandomly.Infact,itisnotthecase,andtheseplacesareselectedbyconsideringvariousfactorscomprehensively,whichmustbethesafeandeasylandingplaces.Theprincipleofthelandingsiteselectionistofacilitatetheintegrateduseofthecountry‘sspacetracking（航天跟踪）andcommunicationsnetwork.Thelandingfieldmustbelargeenoughtoaccommodatealargerlandingdeviation（落点偏差）.Theclimaticconditionsofthelandingfieldmustbeverygood,whichcannothavestrongwindsorthunderstorms（雷暴）.Accordingtothecountry’sgeographical（地理）characteristicsandconditions,thelandingfashionsuchaslandlandingorsealanding,shouldbechosen.34Thelandingfieldsofthemannedspacecraftgenerallyhavetwokinds:mainlandingfieldanddeputylandingfield（副着陆）.Inthecaseofthebadweatherconditionsinthemainlandingsite,thedeputylandingfieldcanplayarole.Inaddition,thereareemergencylandingfields（紧急着陆）foremergencyuse,andtheseemergencylandingfieldsshouldchoosesomeregionsaroundtheworld.Thelandingfieldsshouldhavenotonlythefunctionsofthesatellitelandingfields,butalsothefunctionofcommunicatingwiththeastronautsinsidethespacecraft,aswellasthefunctionofrescuingandfetching（救援和接回）theastronauts.35Groundradarvehicleissearchingforspacecraft36"Discovery"spaceshuttleislanding通信技术

信息的具体形式：声音、图像、文字、数据等。消息（NEWS，MESSAGE）：——关于人或事物情况的报道。——通信过程中传输的具体对象：文字，语音，图象，数据等。信息（INFORMATION）：——有用的消息信号（SIGNAL）：——信息的具体存载体。信息技术的处理对象：信息经过传感器转换为电信号，就成为信息技术要处理的对象。信息技术概括起来主要包括两类技术，即信息处理和信息传输。通信系统

自古以来，信息就如同物质和能量一样，是人类赖以生存和发展的基础资源之一。人类通信的历史可以追溯到远古时代，文字、信标、烽火及驿站等作为主要的通信方式，曾经延续了几千年。

烽火导航通信（communication）：一切将信息从发送者传送到接收者的过程都是通信过程。通信系统的主要任务是传递信息。通信系统实现信息传送过程的系统。无线通信系统

通信也叫信息传递，它的主要任务是传递信息，即将经过处理的信息从一个地方传递到另一个地方。对信息传递的要求主要是提高其可靠性和有效性。信息处理的目的是为了更可靠、更有效地传递信息。电通信的发展历史从1837年美国人莫尔斯发明人工电报装置开始，至今不过170年。翻开厚厚的电信史册，沿着历史的脚步一路走来，在技术和市场需求的双重驱动下，仅有一百多年历史的电通信发生了翻天覆地的巨变，取得了令人惊叹的辉煌成就。模拟通信系统模型和数字通信系统模型模拟信号和数字信号模拟信号：代表消息的信号参量取值连续，例如麦克风输出电压：(a)话音信号(b)抽样信号模拟信号数字信号：代表消息的信号参量取值为有限个，例如电报信号、计算机输入输出信号：通常，按照信道中传输的是模拟信号还是数字信号，相应地把通信系统分为模拟通信系统和数字通信系统。(a)二进制信号(b)2PSK信号

数字信号

数字通信的特点优点抗干扰能力强，且噪声不积累传输差错可控便于处理、变换、存储便于将来自不同信源的信号综合到一起传输易于集成，使通信设备微型化，重量轻易于加密处理，且保密性好缺点：需要较大的传输带宽对同步要求高

通信系统主要性能指标通信系统的主要性能指标：有效性和可靠性有效性：指传输一定信息量时所占用的信道资源（频带宽度和时间间隔），或者说是传输的“速度”问题。可靠性：指接收信息的准确程度，也就是传输的“质量”问题。模拟通信系统：有效性：可用有效传输频带来度量。可靠性：可用接收端最终输出信噪比来度量。数字通信系统有效性：用传输速率和频带利用率来衡量。码元传输速率RB：定义为单位时间（每秒）传送码元的数目，单位为波特（Baud），简记为B。 式中T－码元的持续时间（秒）信息传输速率Rb：定义为单位时间内传递的平均信息量或比特数，单位为比特/秒，简记为b/s

，或bps码元速率和信息速率的关系 或

对于二进制数字信号：M=2，码元速率和信息速率在数量上相等。对于多进制，例如在八进制（M=8）中，若码元速率为1200B，则信息速率为3600b/s。频带利用率：定义为单位带宽（1赫兹）内的传输速率，即 或可靠性：常用误码率和误信率表示。误码率误信率，又称误比特率 在二进制中有

噪声是通信领域中出现频率很高的一个词，但通信领域中所谓的噪声不同于我们所熟悉的以音响形式反映出来的各种噪声（如风声、雨声、人们的吵闹声、机器轰鸣声等等）。

噪声其实是一种不携带有用信息的电信号，是对有用信号以外的一切信号的统称。概括地讲，不携带有用信息的信号就是噪声。显然，噪声是相对于有用信号而言的，一种信号在某种场合是有用信号，而在另一种场合就有可能是噪声。

数据通信是随着计算机和计算机网络的发展而出现的一种新的通信方式，它是指信源、信宿处理的都是数字信号，而传输信道既可以是数字信道也可以是模拟信道的通信过程或方式。

通信系统示意图51单工通信：指消息只能单方向传输的工作方式，如广播、遥控等；半双工通信：指通信双方都能收发消息，但不能同时进行收发，只能分时工作，如使用同一载频工作的无线电对讲机；全双工通信：指通信双方可同时进行收发消息的工作方式，如普通电话。

点对点之间的通信又可分为：5253串序传输：是将数字信号码元序列按时间顺序一个一个地在信道中传输；串序传输与并序传输并序传输：是将数字信号码元序列分割成两路或两路以上的数字信号码元序列同时在信道中传输。World'stoptenscientificandtechnologicalprogressin2004“Spirit(勇气)”and“Opportunity(机遇)”rover（漫游器）landedonMars(火星)andfoundthattherewasevidenceofwater“Cassini(卡西尼)”spacecraftsuccessfullyenteredorbitaroundSaturn(土星)54

DeepSpaceCommunicationsOverviewTheactivitiestoexploretheuniversewillcontinuetogreatlypromotethedevelopmentofthefollowinghumanspaceflightsystems(载人飞行系统)sensordesign(传感器设计)long-distancetransmissionofinformation(远距离信息传输)security(安全保障)somanyotheraspectsofengineeringandtechnology.ThefunctionsofSpacecraftcommunicationsSpacecraftcommunicationistomaintainalinkbetweenHumanandthespacecraftSpacecraftcommunicationisanessential(基本)partofSpaceexploration（空间探索）activitiesGuidanceandcontrolSpacecraftSenddetectedscientific（科学）databacktoEarth55Outerspace(外层空间):thescopeoftheuniverseoutsidetheEarth‘sdenseatmosphere（致密大气层）,referredtoouterspaceorSpace.Geospace（地球空间）:thespatialextentoftheEarth‘sgravitationalpull（地球引力）,whichbelongstotheplanets（行星）space.(Near-Earthspaceandfar-earthspace)IntheITUWorldRadioAdministrativeConference,todevelopa“RadioRegulations（规章）",theaveragedistanceoftheEarthtotheMoon(3.844×105km)isdefinedastheboundaryofthenearanddeepspaces.5657Thelate1980s,theboundaryofthenearanddeepspacesisdefinedas2×106kmbyITU.InChina'saerospacesector,thedeepspaceisgenerallydefinedastheouterspacebeyondthemoonincludingthemoon.WhatisDeepSpaceDeepSpaceNoclearuniformdefinitionandclassificationITU's"RadioRegulations“(1988)Thespace,whosedistancefromEarthisgreaterthanorequalto2×106kmChinaEncyclopedia-Aerospacevolume（中国百科航天篇）Thespace,whosedistancefromEarthisgreaterthanorequaltotheaveragedistanceoftheEarth-Moon(about3.84×105km)ChinaAerospaceWhitePaper（中国航天白皮书）Amajorpre-researchobjectofspaceexplorationismoonexploration58

SolarSystem(太阳系）：

thesunandalltheplanetsthatgoroundit

GalacticSystem（银河系）:Verylarge,made

up

of

many

fixed

stars.59WhatisDeepSpaceCommunicationMoontoearthDistance:0.36~0.41×106kmCommunicationDelay:1.21~1.35sSpark(火星)toearthDistance:59.6~401.3×106kmCommunicationDelay:3.3~22.3sPluto(冥王星)toearthDistance:4297.9~7535.1×106kmCommunicationDelay:3.98~6.98h60Distanceandtimedelaybetweenearthandplanets61Spaceradiocommunication:radiocommunicationsbetweenthespacecraftsbeyondtheEarth'satmosphere,betweenthespacecraftandtheearth,orbetweentheearthstationsviathespacecraftrelays.Nearspacecommunication（近空通信）:radio

communicationbe