第一章航天器通信概述

DevelopmentandApplicationofSpacecraftCommunication（航天器通信的發(fā)展和應用）LLIUXLiuXinReferenceBooks2王建萍，劉濤，鄧忠禮，鄭雪峰

著

周賢偉

編叢書名：現(xiàn)代通信高技術叢書----深空通信國防工業(yè)出版社Overview（緒論）3SpacecraftsandCommunications4Whenthespacecraftroams(漫游)intheexpansive(浩瀚)space,thestaffonthegroundwillneedtogetintouchwiththespacecrafttimelyandeffectively,inthiscase,thespacecraft‘scommunicationsystemwillplayahugerole(發(fā)揮巨大作用).Byspacecraftcommunicationsystem,peoplecanlearntheintuitive(直觀)flightconditions,andformannedspacecraft,agoodcommunicationsystemcandisplaythedetailedstatusoftheastronauts（宇航員）inthespacetothegroundstaff.5ClockonthespacecraftAfterthespacecraftgoesintoorbit（軌道）,thegroundmonitoringstations(地面監(jiān)測站)willalwaysobservethespacecraft'sactivities.Forthesatellitesandthemannedspacecraft,theaccuracyofthetimeisparticularlyimportant,whichrelateswiththereturnofthespacecraft,andevenaffectsthelivesoftheastronauts（宇航員）.Therefore,itisveryimportantthattheclocksonthegroundandthespacecraftbecomesextremelyaccurateandconsistent（一致）.6AccordingtotheEinstein’srelativitytheory（愛因斯坦相對論）,theclockinaweakgravitationalfield(弱重力場)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（旋轉）,thesunwillgooveraplaceoftheearthperiodically,andtheaveragetimeintervalthatthesunpassesthroughthemeridian（子午線）twiceiscalledameansolarday（平均太陽日）.thetimereferencingthemeansolardayiscalledthemeansolartime;themeansolartimestartingfromtheBritainGreenwichMeridian（格林威治子午線）iscalledtheworldtime.9Atomictime（原子時）StartfromZeroo’clockoftheworldtimein1thJanuary1958.Asthefrequencyoftheelectromagneticwave（電磁波）emitted（發(fā)射）andabsorbedbythechangedatomisextremelystable（穩(wěn)定）,theatomictimingismoreuniformthanthetimingsystembasedontheEarthrotation,thereforetheatomicclockiswidelyusedinthespacecraftcommunications.10Inordertomaketherunningvelocities（速度）oftheclocksonthespacecraftandtheterrene（陸地）tobeconsistent,thescientistsslowtherunningvelocityoftheclockonthespacecraft,inthiscase,thetimedisplayedbytheclockonthespacecraftisthesameasthatdisplayedbytheclockontheterrene,whichgivesaverybighelptothesatellitecommunicationandpositioning.Receptionandtransmissionoftimecommandbythespacecraft11SpacecraftCommunicationsSpacecraftcommunicationsystemreferstoacquireandtransmitthevisual,dataandaudio（視頻音頻）informationbetweenthespacecraftandtheterreneincludingtheenvironmentalimagesinsideandoutsidethemannedspacecraftcabin（載人飛船倉）thelivingimagesoftheastronautsthevoicebetweentheastronautsandthestaffschargingthegroundstationthedatainformationordatacommandbetweenthespacecraftandtheterrene.Voicecommunicationisabasicrequirementofthemannedspacecraft.Voicecommunicationsestablishthemutual（相互）contactbetweentheterrestrial-communicationstaffsandtheastronauts,andsometimesitcanbeconverted（轉接）directlytotheflightcontrolcenter.Byvoicecommunications,thecontrolcentercanreceivetheastronauts’currentsituationstimely,andsendthemactiveinstructions（活動指令）tocompletethespaceflightmissions.1213Informationreceptionandtransmissionontheterrene14Theearlyspacecraftssuchasthe“Oriental”（東方號）spacecraftoftheformerSovietUnion（前蘇聯(lián)）andtheAmerica‘s“Gemini（雙子座）”spaceship,transfertheimagesusingtheanalogsignals(模擬信號).Althoughthetransfertechniqueoftheanalogimageisverysimple,thetransferqualityoftheimageisnotgood.Withthedevelopmentofthespacetechnology,theimage’squalityrequirementsareincreasing,andcurrentlymostofthemannedspacecraftstransmitthedigitalimage(數(shù)字圖像),whichhashigherqualityandcanbetransmittedbysharingthechannelwithotherspacecraftcommunications.15Throughtransmittingthetelevisionimagesfromthespacecrafttotheground,theastronauts’statecanbedirectlymonitoredbythegroundstations.Whentherendezvous（交匯）anddocking（對接）isimplemented,theTVimagescanmaketheastronautsandthegroundstationstointuitively（直觀）understandtherelativemotionbetweenthespacecraftandthetarget,inordertocontrolthespacecrafteffectively.TVcanalsobeusedforpublicity（宣傳）,unexpectedeventmonitoringandflightliteraturecompilation（飛行文獻的編集）etc.16InformationTransmissionandreceptionofthespacecraft17SpacecraftPowerTomakethespacecraftexplore(探索)thespace,thegreatpowerisneeded,thereforethescientistsattach（綁縛）avarietyofpowerequipmentsonthespacecraftforitsnormalwork.Therocketengine（火箭發(fā)動機）isthesolepowersourcetosendthespacecraftintothespace,andafterenteringthespace,thespacecraftwilluseitsowncarryingfuel（攜帶燃料）topushitselftothetarget.Somespacecraftsalsohavesmallrocketenginesonthem,andmaycarrysomefuel.However,therocketengineonthesatellitehavetobeusedrepeatedly,sothatthesatellitecanchangesitsorbitslowly.18Theenergyclassificationusedbythespacecraftpropulsion（推進）includeschemicalpower,airpower,electricpower,solarsailpower（太陽帆動力）,nuclearpower（核動力）andlaserpower（激光動力）.Thepropulsionsusedinthemannedspacecraftarebasicallythechemicalrocketengines,mostofwhichareliquid（液態(tài)）rocketengines.Thesolid（固態(tài)）engineisonlyusedinthesituationforstartingonce,forexample,theescapinglife-saving（逃逸求生）engineandthebrake（制動）engine.19Liquidhydrogen-fueledrocketengine液氫燃料發(fā)動機Ionengine離子發(fā)動機20Thepropulsionsystemofthe“Union（聯(lián)盟）”TMspacecrafthasatotalof35rocketengines,including1brakeengine,14bigattitudecontrol(大姿態(tài)控制)engines,12smallattitudecontrolengines,and8returning-capsule(返回艙)attitudecontrolengine.The“Apollo（阿婆羅）”spacecraftisequippedwith50engines,andsevenpropulsionsubsystemsincludingthelaunchescape(發(fā)射救生)system,theservicepropulsion(服務推進)system,thedecliningpropulsion(傾斜推進)system,therisingpropulsion（上升推進）system,theserving-capsulereactedcontrol（服務艙反作用控制系統(tǒng)）system,thelunar-capsulereactedcontrolsystems（登月艙反作用控制系統(tǒng)）andcommanding-capsulereactedcontrolsystem（指揮艙反作用控制系統(tǒng)）21"Viking"5Crocketengine22Thespacecraftdoesn’tonlysendthepayload（載荷）ontotheEarthorbitorbacktotheEarth,butalsostaysontheorbit,takingadvantageofavarietyoftestinginstrumentsandequipmentstocarryoutvariousexperimentsandstudies.Toaccomplishthesetasks,thespacecraftdoestheentering-orbitflight（入軌飛行）,andperformsorbitalmaneuvers(軌道機動),aswellaschangesandmaintainsacertainflightattitudewiththepropulsionsystem.Thus,thespacecraftrequiresthreekindsofpropulsiondevices,thatisthemainengine,themaneuvering(機動)engineandtheattitudecontrolengine.23Enginesonthespacecraft24ReturntotheEarthSomespacecraftsdon’tonlybeartheburdenofexploringthemysterious（神秘）space,butalsoreturntotheearthaftercompletingthespacemissions.Sincethespeedofthespacecraftisveryhigh,howtoensurethesafereturningandlandingofthespacecraftisveryimportant.25Stepone:orbitalchange（軌道改變）BeforereturningtotheEarth,thespacecraftautomaticallyadjusts（調整）thespaceorbitattitudetothereturningattitudeaccurately,andaftertheadjustment,thespacecraftmaintainsastablerunninginthisattitude.Thenbystartingthebrakerocketengineandgeneratingareversepushforce(反相推力),therunningspeedofthespacecraftisreduced,andthespacecraftisforcedtobeawayfromtheoriginalorbitandenterthepresetreturningorbit(預先返回軌道).26Steptwo:throughtheblackarea黑障區(qū)Whenthespacecraftgoesdowntotheheightofabout40kilometersawayfromtheground,thegas（氣體）andthespacecraft’ssurfacematerialintheseveral-thousand-degreehigh-temperatureareaformedaroundthespacecraft’ssurface,aredecomposed（分解）andionized（電離）intoalargenumberofmolecules（分子）.Thesemoleculesformaplasmasheath（等離子鞘）outsidethespacecraft.Theplasmasheathcanabsorbandreflecttheelectromagneticwaves,andmaketheradiocommunicationsbetweenthespacecraftandtheoutsideworldinterrupted（中斷）.Thisphenomenonbecomestheblackbarrier,andtheareayieldingtheblackbarrieriscalledtheblackbarrierarea.27Step3:SoftlandingThespacecraft’ssoftlandingisthatthespacecraftlandedsafelybythedeceleration（減速）meanssuchasbrakerocketandparachute(降落傘).Toensurethespacecraft’ssafereturntotheground,itisnecessarytodevelopareliableparachutesystemthatallowsthespacecrafttolandatlowspeedbyparachutedecelerationinlowaltitudeclosetotheground,sothatthespacecraftcanbeensuredtoreturntothegroundintactly(完好).28PositioningandSearchingIftheabovekeytechnologiesaresuccessfullyresolved,thespacecraftwillbeabletoreturnsafelytotheground.Butonthevast（遼闊）andcomplexland,wheretofindthespacecraftbackfromthespace?Thisrequiresthatthepositionofthelandingspacecraftcanbeforecasted（預測）andmeasuredtimelyandaccurately,andthestaffintherecoveryarea（回收區(qū)）canfindthelandingspacecraftassoonaspossible.29303132ImportanceofpositioningandcommunicationwhenlandingWhentheRussia“Union”TMAlmannedspacecraftreturntothelandonMay4,2003,itdeviates（偏離）460kmfromapredeterminedlandingsite,andoncelosesthecontactwiththegroundcontrolcenterinMoscowforuptotwohours.Fortunately,thethreeastronautsonthespacecraftaresafe.Thisisthefirstmannedspacecraftreturningfromthespace,sincethewreck（失事）oftheUnitedStates“Columbia（哥倫比亞）”spaceshuttle（航天飛機）inFebruary2003.

33LandingfieldselectionAtfirstglance,thelandingfieldhasnodifferencefromthegeneralgrassland（草原）andsea,whichseemstobechosenveryrandomly.Infact,itisnotthecase,andtheseplacesareselectedbyconsideringvariousfactorscomprehensively,whichmustbethesafeandeasylandingplaces.Theprincipleofthelandingsiteselectionistofacilitatetheintegrateduseofthecountry‘sspacetracking（航天跟蹤）andcommunicationsnetwork.Thelandingfieldmustbelargeenoughtoaccommodatealargerlandingdeviation（落點偏差）.Theclimaticconditionsofthelandingfieldmustbeverygood,whichcannothavestrongwindsorthunderstorms（雷暴）.Accordingtothecountry’sgeographical（地理）characteristicsandconditions,thelandingfashionsuchaslandlandingorsealanding,shouldbechosen.34Thelandingfieldsofthemannedspacecraftgenerallyhavetwokinds:mainlandingfieldanddeputylandingfield（副著陸）.Inthecaseofthebadweatherconditionsinthemainlandingsite,thedeputylandingfieldcanplayarole.Inaddition,thereareemergencylandingfields（緊急著陸）foremergencyuse,andtheseemergencylandingfieldsshouldchoosesomeregionsaroundtheworld.Thelandingfieldsshouldhavenotonlythefunctionsofthesatellitelandingfields,butalsothefunctionofcommunicatingwiththeastronautsinsidethespacecraft,aswellasthefunctionofrescuingandfetching（救援和接回）theastronauts.35Groundradarvehicleissearchingforspacecraft36"Discovery"spaceshuttleislanding通信技術

信息的具體形式：聲音、圖像、文字、數(shù)據(jù)等。消息（NEWS，MESSAGE）：——關于人或事物情況的報道?！ㄐ胚^程中傳輸?shù)木唧w對象：文字，語音，圖象，數(shù)據(jù)等。信息（INFORMATION）：——有用的消息信號（SIGNAL）：——信息的具體存載體。信息技術的處理對象：信息經(jīng)過傳感器轉換為電信號，就成為信息技術要處理的對象。信息技術概括起來主要包括兩類技術，即信息處理和信息傳輸。通信系統(tǒng)

自古以來，信息就如同物質和能量一樣，是人類賴以生存和發(fā)展的基礎資源之一。人類通信的歷史可以追溯到遠古時代，文字、信標、烽火及驛站等作為主要的通信方式，曾經(jīng)延續(xù)了幾千年。

烽火導航通信（communication）：一切將信息從發(fā)送者傳送到接收者的過程都是通信過程。通信系統(tǒng)的主要任務是傳遞信息。通信系統(tǒng)實現(xiàn)信息傳送過程的系統(tǒng)。無線通信系統(tǒng)

通信也叫信息傳遞，它的主要任務是傳遞信息，即將經(jīng)過處理的信息從一個地方傳遞到另一個地方。對信息傳遞的要求主要是提高其可靠性和有效性。信息處理的目的是為了更可靠、更有效地傳遞信息。電通信的發(fā)展歷史從1837年美國人莫爾斯發(fā)明人工電報裝置開始，至今不過170年。翻開厚厚的電信史冊，沿著歷史的腳步一路走來，在技術和市場需求的雙重驅動下，僅有一百多年歷史的電通信發(fā)生了翻天覆地的巨變，取得了令人驚嘆的輝煌成就。模擬通信系統(tǒng)模型和數(shù)字通信系統(tǒng)模型模擬信號和數(shù)字信號模擬信號：代表消息的信號參量取值連續(xù)，例如麥克風輸出電壓：(a)話音信號(b)抽樣信號模擬信號數(shù)字信號：代表消息的信號參量取值為有限個，例如電報信號、計算機輸入輸出信號：通常，按照信道中傳輸?shù)氖悄M信號還是數(shù)字信號，相應地把通信系統(tǒng)分為模擬通信系統(tǒng)和數(shù)字通信系統(tǒng)。(a)二進制信號(b)2PSK信號

數(shù)字信號

數(shù)字通信的特點優(yōu)點抗干擾能力強，且噪聲不積累傳輸差錯可控便于處理、變換、存儲便于將來自不同信源的信號綜合到一起傳輸易于集成，使通信設備微型化，重量輕易于加密處理，且保密性好缺點：需要較大的傳輸帶寬對同步要求高

通信系統(tǒng)主要性能指標通信系統(tǒng)的主要性能指標：有效性和可靠性有效性：指傳輸一定信息量時所占用的信道資源（頻帶寬度和時間間隔），或者說是傳輸?shù)摹八俣取眴栴}?？煽啃裕褐附邮招畔⒌臏蚀_程度，也就是傳輸?shù)摹百|量”問題。模擬通信系統(tǒng)：有效性：可用有效傳輸頻帶來度量?？煽啃裕嚎捎媒邮斩俗罱K輸出信噪比來度量。數(shù)字通信系統(tǒng)有效性：用傳輸速率和頻帶利用率來衡量。碼元傳輸速率RB：定義為單位時間（每秒）傳送碼元的數(shù)目，單位為波特（Baud），簡記為B。 式中T－碼元的持續(xù)時間（秒）信息傳輸速率Rb：定義為單位時間內傳遞的平均信息量或比特數(shù)，單位為比特/秒，簡記為b/s

，或bps碼元速率和信息速率的關系 或

對于二進制數(shù)字信號：M=2，碼元速率和信息速率在數(shù)量上相等。對于多進制，例如在八進制（M=8）中，若碼元速率為1200B，則信息速率為3600b/s。頻帶利用率：定義為單位帶寬（1赫茲）內的傳輸速率，即 或可靠性：常用誤碼率和誤信率表示。誤碼率誤信率，又稱誤比特率 在二進制中有

噪聲是通信領域中出現(xiàn)頻率很高的一個詞，但通信領域中所謂的噪聲不同于我們所熟悉的以音響形式反映出來的各種噪聲（如風聲、雨聲、人們的吵鬧聲、機器轟鳴聲等等）。

噪聲其實是一種不攜帶有用信息的電信號，是對有用信號以外的一切信號的統(tǒng)稱。概括地講，不攜帶有用信息的信號就是噪聲。顯然，噪聲是相對于有用信號而言的，一種信號在某種場合是有用信號，而在另一種場合就有可能是噪聲。

數(shù)據(jù)通信是隨著計算機和計算機網(wǎng)絡的發(fā)展而出現(xiàn)的一種新的通信方式，它是指信源、信宿處理的都是數(shù)字信號，而傳輸信道既可以是數(shù)字信道也可以是模擬信道的通信過程或方式。

通信系統(tǒng)示意圖51單工通信：指消息只能單方向傳輸?shù)墓ぷ鞣绞?，如廣播、遙控等；半雙工通信：指通信雙方都能收發(fā)消息，但不能同時進行收發(fā)，只能分時工作，如使用同一載頻工作的無線電對講機；全雙工通信：指通信雙方可同時進行收發(fā)消息的工作方式，如普通電話。

點對點之間的通信又可分為：5253串序傳輸：是將數(shù)字信號碼元序列按時間順序一個一個地在信道中傳輸；串序傳輸與并序傳輸并序傳輸：是將數(shù)字信號碼元序列分割成兩路或兩路以上的數(shù)字信號碼元序列同時在信道中傳輸。World'stoptenscientificandtechnologicalprogressin2004“Spirit(勇氣)”and“Opportunity(機遇)”rover（漫游器）landedonMars(火星)andfoundthattherewasevidenceofwater“Cassini(卡西尼)”spacecraftsuccessfullyenteredorbitaroundSaturn(土星)54

DeepSpaceCommunicationsOverviewTheactivitiestoexploretheuniversewillcontinuetogreatlypromotethedevelopmentofthefollowinghumanspaceflightsystems(載人飛行系統(tǒng))sensordesign(傳感器設計)long-distancetransmissionofinformation(遠距離信息傳輸)security(安全保障)somanyotheraspectsofengineeringandtechnology.ThefunctionsofSpacecraftcommunicationsSpacecraftcommunicationistomaintainalinkbetweenHumanandthespacecraftSpacecraftcommunicationisanessential(基本)partofSpaceexploration（空間探索）activitiesGuidanceandcontrolSpacecraftSenddetectedscientific（科學）databacktoEarth55Outerspace(外層空間):thescopeoftheuniverseoutsidetheEarth‘sdenseatmosphere（致密大氣層）,referredtoouterspaceorSpace.Geospace（地球空間）:thespatialextentoftheEarth‘sgravitationalpull（地球引力）,whichbelongstotheplanets（行星）space.(Near-Earthspaceandfar-earthspace)IntheITUWorldRadioAdministrativeConference,todevelopa“RadioRegulations（規(guī)章）",theaveragedistanceoftheEarthtotheMoon(3.844×105km)isdefinedastheboundaryofthenearanddeepspaces.5657Thelate1980s,theboundaryofthenearanddeepspacesisdefinedas2×106kmbyITU.InChina'saerospacesector,thedeepspaceisgenerallydefinedastheouterspacebeyondthemoonincludingthemoon.WhatisDeepSpaceDeepSpaceNoclearuniformdefinitionandclassificationITU's"RadioRegulations“(1988)Thespace,whosedistancefromEarthisgreaterthanorequalto2×106kmChinaEncyclopedia-Aerospacevolume（中國百科航天篇）Thespace,whosedistancefromEarthisgreaterthanorequaltotheaveragedistanceoftheEarth-Moon(about3.84×105km)ChinaAerospaceWhitePaper（中國航天白皮書）Amajorpre-researchobjectofspaceexplorationismoonexploration58

SolarSystem(太陽系）：

thesunandalltheplanetsthatgoroundit

GalacticSystem（銀河系）: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