太空电梯的经济学外文文献翻译中英文翻译外文翻译.docx
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太空电梯的经济学外文文献翻译中英文翻译外文翻译.docx
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太空电梯的经济学外文文献翻译中英文翻译外文翻译
Spaceelevatoreconomics
Spaceelevatoreconomicscomparedandcontrastedwiththeeconomicsofalternatives,likerockets.
Costsofcurrentsystems(rockets)
Thecostsofusingawell-testedsystemtolaunchpayloadsarehigh.Pricesrangefromabout$4,300/kgforaProtonlaunch[1]toaboutUS$40,000/kgforaPegasuslaunch(2004).[2][3]Somesystemsunderdevelopment,suchasnewmembersoftheLongMarchCZ-2E,offerratesaslowas$5,000/kg,but(currently)havehighfailurerates(30%inthecaseofthe2E).Varioussystemsthathavebeenproposedhaveofferedevenlowerrates,buthavefailedtogetsufficientfunding(Roton;SeaDragon),remainunderdevelopment,ormorecommonly,havefinanciallyunderperformed(asinthecaseoftheSpaceShuttle).(RocketssuchastheShtil-3a,whichofferscostsaslowas$400/kgrarelylaunchbuthasacomparativelysmallpayload,andispartiallysubsidisedbytheRussiannavyaspartoflaunchexercises.)
GeosynchronousrocketlaunchtechnologiesdelivertwotothreetimessmallerpayloadstogeosynchronousorbitthantoLEO.Theadditionalfuelrequiredtoachievehigherorbitseverelyreducesthepayloadsize.Hence,thecostisproportionatelygreater.Bulkcoststogeosynchronousorbitarecurrentlyabout$20,000/kgforaZenit-3SLlaunch.
Rocketcostshavechangedrelativelylittlesincethe1960s,butthemarkethasbeenveryflat.[3]Itis,however,quitereasonabletoassumethatrocketswillbecheaperinthefuture;particularlyifthemarketforthemincreases.Atthesametime,itisquitereasonabletoassumethemarketwillincrease,particularlyifrocketswillbecomecheaper.
Rocketcostsaresignificantlyaffectedbyproductionvolumesofthesolidpartsoftherocket,andbylaunchsitecosts.Intuitively,sincepropellantisbyfarthelargestpartofarocket,propellantcostswouldbeexpectedtobesignificant,butitturnsoutthatwithhydrocarbonfuelthesecostscanbeunder$50perkgofpayload.Studyafterstudyhasshownthatthemorelaunchesasystemperformsthecheaperitbecomes.Economiesofscalemeanthatlargeproductionrunsofrocketsgreatlyreducecosts,aswithanymanufactureditem,andreuseablerocketsmayalsohelptodoso.Improvingmaterialandpracticalconstructiontechniquesforbuildingrocketscouldalsocontributetothis.Greateruseofcheaplabour(globalisation)andautomationispracticallyguaranteedtoreducemanpowercosts.Othercosts,suchaslaunchpadcosts,canbereducedwithveryfrequentlaunches.
Costestimatesforaspaceelevator
Foraspaceelevator,thecostvariesaccordingtothedesign.Dr.BradleyEdwards,whohasputforthaspaceelevatordesign,hasstatedthat:
"Thefirstspaceelevatorwouldreduceliftcostsimmediatelyto$100perpound"($220/kg).[4]However,aswiththeinitialclaimsforthespaceshuttle,thisisonlythemarginalcost,andtheactualcostswouldbehigher.Developmentcostsmightberoughlyequivalent,inrealterms,tothecostofdevelopingtheshuttlesystem.Themarginalorasymptoticcostofatripwouldnotsolelyconsistoftheelectricityrequiredtolifttheelevatorpayload.Maintenance,andone-waydesigns(suchasEdwards')willaddtothecostoftheelevators.
Thegravitationalpotentialenergyofanyobjectingeosynchronousorbit(GEO),relativetothesurfaceoftheearth,isabout50MJ(15kWh)ofenergyperkilogram(seegeosynchronousorbitfordetails).Usingwholesaleelectricitypricesfor2008to2009(7.1NZcentsperkWh)andthecurrent0.5%efficiencyofpowerbeaming,aspaceelevatorwouldrequireUSD220/kgjustinelectricalcosts.Bythetimethespaceelevatorisbuilt,Dr.Edwardsexpectstechnicaladvancestoincreasetheefficiencyto2%(seepowerbeamingfordetails).Itmayadditionallybepossibletorecoversomeoftheenergytransferredtoeachliftedkilogrambyusingdescendingelevatorstogenerateelectricityastheybrake(suggestedinsomeproposals),orgeneratedbymassesbrakingastheytraveloutwardfromgeosynchronousorbit(asuggestionbyFreemanDysoninaprivatecommunicationtoRussellJohnstoninthe1980s).
Forthespaceelevator,theefficiencyofpowertransferisjustonelimitingissue.Thecostofthepowerprovidedtothelaserisalsoanissue.Whilealand-basedanchorpointinmostplacescanusepoweratthegridrate,thisisnotanoptionforamobileocean-goingplatform.Aspeciallybuiltandoperatedpowerplantislikelytobemoreexpensiveup-frontthanexistingcapacityinapre-existingplant.Up-onlyclimberdesignsmustreplaceeachclimberinitsentiretyaftereachtrip.Somedesignsofreturnclimbersmustcarryupenoughfueltoreturnittoearth,apotentiallycostlyventure.
Contrastingrocketswiththespaceelevator
Governmentfundedrocketshavenothistoricallyrepaidtheircapitalcosts.Someofthesunkcostisoftenquotedaspartofthelaunchprice.Acomparisoncanthereforebemadebetweenthemarginalcostsoffullyorpartiallyexpendablerocketlaunchesandspaceelevatormarginalcosts.Itisunclearatpresenthowmanypeoplewouldberequiredtobuild,maintainandruna100,000kmspaceelevatorandconsequentlyhowmuchthatwouldincreasetheelevator'scost.Extrapolatingfromthecurrentcostofcarbonnanotubestothecostofelevatorcableisessentiallyimpossibletodoaccurately.
Spaceelevatorshavehighcapitalcostbutpresumablylowoperatingexpenses,sotheymakethemosteconomicsenseinasituationwheretheywouldbeusedtohandlemanypayloads.Thecurrentlaunchmarketmaynotbelargeenoughtomakeacompellingcaseforaspaceelevator,butadramaticdropinthepriceoflaunchingmaterialtoorbitwouldlikelyresultinnewtypesofspaceactivitiesbecomingeconomicallyfeasible.Inthisregardtheysharesimilaritieswithothertransportationinfrastructureprojectssuchashighwaysorrailroads.Inaddition,launchcostsforprobesandcraftoutsideEarth'sorbitwouldbereduced,asthecomponentscouldbeshippeduptheelevatorandlaunchedoutwardfromthecounterweightsatellite.Thiswouldcostlessinbothfundingandpayload,sincemostprobesdonotlandanywhere.Also,almostalltheprobesthatdolandsomewherehavenoneedtocarryfuelforlaunchawayfromtheirdestination.Mostprobesareonaone-wayjourney.
Fundingofcapitalcosts
Notethatgovernmentsgenerallyhavenothistoricallyeventriedtorepaythecapitalcostsofnewlaunchsystemsfromthelaunchcosts.Severalcaseshavebeenpresented(spaceshuttle,ariane,etc),documentingthis.RussianspacetourismdoespartiallyfundISSdevelopmentobligations,however.
Ithasbeensuggestedthatgovernmentsarenotusuallywillingtopaythecapitalcostsofanewreplacementlaunchsystem.Anyproposednewsystemmustprovide,orappeartoprovide,awaytoreduceoverallprojectedlaunchcosts.ThiswasthenominalimpetusbehindtheSpaceShuttleprogram.Governmentstendtoprefertocutcostsinmanycases.Spendingmoremoneyissomethingtheyareusuallyloathtodo.
Alternatively,accordingtoapaperpresentedatthe55thInternationalAstronauticalCongress[5]inVancouverinOctober2004,thespaceelevatorcanbeconsideredaprestigemegaprojectandthecurrentestimatedcostofbuildingit(US$6.2billion)isratherfavourablewhencomparedtothecostsofconstructingbridges,pipelines,tunnels,talltowers,highspeedraillinks,maglevsandthelike.Itisalsonotentirelyunfavourablewhencomparedtothecostsofotheraerospacesystemsaswellaslaunchvehicles.[6]
TotalcostofaprivatelyfundedEdwards'SpaceElevator
AspaceelevatorbuiltaccordingtotheEdwardsproposalisestimatedtocost$20billion($40Bwitha100%contingency)[7].Thisincludesalloperatingandmaintenancecostsforonecable.Ifthisistobefinancedprivately,a15%returnwouldberequired($6billionannually).Subsequentelevatorswouldcost$9.3Bandwouldjustifyamuchlowercontingency($14.3Btotal).Thespaceelevatorwouldlift2millionkgperyearperelevatorandthecostperkilogrambecomes$3,000foroneelevator,$1,900fortwoelevators,$1,600forthreeelevators.
Forcomparison,inpotentiallythesametimeframeastheelevator,theSkylon,12,000kgcargocapacityspaceplane(notaconventionalrocket)isestimatedtohaveanR&Dandproductioncostofabout$15billion.Thevehiclehasaboutthesame$3,000/kgpricetag.Skylonwouldbesuitabletolaunchcargoandparticularlypeopletolow/mediumEarthorbit.Anearlyspaceelevatorcanmoveonlycargoalthoughitcandosotoamuchwiderrangeofdestinations.[8]
References
1.^SpaceTransportationCosts:
TrendsinPricePerPoundtoOrbit1990-2000(PDF).Retrievedon2006-03-05.
2.^Pegasus.EncyclopediaAstronautica.Retrievedon2006-03-05.
3.^Theeconomicsofinterfacetransportation(2003).Retrievedon2006-03-05.
4.^WhatistheSpaceElevator?
.InstituteforScientificResearch,Inc..Retrievedon2006-03-05.
5.^55thInternationalAstronauticalCongress.InstituteforScientificResearch,Inc..Retrievedon2006-03-05.
6.^Raitt,David;BradleyEdwards.THESPACEELEVATOR:
ECONOMICSANDAPPLICATIONS(PDF).55thInternationalAstronauticalCongress2004-Vancouver,Canada.Retrievedon2006-03-05.
7.^[1]
8.^TheSpaceElevator-Chapter7:
Destinations.Retrievedon2006-03-05.
太空电梯的经济学
太空电梯经济学和火箭经济学的对比与比较。
目前(火箭)系统的成本
使用完善的测试系统发射有效载荷的成本是很高的,2004年其价格范围是从约4300美元每千克发射一个质子到40,000美元每千克发射一个飞马座。
一些处于发展中的系统,如长征系列的新成员长征CZ-2E,其提供的价格低至5000美元每千克,但是它(目前)具有较高的失败率(2E的失败率为30%)。
各种被推荐的系统,有的甚至提供更低的价格,但是未能获得足够的资金支持(如roton;海龙),仍然处于发展之中,或更为普遍,没有财政补助(如太空中的穿梭机一样)。
像shtil-3A型火箭,其成本低至400美元每千克,很少发射,但其有一个相对较小的有效载荷,得到了俄罗斯海军的部分资助,他们将其用于发射演习。
地球同步轨道火箭发射技术向地球同步
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