轨道炮.docx

轨道炮.docx

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轨道炮

Railgun

Arailgunisanelectricallypoweredelectromagneticprojectilelauncherbasedonsimilarprinciplestothehomopolarmotor.Arailguncomprisesapairofparallelconductingrails,alongwhichaslidingarmatureisacceleratedbytheelectromagneticeffectsofacurrentthatflowsdownonerail,intothearmatureandthenbackalongtheotherrail.

Railgunsarebeingresearchedasaweaponwithaprojectilethatwoulduseneitherexplosivesnorpropellant,butratherrelyonelectromagneticforcestoachieveaveryhighkineticenergy.Whilecurrentkineticenergypenetratorssuchasanarmour-piercingfin-stabilizeddiscarding-sabotcanachieveamuzzlevelocityontheorderofMach5,railgunscanpotentiallyexceedMach10,andthusfarexceedconventionallydeliveredmunitionsinrangeanddestructiveforce,withtheabsenceofexplosivestostoreandhandleasanadditionaladvantage.Railgunshavelongexistedasexperimentaltechnologybutthemass,sizeandcostoftherequiredpowersupplieshavepreventedrailgunsfrombecomingpracticalmilitaryweapons.However,inrecentyears,significanteffortshavebeenmadetowardstheirdevelopmentasfeasiblemilitarytechnology.Forexample,inthelate2000s,theU.S.Navytestedarailgunthatacceleratesa3.2kg（7pound）projectiletohypersonicvelocitiesofapproximately2.4kilometrespersecond（8,600km/h）,aboutMach7.TheygavetheprojecttheLatinmotto"VelocitasEradico",Latinfor"I,speed,eradicate".（Inthevernacularusage,"Speedkills."）

Inadditiontomilitaryapplications,NASAhasproposedtousearailgunfromahigh-altitudeaircrafttofireasmallpayloadintoorbit;however,theextremeg-forcesinvolvedwouldnecessarilyrestricttheusagetoonlythesturdiestofpayloads.

Basics

Thissectionneedsadditionalcitationsforverification.Pleasehelpimprovethisarticlebyaddingcitationstoreliablesources.Unsourcedmaterialmaybechallengedandremoved.（August2013）

Schematicdiagramofarailgun

Initssimplest（andmostcommonlyused）form,therailgundiffersfromatraditionalelectricmotorinthatnouseismadeofadditionalfieldwindings（orpermanentmagnets）.Thisbasicconfigurationisformedbyasingleloopofcurrentandthusrequireshighcurrents（e.g.oforder106ampere）toproducesufficientaccelerations（andmuzzlevelocities）.Arelativelycommonvariantofthisconfigurationistheaugmentedrailguninwhichthedrivingcurrentischannelledthroughadditionalpairsofparallelconductors,arrangedtoincrease（"augment"）themagneticfieldexperiencedbythemovingarmature.Thesearrangementsreducethecurrentrequiredforagivenacceleration.Inelectricmotorterminology,augmentedrailgunsareusuallyseries-woundconfigurations.

Thearmaturemaybeanintegralpartoftheprojectile,butitmayalsobeconfiguredtoaccelerateaseparate,electricallyisolatedornon-conductingprojectile.Solid,metallicslidingconductorsareoftenthepreferredformofrailgunarmaturebut"plasma"or"hybrid"armaturescanalsobeused.Aplasmaarmatureisformedbyanarcofionisedgasthatisusedtopushasolid,non-conductingpayloadinasimilarmannertothepropellantgaspressureinaconventionalgun.Ahybridarmatureusesapairof"plasma"contactstointerfaceametallicarmaturetothegunrails.Solidarmaturesmayalso"transition"intohybridarmatures,typicallyafteraparticularvelocitythresholdisexceeded.

Arailgunrequiresapulsed,directcurrentpowersupply.Forpotentialmilitaryapplications,railgunsareusuallyofinterestbecausetheycanachievemuchgreatermuzzlevelocitiesthangunspoweredbyconventionalchemicalpropellants.Increasedmuzzlevelocitiescanconveythebenefitsofincreasedfiringrangeswhile,intermsoftargeteffects,increasedterminalvelocitiescanallowtheuseofkineticenergyroundsasreplacementsforexplosiveshells.Therefore,typicalmilitaryrailgundesignsaimformuzzlevelocitiesintherangeof2000–3500m/swithmuzzleenergiesof5–50MJ.Forcomparison,50MJisequivalenttothekineticenergyofaschoolbusweighing5metrictons,travellingat509km/h（316mph）.Forsinglelooprailguns,thesemissionrequirementsrequirelaunchcurrentsofafewmillionamperes,soatypicalrailgunpowersupplymightbedesignedtodeliveralaunchcurrentof5MAforafewmilliseconds.Asthemagneticfieldstrengthsrequiredforsuchlauncheswilltypicallybeapproximately10tesla,mostcontemporaryrailgundesignsareeffectively"air-cored",i.e.theydonotuseferromagneticmaterialssuchasirontoenhancethemagneticflux.

Itmaybenotedthatrailgunvelocitiesgenerallyfallwithintherangeofthoseachievablebytwo-stagelight-gasguns;however,thelatteraregenerallyonlyconsideredtobesuitableforlaboratoryusewhilerailgunsarejudgedtooffersomepotentialprospectsfordevelopmentasmilitaryweapons.Anotherlightgasgun,theCombustionLightGasGunina155mmprototypeformwasprojectedtoachieve2500m/switha70caliberbarrel.Insomehypervelocityresearchprojects,projectilesare"pre-injected"intorailguns,toavoidtheneedforastandingstart,andbothtwo-stagelight-gasgunsandconventionalpowdergunshavebeenusedforthisrole.Inprinciple,ifrailgunpowersupplytechnologycanbedevelopedtoprovidecompact,reliableandlightweightunits,thenthetotalsystemvolumeandmassneededtoaccommodatesuchapowersupplyanditsprimaryfuelcanbecomelessthantherequiredtotalvolumeandmassforamissionequivalentquantityofconventionalpropellantsandexplosiveammunition.Suchadevelopmentwouldthenconveyafurthermilitaryadvantageinthattheeliminationofexplosivesfromanymilitaryweaponsplatformwilldecreaseitsvulnerabilitytoenemyfire.Inpractice,developingarailguntobelightweightandcompactcouldbedecadesawayandwillrequiremajorbreakthroughsinseveralareasofscienceandtechnologyincludingmaterialsscience,guidancepackagehardening,andenergystoragedensity.

History

In1918,FrenchinventorLouisOctaveFauchon-Villepleeinventedanelectriccannonwhichisanearlyformofrailgun.HefiledforaUSpatenton1April1919,whichwasissuedinJuly1922aspatentno.1,421,435"ElectricApparatusforPropellingProjectiles".Inhisdevice,twoparallelbusbarsareconnectedbythewingsofaprojectile,andthewholeapparatussurroundedbyamagneticfield.Bypassingcurrentthroughbusbarsandprojectile,aforceisinducedwhichpropelstheprojectilealongthebus-barsandintoflight.

In1944,duringWorldWarII,JoachimHänslerofGermany'sOrdnanceOfficebuiltthefirstworkingrailgun,andanelectricanti-aircraftgunwasproposed.Bylate1944enoughtheoryhadbeenworkedouttoallowtheLuftwaffe'sFlakCommandtoissueaspecification,whichdemandedamuzzlevelocityof2,000m/s（6,600ft/s）andaprojectilecontaining0.5kg（1.1lb）ofexplosive.Thegunsweretobemountedinbatteriesofsixfiringtwelveroundsperminute,anditwastofitexisting12.8cmFlaK40mounts.Itwasneverbuilt.Whendetailswerediscoveredafterthewaritarousedmuchinterestandamoredetailedstudywasdone,culminatingwitha1947reportwhichconcludedthatitwastheoreticallyfeasible,butthateachgunwouldneedenoughpowertoilluminatehalfofChicago.

During1950,SirMarkOliphant,anAustralianphysicistandfirstdirectoroftheResearchSchoolofPhysicalSciencesatthenewAustralianNationalUniversity,initiatedthedesignandconstructionoftheworld'slargest（500megajoule）homopolargenerator.Thismachinewasoperationalfrom1962andwaslaterusedtopoweralarge-scalerailgunthatwasusedasascientificexperiment.

Design

Theory

Arailgunconsistsoftwoparallelmetalrails（hencethename）connectedtoanelectricalpowersupply.Whenaconductiveprojectileisinsertedbetweentherails（attheendconnectedtothepowersupply）,itcompletesthecircuit.Electronsflowfromthenegativeterminalofthepowersupplyupthenegativerail,acrosstheprojectile,anddownthepositiverail,backtothepowersupply.

Thiscurrentmakestherailgunbehaveasanelectromagnet,creatingamagneticfieldinsidetheloopformedbythelengthoftherailsuptothepositionofthearmature.Inaccordancewiththeright-handrule,themagneticfieldcirculatesaroundeachconductor.Sincethecurrentisintheoppositedirectionalongeachrail,thenetmagneticfieldbetweentherails（B）isdirectedatrightanglestotheplaneformedbythecentralaxesoftherailsandthearmature.Incombinationwiththecurrent（I）inthearmature,thisproducesaLorentzforcewhichacceleratestheprojectilealongtherails,awayfromthepowersupply.TherearealsoLorentzforcesactingontherailsandattemptingtopushthemapart,butsincetherailsaremountedfirmly,theycannotmove.

Bydefinition,ifacurrentofoneampereflowsinapairofinfinitelylongparallelconductorsthatareseparatedbyadistanceofonemetre,thenthemagnitudeoftheforceoneachmetreofthoseconductorswillbeexactly0.2micro-newtons.Furthermore,ingeneral,theforcewillbeproportionaltothesquareofthemagnitudeofthecurrentandinverselyproportionaltothedistancebetweentheconductors.Italsofollowsthat,forrailgunswithprojectilemassesofafewkgandbarrellengthsofafewm,verylargecurrentswillberequiredtoaccelerateprojectilestovelocitiesoftheorderof1000m/s.

Averylargepowersupply,providingontheorderofonemillionamperesofcurrent,willcreateatremendousforceontheprojectile,acceleratingittoaspeedofmanykilometrespersecond（km/s）.20km/shasbeenachievedwithsmallprojectilesexplosively