Nuclear pulsed space propulsion systems project orion, 1970, 35p


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Nuclear pulsed space propulsion systems project orion, 1970, 35p

  1. 1. APPROVED FOR PUBLIC RELEASE q A b . VERIFIED UIVCLAslFIED UN CLA~S”iFliii LA-4541-MS ‘NJ ‘% ff. /?~y CIC-14 REPORT COLLECTI _~— REPROEXJCTK’N ~; ~ ~- COPY ‘i LOS ALAMOS SCIENTIFIC LABORATORY ~ of the University of California LOS ALAMOS q NEW MEXICO i VERIFIED UNCLASSWIED Per 7-/0-79 . Nuclear Pulsed Space Propulsion Systems (U) -1= _ =U):=_b ATOMIC UNITED STATES ENERGY COMMISSION CONTRACT W-7405 -ENG. 36 = ma“=%kg AEC RESEARCH AND DEVELOPMENT REPORTs===~— m_——0~~-o ~-ca 3=-m .sSm cJ— —m -1- = m ..-. .—_. .1 ____ .— ~’i . .— APPROVED FOR PUBLIC RELEASE
  2. 2. . APPROVEDm FOR PUBLIC RELEASE qm. q .’. 9 q O9 q . .*!i.‘ i . : q . c “.,.:”~’+.: .,* q * q ... ~.. ... ’ 89m ‘ 0:: .: q . :. :: q :: : .:. ::. OQ q . . : q 00 , . b This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contrac- tors, subcontractors, or their employees, makes any warranty, expre= or im- plied, or assumes any legal liability or responsibility for the accuracy, com- pleteness or usefulness of any information, apparatus, product or process dis closed, or represents that its use would not infringe privately owned rights. . . ,. This report expresses the opinions of the author or authors and does not nw- essarily reflect the opinions or viewa of the Los Alamos Scientific Lalmratory. s- q q q 9** q q 9 q q 9* q 90 0 * q 8 q 0 q e q q, qq:00 q q *9 q m q * q C: :00 ,,, . . q 00 :0. i“; q *em q *a qe q ** q e q q q q q m APPROVED FOR PUBLIC RELEASE
  3. 3. ., , APPROVED FOR PUBLIC RELEASE ‘-” - u~~~AJJ,; .,” * ! q q 9** .:= :~= :* q 00 0:000 ..: 9* .:00 q 0:: ,0 .0Written: October 1970 q ..* q . . . 900 ba LA-4541-MS C-91, NUCLEAR REACTORSDistributed: November 1970 FOR ROCKET PROPULSION M-3679 (64th Ed.) LOS ALAMOS SCIENTIFIC LABORATORY of the University of California LOS AL. AMOS s NEW MEXICO CtA:SIFICtiTIONH.’dW~ ‘1’O C UNCIA$SIFED BY MJ’I’W=~-f ~~ 4wmGwii.3 VERIFIEDBY (SIGNA’1’JJRE Nuclear Pulsed Space Propulsion Systems (U) by J. D. Balcomb L. A. Booth C. P. Robinson —— T. P. Cotter T. E. Springer J. C. Hedstrom C. W. Watson UNITED STATES ATOMIC ENERGY COMMISSION .-- —————.— — CONTRACT W-7405 -ENG. 36 q m q .* q 90 q *9 q ea qa - **..* APPROVED FOR PUBLIC RELEASE q q *** UNCI .ASNFIED
  4. 4. , .,. APPROVED FOR PUBLIC RELEASE ... - . q q9: 9** .*. . . . . . ::..:.:: -~ . b q. — . k~ .’ ...— . * . .. . . . ‘,. .’-. . . —4 :-” ------- ----- ii :O-s O.. q APPROVED FOR PUBLIC RELEASE
  5. 5. APPROVED FOR PUBLIC RELEASE !l!Ama F (xmENTs O.q Abstract 1 I. Introauctial 1 II. Nucl.cmReactionsfor PulsedPropulsion 3 Fusion 3 Fission 3 Laser Init ion of NuclearReactions tit 3 III. Preliminary DesignConcepts Oeneral 4 ConceptA-1, External~stem with PusherPlate 5 ConceptA-2, ExternalSystemwith Magnet Field and ic PusherPlate 6 ConceptB, InternslSystem 6 PulseUnit DesignConcepts -i’ DesignDsplicat ionsof PayloadShielding 8 Iv. MissicuConsiderations Performance and Estimates 9 General 9 scalingIaws 10 Optimizationrocedure P IL Comparison Externaland ~ternal ~stem Concepts of 12 Performance Limitat ons I u+ Performance Estimates 15 Acknowledgments 17 References l-f Appendices A. LaserConceptsand Consideraticms 18 B. Es* Considerations pusher-propellant for rnte~ction 20 c. NeutronEnvironmentalonsiderations the ExternalSystem C for 22.. 0 -0% q m q om q *O q *9 q 9* qe -MICLAWFIED .** ‘“ 8***** .** APPROVED FOR PUBLIC RELEASE q q
  6. 6. APPROVED FOR PUBLIC RELEASE a Pw3her-plate accelerat im, at end of mission,relative the apacecrdt, to a n/se# a. 2pacec~ accelention at end of mlssl~, relatiwe an Inertial to f’rsms of referunce, m/sec2 b J-, a~--ss 60 Stsntlard accelerat of gravity,9B m/eec2 icn I IIIWIMSdelivered the spacecraft y one @se to b unit,!? Im, (1~ = Ve/go),sec in Pulse-unit mass,kg M Total spacecraft initialnmas,kg Ma M==n*-absor~r IUSSS(Ma = Me + ~), W Initifil. epacecrzt pmpeKlaat mass, kg, consisting of n pulseunits of % m,es Is, (~= nnl) Me Mcmentum-conditioner nuss,kg kg Pavbad mass.k. AnY mass not desimated othexvise; Includesstructure (her than Ma)‘andIs laserunit, ~Mo = M - Ma - H). pusher~latemass,kg % n Numberof @se units,dimensionless q Pulse-unitenergym=lease,J u InitialvelncityOr the pusherplate ($ustafterthe pulse-unitinteraction) relative the spacecraft, /see to m Ve EffectiveVelQCitYof the propellant exhaust,m/see ‘i Averagevelocityof propellantimpinging against *he puslmr-plate surface,m/see w Materialstrength+8eight constantdefinedby Eq. (6),m/see Xa Ma/M, dissmaimless xo Me/M, ditu?nsionkss a DiJIIMMkdlSSE efficiency term definedby lul.(5) for fiteti system at Dinb?nslonlesa efficiency term def Inedby ~. (5) for externe3system 9 collimation factor def tied by Eq. (17), dinmaionless At T- Intenral betueen pulse-unit detonatlons$ sec Relative M.etauce OS travel or stroke, of the pusher plate relative . to the spm2ecraftj m N Mise%on-aquivalant tie-space velocityclmnge,m/see , T Efficiency te= deftiedby Eq. (2),dimensionless v Disk?nsbn.less paramder for en energyscalinglaw, definedby 2q. (8) u’ Dimensionlesster ~ it@ e”# ~, definedby lzq.(15) .: q :* q . . .- q 9 .* q em q m. 9:9 :.. . .iv q 0s0 --- ; -*- -em APPROVED FOR PUBLIC RELEASE
  7. 7. APPROVED FOR PUBLIC RELEASE ‘@-@q .0 q q 00 :.* q *: :00 q :.* :.O :a *:.: .0 : .:** .*. :** q. q q ** q NUCIEARPUKED SPACEPROPUWION SYslms w J. D. Balcomb L. A. Booth c. P. Robinson T. P. Cotter T. E. Springer J. C. Hedstrom c. W. Watson AWIRACT Inltislconsiderations presented are for advancedspace-propulsion concepts that are based on ener~ product cn by laser-drivenhermonuclear i t pulses. Preliminary designconcepts are comparedin which en individual pulseunit, locatedeitherintemaJJy or externeXly the system,Imparts to ~ me to the SIX?.cecI’Sf’t. pulseunits - Max?v sequentially ischarged d and initiated unt11 the desiredspacecraft velocityis reached. various means Of shockabsorption and shielding againstfast neutronsgenerated by the therwnuclearreactions are investigated.Indications are that the maximumspecificimpulsefor an internal systemwould be . 2500 see, whereasthat for an externalsystemmight attain-7500 sec. 1. INTROI.XJCPION g- be- to studythe application such energy of pulsesfor spacepropulsion.VariousI.ASL groups Studiesat Los AlamosSclent fficLaboratory(IASL)and at laboratorieshroughout t the world have have initiatedsupporting studiesand experiments,indicatedthe passibilityof Lnit ing lcw-yield iat and are particularly activein investigations ofthermonucleareactions the use of an intense r by laser-inducedhe.rnsmucleer t reactions.laserpulseto heat to ignition very smellpellet a The propulsion potentialof nuclear-pulsedys- sof fusionablematerial. If a cuff iciently h%gh tem- tems is extraordinary:It offersthe possibility ofperatureand densitycan be achiwed in the pellet, the optimalutilization the ultimate approaching ofthermonucleareactions r will occur releasingsub- kncwn sourceof energywith minimaladversesidestantialenergy. Presumably, this energyrelease effects.wouldbe much lower (O.1to 100 equivalenttons of The use of nuclearexplosions for propulsion wasTNT) than the minimumpracticalyieldspresently firstproposedby Uleml and has been investigatedinavailable from fission imploson systems. Possible - i detailbetween1958 and 1965 underProjectOrion.*applications f such small,cleanenergyreleases o IiIthe finalconcept,fiss%onexplosions one to ofincludeterrestrial electricpurer generation and 12 lcllotonsequivalent ( m explosiveenergyrelease)the ob~ectof this repoz’t:spacepropulsion. were to be detonated behinda spacec~ to accehr- Activities IL relatedto I.aeer+lriven at ate propelMnt materialthatwould impe.rt momentumthermonucleareactions r have been underway for over to a massivepusherplate;this momentum,in turn,one year, including thermonuclearurningstudies b was to be transmitted more gradusllyfrom the pusherend laserdevelopment.In J’une 1970,the Advanced plateto the spacecraft througha pneumaticspringPropulsionConceptstask grcupwas formedwith the Wstem. @ studyWas terminated becauseof the in-specificob~ective Investigating of advancedpropul- herenjhuge sise of the resultingspacecraft(4000 q 00sion concepts; part of this invest~O~i”~t’ as ~ Uonr$ ,“because the limitations of imposedby the q* q q9 9* :: **C q * 9** q ** q O* q q :0 q 0 1 APPROVED FOR PUBLIC RELEASE
  8. 8. APPROVED FOR PUBLIC RELEASE m q b q *. 3 q ‘. * q*: 9:0 q mm . . . . . :: q* ...: q q: q -o . =**.nucleartest-bantreaty,and becauseof the d~i:”” “%at ~f%k ~2eWurt withoutths eknents deterio-cultyOf testingthe system. N was, however,gen- rat*. Nuclear -@.eed pmgmldcm systems are shi-eI’611Ycknowledgedhat the concept a t was techni- 3x@y mites, but, becanseof the extrewdy shortC- soundmd mighthave achievedthe vem high interaction b of the pulses,at much highertem- tspecificimpulse(1 ) of - 25m sec. Pemtures. The interaction imes,of the orderof t . Sp nKU.iseconde,re simplytoo shortto causemuch a The possibility producingrmIsIJ., of cleannu-cleare@osions mmmves the two primaxyobstacles destnwtive damage,especiaUy if ablative materials are usea to furtherprotectthe expmea surfacesfmm .in the Orionconcept--large size end spacepollu- high temperatures .tion. Spacecraft can now be envisioned that may beeven smallerthen those curnently proposedfor the Although, present,it is assumedthat the atnuclearspaceshuttle,yet be able to greatlyout- genemtlon of laser-drivenhernxmucl.e=eactions t rperformeven that high-performance system. @ ap@kable to apacepropulsion feasible, is i.e.,systemcan also be meenin@iUy testedon or belcw that the largeeffortsat IASL and elsewhere wilJ.-d. AMhou6h a laser-drivenulsedpropulaim p yieldthe expectedresults,It is nevertheless e- dsystem,as any otheradvancedsystem,would requti sirableto obtainan earlyworkingkncwledge the ofa fairlylong devebpmant tires(perhaps until 1985- theories.9na practices high-energy of piked lasers,lW), it shouldbe activelypursuedbecauseit of thenmnucleerburning,and of th th?nmdynamicswould make mannedexploration the solarsystem of of denseplasms. This Inforfmtion neededto isas feasibleas present-day lunarexploraticm, nd a attackthe p-ion problem,to identifythe prod-traveltitoetih orbit inexpensive nd rout5ne. a ucts of suchenergyreleasesand their interactionThese,in fact,are the characteristics the sys- of with the ~ahg6, and to investigate mmns ofternidentified NASA as necessary a long-range by in tailoring the energy=Lesses to specific propulsionspace -exploration progmm. applications. The high potentialperformance a nuclear- of This reportdiscussessome aspects of usingpulsedpropulsion systemis due to (1)high specific nuclearreactions(eitkr fissionor fhsion)forenergyend (2) shortinteract times. The spa ion - piked propildon; cmqxms preliminary designcon-cificimpulseincreases the squareroot of the as c~s$ lncludins pulseunits,ma their performanceepeciflcenergy. Efficientconversion chemical of limitations; pnesentsmissionconsidenxtias; ~areactionenergieswcmld xweultin an I~ofcmly givesprekhmhuuy ~rfonnance estimates.-460 sec. On the otherwa, if a ndierisl were Althougha detailedmeferencedesignhas notusea which had 100 timesthe specificenergyof TNT been prepared,earlypublication theseprelimiruuy ofend this energywere converted kineticenergy, to considemtlonsseeneddesirable disseminate to asvelocit5.8s corresponatig an I of . 3090 sec to Sp quicklyas possiblethe information enerated g and tocoold be reached. E a mixtureof De were totel- indicateprcmleingmea of rese~.Iy fusedand the maulting energytota13yconvertedintobackwardnrnnentum the react of icm products, _ts have been givento namingthe proposed NuclearPulsedPro@.sion Concept,shouldfurthert~ Isp W- be as h%h as 2.2 x 106 sec. Cletwlyt~fcl.e vebcities associatedwith the latterex- consideratimlead to a full. -fled@ pro~ect,and theempk couldnot be tole~ted; this value is cited nann3 Sirius*wcs chosen.only to indicate the upper limitof fusionpro@.- %3.riua, the brighteststar in the heavens,is the principal etfxr the ccmstellfbtion in CenisWjor, .Sion. the GreatDog (n Rover). Cads W@r followsin the sky closeto t~ heels of Orion,the great Nuclearpropulsicmconcepts, general, in are hunter,who by one mythological stay was a “fool-13mitedby the abi13@ of the materielsused to -, heaven-daring bel who was chained the = to . sky for his impie~.” lW nen= SIriueis fran thewm5t6na ext~me tenqwaturesratherthan by the GreekadJective USIPOB,nmaningscorching, per- orspecificenergyavailable. This limit is especial- haps from the Arabicsiraj,the glittering one. The Egyptian veneratedSlrlus,regarding as a itly c0n6tr8tiing n 601ia40r6 UUCLW i rockets. q81Ps. . toti~W tl$”@Ang of tlua : XWLa and a subsequentthe temperature the fuel elennts mwt exc~a of ~ .0go~ h@res$.: q *. 9* q9 q 90 900 q :.. .. :.2 amuMu!@ * .. 00 q q APPROVED FOR PUBLIC RELEASE q q q m
  9. 9. APPROVED FOR PUBLIC RELEASE 9* q 9 q ** q O* q ** : .*8 q .. q *9 9** q :* q . :-c ** q ( q :*O9q * 9* .:0 FOR PULSEDPROIUS616N .:. :q q :““-se hjgh+nergy neutronsrequireshielding II. NUCLEARREACTIONS Of the spacecrrxft.ost efficiently, his shleldlng M tFusion shouldbe placednear the sourceof the neutrons, The isotopesof hydrogen, helium,and lithium particularlyecauseother considerations b also sug-would fuse i.f sufficient a quantity materialwere of gest the desirability f diluting o the initialenergyheatedto a sufficienttemperature and held together release with a surrounding adjacent or mass. Thefor a sufficient lengthof time. In the laser-driven sourceparticles, movingat near relativisticeloc v -fusionconcept,the necessaryconditionsare achieved ities,re simplytoo energetic handle: their a toby coupl.lng outputfroma laserto a small.,f- the e stagnation ould causeexcessive w ablation any offectivelyconfinedregionof fusicmable isotopes. surface,and they would penetrate protective a mag-Only a smallquantity, the orderof one gram,is of neticfield. Also,per unit of ener~ (E = 1/2 n?),required. For example,one gram of deuterium plus theseparticlesare carryingonly a relatively smalltritium(D+T),totallyburned,wmld producean en- amountof momentum(P = rev). Becausethe momentumergy equivalent exploding tons of m. to 80 per unit energy (P/E)is equalto 2/v, it would be In the propulsionconceptdiscuesedherein,the wastefulof energyto impartmomentumintohighamountof energyreleased what seemsat the present velocities. Some nonreacting ass,much larger in m than the fusioningmass,must be used to dilutethetime a plausiblesize for a lasar-drivenusionre- f energyintoa more usableform. mis UULSS, ca.ueaactionis clearlyfar belowthe amountof energythat the propellant, ight also providethe desired mis desiredfor each pulse,i.e.,a few to many tens shielding function.of tons TNT equivalent.It does not seem necessaryto dwellhere on how one might proceedfrcsn the Fissioninitialsmellamountto the required largeemouut; In a vexy analogous manner,fissionable isotopesit is simplyassumedthat a solution the problen to can be compressed the pointwhere a very smell towill be available the time it is needed. at quantitybeccsnesupercritical. s Such a fissioning The productsof the basic reactions wIIJ. be systemmey producefewernet neutronsper unit ofhigh-energy chargedparticlesend neutrons. The usableenergyreleased, but would form radioactivefollcwing basic fusionreactions are being con- fissionproducts--an ndesirable u byproduct. HCW-sidered: ever, releaseof this smellamountof radioactivity D+D may be tolenble in the alreadyhostileenvironment + 3He (0.82MW) +n (2.45 WV) D+D + T of spacebecausethe mwt majorityof the debriswill (1.OIMeV) +H (3.02MeV) have velocitiessufficient escapethe solar to D+’l! +4 He (3.5 MeV) +n (14.1MeV) D+3He -$ ‘He system. (3.6 MeV) +H (14.7MeV) Laser Ihitiatlon NuclearReactions of The easiestto initiate the D+T reaction iswhich has a reactioncrosssectionat lW tempera- The followingcharacteristicsmake a laserturesmore than two ordersof msgnitudegreaterthan eminentlysuitablefor achievingextremecompressionthat of the otherthreepairs. However,its usefiiL- end heatingof smallpellets:ness w be impairedbecause80$ of the fusionenergy q High energydensity. Ener~ storedas excitedis carriedoff by the 14.1-W? neutrons, which have molecularstatesof a suitableI.asingaterial ma longmean free path. Even in burningdeuterlum, a can be sweptout of a largevolumeand focusedsubstantial raction the total fusionenergyis f of on a smallarea.carriedoff by 14.1-MeVneutronsfrom the D+l! reac- q ShortPUI.S duration. Pulsewidths in the etion,whichwil.1 normallyfollcmthe tritium-forming rangeof 10-1 to 10-7 sec can be achieved. 0branchof the D+D reaction; anotherportionof theenergyis dissipated 2.45-MeV by neutrons. 13urning q Controllability. Iaserpulsescan be shapedan equalatomicmtitureof D+%iewill also produce and selected the desiredtime in a low-energy atso= 14.1-Mev neutronsdue to the CO~$iW$+3:. ** stageend then amplifiedin successive high- q q q 0:0 qreactionend the foUloulngD+’l? reactidn: .: : q: : ee q energystages. q 0 q q 9 q0: q:0 q e* q 00 qm mmmm * ** * q q APPROVED FOR PUBLIC RELEASE q q q q
  10. 10. APPROVED FOR PUBLIC RELEASE q q O q b* q q q q :O q *. . . . . . q 0 ::* : q q q bg- :.. . :0 Presentestimate8of the laserenergyXV”-: q ** q q:. :0 .to heat and compressD-W! mllligmm quantities, in GENERAL NOMENCLATURE Maend to achievea net energygafn, rangefrom 2 x i04 / MO Mb M, M;to 1 x 106 J (joule) delivered a periodvarying in PROPELLANTfm 10-10to 10-7 sec. A laserof this magnitude .msy requirea hge volumeof I.asingediumfor the mfinal stage (ofthe orderof 1 m3),which msy be CONDITIONINGUNITexpendedaftereach laserpulse. AlthoughgLass MOMENTUM ABSORBER CONFIGURATIONS .and gaseouslasersare presentlythe most advanced, A. EXTERNAL SYSTEMSlasersystemsutilizingchemicalreactionenergyto 1. PUSHER PLATE nachievethe requiredmolecularexcitedstatesare PULSE UNIT l/more prumisingfor spacepropulsion.Chemical -o- /llasershave a relativelyhigh energydensi~ and +offerthe possibility expending of the unusedenergy 2.MAGNETIC BLANKETtogetherwith the spentreact ton products. AU at- ELECTRICAL CONOUCTOR cO’Ls-Yxl -(tract ive possibili~ is to assemblethe finalhigh- PULSE UNITenergylaserstageand the mirror-focusing system l/ -o-with the individual pulseunits so that they cmld /lbe deployed one packagejustpr20r to pulse-unit asinit iatlon;the,lcw-ener~ laserstageswould ramsinin the spacecraft.Thus,positioning B. INTERNALSYSTEMS PULSE UNITof the pulseunit aft of the spacecraft ouldbe wnot nearlyas crft icalas had been expected. ,1 71C NOZZLE A more completedescription laserconcepts of ~R~~S”R~and considerationsrelevant pulseprepzlaion to arepresentedin AppendixA. Fig. 1. Nuclearpulsedprqmlsion concepts. configuratimsare being cataloged according to III. PKELININAKY DESIGNCONCEPTS whetherthe pulseunit is explodedexternally, asGeneral depictedIn Fig. IA, or internally, s depictedin a Three designsfor converting tha energyfrom F@. 113. Tt will be sham in SectionIV that, atan explosionintopropulsive thrustare shownin leastto a first-order approximation, mass of theFig. 1. Ih each case it is eupposedthat en indi- the mcns?ntum absorberis proportional o tb? impulse tvidualpulseunit is properlylocatedand then init- delivered the pusherphte (inan externalsystem) to or to the pulse-unit energyrelease(inan titernsliated by a laserpulse. m the resulting nuclearexplosion a quantity of propellant heatedby the is system).releasedenergyand expendsas a high-energy plasma. Becausea aignif’icant fraction the mass ofA potiionof thla expanding plasmainteractawith spacecraft ill be allocated the nxxn?ntum w to ab-the spacevehicle,therebyimpartingxm?ntum to it. sorber,it wiJl be desirable selectths proper toMaw PUISeunits are sequentiallyischarged d and value for tk impulsedelivered(or a @se-unitInitiated, probablyat equal Intervals, resulting energyrelease which la appropriate ) e for the mfnimum .in the desiredspacecraft elocitychange. v feasiblepulse-unit mesa. m too high an impulseis The spacecraftmass is considered consist to delivered too mch energyreleased, or the increasedof a payloadplus supporting structure, propellant maaa of the nxam?ntum absorber will more than offsetstorage,and a momentumabsorber, which smothes the gain in performance; conversely, too low an ifout tk shockor inqmlseresultingfran the explo- impuhe is delivered too littleenergyreleased, orsion of the @Lee unit. VariousmnmMaan-abas%@ ~q q thaikxxhtnq~rfornuncewill nmre then offsetthe q a :: : q 9 q9 qa :: q0 q q q : q * :0 q *9 q .* :.* be4 q me q ******* .. APPROVED FOR PUBLIC RELEASE
  11. 11. APPROVED FOR PUBLIC RELEASE q O q 00 :00 q :*. :-c :0 * q q. 0:..: q ‘*.be si q q * q reduction nmmentum-absorber in “:” “*;h; ”spacecreft, mass. fn $0%% Zases attaining finalvelocitYeq~ to a (externalend internelsystem) an optimumnsnnantum- the initial velocitybut -site in direction. At absorbermass fraction of the spacecraft corresponds this tius?, pulseunit is firedconverting a the to a mxinmm pwload del.ive=d which, in turn, cor- Propemt intoa plasmawhich acts at high pressure. responds an optimumspecificimpulse to and deter- wer the surfaceof the ~sher plate for a very minesthe impulsedelivered(external system)or the shorttime interval. @ net effeCt iS EUI~lse pulse-unit energyrelease(internal system). delivered the pusherplate neversing to its direc-. tion. The cych is then repeated. For the samepulse-unitmass,the externaleys- tem will greatlyoutperformthe internalsystem, Functionary,the momentumconditioner acts as S@lY becausethe nmmentum-absorbermaSS in the in- a long coil springseparating th spacecraft from ternalsystemmust be largerto containthe pulse the pusherplate. If the springis greatlycom- energy,ratherthan only to absorbthe impulseas in pressedso that the nmtionwer a cycle is only a the externalsystem. SUELUfractionof the total compression,hen the t forceexertedon the spacecraft nearlyconstant, is CanceptA-1, ExternalSystemwith PusherPlate approximate the idealcondition ing describedabwe. The pusher-plate concept(Fig.IA-1)was devel- The totelmass of the momentum-absorber system oped in the Orion studiesand, at this juncture, ap- is the sum of the messesof the pusherplate and of pearsto be the most premisingfor the smaLlerlmer- the energy-storage momentum-conditioning or unit. drivennuclear-pulse propuJ.eion systems. The pulse- 1% v illbe demonstmted in SectionIV that the total unit enemg releaseoccursat some distancefrom the mass shouldbe dividedequeUy betweenthe momentum- spacecraft, nd a strong,probablyflatmtal 6truc a - conditioningnit and the pusherplate if the tal u ture, calleda pusherplate,absorbsthe shockof mass is to be minimized. the explosion.A momentum-conditioning is =- unit quiredfor a gradualmonmtum transferbetweenpulses ConceptA-1 can be designedfor a high specific and for returnof the pusherplateto the proper impulse becausethe pusher-plate surfaceis exposed locatim for the next pulse. to the propellant very shortpulsesand the pro- in pellantenergydensitycan be therefo~ quitehigh. The magnitude the kineticenergystoredin of the pusherplate afterthe impulserequiresthat the As the propellantmaterialpilesup againstthe mowntum conditioner ust a~roximate a conservative m pusher-platesurface,the temperature increasesdue system,that is, a systemin which kineticenergyis to stagnation end much of the originalkineticen- converted a potentieJ. to ene~ and vice-versa, with- ergy is radiatedway t~ space. Ablativematerial out appreciable ener~ dissipation.(In a dissipa- cwering the platevaporizes form a thin film to tive systemquiteunrealistic quantities heat en- of furtherprotecting the subsurface.Orion studies ergywould have to be radiated spaceor othezwise to verifiedthat ccmmonmateriels, e.g., aluminumor removed. Thus the pusherplate and the momentum ) steel,can withstandsurfacetemperatures xceeding e conditionerndergoa cyclicinteraction. u 80,000°Kunder euch conditions with only nominaJ. 3 ion. At the beginning a typicalcyclethe pusher of plate is assumedto be pmitioned at its maximum The an externalsystemis of distancefrom the spacecraft end movingtcwaxxihe t the integral the changein the axialccznponent of craft. As the pusherplate approachesthe space- of the momentumof the propellant a resultof its es craftit is decelerated y the momentum-conditioning interactionith the pusherplate.* !12his b w specific unit (witha nearlyconst~t force),which bringsthe impuleeis approximatelyqualto the productof the e plateto restwith respectto the spacecraft%.t A propdlant impingementelocitytimesthe fract v ion this point all the original. kineticenergyof the * pusherplate is storedin potentialenergyof the The specfiicimpulse,so defined,shouldbe divided momentum-conditioning unit. Over the ne~e~o $$ by go, the2stsndh acceleration ue to gravity d “ “:%9#,m/sec ), in orderto obtatithe UZUIQY the cyclethe pusherplate is accelen$e? w.* ?@n q : : a~gpted unit of seconds. * 9*9*** q ** q aa 9** q ob q ** q . APPROVED FOR PUBLIC RELEASE
  12. 12. APPROVED FOR PUBLIC RELEASE .=: q q m, q 00 q *O . . q .*.:.:: q * :: : :of the pulse-unit masswhich strikesthe ~her .q qqq .‘~t~r ‘~~ed Performance ill offset*W wpkte. mitid perfomuence estimates, presented in eddit ionril- and complexity the superconduc- mass ofSectionIv, indicate that the desiredpropelbnt im- tive coils,etc.pingementvelocitiesare withinthe constraint of Conce @ B, InternalSystem150 km/seeimposedduringthe Pro$ectOrion study; Xn this configuration energyis released the .furtherinvest at ions,however, @ w disclosethat insidea pressurevesselthat is equippedwith aplate-surface energydensitywiJJ. eventually Unit conventional ocketnozzlefor the discharge the r ofthe perfomasnce this cmcept. Presentspecific- of heatedpropellant(Fig.I@. Varicus@ssibil.itiesimpulaeestimates for the pusher-plate conceptfi- for controlling he processhave emx’ged. B one tdicatean upper limitof - 7P sec. conceptliquidhydrogenis fed intothe pressure Anotherconstraint hich ~ w limitthe perform- vesselradia13ythrwgh the weJl and acts as aance of the pusher-plateconceptis tbs totalpres- coolantbeforeuniformlyfillingthe vessel. Thesure of the propellant actingagainstthe surfaceof energyfrom the pulseunit is released the center atthe plate. Excessivepressures will causeapeXla- of the tank afterthe vesselhas been xx?charged totion U the resultinginternal. tensilestrescesex- the fallpropellant mass. A shockwave is propa-ceedthe strength the platematerial of when the gatedthroughthe hydrogenuntil it nsachestheinternal pressurewave is nsflected from either wallswhere it le reflected back towardthe center.surface. Becausethe stagnationpressureat the wall. is Esign considerionsfor propellant-pusher higherthan the frontalshockpmsaum by an orderpbte interactions ~ present in AppendixB. ad of mgnituae, this delivers sharpinitialimpulse a to the wall. @ wave is subsequently eflected rConceptA-2, Externalsystemwith MagneticFieldand PusherPlate back and forth in the vessel,continually increasing the internalenergyof the l@rogen until. equilib- The limitations imposedon ConceptA-1 by abla- rium is established.w this t5me,which is of thetion and spellaton of the pusherpkte mightbe i orderof milliseconds,ti hydrogenhas reacheaan twere- with a magnetic-field blanket” protect “ to averagepressureand an isothemal ccfxlition to duethe plate surfacefrun the high-energy ropellant p the transferof shockqave kineticenergyto hydro-plasm. Figure1.B-2 showsa cusp-shaped,lectri- e gen internalene~. The hot gas is then expandeacaUf conductive pusherplate and a superconductive througha nozzlewhile the tank is being =filledcoil to generatestrongmagneticfield Unes paral.- with propellant.The expansion processis continuedIel to the pusher-plate surface. As the denseplaa- untilthe previousinitialconditions the tank inms from the e@osion expendsit pushesthe magnetic are attainea, then the cycle is repeated.field linesagainstthe conductor, increasing he tfield strength inducing circular by a currentin ths Otherpossibleinternaldesignconceptshaveconductr. The increased o me8netic pzwaure (B2/8n) been considen?dbut no designwork has been ini-sbs dcwnthe plasma,turns it, and accelerates it ttitea. One of these is a pressurevesselUneaaway fran the laasherlate. The impulseis trans p - with a thick ~er of lithiumhydriae(Li@. Theferredto the pusherplateby magneticinteractions internalenergyreleasevaporizesS- of the Lili,which spreadout the force in apaceand time end which collects a hot gas in the cavity,ana then asprotectthe surfaceof the plate fraz particleim- flm?sout of the pressurevesselthrougha nozzle.pingement. Eecausetlw propellant particleveloci- Thus the pressure-vessel liningis the propellant,ties can be higherthan for a plainpusherplate, whfch is graduUy vaporized successive by explo- . Ithe specifichpulse of this conceptcan also pre- sions (similar coreburningIn a soliil-fuelea tosumably higher. whethertbs apecfficimpulsede- be rocketnmtor).rivedby the optimizationrocedures p will implythe Althoughthe intexnalconceptinitially seemxlneed for zmgneticfieldsto protectthe puahe~ att.met ve, so many inhen?nt I drawbacks have emerged. -.plate surface will be determined futureatua~s ~ .e . as ~a in @..ththe extexmilsystem,that furtherIY so, it w5J.1 o be necess~ to deterzdnee.: { : : : . .6 w q m q *99,.* q APPROVED FOR PUBLIC RELEASE