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

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






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

    • 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
    • . 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
    • ., , 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
    • >, .,. APPROVED FOR PUBLIC RELEASE ... - . q  q9: 9** .*. . . . . . ::..:.:: -~ . b q. — . k~ .’ ...— . * . .. . . . ‘,. .’-. . . —4 :-” ------- ----- ii :O-s O.. q APPROVED FOR PUBLIC RELEASE
    • 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
    • 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,!?-e.ec Im 2pectiichqnil.ee, (1~ = Ve/go),sec in Pulse-unit mass,kg M Total spacecraft initialnmas,kg Ma M==n*-absor~r IUSSS(Ma = Me + ~), W Initifil. epacecrz&t 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)‘andI&s 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
    • 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 I&L 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
    • 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 ~2&eWurt 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 D&e 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
    • 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
    • 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 prelim.in~,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
    • 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 t&al 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. abl.at 3 ion. At the beginning a typicalcyclethe pusher of plate is assumedto be pmitioned at its maximum The specificiqnil.se 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$e? w.* ?@n q : : a~gpted unit of seconds. * 9*9*** q ** q aa 9** q ob q ** q . APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE .=: q& q m, q 00 q *O . . q .*.:.:: q * :: : :of the pulse-unit masswhich strikesthe ~her .q qqq .‘~t~r & ‘~~ed Performance ill offset*W wpkte. mitid perfomuence estimates, presented in eddit ionril- and complexity the superconduc- mass ofSectionIv, indicate that the desiredpropelbnt im- tive coils,etc.pingementvelocitiesare withinthe constraint of Conce @ B, InternalSystem150 km/seeimposedduringthe Pro$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 consider&ionsfor 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
    • APPROVED FOR PUBLIC RELEASE ,. q .0 ’300 q :- :.. :o q .:ee. . . . m q q .:;: q .0 e work does not eeemwarranted, leae;”~~:f’n6 at % ““” ‘“• “q In an intexmal. system,spherical geometries = near future. Eaeicpmbleme am: genemlly indicated, hich offerlittlelat w Itudefor swat effective placingof the pmpell.ant material.: q For the samepulse-unit ZSMS,the perfonssnce it WOUld S@~ fOllS 8 @ObS aroundthe pl’O_@biOfl of the Intenml zyatemla at laaatan orderof. pellnt. Calculations hw that 20 kg of a good s magnitudepoorerthan that of the external shielding material,e.g.,llthium-6 hydride(6LiH), system. would remoreonly b5$ of the 14-MW neutronsgenerated. q m spectfic-impulze limlt la alxmt 2500 aecj in the fusionmactlcsxs, and that hundredsof ki.lo- corresponding excessive to radiat heat %ve gramaW- ~ requiredfor effective shielding from transfer the pressure to vesseland nozzle aD+l!pulae. from a hydrogenpropeht. In addition shielding, to the major considera- q l!here no apparent is ww to solvethe shielding tion in the designof tk pulseunit for an external problem. Isotropicshieldlng will be required systemis propercollimation f the expanding o propel- to protectthe pressurevessel. lant so that a major fmction impinges the space- on q Positioning and init ing the pulseunitwith- Iat craft. in the gas-filled pressurevesselmay be much With respectto shieldlng, the externalsystem more difficult than in the vacuum&&t of the benefitsfrem an inherentadvantage becausepulse spacecmft. aIW p~sicslly separated. This unit and spacecraft The only significant dvantage the concept a of will significantlyecreasespacecraft d radiation is the nrlmimel. raquinenmt for momentwm-condition- doses,mainlyfor the follwing masons. ing;thfs functionis predominantlyerformed the p by q The qnicecraft subtends amsXL solidangle a pressurevessel. Althoughthe thrustfmns the noz- frms the pulseunit. Becauseradiations will zle mW vaxy by an orderof magnitudeover a propul- emanateisotropica13yras the detonation, f only sion cycle,the msss raqu~zsmts for snmothing a smtill racbion f must be dealtwith. For ex- thesevariations out in the ~cecrd’t are small ample,at a dlatanceof 8.5 m fmm a point,a compared with the pressure-vessel mass. 4.72-m4iam plate subtends 30° included-angle a PulseUnit DesignConcepts ccme representing nly 1.T? of the total solid o anglearoundthe point. To mininrlze mass of the sum?ntumabsorber, the the mass of the pulseunit shouldbe as smallas q Propellant materielcan be positioned form a to possible. ~ factorswhich tend to increase the shadowshieldbetweenthe radiationsource sizeof the pulseunit are the requirementsor f (whichis nearlya point source)and the space- spacecrsd’t shielding, he desireto limitthe number t craft,i.e.,shielding mass is requiredonly in of laserpubes, and the maintenance a hfgh aver- of the solidangle subtended the spacecraft. by age thrustwithinthe limitation laser-pulse of ra- From a shield5ngstandpoint, logicalgeometry the cycletires.As mentionedearlier,spacecraft is a cone of pzwpetit materialwith the energy shielding of particular is concernbecauseof the sourcelocatedat the apex of the cone and with 14-MeVneutronsproducedto a greateror lesser the cone axis orientedalongthe spacecraft degreeby the fusionreact%ons utilized. Ih any axis. case,the pulseunitwill consistpmedaninantlyf o q Singlefast -neutronscatteringwill removemost propellant materialwhichwill servethe dual fsnc- of the neutronswithinthe cone anglefrom fur- tion of (1) dilutingthe energydensitythmeby re- ther conel.derati~. For sskllangles,the prob- duclngthe specificimpulseto acceptable levelsand abiltt of a scattering y neutroncolltsionre-. increasing he impulseobta%ned t per unit of energy; eulttngin a new path stlXlremaining within and (2)pmvidlng priswu’yhlel.ding the apace- s for the cone angle is exceedingly small. The prob- craft. Pulse-unit massesin the rangeof 1 to 100 , ,.. #blllty for msltiplescatteringback intothe ,* q ** q *9 kg am thoughtto be appropriate. . q : : q *** * q q ,original one angle is even smaller. Thus the c q qa q q a. 9 : :: q q * 9*: q :a q q q * 0: :* 7 APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE q be q ’e ...- q 0 q 08 .:0 q 9S . . . q. ::0: q a: . 9* neutronshielding problemis reducedf~ ~b#,~ : .. .4t$.td:* ---- pm~t at-p imPIYing same usual requirement slcwingdcsrn of and captur- directpropellantheating. lh one ccnceptthis is ing the neutrons one of simplycausing to supposed be the dcsninant to sourceof propaldant s%l.e scatteringevents. Calculationsave h energy,and the designreducesto the determinathn conflrmd that,even for largeshielding fac- of gecsmstries leadingto good collimation f volu- o tors,mat neutronsstrikingthe spacecraft metrically heatedmaterials,somewhatsimilar the to . v illbe uncollided. designof shapedchargesfor the formation ex- of Monte Carlocal.culat ions,presentedin Appen- plcmivejets. One possibility to surround is the neutron-heated propellantwith a pressurevessel-dix C, indicatethat 3.8 kg of bary~ium in theshapeof a 30” inchided-angle cone,30 cm high, end-nozzle configuration thin, heavy material ofwiJJ. absorb~.~ of all 14-1.wfeutronsoriginally n which wiX1. direct the propellant toward the push?rdirected withinthe cone angletcxmrdthe space- plate in a supersonic stream.C-. Thus, in this example,only 0.010 x 0.017 = Another,ssn?a attractive, ssibility is to ~0.017$ of sXLneutrons emanatingfras the source desfgnfor utilization the energycarried the of bywill traveltad the craft. chargedproductsof the fusionreactions.This en- For an extemel system,a sophisticated hydro- ergy CU be absorbedin a she= of highansitydynamicdesignof the pulseunitwaild favora ley- materialsurrounding he pelletwhichwouldthen tered flat plate ratherthan a cme with the pellet confinethis ener~ to a channelaroundthe p~l-at its apex; caspromiae geometries w eventually lant-conesurfacewhere it waildbe absorbedin aenrge. In general,if the pulse d~cts one ele- thin layeron We surfaceof the propellant cone.ment of msss towardthe pusherplate,an equal This heatedsurfacewould blow off at highvelocitymomentummust be carried snotherelementof mass by ProPeUiW t~ re=fi~ cone at lcwervelocitiesaway from the spacecraft.Also,the fractionof touardthe pusherplate.total ene~ carriedby tlx? firstelementis equal Othergeetries, e.g.,lqferedplatesofto the fraction totalmass carriedIn the second of varim matefi la, are also being considered. aelementand vice-versa.One maximizesth nmmentum Designmp I.icaticns PayloadShieldin& ofcarriedoff,per unit of ener~ expended, equal- byizingthe massesof the two elem?nts, which,how- Payloadshielding a ma~or designconsidera- isever,w not be a desirable goal. ticm for all spacecrdt. ccsspcments particularlye- b causemannedmissionsare aasumd. !lU spacecraft If the laser-drivenusionconceptcan be made f am thensefore be designedso as to prwide the toto work, it can probably made to give any desired be ~st favorable Bhielding.Theywill be of elmgatedenergy,and the costmightbe nearlyIndependent of gecm&ries,with as much distanceand spacecraftthe energylevel. This reasoningmay lead to de- materl.al betweenthe energystaarcend the peylcd ast~s that are wastefulof energyin orderto save as possible. N@nte Carloneutron-shielding calcula-propellant. tionshave been perfo~d for a reference casewith If the pusher-plate impingementelocityis v the assumption that the primaryenergysmrce is thefixed,t~ mexisum-e transferred the to D+T reaction; detailedresultsare presentedinpusherplate,per unit of totalmass expended AppendixC. Conclusicas are that s- attenuating(i.e.,the specificimpulse), can be cle~ly ob- medium,in addition tk p~H, to iS requiredtainedby I.ettlng ma~orityof the mass impinge the to protectthe payloadit’ th? D+’l! reactionis uti-on the puskr plate at this maxhum velocity. The lized;but calculations hou that the shielding s .mmainlng mass carriesthe ma$orltyof the energy maesesare acceptable:a nmdmum of 15)~ tooff in the oppositedirect ton at highervelocities. 40)000 kg if the mass is at the payloadlocation, .selection materials of for the propellant will. de- or 20C0 to 5000 kg if the mass is more favorablypend on the effectiveneutxmnscattering that can --d nearerthe energysmrce, but sti31withinbe achievedfrom a givenmass. Iieutrcas scat$er& b %?.V.?%* “ lhese-ses can be included within  qout of the propellantcone impartsam of ttiec& ~ q a $ai#ct~ spacecraft mum of 100,000kg, etther e* some q : q :* S* q 9 q ** Bee b.. 4.. ..8 APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE as structural components, utored pulse unit St or pressurevessel,of the -ntum-conditioning SYS- Me-support aupplles. Thust psvloed shielding con- tam, and of the lasersystem. l%e size of these sldemt ions, although be recognised the design to in cmsponents ill dependon the stie of the pmpuls ion w from the beginning, apparently U W not Invalidate pulse. Althoughthe detailsof this scalingare not, th entk nuclear-pulsed prepulslonconcepteven In yet well understood, o@imlzatims for two possible the unllkelyeventthat the DW reactionis t,be sce3inglaws We been analyzedand EUW presented pra energysource. be~.. Consider apacecmft of total initial a mass, IV. MISSIONCONS ~~S AND PESFOIU4ANOE ESllR4WES M, ccnslating ccmpncnts of threekinds:Propel- of lant,of mass h$; a momentumabsorber) mss Ma; of Geneml and the remainder(1.e.,payloadand other strut- m the normelrockatequat ton, it is aaaum?d tures)of mass MOO Thus that the spacecraft consists two components of --a M= Mo+Ma+k$. (1) pwload, Mo, and a propellant that fs e~nded over a periodof time at a conBtantexhaustvelocity, Ve. ID this allocation It is appropriate o ascribeto t Giventhe mission-qulvalent free-space velocity Ma anY mass that scaleswith the pulse size. c-e ~ C.V, the requiredpropellantfractlonis de- AssusEthat the propellant consistsof n iden- termined the rocketequation: by Me/M ‘ exp(~Vh7e)? ticalpulseunitseach of mass m. Althoughthe use whereM is the total initialmass of the spacecxwd?t. of nonuntfons pulseunitsmsy be desirablein some In enY propulsionsystemtherewill be an additional circumstances,this generallsations deferred. i mass in the .vp.acecrd’t, associated with the propul- Only a minorfractionof the @se unit consistsof sion system,which scalesin som mannerwith the fiel. Tbs main mass is a suitablearrangement of enginecharacteristics. his mass must be imcluded T prope~t materielsdes!gned maximizethe total to in M. For example,in an electricpropuleicmsys- me of the explosion while dilutingthe fuel tem, an extm ~er-supply mass must be includedin energydensi~ to a tol.erable levelat the monEntum the spacecraft determined the requiredset as by absorberand shielding the spacecraft from radia- ~er and the efficiency the system. The ticlu- of tions originating the fuel. AU ancillary in ex- sion of this enginemass usueXlyresultsh sore? de- pendedmaterialis also includedin the pulse-unit signfI.exibflity choosing in the fractionof the mass. total spacecraft mass sillocated thle enginemass to As a resultof the explosion the pulseunit of end in a resulting variationin engineperformance, end its Interact ionwith the spacecraft, total a Ve. Frequentlythere 1s en optimumenginemass impulse, will be Imparted the spacecraft 1, to along fractionI.eedlng a msximumspacecraft to pe@Oad Its axis. In a epectiiccasethis impulsecan be fraction. As is well lawn, this is th? case for detensined integrating tw axial. by t component the of the precedingexampleof electricpmpulslon--there velocitychangefor each cmsponent the pulse mass of existsan optimumfraction the spacecraft of mass as a resultof its interactionith the spacecraft. w which shouldbe allocated power supplyand a cor- to Tt is convenient represent to the impulseas a frac- responding optimumspecificimpulsedepending the on titm of the total impulsewhich tail.de realized b thrusterand power-sup@y characteristics on the and if all the energy,q, were ccmvertedintokinetic mission. Tn otherWOXRIS, he inclusion the en- t of energy,uniformlydistributed the pulse-unit in mass, ginemass in the q!acecraftprwides en appment end whollydirectedopposite the apscecraft to extradegreeof freedcssn the design, I which,how- Untiono Thus ever, Is usuallyonly definedduringoptimizaticm f o. the system. 1=7~ (2) The abwe generalizations also tme for are where the coefficient TIis the effici.ency con- for pulsed-propulsion systems. In this case,the*extra vertingenem into Im@ae end O S T ~ 1. e-e q ** q ** q . q spacecraft masses consistof a pusherplate 8r~ ~ :0 :; *9 q q e&* e ve93 q* q:9 8*C G** 9*O *8 APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE .* -* q  q b. .: * :*:,* q 1% is convenient to cluuacterise the space- Ma = u q/k2. (5)craftperfoxmmnce tennaof tha payloaddelivered h lb? qusnti~, W, which has units of velcdty, char-thrcnIgh totalvelocityincrem?nt, V, in a n?c- a A acterises the specificstrength the presaum- oftilinearflightwith~t externalforces. The wer- vesselmaterial,and Is definedbysLU re@_retnent an actualspacemission, of which .will involveseveraldistinctin planetary propulsiontitemala and SOI.SX ravitatonslfie~, g i wt “f===” (6) .then be expressed the total rectKUnearfree- as The quantity, is ve~ nearlythe maxhmm periph- W, eralvelocityof a flywkel made of the preseure-fl.ight velocitychange,AV, to which It is dynami- vesselmateriel. The quantity is a dimensionless acallyequivalent.@ totalAV will be made up of factorwith a magnitudeapproximatelyqualto unity. en velocityincrenmtswhich increasesllghtlyaethe totalmass of the spacecraft decreases.Rather The precisevalue of a wUl dependon des%n details, on the allowanceneededfor shock-leading the ofthan to expressthe totalAV as a sum it is conven- pressurevessel,cm the safetyfactordesired,andientto approximate by en intagrel. ~ it differ- on th? equation stateof the heatedpropellant ofentid effectof one impulseis to changethe veloc- gas.i~ of the spacecraft BSLSS CIV by where: Eliminaticm the quantities of ~, 1, and q MdV=I =:(44). (3) fromEqs. (1), (2), (4),and (5) leads to the expressionThe mass ratiofor the totalmisdon is obtainedbyintegratinghis equation obtain t to Me/M = exp [ -2/(v _ ] - Ma/14 (7) Av . (1/xn) b [M/(M-~)] . (4) where the pmameter p is dafinedas v = (m(W/AV)(Il~ . (8)~is approximate procedure will overeatimatahe tcorrectvalue of AV by a fractional amountof B?f one discussingtlx?implicationsf Eqs. (7) and oofiern/M. (8), equivd.enteqpationsfor impulsescalingwiI.I. be derived. The pulseunits cannotpmctically be made sosmalland so numerous to simultaneously as achieve ImpulaaScalingan interestingelocityincrement v and nuintainthe l% is assumedthat Ma is proportional o the tpeak vehicleacceleraticm t an acceptable a level. total @uMe, I, delive~d to tlzsmmm?ntumabsorberThus the mc!u?ntum-absorber systemperfonna the main per @se. A ccmvenient expression the propor- offunctionof acceptingthe short4xration impulses tionalityisand delivering them to the spacecraft ith a nearly wcent tiuonsfo=e over a longerth. This is true . (9)for eitheran external(or iqinge~nt) systemoran internal(or ccmtaintrsmt ) system as described in It wIU. be seen that this scaling may be appropriate to an external concept.the previma section and sa U1.ustrnted in Fig. 1.scalingIaws The totalmass of the manentum-absorber system in an externalconfiguraticms tti sum of the masses i No scalingIswaj energyscalingand Inqsilae of tha puslmrplate,1$, and the energystorageorscaling,have been Constde=d for the totalmass of nsxaentum-conditioning system, Me. !12x? cyclicnature .the nsm?ntumabsorber. of the pusherpl.ate-~ntum conditioner systemshas EnergyScaling been described SecticaIII. m a typicalcycle in the changein velocityLa twicethe initialvelocity It is as-d that Ma is proportional o the h and the initial kineticenergy is I?/8 F$. ~iSenergyreleaseper pulse,q. This @pa of scaling energy must be storedwkn tha pusherptite isshouldbe appruprlate, or exa@n, in en internal f .s **a *** :bft#g$tP$o rest.systemwhere the energymust be contain@+ A @n: q *9 :0*.venientexpression this pzwportional~ la’ of t e q *O q ~ **i q q . @* ;* . s-10 APPROVED FOR PUBLIC RELEASE
    • . 9mi$di@: APPROVED FOR PUBLIC RELEASE :. It can be shownthat Eq. (5) to a ve~ generul q q :=. q . & Optimizatim q * em . Procedure relation betweenthe energyand the minissam mm of IXpmsaions have been obtainedfor two possible a 6yatem~quired to ato~ it. It aPPliesregard- WIKYCJ which the mmentum-aboorber in mass, Ma, scales less of the mannerin which the energyis stored, with the pulse size. As a fIrst conaiderat ion, it i.e.,as compressed gas, as a rutatingMSS, or in is clearlydesirable minimizethe pulse size in to a magneticfield. Only the quantity variesand a orderto minimizethe corresponding Ma. Several only over a rangeof about a fqctor of two. Hm - factors,-ever, will llmitthe minirmmsize of the ever,the requiremmtsof the maaentumcondit oner l pulseunit. exceed$ustthe raw requirement ener~ storage. of The momentumcondit lonernsm.t also bQ ablo to cope q Shielding requirezmnts.For the Internalsys- ten this requirement ~ imposea largeluier nondest~ctively with a failureof the pulseto fim at the correcttIms. If it is furtherrequiredthat limit,of tha orderof 100 kg. The limitfor the accelemtion of the spacecraft relatively be an externalsystemmey be much lower--ofthe unifonzit will becomenecessary increase to the orderof five kilo-. mss of the momentumcondlt lonerabovethe minimum  Wastageof laserreactants.A ftiedquantity by an orderof nwnitude. coding systemsto remove of gas mev be expendedaftereach pulse and the the dissipativefraction the energy,lubrication of amountwill probably independent f pulse be o systems,and othercomponents ill ultimately w in- size. It can be shcwnthat this leadsto a creasethe required to well abovethe minimum a desireto selecta pulse-unit mass whichwould value of unity. be of the saaE orderas the laserreactantmass The mass of the mcmmtum-conditioning unit can expanded. be relatedto the energyterm in a manneranalogous q Minimumth!e Intervalbetween@ses. To avoid to Eq. (5), inefficientropulsion, p the net averagethxust .a- shouldbe ccsmparabla the localgravitational to , (10) attract on. The averagethrust is equalto the i e w’ me tfiesthe Pube rate. For a ftiedmaxi- where the primedenotesthe mcmentum-conditioning mum pulse rate,thiswill tend to set a minimum unit. The totalmass of the nmnentumabsorberis impulse. then These cons idemtions--in particularthe last two--mayleadto an optimumpulse-unitmass; how- Ma=~+l.ie=Mp +a’?/8~w2. (Il.) ever, In the presentdiscussion will be assumed It Ma wIll have a minimumvaluewhen l.$is appropri- that the minimumpulse--unit mass is fIxed. In each atelychosenas of the expressions for w end v‘ given in Eqs. (8) and (15 the quaint M/m appearsas a rat which, ), ity 10 Mp’”e=Ip~ (1’) In a given case,will be determined.The quantity so that W Is determined the choiceof materials. The by Ma= I~h. (13) missionAV will be givenand the quantities ‘tl~ in Eq. (8) and ~ in Eq. (15)will. deter- be Elimination of% end I from Eqs. (1), (4),-d (13) i ion of the system design. minedby the sophist cat leadsto the expression Thus a maximumv or p‘ will be determined.. Me/M = exp(-M/11’ a) -Ma/M M (14) where p‘ is definedae v ‘ = (M/m)(W/LS?) ~ . (15) q 9* q q ** q ** q * 99* : : :e q q q m 9 q q *B- q *** q : q * q* ** q *= 99* q 00 :00 q 0 IL APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE !@m!!!m . .: .:*:.* q q q Plots of Eqs. (7) and (14)are presentedin Smctiea for an energy scaling law is 0.86,whereasFigs. 2 and 3, respectively,or ccmatent f valuesof for an impulsescalinglaw it is 0.80. Houever,forIlendv’. It can be observedthat there is in each valuesof p end p’ in tlm rangefran 2.7 up to 10.0case a maximumpayloadfracticu,Me/M,and a corre - the correspondence within3$. Thus the perform- isspondlngoptiuumsmm?ntum-abaorber fraction, Ma/M. ance of tbs two typesof systemscan be compared .Clearly,largevaluesof v end II’m desirable. directly C-- by y end v ‘. The ratio,P’111,TM locusof the maximsis indicated each figure, on can be obtatneddirectlyfran Eqs. (8) and (15)asand the corresponding optimm allocations the of (16)spacecraft mass betweenpayload,pzwpellent and From this expression %s char that p‘ is signifi- itmonmtum absorberare plottedin Figs. 4 and 5 as cantlygreaterthan v in any practicalcase. Anfunctions of v end W’$ respectively. IX can be example,hrtentionalJy chosento favorthe internalseen that there is a limiting minimum value ofp = p‘ = e for which the pwload vanisks and the system,1s: M = 100,OCOkg, m = 2CIkg, ~ = 0.9,missioncannotbe perfor!wd. a = 2.0, a’ = 47. From K. (16)we obtainV’/B = 8.1. Bscausep and v‘ appearin Eqs. (T) end (14)as isonof Ilxternel InternalCo!lq)ar and SYstem Concepts dinmsionlessspecificInqxlse, followsthat the it The scalingconsiderate ionsdiscussed aboveper- optirmus specificim@.ee of en externalsystemismit a directperfomnancecomparison the extemel of eightttis higherthan that of an intemsilsystemand internalsystems. ‘J@ Pareme ers p (forenergy t for th senE spacecraft/pulse-unit ratio. In XBSSSscaling)end v ? (forImpulsescallng) have titen- fact,largerpulse-unitmassesmey be requiredfortional.ly been def.i.ned rcu@ly comparable.In aa an internalsystemthen for en extezzvi!. system,each casethe minimumusablevalue is e. ~er prcwtdlnganotherargumentagainstan internalvaluesresultin comparable maximump@nad frac- design.tions,Me/M,as can be demonstratedy reference b toFigs. 4 end 5. The correspondence not exact; 18for exempk, at v = p ‘ = 100,the Illaxiaslm p@loed 1.0 Lop I I I I I 1 I I I I I I I I I .” ‘ LOCUS OF MAXIMA ~&LOCUS OF MAXIMA ~/- s! i ~ {-./ ! I 31 I o 0. I 0.2 0.s 1 0.4 I ABSORBER MASS FRACTION, Me/M X,.: q *m 9** -. XOC9P- . -*. . q x,. .-h - ,,Fig. 2. Pwload fractionfor m ene~ &aY$g ~.e~ P@oad fxwtion for an iqnihe scalinglaw. q 9 q 00 q mm q 00 —- .-32 99* q q q .**. q *O q* APPROVED FOR PUBLIC RELEASE
    • q APPROVED FOR PUBLIC RELEASE PROPELLANTz (PULSE UNITS)~ 0.6 —k .—uaEm Ma/Mm ().4 — x~=4z PAYLOAD PLUS REMAINING )(.= MO/M STRUCTURE 0.2 — ,= a (Vv)(.m Ma= a~/@ I I 11111 I I 20 40 60 80100 200 ‘p, minimum =e PARAMETER p Fig. 4. Optimm elJooatlon sp.ececmft of nmss for energyscalinglaw. I .0 I I I I I I I I Ill I PUSHER PLATE ‘ — PLUS MOMENTUM 0.8 — CONDITIONINGz .—op 0.6 — )(0 .eP’xa. xa~ PROPELLANT I — (PULSE UNITS)Em xa . MoMUJ().4 —s — PAYLOAD PLUS REMAINING Xo = ‘O/M STRUCTURE 0.2 — p’ ‘(”/m) (w/AV)~ — Ma+ $ r a I 1111 I L 4 6810 p’, minimum =e q 20 PARAMETER 990 40 q p’ q ea q *D q * 60 80100 200 Fig. 5. Optimumallocation @@~m&.s Sf fsrgimpulse scalinglaw. q“ q ;0 bbO*– q q : q * qO q:0 q 9* q *O :00 9* -<” q0 q ** APPROVED FOR PUBLIC RELEASE q q q q*
    • APPROVED FOR PUBLIC RELEASEP8X’’fOXVUUMt3 Limitations The corresponding maxlmm epecificimpulseis The basicperfonmnce limitation, hat of mini- t ISp “ T !/ml /80.mum pulse-unitmass,has been diecuesed.However, FOr hydrogen 83339X (1.5,000”R), = 3.5 x I-Oa at q/motherdesignlimitat ~ons x praventthe selection J/kg, corresponding an IW of 2430 sec. At this toof tk uptinumpulse-unitIm@ne or energy. point the hydrogenis toteUy dissociated end Is specific-e Limitation only slightlyionized. Radiativeheat transfer would beccamexcessive highertemperatures. at !l!his limitation smnifeatad, in both sdhemati- .C~ end @YB$CWP In diffexmt wws for the en- Mamntum Ccmditioner Limitationsergy scaling W and the Impulsescalingk. These In the mmmtum-conditionerconceptdescribedtvo casesare thereforetreated8eparately. above, the pusherplate exetisa constantforce,F, ImpulseScsling. In th Orion systemstudies, on the Spacecmft throughout cycle a of duraticnAt.the implngesmtveloci~ of the propellant the on A forceb616UICe at a time when the propellant ispusher plate was Mmlted to 150 km/see. The llmft $@ expendedcan be vrittenas:vas not baaed upon plwsical Mmita, which vere un - (20) a. (M. + Me) = Ma (a - ao) aknam, tmt ratkr on a bmdcdcun of the validityof wham :the modelswhichwem used to predictqblationof = epacec~ acceleration,t the end of athe pusher-plate surface. In any case,surface 80 mission,=Iative to an inetiialframe ofablation wi21 Imposesouw 13miton the impingenmt reference.velocity,Vi. The net impulsecan be written a = Puekr-plateacceleration,t the end of a a mlaslon,mslative the spacecraft. to I=i3n vi, (17) TM distance traveled the pusherplate,relative bywhich sewes as a definition P. In the case of to the spacecraft, the stroke, is Ax. In terms ofvhere the pmpallant impinges tk pusherplate on acceleration nd time interval a betveen@.zes, it isaxiallyand does not ncoil with appreciable eloc- v & = aa At2/8. (21)ity, p Is equalto the fraction tm pulse-it ofmass which @lnges on tk pusherplate. Elimina- The tiitialvelocityof tbs pushr plate,relativetion of I betweenEqs. (4), (14),and (17)leadsto to the spacecraft ist~ follcxfing expression: lJ=J’=L. (22) P vi = tw p’ (Ma/M) . (18) 2% Elimination aa end I fras %s. (10),(21),and ofIf the optimizationrocedure p described pxwiously (22)resultsin an expresslcm for the mass ratio,I.eaiso a value of Av v‘ (Ma/M)gxeaterthan the t b2 E Me/k$:eUouable value of S Vi, then the systemis limitedtoa-lmm I = P@. and the p@oed plus b2 = Me/l$ = 8 a’ (AX/w At)2 . (23)manmtum-absor%’rfracticuis Bi@y Limitations u!q’ imposedon the maximumstroke, s be (M. + Ma)/M . eQ(+Jv/&fi) . (19) Cx? and on the minimumtire? betveenpulses,At. TO minimize the totalmamntum-absorbermass, The hpulSe is givenby Eq. (17)sad the design Ma= ~ + Me, it is desi.xable splitthe mass tobeccms!ane of minimizing o Ma. ‘qxsOttit ~= Me=db=l” ~isc-h Energy Sml.ins . The final Imperature of the shwn to be the case~ dll’ferentiating (u) Eq.heatedpropellant fiJlingth pnmure vessel (prob- with respectto 1$. Hw?ver, if the mmclmumper-ably hydrogen) limited the acceptable la by level mittedatrolm,AX, and the mininans permittedt~of heat transfer the cooledpxwmure-vessel to and Intemnal., are suchthat b as givenby Eq. (23) At,nozzlewalls. This imposesa limlton the mximm Ie 38ssthaa unity,then the sdniasnn cannotbe ~value of the energydensity, q/m, and sets a limit used and Eq. (15) for v‘ mat be modifiedas follcus:on the productp ~ thrcnagh rebt ionahip the q ** q q 9 q q : 00 q q m k’ “ oh) (U/AV) ~ [2/(b + l/b) I q . . .14 q°0 q q OO** q m. .0 APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE q q .OO The fInal factor, 2/(b + l/b),VU be lessthen PeyloadPlus uther structures ) = 52,542 (M =unity if the pensittedstmb and tim Inlxnwal XWload aocelerat = 19.6 m/se~2 (2 g) j end of ion rntssioncombtieto limltthe designflaxibiliti.The net Pueher*kte stroke (a) = 14.4 mresultis a decreased p~ter 1A’and, consequent- lhtennd. between pulses (At) = O.% eec payload. AS with mat mwoth mexi-Iy, a decreased Totalpmpulaion time = 20 min/missiOn.ma, aevbtions from em optimumparameterresultin reductions.For example,onlyminorperfonsance Thesevaluesare bsbsea en optiammallocation on~ti~~.2 ‘.$ t~n b = ~ and V’ is reduced~ of massesfrom a mlsstinpoint of view; no corres- pondingdetailaddesignexists. cl.earti~ S- Wr- tion of =ss ~ wiU. be requ~d for tls?laser,forPerfcnammeEstimates pilee-unitconveyance and storagemechanism,shield - ExternalSystem ing,etc. (Neutron envfronmsntelonsiderations c for To estimate the perfonmnce of an external such en externalsystemcue presentedin App?ndixC.)system, example pamunaters ans chosen as follows: Each of the pazzunsters affecting has been p‘M = 100,000 kg. Thls initialspacecrdt mass is variedto studythe effecton systemperformance; comparable that of the -eat to spacecraft the nmitts are presentedin Table 1. The ffist contemplated n earthorbit in tb? tires i exampleis the base casepresentedabove. The ~riod 1970-85. ~ters which Isnre been modifiedfrom this base case are underlined.Examplesof the effeetsofn = 20 kg. TMS pulse-unit mass ehouldprovide variouscmstxdnts em listedin the last five rOUI@Y a factor-of-tishielding egalnst cases. Table I clearlyillustratesk extraordi- t 14-MeVneutronstf only half the muss is naryperformance hich can be expectedfrom an ex- w berylliumconfigured a 15” (hdf’-angle) in ternalpulsedpropulsionsystem. conebetweenthe sourceend the spacecraft. = 3m m/see. !l!his m the baae casep=sented, the specificim-Ii quantitycorresponds o the t use of steel with a lOOJOOO-PSi ieM Y pulse desiredcouldbe achievedif one haE the strength. prope~t @mea on the Pusherp~te at a velac- ity of 135 km/see. This is barelywithinthe im-(w . 20 km/see (65,616ft/see). This free-space pingementvelocityconstraint 150 lun/sec of imposed velocitychangewtia occur in a very advanced duringPro$ectOrion. It is not p=sently known mission. It wouldprovidefor a fast round whetherthis fmpingenmt fractioncan be achieved trip to MWS f= low earthorbit. withinthe gemnetrlcconstraints werned by shield- ga’ . 4’7.!l?his efficiency value is taken frcmthe ing considerations. OrIonstudyfor an actualnwmentum-condlt toner internalsystem design. TO some degree,this high value can be attributed the complextwo-stage to design If the internalsystemis to delivera positive employedand to the largenumberof parts p@.oad, tlw value of p in Eq. (8)must exceede. which serveno enerw-storagerole. If the pelletis a major sourceof neutronsthat requireahieldlng, then the impliedus is very value of P’ iS 15.57 (f- Eq. 15)) The resulting hfgh--Ofthe orderof hundmedsof kilogram. Two end corresponds o a maximumpayloadfractionof t additional parameterestinmtes, for a end for Tl,are 0.525. Cm?reepOndi”.g spacecraft parameters are: required obtaina numerical to estimateof v (other Optinmn epecl.fic impulse= 6$?27 sec parameters - definedin the previousdiscussion Numberof pulses = 1275 (for ~ = 25,515 @ of externalsystems): Energyper pulse = 44 equivalent tons of m a= 2. This selection based on the observation is (=- 5% Of propellant impin8es pusherplate) on that the mass in an internaldesignis very Pusher-plate ass (%) = 10,9(0kg m q 00 q .0. w@.x O@t t~t of a s-le PXWWS Vessel. q m Momentum-ccmditioner -s (Me) = 10)970 kg “I: ~ ~( q : ~. cd & demonstratedhat the mass of the t q m q :00 q :00 q q 0 :0 :0 q 0 15 APPROVED FOR PUBLIC RELEASE
    • q.9 q-. : q q*m aa .** q q APPROVED FOR PUBLIC RELEASE !kkj!bsm :@:.* q q =1 EXTEMAL NUCLEARPUU3EDPR@UIi310N SYm PAMMWCER S’NIDY U, bv, u, m I , Mo, Ma, 1$, NP, 310, Ax, At, %* A-.2- G .— .’~b —J&kkkkk 2&_ ~ tala . 100000 21-I.O300 20000 47.00 15.47 1.000 6927 52542 21941 25515 10970 10970 2.0 14.39 .930 46.0 100000 yJ 300 20000 47.f10 61.88 1.000 14998 75602 11875 12721 5937 5937 2.0 6.64 .429 51.6 loclorlo ~o 300 20000 47.00 30.94 1.000 10279 65714 16278 180n6 8139 8139 2.0 9.69 .626 48.5 lwlmlfl 50.0 300 20000 47.00 6.18 1.000 3910 28377 30966 40655 15483 15483 2.0 25.49 1.647 35.1 . 100000 lmo 300 20000 47.no 3.09 1.000 2306 4754 3652.4 58721 18262 18262 2.0 43.22 2.793 24.4 100000 20.0 150 20000 47.00 7.73 1.000 4531 35035 28705 36258 14352 14352 . 2.0 5.49 .710 18.8 100000 20.0 ~ 20000 47.00 30.94 1.000 ln279 65714 16278 18006 8139 8139 2.0 38.79 1.253 97.0 100000 20.0 300 _ 47.00 30.94 1.000 5139 65714 16278 18006 8139 8139 2.0 9.69 .626 24.2 100000 20.0 300 ~o 47.QO 7.73 1.090 9063 35035 28705 3625S 14352 14352 2.0 21.99 1.421 75.6 100000 20.0 300 100000 47.00 3.0!) 1.000 11532 4754 36524 59721 18262 18262 2.0 43.22 2.793 122.1 100000 20.0 300 2ooofl 2.00 75.00 1.000 16621 77586 10859 11554 5429 5429 2.0 140.94 1.879 253.7 100000 20.0 300 20000 ~ 47.43 1.000 12994 72042 13423 14534 6711 6711 2.0 72.11 1.520 155.0 100000 20.0 Ino 20000 20.90 23.71 1.000 8857 61121 18299 20579 9149 9149 2.0 26.45 1.115 72.0 100000 20.0 300 20000 U 10.60 1.000 5525 43592 25527 30880 12763 12763 2.0 8.47 .799 28.0 Constrdned 100000 2n.o 300 20000 47.00 15.47 1.000 ~ 59S73 16158 32967 8079 8079 2.0 .761 23.9 100000 20.0 300 20000 47.00 15.47 l.mlo 6?27 5254? 21941 25515 lo970 lo970 5.7 .323 44.0 100(IOO 2n.@ 300 20000 47.00 15.47 1.000 6927 52542 21941 25515 10970 10970 .9 * 44.0 100000 20.0 300 20000 47.00 4.87 .161 3309 2t_16~4332.?2 46022 32435 846 .6 — 10.0 100000 20.0 300 20000 47.00 14.10 .646 6561 50477 22790 26732 16074 6715 1.7 &WQ 39. s q MinizNzu kinetic energy carried y pulse-unit b mass,in equivalent toneof ~ (4183347/tan). ibissscss tket 50$of theprope.llent maa8lmpinszmn thepusher o platscarryins0$of theemrw. 5 mcmmtum-conditioning systemis veg mmi!l--of thosefor the externalsystemexampleused previously the ofierof ten tiresthe pulse-unit mass for SUuatratesthe disadvantage f the internel o sys- a consez-mtive esign. The value of a for an d tem: In the externalsysteman energyreleaseof actunlInternaldesignwhich baa been studied 44 equivalentton6 of TNT required nnmmtum- a la 1.2. If Supporting Structures,arts in the p abaorbern!as6 Of ody 21,941 kg-+! much s!d.br preseum vessel,pumps,a nozzh?,end otherre- mm per unit of ene~ or per unit of impulse im- quimxmsnts amountto 2/3fithe mass of the bare partedthan in the internalsystem. vessel,a will increase 2.0. to AU Intend. systemwith a reasonable performanceTl = 0.9. This value is takenfraa an intermitsys- can be envisionedon3yby igno~ the shielding re- tem that has been analyzed. m no case can II quinmm?nt and choosing acceptably an smallpu3.ae - be less than 0.75. unit =ss. TMS may bs practical suitable if fusionWith thesevahes, II= 0.8s (fran Eq. 8) indicating or fissionreactionscan be used as the energythat the chosenmiesionexceedsthe ca~bility of an fxxxce.internal designsystem. One such internaldesignhas been partially The mcdzzuz pulse-unitE43s6 which can be used studied. A pressure-vessel diam?ter 3.658m offor tbse given~tera can be obtained set- by (12 ft) was chosenarbitrarily and hydrogenwas aammed tO be the Px’O@lant. l!hl CYCliCOperationtlng v = e. IIIthis casem = b91w. lb s~ce-crsftmass is apporticued ~ = 86,470 kg (pulse as of the systembaa been described SectionIII. inunits or propellant)and Ma = 13$530 kg (pxws~ The byd.ax?gen stagnation ccmditlma in the vessel, .vessel). The cormwpondingene~ mleaae per after the shockwave baa decayedand before expan- Sh *- the nozzl.n has begun, wen? chosentopulse unit is q = MaI#Ia = 609 W or 0.19 . . . . . . equiva- .-. . --- q. -lent tons of TNT. cazparison thes~‘~ue$ w~h of ~ “p .“. q q* b q qm q :0 .:O q q m. q m 00 q m q *9 .:16 “:~ q*em.. APPROVED FOR PUBLIC RELEASE . . . .
    • ,e Sq@diii! APPROVED FOR PUBLIC RELEASE q:’. :* q D. :*:__a ~m ..: *:. i;m * lwperature = 8333”K(15, CK@R) use%334 de %elios system. The resultis a steel Pressure = 689 N/cm2 (1~ pSi.9) . pressuxwvesselwith a wall thickness 3.66 cm of (1.44 in.) and a mass of 12,800kg. DetaUd hydr- At this temperature I@rogen is almostcompletely odynamicalculationsave been perforss?d study c h to disassociated, ionization insignificant. and is At the effectof shockwaves generated the hydrogen in highertemperatures, onization i increases, the. end t~ peak pressures which resultfrom their reflec- hydrogen becons?spaque,and rdiation heat trans- o tion off the pressure-vessel WS3J-.The celmted fer from the opaquehydrogento the walls probably peak pressureof the radial.ressure p wave in the wall. becomesexceseive. is 2.5 kilobars(36,!250 psi), which shouldnot cause With the above assumptions the mass of hydro- failure. gen in the vesselis 2.53 kg end the corresponding The difference 5430 kg betweenMa and the of value of v from Eq. (8) is 5.37. A mexiummpayload p=saure-vesselmass is resewed for nozzle,momentum of 23,550kg can be delivered the @- if Ma and conditioner,nd relatedstmctures. ~ eddit a Ion, energyreleaseare selected 18,230kg and 0.196 as scm part of the pt@oad mass must be resexvedfor equivalent tons of TWT, respectively.This is the lasersystem,tih.er structures, and perhaps aboutequalto the energyrequired heat the to shielding. hydrogen the postulated to conditions. * Helios: An internal cept studiedin parallel co t with the Pro~ectOrion. ccmvent onalfissicmex- i A pressurevesselhas been designed for this plosions were utSlized with a yield rangingfrom 1 exampleby applyingsome criteriathat had been to 40 equivalent tam of m and a repetition rate of about10 sec or longer. A plug in the nozzle was used to allcw recharging the vesselwith of the propellant (hydrogen).These constraints ade m the Heliossystemvery large. ACXNC%U.EIXMlmls Specialacknowledgments due to KeithBoyer,IASL,DirectorLaser i Pro$ects,who intreducedthe contributorso this re~rt to the concept t of laser-drivenhernmuclearreactions t for space-propulsionapplications. 1. C. J. Evezvttand S. M. Ulem, “On a Methodof propulsion of Particles by Means of ExternalNuclearExplosions, TASL ReportTAMS-1955, ” August 1955 (m) . 2. 17uclearpulsedPzmpukion Project(Pr@ect Orion),~chnical summary Report (4 vol.um?s), General15mmics Corp.,GeneralAtomicDiv., RTD4?ln?-63-3o06, 1%3-1964 (SR.D) q 3. J. C. Nence, !Nucleer PuleePropulsion, ReportGA-5572, ” Odmber 5, 1%4. 4. J. W. Hadley,T. 1?.Stubbs,M. A. Janmen{,ud L. A. Simons.‘- Helios a PulsedNuclearPropulsion Concept(~), LawrenceRadiation Lab., Livermore,Callf.,ReportUCRL-14238, June 2, 1965 (~)., q q q*9 q** q “ i& : * q * q :0:: .Cs C:t ‘ q o 17 ‘. ..,, :*. q **. APPROVED FOR PUBLIC RELEASE q q * q * U*U q *
    • APPROVED FOR PUBLIC RELEASE APPENDIXA Nd!l&ML *::**:* q ;: u .:. .ss : q . .0 B -. ,.&&eu~*~as reactants. LZZerpumpingis the method of providingthe Inputenergyrequired excite to - CONCEPTSAND CONSIDERATIONS the materialto its upperlasinglevel. The Nd/gl.ass lasertransition centerad is at Introduction -6 a wavelength 1.o6u (1.o6x 10 m). The state of The essentlslch=acteristics en energy of of the art of theselasersfor producinghigh-power, . pulse requiredfor thermonucleargnition i are high ultrashort pulees ia quiteadvanced. These systems power end shwt pulsewidth. b pulsedfusion are optice3Jy pumpedvia xenonflashtubesand at reactions sufficient a quantity materialis ion- of presentcan produce200 J in a few picosecond. . ized, confined, and heatedto suchhigh levels However,the possibility considerably ncreasing of i that nuclearfusionwill occurduringthermalcol- the outputappearslimited. It is anticipated hat t lisionof the ions. Becausea laserener&ypulse the maximumoutputobtainable will be of the order can be concentrated n both spaceand time, it is i of 2000 J In a few picosecond becauseof the energy believedthat alight pulse canbe generated which densitylimitation the glasscoupledwith the in will satisfythe specificrequirements or initiating f limitation uniformly of pumpingthe glassvolume. a fusionreaction. Also, the ener~ inputfor the requiredhigh-power pulseswouldbe excessive becausethe overalleffi- GeneralFeaturesof LaserPulse ciencyof these systemsis orily-O.3$. lhus it is Calculations indicatethat the minimumlaser not ent%cipated that a Nd/gl@%ssystemcouldproduce energyrequired burn D+T in milligram to quantities more fusionyield energythan that requiredto power 4 6 rangesfrom 2 x 10 to 1 x 10 J. Thesevaluesare the system. Neodymium/glass laserswidl therefore being revisedas more optimalmeansfor confining be usedprisuxrily experimmts to studythe inter- in and heatingthe fusionable materielare examined. actionof high-energy laserpulseswith matter,and The D+T reactionis usue3Jyconsidered becauseits to verifythe correctness the mathematicalodels of m fusionthreshold lowerthan that of the D+D or Is used to calculate laser-initiated fusion. To date, D+3He reactions. The optimumtime width of the neutronproduction has been observedin experiments beer pulse is thoughtto be between10-~0 and 10-7 where laserpulses from Nd/glasssystemshavebeen see,to take advantage the resonantabsorption of focusedon fusionpellets. which occursnear the plasmafrequency the mdium. of The CO~N2 laserutilizesaresonaut energy An alternative approachconsistsof usinglonger trausferbetweenthe firstvibrational statein N2 pulsewidthsfor directcouplingof the fieldto the and the upperenergycoincident laser statein C02. ions,therebypredominantlyeatingthe ions. h The lasertransition centered a wavelength is at of Laser SystemsUnderStu~ 10.6U (1.o6x10-5 m). Becausethe energyis dis- The laser systemmust possesssassbasic char- tributedamonga largenumberof rotationalstates, ecteriatlcs the requiressmts or the lightpulse if f it is necessary promotetransitiona to amongvery are to be met. Becausethe energyneededis high, _ of these statesto obtdn high efficiencies a reasonable efrlciency converting in inputenergy with shortpulses. This canbe dcme by operating intolaser energyis essential. ti attempting to at high pressures(1 to 10 atm) to collision- minimizethe energyrequiredto triggerthe fusion broadenthe lines,and then mode-locking he laser t reaction,pulse-shaping s critical. Pulse-sha@ng i outputso that all rotational lineswill lace simul- and timingare performed en Initial, in low-power taneously. Ccasserciel /N2 lasersusuallyoperate CO -22 stage(oscillator)eforatha pulse is transmitted b at pressuresof only 10 atmo . throughone or more successive empllfierateges The pumpingschemeunder studyfor the hiCh- where Its desiredhigh power is prcduced. PressureC02/N2laser is an electrical dischargein . Threetypesof lasersare underconsideration: which the ionization produced a high-energy is by (1) o@icQp_d Nd/61ass,(2) eleotricslkvm- p electronbeam,while the discharge-electron tempera- pedc02/N2, and (3) ch~c~px~ers US* ture and enerqpumplng are providedby an applied .* q9- * .* **818 ***: . . APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE -- .:*. q0 ..: q electricfield. !lhe overallefficiency this of & “he”kfber couldeitherbe expendedwith each lasershouldbe..- 1O$ and the maximumoutputis ~losion or couldremdn on board the spacecraft eWeCted to be 105 J In severaltenthsof a nano- for continued reuse. second. me outputper volumeof C02/N2operating For an expendable system,the problemsof at a pressurebetween1 and 10 atm is expectedto focusingthe laserbeam onto the fuelpelletwould. 5 be 10 J/m3. be essentially eliminated becausethe laser,the The chemicallaser is self-pumped,tilizing u fuel pellet,and the propellant materielcouldbe. the ener~ output of the chemicalreactionof the constructed one unit. Such an approachappears as materialswhich form the lasermedium. The require- essentie3for internal pulse-propulsion systems, ments of the chemicalreactionare that It be very materialcanplet.ely wherepropellant surrounds the fast (explosive) nd that the resulting a mediumhave energydevice. Use, from a propulsion viewpoint, a largeexcitedpopulation the upperlevelof a in it wouldbe much nsYre economical imparthigh to possiblelasertransition.The chemicalreaction velocityto auy not reusablelasermedium (as in a can be initiated eitherby a llghtpulse,an elec- chemicallaser)beforeeqdling it (becausethe tricaldischarge, an electron or beam propagating e~losive sourceis essentially energyunlimited) throughthe activemedium. The energyin the ratherthan to expelthe material. with negligible upperlaser-vibration level is distributed among propulsioncontribution.lhe generation suffi- of a number of rotational. states(thoughnot as maqy cientelectrical power withinthe unit and cost as in C02),and it is thereforeadvantageouso t reduction a levelwhere the disposalof laser to operateat higherpressures(1 atm) in orderto componentsbecomes economically feasibleare some extrectmaximumenergyby the laaingaction. Re- of the problemsto be encountered. searchattention chemical in lasershas been di- For a non-e~endablelaser,the principal rectedmostlyto reactions hydrogen of with the problemIs the focusingof the laser energyonto ~ogens, speciflca13y2~ C12j and (CN)2. Tu F the fuelpelletand the protection the laserfrom of increasethe ener~ densitywithinthe medium,the the ensuingexplosion. Lightweightexpendable chain-branchingreactions, e.g.,N#4 + ~, mirrorscould solveboth problemsfor an external seem quitepromising. The RF lasertransitionis pulse-propulsion system,but the problemswouldbe centered a wavelength 2.7’ at of ~. The overall more acutefor an internalsystembecausethe reac- efficiency chemical of lasersis expected be at to tion must takeplace in en enclosedvolumethat is least16, and outputsof 106 to 107 J in a frec- filledwith propellant materiel. tion of a nanosecond appearto be possible. One Of the two laser systemspresentlyunderde- promisingconceptfor a chemicallaseramplifier velopment, the chemicallaserappearsto be more involvesthe traveling-wavegnition the chem- i of suitablefor a apace-vehiclepplication a than the icalreaction,followedimmediately y the laser b electricallyumpedCO~N2 SYStem. It represents p pulse to sweepthe cavity. The unit outputof a the most compactenergysourcein both volumeand typicelchemicalsystemoperating 1 atm is at 6 weight. The chemicallaser is also Inherently sim- expected be 2 x 10 J/m3. to pler, requixhg littleelectrical power and storing Relatingto Propulsion LaserCharacteristics the requiredenergywithinthe atomsof the chemical Applications elements. In comparison, the electricallyumped p Of prime importance for any laser-pulsed C02/N2laserrequtresSU of its inputenergyin thermonuclear pacepropulsion a systemexe weight the form of electrical power,which is difficultto and powerrequtiements.Becausenone of the laser provideIn a apacevehicle. Even if large amounts systems being considered sufficientlydvanced is a of electrical energywere storedin capacitor banks for use in this application,etailed d planningfor suPPlledfrom a m~est Power sourceover a period incorporating laserinto a spacecraft the must of time,the mass of such a storagebank for supply- awaitfuturelaserdevelopments.However,certain ing 107J of Inputenergywouldbe prohibitive. In fundamental questionsshouldbe con~ereiLamw. ... ...ad..tion,he overallefficiency converting t of the .:*O .- A -— q aukb *. *.. q e* FOR :.: q * “ q APPROVED q : PUBLIC RELEASE q q 19
    • APPROVED FOR PUBLIC RELEASE 9:**: .: !:.ii!idip *.? energyinputto laserenergyoutputshod in~!l& .* .:. q O* q O becauseof the lack of radial.estraint. TO prevent r the largeloss incurred converting by thernuil. yieldingof the platematerial.from heap stresses, energyinto electrical energyin the power supply. the platemust be thick enoughat the edge end must Thus,a theznuCUy pumpedC02/N2,applyingthe ther- increase thickness in towardthe centerto maintain mal energy dtiectlyintolaserexcitation, ight m a uniformaxialplate velocity. Theseopposingre- have a betteroverallefficiency for a space-vehicle quirements . demandan unnecessary ccumulation f a o laserthan the electricallyumpedsystemand, p materialat the centerof the plate to satisfythe Additionally,ould obviatethe demandfor large w yield-strengthriterion c alone,becausethe tangen- . capacitorstoragebanks. A singularadvantageof tial tensilestresses,i.e.,hoop stresses the if eitherthe electrically-pumped thermally-pumped or plate were a sphere,are less than the hoop stresses CO~N2 laser systemis the fact that the laser from the edge moments. mediumis, in principle, reusableafterthe excess l!he manentumexchangebetweenthe expanding ener~ residl.ng the eystemhas been removed. in propellant and a flat,cLrcularpusherplate dtifers from that of the shapedplate in that hoop stresses APPENDIXB do nOt develop. As with the shapedplate,the mass distribution f the disc shouldcorrespond the o to DESIGNCONSIDERATIONS POR radial. mpulsedistribution n the axi.sl irection i i d PUSBER-PROPELLANT IN!lERACl?ION acrossthe surfaceof the disc. Thiswouldprevent General bendingof the plate. Radialstresses~e developed OQV fia the VISCOUSshem of the radialpropelJ.ant- The designof a pusher-end-pulsesystemis velocitycomponent the wave spresdsrsdia13y as constrained y the characteristics the momentum- b of acrossthe disc. Theseradialstressesare much exchamgeinteraction the expanding of propellant less than the tangential tensilestressesin the wave with the pusherplate,the designcriterion shapedplate. being amaximum momxtum exchangewith no destruc- tive effectson the pusher. In sddition,the Althoughthe mcmentumexchange with a shaped optimummass of the pusheris determined mission by pusher is greaterthan that with a flat disc,the considerations. extraweightof the shapedpusherto compensate for hoop stressesq be amore severepenaltythan the PusherShape pert’ormance the flat disc If both sub- decreased of The msximummomentum exchangebetweenan ax- tend the sane solidangleof the propellant eqxin- psndingpropellantand a solldpusherplate is ob- sion. tainedwhen the shapeof the platemirrorsthe sur- PusherStresses face of the propellant cloud. Assumingthat the propellant~snsion is divergent,the shapeof the Althoughthe hoop end rsdialtensilestresses pusher surfaceshouldbe spheroidal; nd the use- e are not a designconsiderationor the discpusher, f ful momentumexchange any point on the plate is at both plane and raiialstrainwaveswiJl be trans- a resultof only the axialcomponent the local of mittedthroughthe materialfran the shockof the propelJ.ant velocity,i.e.,the direction vehicle of propa~t interaction.If the acousticthickness motion. If the mass of the plate is u!xlform, the (platethickness/speed soundof material) of is locslplate velocltyvariesawi bendingoccurs. much less than the propellant pulse width (inter- The plate canbe designed resetat uniform to actiontime for propellantstagnation),he plane t wave will reverbe.rati repeate&Lyand dissipateas , velocitylf its mass distribution made to vary is radially in order to match the axialccanponent of the st.egnation pressurebufldsto maximum. There- the locslpropellantimpulse. The cross-sectionf o fore,the strength the materiel of must be suffi- . sucha plate is then a crescent. However,the cientto prevantthe “blowing-off”f the pusher o stagnation-pressure buildupon the plate surface back sidewhen rsxefectlon occursfran the reflec- developshoop stressesfrom the edge munents tion. .=e$e ~edielwavestraversethe plate in mm .0 .0 q ** .0: q q ::0 .* .00. q q q0 : q .20 APPROVED FOR PUBLIC RELEASE
    • — q q  APPROVED FOR PUBLIC RELEASE q q6 ..: .:. ;:*timesexceeding the pulsewidth,stressconcentra- g:e$+%%&n 1.5 x 107 cm/Oec,convective-flowtionswill be producedat the center. However,the Instabilitiesre calculated, a thus renderingtheradialtfaves will be weakerthan the planewaves, diffusionmodel invalid.and the stress-concentration levelmay therefore be OtherEngineering Aspectsless than the yield strenbth. This stressconcen-trationfrom radialstrainwavesmust be carefully Becauseof the Inherenthigh acceleration f o the pusher,a shock-abeorberystemmust be designed ssntiLyzed any pushe~platedeeign. for to reduceaccelerationsf the payloadmass to oPusherAblation tolerablelevelsfor mannedflight. This shouldbe The energyreleasefrom the stagnating pro- accomplishedith a minimumdissipation energy. w ofpellantat the pushersurfacecausesthe pusher The attachment the shock-absorber of systemto thesurface heat with attendant to ablationof pusher pusherplate requiresa minimumedge thickness,materiel. To preventthis loss,the plate surface which,in turn, is a factorIn determining theshouldbe coatedwith an ablativematerialof high pushermass. The kinematics the shock-absorber ofheat capacity, low thermalconductivity,nd large a systemis stronglydependentupon the pulseperiod,Rosselandopacityat the stagnation conditions. one of the free parameters a pulsed-propulsion ofPreferably, this materialwouldadhereto the plate system. Becausethe pusheracceleration s inversely iend be of sufficient thickness last throughout to proportional the pushermass,a minimumpusher tothe firingpulsesfor the mission. If sucha mate- mass wII.I. determined the msximumacceleration be byrisJ. unavailable,n ablative is a film couldbe de- that the pushermay be subjected in orderto en- topositedon the pushersurfacebetweeneachpulee or sure the structuralintegrity the shock-absorber ofaftera groupof successive ulses. p system. The ablationphenomena, althoughcomplex,=e Althoughhoop and tensilestressestheoret-predictable for stagnating plasmaswith incident icaJJ.yre not developed, mismatchof the pro- a aenergyfluxestypicalof plasmasd-riveny high b pellantwave and the pusherfrcmpulse-systemexplosives. n analytical A aproximatlondeveloped positioning and nuclear-yieldolerances t will resultin the Orionprogram2successfullyredictsabla- p in bendingstresses. Thesecriteria probablywilltion ratesf? experiments ith propellant w velocities not affectthe pusherdesign,but must be analyzedup to 4 x 10 cm/sec. lh applying this expression to determinethe positioningand yield tolerances.for energyfluxesfrom a nuclear-pulse-driven plas- RelevantInformation ras ProjectOrion fma, the ablationratesbecomeunpredictablet pro- a A wealthof Information available is aboutthepellantvelocities greaterthan 1.5 x 107 cm/sec. interaction propellant of and pusherfrom the design The ablationphencmena occur In stages. studiesof the Orionproject. Unfortunately, muchDuringthe earlyphases,the phenomenon predic- is of the information empirical is and relevantonlyted by a kinematic model,involving partlcle-to- to the referencevehicledesigns,and thereforemaypsrticlecollision transferof kineticenergyand not be applicable pulsedsystemsin general. toindicating e~onentisl increasein the ablation an However,some calculationalechniques, t e.g., therate. As the propellant plamna,due to compression kinematics the shock-absorber of systemand theat the pushersurface, heats to temperatures n the i strainpropagation the pusher,shouldbe appli- IneV range,radiationtransport predominates,esult- r cable.ing in a net decreasein the shlationrate. Next, The Informationfrom OrIon ablationexperimentsas the ablatingmaterialincreases temperature, in is relevantonly for verifyingthe analyticaltech-the ablationrate is determined diffusion by of nique,and is largelyempirical. The lack of ex-the ablatingmaterialintothe propellant.For the perimental data for propellant velocities inter- ofOrionconfiguration, bulk of the mass was cal- the est (> 105 m/see)resultedin a conservative on- cculatedto be ablatedby the diffusion process. strainton propellant velocity(1.5 x 105 m/see)forWith the Orionanalyticaltechnique. velocities at q  &   ... .OodeSignsof Orionvehicle~. dJP51Bb 21 *. * q q @aq : . q :.: . q q APPROVED FOR PUBLIC RELEASE q 90
    • APPROVED FOR PUBLIC RELEASE APPENDIXc %iiidib q:..::* . .. q .* . ,:0 ..@ S* Totalneutronenergy= (1.275)(176)=2.24 x 105 tons 8 =9.39 x 10 Mlhec 14 ~ NEUTRON ENVIRONMENMLCONSmERATIONS =9.39x 10 POR TSE EXIERM& SYSTR.f =5.87X 10w MeV. 26 l?o= neutronsource= 4.16 x 10 neutrons. This appendixpresentsmum general conclu- . slona regardingthe effectof neutronenvironmental Thesemagnitudes are so largethat “attenuation”n I considerations upon the performance and overall the usualsenseof slowingdownand/or capturing the neutronsimpliesnon-survival f the attenuating o . eyatemconfiguration the external of pulsed-prop- ulsion concept. Resultsfrom initialoalculation- medium. For examtple, (uncooled) usherplate the p el studiesleedlngto theseconclusionsare also in the aforementioned referencecase can survivea given. ‘total heat load of ~ 109 J, or some sti ordersof magnitudeless thanthe neutronenergyfrom the The calculations enerally g estimaterelative source. An unshielded mannedpeylosdlocatedat quantities(e.g.,neutronreactionrates,attenua- ten metersfrom the sourcewouldreceivea total tion factors,end weight-effectiveness source per 12 dose of ~ 10 rem, which is 11 to ).2ordersof neutron). An absolutesourceintensity must be magnitudehigherthan couldbe allowed. Further- assum?d,however, estimate to neutroneffects (e.g., more, capturey-rqf sourcesresulting from the temperature rise,radiationdamage,azxl dose rate). absorption even aminute fraction these gen- of :; A referencemissionwaa therefareselected eratedneutrons(perhaps few as 10 as to lo-’+) consisting 1275 (identical)ulsesover a thrust of p wouldproduceheatingproblemsat most locations periodof 20 rein, with ~ tons (~ equivalent) of throughout the spacecraft. energytransferred o the propellant eachpulse. t In This energywas furtherassumedto includeall non- Two basic approachestowardalleviatingthese neutronenergyfrom the pulse and ~ neutronenergy. problemsare apparent: (1) An expendable attenuating materielcan be Interposed betweenthe sourceand The D+T reactionwas takenas the energysource, the pusherplate for eachpulse,and (2) the pulse which Introducesthe most severeneutronenviron- unit-spacecraft configurationan be stretched c out mentalproblemsof all possiblefusionsources. so that critical parts subtendrelatively small The resultstherefore are indicative the upper- of solidanglesfrom the pulse location. Expendable llmit,or worst,case,end will providereference shielding mass will reducethe sydsm specific im- valuesfor comparison with calculationsaaed upon b pulsedirectlyas thismass is tireased; the stretch- otherfusionreactions.Furthmmare,aD+Tburn is ing-outimpliesp@oad lossesdue to addedstructure, the easiestto achieve, axxlthis whoicecouldbe, and, m~e ~ortant~, a possible pulse-unitdesign , therefore, realistic. problemsinceit -be more difficult collimate to The impliedtotalenergyfor each pulse in the the pulse-unit mass (to utilizeeffectively dl non- assumedmissionis 220 tons/pulse(&$ in 14.1-MIsV neutronenergyfrcm the pulse as assumedearlier) neutronsand 2@ in non-neutron ener~). l%e than If the systemwere more ccmpact. followingsourcetermsresult. l%ereare otherfundamental considerationsIn Neutronenergy/pulse (0.8)(220) 1T6 tons = = such a propulsion system whichalso requireboth or (176)(4183) 7.36 x 105 Mf-sec = expendable mass at the energysourceend elongation or .. = 7.36 X 10~J of the spacecraft. For example, propellant a mass (7 . 3 6)(10U~ ;“; &x1024wv0 must be expemiedto ~ovide the impulsive force . ‘(1.6) (1.0-13~ “ - i4.60)(lo24} - which drivesthe spaceship, ad the shock-absorber Neutrons/pulse 3.26 XI.023 strokemust be long to keep the payloadacceleration (14.1) neutrons/pulse. . within acceptable limits. Presumably, maJor a . q 00 q * q ** .:0 q q .em22 *6 q APPROVED* FOR PUBLIC99RELEASE .O . q * q q q q
    • .* 9.*9 APPROVED FOR PUBLIC RELEASE fraction thispropellant of -. Udi!w? ::*::.:: mass can also be” ?M&I:W:0 q * ~ .!. : . .--O .0 PAYLOAO LOCATION shielding.In addition,typicalpulse-pusher late p WWC R PLATE LOCATION (oURI NO PULSE ) separaton distance a!xi I e overallspacecraft dimen- PROPELLANT CONE SOURCS SMOCK STRUCTURE, sionsimplied otherconsiderations such as by are ABSORSER UNUSEO PUUE - .—-~ SY$WM uNiTs, qto to provideImportant geometrical attenuation the of J> neutronfluxesthat impingeuponthe pusherplate end upon the payload. % ‘“.’+-+=+= Sores basic overallconsiderations thusbegin Fig. C-1. Basic spacecraft schematic.A to emerge. We are led to consider petit source a have undergone one, or at umst a few, scattering of neutrons the uis of a circular on pusherplate, eventsescapeinto spaceand can no longerIntercept at a distance, from the plate as shownIn Fig. a, the targetma. Ideally,every scatteringevent c-l. l%e plate subtends relatively a smellsolid would,with high probability, emovethat neutron r anglefrom the source,as definedby the angle 9. from considerationnd the neutronfieldsin the a For maximumshielding effectiveness unitmass per eystemwouldthenbe prcducedpredominantlyy un- b (thiswil.lbeelaborated upon later),the pulse- * coXllQedlk-MeVneutrons. As we shellsee later, unitmass or someportionof it is placedin a cone this idealcan be approached closelywith a rather of height,1, with its apex at the source. A p8Y- * straightforward, albeitelongated,systemconfigura- load regionis locatedat a distance, from the b, tion. positionof the pusherplate at the time the fusion The neutronenvironmental problemareasas pulse occurs,or at a distancea + b from the neu- currentlyenvisioned for sucha spacecraft can be tron source. The intervening spaceis occupiedby S.s classified follows: as a shock-absorber system,the spacecraft structure, propellantstorage,etc. 1. Neutronheatingof the pusherplate. 2. Neutronheatingami radiation damagein the The principelneutron attenuators for each remainder the spacecraft of (the stored main componentcan be identified follows: se pulse unitsmay pose a particular problem). 3. payloaddoses (e.g.,crew shielding). Comporient Attenuators 4. Neutroncapturey-rw effects. (lllisay m Pusherplate The “propeU.ant” be en importaut factorIn Items2 and 3.) The separation distance,a 5. Neutronactivationlevels,particularly Shockabsorber The above frau the standpoint long-term of crew doses. (Thisis closelyrelatedto Item 4). The pusherplate Main spacecraft The above Althoughthese areasare clearlynot independentof (incl;dingun- one enother,they are being emphasized the order in The shock-absorber usedpulse units) system The distancec given. Most calculations o date have been directed t Payload The above towardItem 1; the remainder this appendix of will Main spacecraft structure deal mainlywith theseresultsand with somere- Unusedpulse units sultsfor Item 3. The distanced In additionto the .sIngle-scattering neutronic If the pertinentsolidauglesare kept small criterion mentionedearlier,smallness the solid of enough,materielattenuation etweenthe source b angledefinedby the angle9 might also be deter- end any positionin the system(asmeasuredalong mined on the basis of geometryrequiredto minimize the x-axis)will be primarilyvia scattering-out of the solidangle subtended from the sourceby the * ~deed, this is the principal neutronicscriter- component question; in i.e.,all neutronawhich ion by vhichthe smallness the solidangle can of be judged. * *In the remainder this appendix, of “prOpell~t” This listingis in orderof decreasingexpected will mean only that portionof the pulse unit seriousness(on a ratherintuitivebasis)from which is In the indicatedshielding cone. the standpoint overallmissionperf of ormanceand q O* . conceptualfeasibility. 9** . . q q *. .. :O q : :0- 23 APPROVED FOR PUBLIC RELEASE
    • !i!iMi@f APPROVED FOR PUBLIC RELEASE ::.*:. q .* q q q :: ““”& .:O C-I q :.* .b q q 0 * Cone bd.f+agls (9),og d 15 15 u 30301515 15 15 15 Prqd.bnt terlal 6 m so so ~o ~o so Cl$ ~ %2 LIE ‘~ ~ -at d-Kv (P), TfCX3 L 1.0 1.0 1.0 1.0 1.0 O.sl o.91 0.65 0.65 0.65 0.65 1.87 . P=JPuant length(t),m COna 10 20303.0202030 20 30 !WW30 R’cpel.lant attemxtlca factor (A) 2.5 6.%? 15.9 2.2 5.0 7.4 19.8 8.0 z?.8 I@ 1339 la? . Frsctimxl solidawl.exubtxuded W l ~nher plxti, $ 1.? 1.7 1.7 6.7 6.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 &emll ttenuat fxctor q lm 144 365 935 33 74 433 11.65 459 3339 9e60 ?8,803 6W0 Frxct orneut.mus i.m atpuxber plxta tint emeatlal.ly XM uncollldml o.g9 O.* 0.80 0.89 O.* 0.94 O.SO 0.95 0.89 0.74 0.66 O.* E - (in c -1 A)/l,x 0.0!3% o.og12 0.0922 o.cq79 0.0803 0.1001 0.0935 0.1040 0.1042 o.mm 0.1029 o.15~2 0.0962 0.0962.qx2 0.0962 O.* o O.uyd0.1051 o..Ll360.L156 o.Iv6 0.u56 0.u363 Elq 0.93 0.93 0.96 0.81 0.84 0.95 0.95 0.90 0.9 0.89 O.@ 0.83 Propalxnt (m), -s g 219 5433 WE 391 1320 61.10 @770 37W x/(;. A)3 6P 68 69 43 43 46 45 38 the propellant mass neededto achievea givenneu- As we shall see laterfor severalcasesof tron attenuation.A coro31aryquestion-lees as Interest, is (almost) Z independent 1 and 16 of to the sensitivity f the propellant o mass to pro- approximatelyqualto the macroscopic e total pellantshape,for a givenoverallattenuation. (lk-MeV)neutron cross-sectionof the propellant, Zt. To addressthis question,equat Ionswere derived Further,if the propel.Umt a simplecme, its is which relateboth totalpropellant mesg and the mass is givenby radialvariation pugher-plate eutroncurrent of n (c-2) to prope3knt shape(e. g., convexor concavecone face) and to 9. Thesegeometrical relationships becomecomplex,and overeJloptimization s not i straightforward. owever,someprincipal H con- where pis propellant densityand A is the propel- clusionsare apparent:(1) the propellant mess is lant attenuation, efinedhere as (pusher-plate d insensitive o variations the shapeof the conets t in neutron-ener~currentwith no propellant ccae face (thus,the simplecone is very near3yoptimum), present)+ (pusher-plate neutron-energy current end (2) the radialdistribution f pusher-plate o with the propellantcone in place). Note that,for heatingIs relatively flat and also Insensitive o t a givenpropellantattenuation factor,the propel- the cone shape,es well as to 9. This is true for lantmass dependsvery simp3yupon 8, i.e.,m= W valuesof 13considered, to 13= 30”. up (tan8)2, becausep, Z, endAare independent fe. o We can arrivevia theseoverallconsiderations Sone calculat&l quantitativeesultsmay help r at saneusefulshplified relationships.If the to clarlfythe abovediscussions.*mble C-I shows neutronsarriving the pusherplate are essen- at pertinentresultsfor s- typicalconfigurations tiallyuncollided, the propellant attenuation ec- f (seeFig. C-l). tor la very near3yJugt * n (c-1) Because of the diversity and multidimensional A=e character of the geometries of interest, end be- causeof the rathersubstantial ttenuation a fac- whereZ is a constantappropriate the propellant to tors lilcelyto encountered,onte Carlo has been be M selected as the c.elculational method of choice. materiel,and 1 is shownin Fig. C-1. w ** ::..** q  .mo 8~* . q *9 .24 APPROVED q q q q FOR PUBLIC RELEASE q0 q q 98 q *
    • q APPROVED FOR PUBLIC RELEASE q q & && &&  q Fran TableC-I we see the fo3J.owing: q0 .: .:O q q .{. :o~ TABLEC-II 1. Z is generallywithin1O$ of Et (at least fore _15°). FIGURE-OF-MERIT V- FOR VARIOUS SIIUi!LD~G MATERIALS 2. Between70 and lC@ of the neutronsIncident CromSOoticm upon the pusherplateare uncollided, e- d .Jt(14.1 rev), pendingupon the propellantattenuation Msterlnl 0/(0 n@3 factor. 2 0.69 1.4 612> ~2 3. The relative shieldingperformance per unit 6Li2 ‘r 0.65 2.ca 90 mass of the variousmaterialsis. evident, e.g., 7LlS 8 0.75 2.16 @o. A)3, g = 15” H20 : m S 100 (fin M 9.0 1.86 1.49 64 ~ 700 (ln A)3, t3 = 30° B lo.a 2.54 1.3k 80 CH2: m: 70 (ln A)3, e =15” c K 2.2 1.30 163 LiR: m> 45 (4nA)3, s = 15” ‘% 14 0.91 2.7 168 Be: m: 40 (enA)3, e =15° qo U 1.0 2.89 2k2 U 27 2.7 l.p 5& The approximate elfdityof Eqs. (C-1)and v T1 47.9 4.5 2.26 470 (C-2)for the configurations TableC-I sIJ.ows of Cr 52 7.1 2.k2 197 us to derivea convenient figureof meritwith Fe 55.9 7.9 3.14 90 whichto screenpotentitipropellantshielding nl !3.? 8.9 2.a 133 materiels. For this purposewe assume Cu 63.5 8.9 2.?5 125 Z ~Zt (14.1MeV) Sr 91.2 6.4 4.cA 280 .Q@Q=t m 95.9 8.k 2.1 w M no 96 10.2 4.03 130 whereM is the propellant molecular weightand Ot cd 1..12 8.6 4,4 223 is the microscopic totalcross-sectionor 14.1-MeV f T8 101 16.6 5.07 165 neutrons. w 184 19.3 5.3 1.12 E% 207 Ilk 5.32 453 Thus, u 23a M.’r 6.23 159 or SinceEq. C-3 Is approximateand,more im- portantly, becausethe relativeimportance (n,2n) of Also, reactions variesconsiderably rom speciesto spe- f cies,thesevalues are not an exactmeasureof re- lativepropellant effectiveness.However,they are consistent with the calculated relativemassesin Thus , 0.0752 0 TableC-I, with Be being the predictedbest propel- (In A)3 m = (0.6023)3(Pt/M)3 m lant shielding materialon a mass basis. However, . detailedcalculations ndicate i that Be is only about =0.344 (4nA)J ~ . 5 to 10% betterthan LiH. (P et/M) 3 For two propdlants,1 end 2, and a givenattenua- AS an approachto examining more realistic a tion,A, v: have pulse unit,attenuation curves*have been calculated for the configurationf Fig. C-2. The variation o, ~ [P/( PCJt/M)3]1 . *Here,thepropellant attenuationfactoris defined ~= [o/(oc@312 as (pusher-plateheatingwith no propellant cone. is a measureof the propel- present)+ (pusher-plate heatingwith the propel- The quantity~ (P u /M)3 lant cone). Note the differencefrom the previous lent shieldlng~s requiredto achievethe given definitionbaaed upon neutroncurrent attenuationfactor,A. TableC-II givesvaluesof this parameterfor severalX%?pHW?d&$V@~$ritQ~e :.O .. 25 #Jdhbhh APPROVED FOR PUBLIC RELEASE * q q : 9e9 * q q
    • q a 1 APPROVED FOR PUBLIC RELEASE C= be cotiigmed as In Fig. c-2, the pusher-plate PUSHER PLATE Y PROP heatingfrom Fig. c-k is stilltoo largeby a fec- tor ofN25. (LO: The implicationsre fairlyobvious. Either a the pulse-unitshieldlng mass must be substantially , CASE increased(introducing severeperformance a penalty), or the pusherplatemust have a coolingmechanism that acts duxingthe courseof the propul.sion per- . I configuration. +#--- Fig. C-2.Pulse-unit icd (whichmight seriously compromise its struc- of X, ~rw , and m with t iS shownin Fig. tural inte~ity),or the pulse energymust be ob- C-3 for a LIH prope~~~. Using thesecurvesand tainedfrom a fusionreactionotherthan D+T (e.g., the neutronsourceintensi~ presentedearlier D&e). Roughly40 kg of pulse-unitshielding mess, (appropriateo a D-T energysourceaud the given t or- ~olo 11. to 10 J of pusher-plate ooling,or c referencecase),the pusher-plate eatingcurveof h some appropriatecombination theseapproaches of is Fig. C-k can beplottid. (FigureC-4aJ.eoshows requiredif D+T fusionis to be the energysource. one calculation singBe as the propellant. u ) Certainly, the prisxxrynergycomesfrom the if e D+3Hereaction, even from D+D, the pueher-plate or The result@ pusher-lateheat load is too heatingproblemis greatlyrelieved;however,no high to be tolerable. It has been estimated that quantitativeesultsare as yet available r for such the pusherplate of Fig. C-2 (uncooled) can survive systems. a neutronheatingload of- 109 J duringthe course of the reference mission. Thus,even if we assume In concludingthis discussion, few comments a perfecthydrodynamic ollimation, o that the en- c s will be made regardingthe payloed(crew)neutron tire 20 kg of pulse-unit mass in the referencecase dose to be expectedin the D+T drivensystem. Some Initialcalculatlonalesultsare also available. r I I I I I I I 24 — 2, I I I I I I I 22 — 20 — ~G” ~ASS 18— 16— 00 lo 20 so 40 50 I 60 I 70 I 00 60 0.090 ,ocLJJ_LLd o 4 8 20 24 2S , 2, cm iiASS,; k Fig. C-3. Variationwlthk of massesand~ for Fig. C-4U Neutronheatinginpueher plate vs configurationf Fig. C-2. o .0 be* .:- . •~~&~ q canpinents, c–tiiguration in Of26 w: APPROVEDO*’ q FOR PUBLIC RELEASE 9* •~ q q
    • q e APPROVED FOR PUBLIC RELEASE -:;; q:.:. ::. : q: .’ q q o q 0: : : TABIAC-II; q “.o :. PAYLOADBIOLOGICALDOSE CA14ULATIONS Unshielded Shield “Shield”Masses,W PropelJ.ant Length (i), P&ell.ant E@fload Shield Thickness Material cm Mass, h Dose, rem Material _&k?& !!z?241Wl?!41, LIH 20 0.39 7.8 x 108 LiH 205 21,8&3 2790 LIH 20 0.39 7.8 x 108 B 145 44,300 5540. LIH 50 6.11 4.09 x 107 LiH 175 18,600 2350 LIH 50 6 .U 4.09 x 107 @ 125 38,200 4736 Be 30 3.80 7.02 x 107 LiH 181 19, 2C0 24L0 B 30 3.80 7.02X 107 Be 129 39,4~ II$X20 Be 60 30.40 1.58 x 106 LIH 143 15,200 190 Be 60 30.40 1.58 x 106 Be 102 31,100 3830 Once again it is evidentthat elongation the of Pusher-plate thickness ‘7.62 = cm spacecraft advantageous.Indeed,thisproblem is Source= D+T neutronsource(described earlier) is quiteanalogous the pusher-plate roblemin to p Flux-to-dose conversion factor(~ 14-MeVneutrons) that the requiredattenuation can best be achieved = 4.2 X10-8 rem/(neutron/cm2 ) througha smallsolidangle (subtended y the pay- b t = variable. load)and throughmaterialattenuation via scatter- The fractional solidangle subt~ded by the ing-outof this solidangle. payloadfrom the sourceis 2.77 x 10 , and for a However,thereare fundamental ifferences d be- totaldose of-. 1 rem, the additional material tweenthesetwo problems. Much largerattenuation attenuation requiredis factorsmust be attainedfor payloadprotection, A = (k.16)(lo26)(2. ~)(lo-4)(4.2)(lo-8) and the resultingimplicationsre quitedifferent a o (1.63)(105) from thosefor the pusherplate. Any shielding = 2.97 x 101O. mass thatmust be addedfor payloadprotection does This must be providedby the combinedpropel.lant- not affectperformance diminishing by the factorP. materiel, pusherplate-spacecraft plus any necessary pound-for-pound) additional Rather,it simplyreplaces(roughly shielding. payloadthat can be carried. Furthermore, “useful” The actualmaterialattenuation that might be Interveningass (e.g.,storedpulse units)that m availablecannotbe calculated withoutassuming many must be carriedanywaywill substantially reduce of the spacecraft designdetails. However,the (or eliminate)the payloadshielding mass that must attenuationavailablein a propellantand pusher be carried. plate can be estimated, whichgivesan indication of To help put theseconsiderations perspec- in how much shielding must be acccmrplished the re- by tive,we considerthe “generalized”pacecraft s con- mainderof the system. TO do this, a vacuumbetw~n figuration Fig. C-1, with the pulse-unit of and the pusherplate and the payloadis assumed,end the pusher-plate configurationf Fig. C-2. We assume, o resulting(upperlimit)payloaddoses are calculated.* consistentwith the aforementioned referencecase, TableC-III showssuch resultsusingthe configura- 9 = 15° tion shownin Fig. C-2. Also given in TableC-III Pusherplate diameter= 4.5T2m are two estimatedshieldingmasses. Shieldmass. Payloaddiameter 4.572m (area= 1.63x105 = cm2) Type (1) Is the estimated mass of the given shielding a=8.5m materialthat wouldbe requiredat the payload(diam- b=60m eter,4.572m) to reducethe dose to 1 rem. Shield 27 APPROVED FOR PUBLIC RELEASE
    • APPROVED FOR PUBLIC RELEASE !Mii&F$ :*. q. :.. q q b. a* ~: -– that these shielding massesassumethat no other mass Is locatedbetweenthe pusherplate and the ‘~~~~y$~~~: ‘:~~~~~~”a~~=le 8oSm~ ~x-=1-= x l-T’pE(’) for the shielding require=nts. Indeed,it seems l===< likelythat a much more serloueneutronenviron- mentalproblemwill be that of protect- the structure and equipment(including he lnitisJ- t . Fig. C-5. Psyloedshieldconfigurations. 25,000kg of storedpulse units)betweenthe pusher r in mass Type (2) is the correspondingequirement plate and the pwlosd location,Wd tmt littleor a shedowshieldplaced15 m from the pusher-plate no additionalshielding mass wiJl be requiredto positionat the time of the pulse (seeFig. C-5). protectthe payload. Note that l!ype (1) is indicative the maximum of shieldmass that couldbe implied,whereasType (2) , , . . 9** .:= . . q *O . q*. q28 M; FOR q q.** APPROVED * q 9** PUBLIC RELEASE O q q q 99 q
    • 9 ------ mmo-~~:~:- -~ —— —— —— — ---m-m- .0 =:.:FOR APPROVED .0 . q q PUBLIC** RELEASE q .:. .,0 q q•l 1: uNcLAsslFED - I I I I I I I I I I I I I I I I I 1 t1 I APPROVED FOR PUBLIC RELEASE