1991012826-321
:1 TRANSPORTATIONACHIEVABLE SPACEAND ELEVATORSTARSHIPSACCELERATFOR SP_CEION ._
Fl_t_ Dynamic_L',_rator_ N91-22162 Wright-PattersonAFB,Ohio
ABSTRACT
Spaceelevatorconceptslorlow-costspacelau,'x,,hea_rereviewed.Previousconceptssuffered;rein requirementsforultra-high-strengthmaterials,dynamicallyunstablesystems,orfromdangerofoollisionwith spacedeb._s.Theuseofmagneticgrain_reams,firstF_posedby BenoitLeben,solvestheseproblems. Magneticgrain_reamscansupportshortspace6!evatorsforliftingpayloadscheaplyintoEarthorbit, overcomingthematerialstrengthp_Oiemin.buildingspaceelevators.Alternatively,thestreamcouldsupport an internationaspaceportl circling__heEarthdailyt_nsofmilesabovetheequator,accessibleto adv_ncad aircraft.Marscouldbe equippedwitha similargrainstream,usingmaterialfromitsmoonsPhobosandDefines. Grain-streamarcsaboutthesuncould_ usedforfastlaunchestotheouterplanetsandforaccelerating starshipsto nearikjhtspeedforinterstella:recor_naisar',cGraie. nstreamsareessentiallyimperviousto collisions,andcouldreducethecost_f spacetranspo_ationbyan o_er c,,fmagnih_e.
iNTRODUCTION
Themajorob_,tacletorapi( spacedevei,apmentisthehighco_ oflaunct_!,'D_gayloadsintoEarthorbit. Currentlaunchcostsare morethan_3000per kilogramand, rocketvehicles_ch asNASP,S,_nger_,'_the AdvancedLaunchSystemwiltstillcost$500perkilogram.Theprospectsforspaceente_dseandsettlement. arenotgoodunlessthesehighlaunchc_stsarereducedsignificantly. Overthepastthirtyyears,severalconceptshavebeendevelopedforlaunchir_la{_opayloadsintoEarth orbitcheaplyusing"_rJeceelevators."The._estructurescanbesupportedbyeithe.rs_ati,for:: cebalarl,_or bythe dynamicsof movingmas._es.Theirconstr_Jctionfacesseveraltechnk_ldifficultiesI_J, wever.Encrmous massesmust be launchedintoorbitby conventionarocketl stostagthesystems,extr_.melhyigh-s_e=--_.h n_aterialsmuatbeusedto buildthestructuresand, collisionwithnaturalmeteoroids_':man-madedebriswou¢l _h_rtentheirlifetimes.
Thispaperdiscussesa completespacetransportatiosnysteme_ompassingEarth-to-orbitlaunchi_,9 of largequantitiesof material,easytransportationwPhout, rocketpropellantbetweenEarthorbit andthe moon or M3rs, solar la,Jnch!ngfacilitiesforhigh-_peedtransportationto theouter,solarsystem,and theaccelelation ol near-iightspe¢¢dinterstellarspacecralt.Theconceptsarebasedon theusaof a streamof magneticgrains actingas the current-carrylngelementof an electricmolor. Spaceshipsequippedwith superconducting solenoidstogeneratesupe:'nighmagneticfieldscouldinteractwiththe magneticgrainstreamto propel themseivesat highaccelerationsthroughout,the solarsystem.Similargrainstreamsatthedestinaiionscould ,-leceler_tethe spaceshipswithoutrequiringon-boardrocketpropellaz,is.The resultwouldbe sm.',lle_,more capahiespacesl_ips.An even moreirnportantadvantagewouldbe thedrasticreductioninthe costper kilogramof Earth-orbitlaunches.
321 1991012826-322
ip _/ LUNAR'PLANETARY t/`/ 1/ LAUNCHES :,,
COUNTERWEIGHT If j!i
ELEVATORCAPSULES I I .i :_r---..
/ ",, / \ / # t GEOSTATIONARYORBIT
FIGURE1. THESTATICSPACEELEVATOR
ThedassicaJconcoptfora spaceelevatoristhestaticallybalancedstructurecenteredon theg_ostationary odYI,andextendedbothupwardand do_,mwardinbalanceuntilt,heIow(_r¢ndtouchesthe equatort;he upper e,t_ ismenoounterweightedto putthe entirestructureintotension,al_ving ittoliftpayloadsfromthe Earthinto geostationPryorbit.TheconceptwasinvertedindependentblyyYunArtsutanov(ref. 1.),JohnIsaacs,etal. (rel2), andJeromePearson(ref.3). Artsutanovproposedthe launchi,_ofg Earth-escapelaunchesfromthe uppertower,andP;amonproposedthetwo-waytrafficof elecirornagnaticvehiclesfromthegroundtothe geostatlonaryr_ce oomplexwithoutexternalpower.Theconceptrequiresanenormousamountof high- strengthmaterialandisvuLner1_tod_severinge I'ffool;;.slowithn debris.
322.
%
d 1991012826-323
. q
1 PAYLOAD ": LAUNCH LOOP
STARBRI&X3E ___,%.,J , , / \ \ II i
i
!
!
\
i
\ ORBITA'L RING . JACOB'SLAOOER
_HIGH VELOCITY CABLE
FIGURE 2, DYNAMIC SPACE ELEVAfOR
To overcome the matedal strength and mass requirements of the static space elevator, several conceits were proposed to supl_rt space elevators by the dynamic forces of mass in motion. Paul Birch (rat. 4) proposed an orbital dng of conducting maierial rnovi_Kjfaster than orbital velocity inside a thin toms circl;ng the Earth. The moving cable produces an upward force on the toms. allowing Ihe toms to suppo,'l "Jacob's ladders" the few hundred kilometers down to the surfaco. Keith Lofstrom fret. 5) and i_i_h proposed a similar moving concknctor in a shorter "launch _oop"that could a_qe!orate, e!_ctromagnet0cvehic',es to o_ital velocity along the loop. Rod Hyde fret. 6) proposed _ purely vert{cal, "starbridge" supported by the reaction iorce trom :._',x;elerating downward a series of con_cting rings tir_t upward fromthe base. These dynamic concepts solve the material strength problems of the space elevator, but they depor...,on the tail-safe opera_,,,, ,;' *,,ndamentalty unstable dynamic systems. 323
---- a ...... I r -- _---- i :1 TO HEO OR ESCAPE_ RELEASEAT SUPER- ORBITAl..VELOCITY'
TETHERORBIT "-..
l ROTATINGTETHER
RENDEZVOUSAT :_:...... '_i SUB-ORBITALVELOCri'Y --- ,_:_::y"-
I ....,_ . _---.__ __"-.::_;_7 ',,,,, k i
t/_/__ " _--__" -'/_'_"_ ,,,,/,,!/t' 'ii
FROM GROUND ,' t
RGURE 3...rilE ROLLINGSATELLITE
Yet =zthirdway to producethe spaceelevatoris to set thestatic spaceelevatorinto rotation,and catchand launchpayloadsfromthe rapid_movingendsofthis"rollingsatellite."A rotatingtetherino¢oitcouldprovide mostof the,orbital_nergyneededfora payloadlaunchedfromthe groundby catchingit onthe io,,,,erend; the tetllercouldther launchthe payloadintoa higherorbitorto Earth-escapeby releasingit from_heupperend, halt a tetherrotationtater.If payloadsreturningfromhighe="orbitsare alsocaughtand releasedfor Earthentry,no netenergyis requiredby therotatingtether. Artsutanovoriginatedthe con'.;eptin 1969(ref.7); il was inventedindependentlyby HansMoravec(ref.8) and putintoa practicalform by Pea,_,son(ref.9). ],he cor_cept facestheproblemsof high-speedrer_Jezvousandtetherdynamics. " 1991012826-325
SHORT SPACE ELEVATOR PERIGEE SKYHQOK
FIGURE 4. THE GRAIN-STREAM SPACE ELEVATOR
A spaceelevalorconceptthatovercomesalltheproblemsofpreviousa_ernptswasproposedbyBenoi_,Leben in 1986(_ef,10,"_1)andelaborateduponin1987(rel.12).Theconcepist similartoBitch'so,'bitaringl ,butit usesa muchlessmassivestreamof magnetigrainsc ar,d dispenseswiththe.massiveenclosirN3 toms.Theg;ain streamiskeptin placebyshepherdingsolenoidstha;moveslowlyalongthestream.Thisshep_rdingaction isdonenaturallybythegravitationalfieldsof smallsatellitesonthinrirJgsaboutSaturnandtheothergiantpl_'qP,tS. ThesolenoidavJehicleswouldhavea mucheasierjobbecauseofthetarstro..ngermagneticforcesavailableA. grainstreaminellipticalorbit.coulds_pporta largespa_estationingeosiationaroyrbitandashortspaceelevator froma perigeeskyhook.Thesystemhastheadvantagesthatit couldbebuiltin stages,increasin£_thestream densitytoca,ry h_herpayloads,andthatit i_;'_wious tocollision.Theshortspaceelevatocouldr bealmost entirelyintheatmosphere,wheredebriscoufonotpenetrate.Themagneticgrainscouldbeobtainedfromthe _:_n orfroma nearbyast,,,mld. 325
5,t 1991012826-326
SPACEPORT(MOVES AROUND EQUATOR IN ' 24 HOURS)
FIGURE 5 THE INTERNATIONAL "SPACE TELPHER" SYSTEM
In 1988, Leben Irel. 13) proposed an alternate grain-stream laur_chsystem that is even more advantageous than the original. He replaced the short space elevator v_itha "space telpher," or travelling ,spaceportsupported by the grain stream and moving cnr,_pletelyaround the equator once per day. This spaceport ¢ouid be at less than 100 ki_omote_ aftit,,_d._,,altowing advanced aircraft from all nations to reach the spaceport d_i!y. Once there, grain..stre,._rnshuttles could move to the n'v_ther station at 12-hour orbital altitude and _ !au.,v'_hetdo Earth,escape. In a sense, this msa space elevator without the elevator, and it would not be tied down to one location on the equator. By not having to support an enom,_')uselevator, the grain stream could be smaller, making the entire;system simpler and cheaper. 326 1991012826-327
i SHEPHERD(DEIMOS)
SOLENOID
lAUNCH ARC _._ :,
_TO EARTH FROM_ .{
MOTHER STATION PHOBOS
../.: .::::::::_.....: ...... •_.""_ ...... ':.'...::-...... :,..::..
"/,/".'t STRE/ _I-KE.PING "_,_ :'•":;i SHUTTLES \
0 /
i!' /
STREAM
SURFACESTATION
FIGURE6. k_RTIAN R!NGTRANSPGRTATIONSYSTEM Onceitischeapand simpletolaunchcargoandpeopleintoEarthorbit,wewillbe ableto develop Marsasa sisterplanet,usinga similargrain-streamtransportatiosystn em.Becauseofthelow atmosphericpressureon Mars,the lowerstationcouldbe rightonthesurface,withthe mother stationbeingat "arestationarya"ltitude. TheMartianmoonPheboscouldI:.'ovldethe raw material forthegrainstream,and itsremnantcouldbemovedtoformthemotherstation. Agrain-stream ring arccouldbecreatedneartheorbitoftheouterMartianmoonDeimos,perhapspartially shepherdedby Deimositself,inadditionto strear,,.keupingshuttles. Thisarccouldaccelerate soler_idalspaceshipsboundfcrEarthanddeceleratespaceshipsank,ingfromE3rth, ,,_similar launci,arc aboutthe Earthwouldcompletea two-planetransportationsystem. 327 ) 1991012826-328
TO OUTER SOLAR SYSTEM I
":"::_t:_,,, GRAIN STREAM su. \ I / i:" "_ f_:-- I" !i_; IO00-TONVEHICLE _ _:i:;i ::::;_: 1 AU _! .__J _. _ii 5-g ACCELERATION ,, / i \ i_i 1000km/s
...;?.'
S? EARTH-ORBIT ARC i
INTERSTEI_LARI.AUNCH
,,::.,, ;.;:... ,.y,.
SUN '::'if", \ I / _! IO00-'ION VEHICLE 0 ,., 3o,,,u i! 1000-g ACCELERATION
/ I \ !/ 9(7/oSPEED OF L.IGHT
_ GRAIN STREAM ..X/" NEPTUNE-ORBIT ARC
FIGURE7. SOLARRUNWAYS
Thepartia!grainstreamconceptwasoriginatedby LebeP.(ref.! !) as a methodforachievingextremely highlaunchvelocities. Heproposedcreatinga partialring insolarorbit at the Earth'sdistancefromthe sun,and usingit to acceleratesolenoidalspaceshipsto about 1000km/s in orderto reachthe outer ._olarsysteminjust a few months. Theaccelerationis limitedby tile magneticfield achievableon the spacecraft. With a field of 0.06tesla,a 1000-tonspacecraftcouldbe acceL,ratedto !000 km/s at 5 g in lessthan _o of the circumferenceof the Earth'sorbit,.A larger"solarrunway"cou_lbe placed about Neptune'sdistancefromthe sunfor interstellarlaunches.A 15-teslasolenoidc,ould acceleratea 1000-tonvehicleat 1000g to 90%the speedof lightfromsuchan arc. Muchmeremodestfieldswould suii;,,,-to launchlast interstellarprobesfor the initialreconnaissanceof nearbyplanetarysystemsin a few decades. Ringorbitperturbationscouldbe minimizedby launchingvehk;lesin, oppositedirections alongthegrain-streamarc.
328
I ..... - ...... -...... 1991012826'329
CONCLUSIONS
Theancientdreamof the spaceelevatorisnowpossible. Magne!_cgr_instreamsand high-magneticfie'tdsolenoidalspacecraftcot_ldsolvethe problemof the highcost of ,_4:)ace launchingand resultin rapidcpace, colonizationand industrializationThis. formof space t_arc._daiioii ,,.;ouidaisogreatlyreducethetraveltimetothe outersolarsystem,bdngingthe resourcesoftheouterplanetsintoour realm. Finally,grain-streamar_ insolarorbit couldbe the launchiqg='ampsfor fast reconnaissancemissionsto the nearbystarsthat couldprovidedataon extra-solarplanetarysystemswithina decadeortwo of launch.
REFERENCES
1. Adsutanov,Y.,"V Kosmo. na Elektrovoze,"KemsornolskayaPravda,31 July(1960). (The contentsare describedin Englishby Lvovin Science,158,946-947,1987.)
2. Isaacs,J., Vine,A. C.,Bradner,H. and Bachus,G. E.,"SatelliteElongationintoa trueSky-Hook," Science151,682-683(1968).
3. Pearson,J., "TheOrbitalTower: A SpacecraftLauncherUsingthe Earth'sRotationalEnergy," ActaAstronautica2, 785-799(1975).
4. Birch,P. M.,"OrbitalRing Systemsand Jocob'sLadders,"JBIS35,475-497 (1982).
5. Lofstrom,K., "TheLaunchLoop--Alow-costEarth-to-orbitLaunchSystem,"AIAAPaper 85-1368(1985).
6. Hyde,R.A., "Earthbreak:Earthto SpaceTransportation,"DefenseScience2003+4, 78-92 (';_?.,5).
7. Artsutanov,Y.,"VKosmosL)ezRaket: 7nanije-Sila7:25 (1969).
8. Moravec,H.,"ANon-SynchronousRollingSkyhook,J" AstronautS. ci.25,307-322(1978).
9. PearsonJ, ., "Low-CostLaunchSystemandOrbitalfuel Depot,"ActaAstronautica19, 315-310(1989_.
10. Lebon,B. A. "Ma_l_ticShepherdingofOrbitalGrainStreams,"JBIS 39,486-490(1985
11. Lebon,B.A.,"M,_gnetiPropulsionc Alongan OrbitingGrainStream,"J Spacecraft23, 141-143(';P,86).
12. Lebon,B.A.,_pace Tran,%x_rtatioThnroughMagneticShepherdingofa GrazingEarthRing: An EcologicalHeart-ShapedEarthRingby2010?,"JBIS40,365-370 (1987).
13. Lebon,B.A.,"AnInternationaSpacl eTelpherSystem(ISTS)Usingan EarthGrainRing," JBIS41,509-518(1988).
329
wr
...... l i ii - _ -- , II I .... i f