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- it is possible to use 8 low level static magnetic field to rench the resonance condition, e.g. 36 GausB for resonance at 100 me. A lower thruster mass can be thus ach ieved : .. slnco the ~avelcnqht 10 much hiyher thar the chamber dimensions, problems arisinq pram energy propagation into plnsna can LU avoided. In case of VllF oxcitation, plasma generation Is infact achieved through a "noar field" mechanism so that no cut-off frequency exists: - it is possible to use coupling olactrodeo. for the VHF RF field, outside the discharqr? chnmbcr, clue to the lini'ced rwor losses for irradiation > 1/~, i.6 about 2 UHZ connidcrinq a pressure of 10'-4 Torr and nn alcctron energy of 13eV. This condltion ensures that electrons turns around the magnetic field many times between consecutive collisions: 2) R 1 cm, whore R~is the qyration radius of the electron in presence of a magnetic field dirocted nlonq tha chamber axis. This condition enquros that the electron trajec'ories are conta,iriwl in the # +ischarge chamber; 3) EM field wavelcnqht >' 3+5 cm. Tnis condition avoids propnqation problems in the plasma. In summary, the ECR technique IR expccted to provide substantial Lmprovenenta in low power ion thrusters pcrformanca, enhancing the advantages of traditions: RF tcchnlqes in combination with qthers typical of the Kaufman technoloqy. The main fotsturcs of the ECR technique are summarized as Io1 lows : - ECR sources do not have components subjected to wearout, as cathodes or accelerating electrodes, l.n the plasma charber. I , Problems of sputteriny erosion inside the chamber are thus eliminated, impac; ing positively the thruster lifet ime. Moreover, it is possible to realize the discharge vessel with materials having high secondary electron emission coefficients, scarcely sensitive to erosion and capable of reducing electron losses from plasma towards tho vessel walls. - T:.e plasma produced by the ECR 1s hiqhly uniform, both in density and t-mperature. Achievable ulec'ron densities ar@ of the order of 10'12 electrons/cm'3 at pressures in the range of 10--4 + 10A-5 Torr, thus facilitatinq beam extraction optimization. - The ECR technique is specially advantageous for ion thrusters operating at' low thrust levels ( 2410 mN) where it reduces considerably the Instability phenomena inside the plasma. Low thrusts ere related to small chamber dimensions, which eimpliliee tho realization of a uniPom magnetic fielc! in tne dlscharge vessel, and requires less Dc power. A small chamber also requires small electrodes for electroinaqnetic energy tranwfer, with lower losses due to EU irradiation and vessel walls absorption. Furthermore, for constant average beam current densities, thruster throttling is accompl isiied keeping the mass flow rate to beam area ratio constant. A reduced flow rat& is associated with a pressure regime within the discharge chamber where ECR proves more efficient and stable than other traditional excitation techniques. - Tho yrid extraction syetcn can be dcsigncd and optimized on the basis of the enhanced plasma characteristics typical of the ECR technique. In this direction PROEL Is investigatinq also new technoloqies (patent pcn-llng) for the realization of qrids with a qcnmstry having a hiqh transparency factor to ions, while maintaining good nechanical rcsistnnce and the capnbillty to survive to sputtering erosion. The USQ of ti hiqh melting point refractory material, coa t ed with sui table anti?putterlng protcctlon layer, is the solution to long lifetime requirements. 6,CONCLOS IOttS Electric propulsion, and in particular advanced ion propulnlon. is an enablinq technoloqy for the feasibility of very low Earth orbit missions, in power-limited liqhtsats, where drag in the doninant effect. Furthermore, low power ion thrusters are a good system alternattve for propulsion tasks requirinq tho stoady application of low thrust levale ovcr extended periods of time to implement a qiven velocity correction. Nevertheless very lon9 lifetimes, of the order of 20000 to 40COO hours, must be reliably demonstrated. Improvements In mass and power efficiency of such low power tiiusters wou!d a!so benefit the liqhtsats design. Lov power arcjets, in the 1 Kw ranqe, have also promisinq applications for certain orbit manoeuvering tasks, and their development s:iould be further pursued. REFERENCES (11 J. Reale "A low altitude Lon-prop-IIf*d remote sensing spiscecrnft ": 27nd IEPC; Viaregqio, October 1991:
[ Z ] C. Purrotta, M.Bieconi, A. Bicci, H.Capacci,C.F.Cirri,G.M~tticnri: I' Ort ita1 control and manoeuvering of lightsats / synchronous natellites: assecww?t or new ion propulsion technoloqioo b m 4 on tho Electron Cyclotron Resonnnce pherrsrnanon to Improve thc poreormancc of thrusters in tho mill iHawton ranqc": 27nd IEPC, Viareqgio, October 1991: [3) C. Pcrrottn SAR wnsors an tACSATS: a eeasibiiity assessment" : this Conference: i (41 C. Perrotto Emerqing new concepts for non-CEO satellite networks: a review*: ICCC '92; Genoa, October 1992; [5! J. Oonodicto, J. Fortuny, P. Rostilla PACSS-11: a medium altitude global mobilo 133tQllitQ system for personal communichtiono at L-bandn: ESA Journal Vo1.16 N' 2, 1992.
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ADVISORY GROUP FOR AEROSPACE RESEAR
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Acccorclinp tto 11s C”liirlcr. th
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0 Im oyi.rationr rcccntc\ *Tcm+tc d
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Theme 'fieme 0 - 0 Avionics Pencl a
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-- Printed in Clawificcl puhlicatio
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1'. 2 c From tplc four pafcn. thcrc
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Talcs. Thc lcchnology emphasis wnr
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These arc three spccific fecornmen&
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when WO Rave gone from one'modsl sa
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3-4 mggd and easily operated. This
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3-6 interim capability should one o
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OI~UI'IS MISSIONS I PAYLOAD TYPE -.
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1 Int raduction The iiotcntial cxpl
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indicated hat an IR vcrsion of the
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a 0 Annex A Radar system A. I Backg
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Annex C ESM system C.1 Background A
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e communications, point to point, p
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(i-4 TACSAT Operations Phase The TA
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6-6 w J > a 3 v, [E ' 0 LL U3 I- Q
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(1-2 rcliabiliry pcrfornianccs, bot
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0 8-4 specific tools for each main
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affichent un coot au kilo de 2 a 3
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I 1 - CONSTELLATION LAIJNCHES COST
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ls FIGURE 3 6-11
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a a
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SYmME DE NAVIGATION PAR SATELLIT'ES
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du sntcllitc fixCe. Aucunc controin
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0 0 ' ml 3200. 2800. 2400. 2000. 16
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A cct instant. ct si IC PDOP cat in
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giostationnaire (RS mlslnn contrc 5
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0 This pqxr is dividcd in lhrcc pat
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0 Grouad-air-ground communication T
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0 a .. . . .I AIR COMMAND AND CQNTR
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ENNEAAV ORDER OF BATLE ASSESSMENT D
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0 0 (CO") -COMMUNlCATlONTACSATSARE
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0 0 . 14-2 xiv)physical attack and
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14-4 There has been a minimum of jo
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Architecture TABLE -1 Number of Sat
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14-8 Table - 3 : The EHF Ground Seg
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0. 16-2 combincd analog and digital
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flgurm 2. Frequency Synlhmrlur Aduc
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L n , JA. " Flguro 5. LlghtwolgM LD
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GEOSYNCHRONOUSALTITUDEORBlT VARIABL
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I SYNCHRONIZATION TECHNIQUES FOR ME
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-U I 1 b I l l . . . . , Figure 2:
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@ & a time acquisition. Due to thc
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6 SYSIXM SYNCHRONIZATION ALGORITHM
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TACSAT payload. Sptinl and time syn
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\ I ..I , .. . . U' c L. rL 50 i !
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It is IqmmtQlive of the ,wc.sa Cmst
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3. IAUWCUU SVSTEM SELECTION CRUQTXO
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19-41 5.8.1.8 A/Im faniity of whicl
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CURRLHT PRowcTKm N DEVELOPMENT " P
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.clrc;lih w m iua thc orhilot planc
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19-10 OcazO midm ~ r nof mp htb~rm
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19-12 0 'I% whicles must PW: lnunch
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8.3 Uniad KingdodWussia Inrtn'm HOT
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SPACECRAIT AND I.AIJNCII SIISlT.MS
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c Firvn 4. Horimld vrhiclr andpaylo
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H 8p~nwmd by DARPA ud will dcliwr8
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20-10 (hcntercoaunnndma have ben di
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RESUME Puisque ks futun lanceun per
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. 232 CdcJ du IIIOIWYHI?~ Mmoeuvm m
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En rcvnnchc, m ce qui concemc la pe
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Lea masses d'ergoh pour les trois o
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- Figure 13 - Les orbiteo intermedi
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SVMMARy - rution inonly I5 monh. Qu
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I f igun 5-1 QulrUfar spcun@ syslrm
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?- I
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* Snull ground conlrol VMS 1s.a.a F
Page 305: .. 1. INTRODUCTION Attitude- and Or
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Page 313 and 314: sensors, gyros) intorporated in the
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e The SAW must possess a raa)is$wet
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I I I ! 27-9 Different data rate: c
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In resent ears, industry made gr0fp
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LOW.oIlN ANTENNA b ClsLEWRIP 4 SOWR
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NOI-1-0' MZ-1-90 NO 3- I I 57 NO1-1
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Cost Efl'ectivc TacSats for Militar
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' Figure 3. Usa Driven Dwign Future
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L Figure 6. Tu&oprrpliom Rovi Usus
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Vlrtbl~ D~tect~n b Rows of 18um qua
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covering a variety of scenes, asses
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AbsltmsU 'E'AC.WT MEmOROWflCU PAYLO
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I I I I Trtarasiaiaand Pnogramme (M
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several chys. If S~CDPO term foreca
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e: l , / I Discussion Question: You
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7 t!lETTl?3T iDOCWMEWAmOT'd PAGE AG
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