NASA Technical Memorandum 107246

IAF-95-S.3.02

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Electric Propulsion Applications and Impacts

Frank M. Curran and Timothy J. Wickenheiser

Lewis Research Center

Cleveland, Ohio

Prepared for the46th International Astronautical Congress

sponsored by the International Astronautical Federation

Oslo, Norway, October 2--6, 1995

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National Aeronautics and

Space Administration

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National Aeronautics and

Space Administration

Lewis Research Center

21000 Brookpark Rd.Cleveland, OH 44135-3191

Official Business

Penalty for Private Use $300

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ELECTRIC PROPULSION APPLICATIONS AND IMPACTS

Frank M. Curran and Timothy J. WickenheiserNASA Lewis Research Center

21000 Brookpark RdCleveland, Ohio 44135

Most space missions require on-board propulsion systems and these systems are often dominant spacecraftmass drivers. Presently, on-board systems account for more than half the injected mass for commercialcommunications systems and even greater mass fractions for ambitious planetary missions. Anticipatedtrends toward the use of both smaller spacecraft and launch vehicles will likely increase pressure on theperformance of on-board propulsion systems. The acceptance of arcjet thrusters for operational use oncommercial communications satellites ushered in a new era in on-board propulsion and exponential growth ofelectric propulsion across a broad spectrum of missions is anticipated.

NASA recognizes the benefits of advanced propulsion and NASA's Office of Space Access and Technologysupports an aggressive On-Board Propulsion program, including a strong electric propulsion element, toassure the availability of high performance propulsion systems to meet the goals of the ambitious missionsenvisioned in the next two decades. The program scope ranges from fundamental research for futuregeneration systems through specific insertion efforts aimed at near term technology transfer. The On-Boardpropulsion program is committed to carrying technologies to levels required for customer acceptance andemphasizes direct interactions with the user community and the development of commercial sources. Thispaper provides a discussion of anticipated missions, propulsion functions, and electric propulsion impactsfollowed by an overview of the electric propulsion element of the NASA On-Board Propulsion program.

INTRODUCTION

The aerospace industry has changed significantlyover the past several years and continued changeis anticipated into the near future. At present,tremendous pressure is being exerted to assurecost-effective mission performance both incommercial and government sectors. Thispressure will force the development andapplication of revolutionary new technologiesacross a broad range of mission sets. Severalimportant emerging technology drivers are shownin Table 1. On-board propulsion systems arerequired in nearly every mission scenario andthese systems are often dominant spacecraft massdrivers. This is true both for traditional spacecraftsuch as large geosynchronous communicationssatellites, and for the spacecraft being designedfor distributed low- and mid-Earth orbitalcommunications systems, commercial remotesensing, and ambitious Earth and space sciencemissions. Examples of typical spacecraft massfractions for several mission classes are shown in

Figure 1 and these data clearly indicate that on-board propulsion is an area of high leverage forimproved mission performance.

Electric thrusters can provide significant fueleconomies as compared to their chemicalcounterparts (from factors to an order of magnitudedepending on the system and application) and

acceptance of these systems is beginning tooccur. The potential benefits of electric propulsionwere well displayed in the recent use of 1.8 kWarcjet thruster systems (Ref. 1) for north-southstationkeeping (NSSK) of the first LockheedMartin Astro Space (LMAS) Series 7000geosynchronous (GEO) communications satellite.The mission average specific impulse provided bythe arcjet was more than 1.5 times that offered bystate-of-practice (SOP) resistojet and bipropellantchemical systems and, in the first mission,propellant savings were used to significantlyreduce launch vehicle requirements. Firstgeneration arcjets are now scheduled to fly on atleast ten more LMAS Series 7000 spacecraft andadvanced arcjets, shown in Figure 2, were recentlyaccepted for a next generation GEO satellite series(Ref. 2). In fact, every major GEO communicationsspacecraft manufacturer now offers an electricpropulsion option for NSSK (see, for example,Refs. 3, 4). Electric systems will be used toperform other mission functions in the near term_For example, resistojets will be used for theinsertion of a near-term distributed

communications system and higher performanceoptions are being considered forinsertion/maintenance, and deorbit of future low-and mid-Earth orbit (LEO/MEO) spacecraft. Ionpropulsion being developed under NASA's SolarElectric Propulsion Technology Application andReadiness (NSTAR) program was recently

This paper is declared a work of the United States Government and is not subject to copyright protection in the UnitedStates.

baselinedfor use on the first New Millenium

spacecraft - the first use of an electric thruster forprimary propulsion in an ambitious (high delta-V)planetary mission. In fact, a general trend towardthe use of electric propulsion, shown in Table 2, isanticipated and these applications will bediscussed in some detail in the body of this paper.

NASA's Office of Space Access and Technology(OSAT) recognizes the benefits of advancedpropulsion and supports an aggressive On-BoardPropulsion program, including both electric andlow thrust chemical propulsion elements,designed to assure the availability of highperformance on-board propulsion systems forboth near and far term missions. The scope of thisprogram ranges from fundamental researchthrough specific technology developments, toefforts aimed at technology transfer. OSAT alsorecognizes the synergism between advancedelectric propulsion and power systems and hasdeveloped an integrated On-Board Power andPropulsion Strategy (Refs. 5, 6) to ensure thesimultaneous advancement of these two critical

technologies. This strategy assumes that theneeds for higher performance propulsion andpower systems will increase over the next decade.OSAT, working in cooperation with industry andother government progams, is committed tocarrying critical technologies to levels required forcustomer acceptance. Direct interactions with theuser community and the development ofcommercial sources for program-sponsoredtechnologies are strongly emphasized. This paperprovides a discussion of both anticipated missionsand propulsion functions followed by an overviewof the electric propulsion element of the OSATOn-Board Propulsion (OBP) program. Details ofthe overall program can be found in a recent review(aef. 7).

CLASSES, MISSIONS, REQUIREMENTS,& PAYOFFS

Electric propulsion devices fall into three generalcatagories denoted by acceleration mechanism -electrothermal, elecrtostatic, and electromagnetic.Examples and a brief description are shown inFigure 3. Each class has attributes attractive forcertain mission applications. For example,electrothermal thrusters offer the highest thrust-to-power ratio and operate on hydrazine, makingthem compatible with many existing spacecraftpropellant systems. Electrostatic systems offervery high specific impulse levels and so areexcellent candidates for missions with very high

delta-V requirements. Electromagnetic systems,can be operated in low power pulsed modesmaking them attractive for missions requiring small

impulse bits or where modest total impulse isrequired and power and simplicity are at a premium.Figures 4a and 4b illustrate required propulsionfunctions for Earth-orbit and planetary spacecraft.To cover the disparate mission requirements. Thissection provides descriptions of several missionclasses and required propulsion functions alongwith a description of potential roles for electric

propulsion.

GEO SPACECRAFT

Commercial GEO comsats will continue to be a

major space sector and fierce competition in thisarena is expected to drive technologydevelopment and application for the forseeablefuture. Current trends are toward increased powerlevels and it is expected that advanced electricpropulsion systems will be used to perform primarypropulsion functions in addition to the traditionalNSSK role. Advancement in this direction will

probably be evolutionary, with electric propulsionused first to improve mission performance throughapogee topping. A recent study indicates that theuse of electric propulsion systems for the finalsegment of the tranfer to the GEO orbit canincrease net spacecraft mass by 20 to 45 percentdepending on available power and allowable triptimes (Ref. 8). Figure 5 shows the general missionorbital strategy for this hybrid type of mission.Higher performance electric power and propulsionsystems (high specific impulse, greatly reducedspecific mass) will allow the consideration of fullelectric orbit transfers. In addition to the

commercial community, the Department ofDefense (DOD) also has a strong interest in theuse of electric propulsion for GEO missions (see,for example, Ref. 9). In addition to NSSK and orbittransfer functions, DOD mission requirements mayalso include on-orbit repositioning. Compared toSOP chemical systems, high performance electricthruster systems can be used to reduce thepropellant load required per reposition manueverfor a fixed transfer time or to reduce the timerequired for reposition. Figure 6 (Ref. 10) showsthe potential benefits of advanced electricpropulsion for a GEO mission in which the on-board system is used to provide both NSSK andtwo repositions per year. For this study, a SOPhydrazine system was compared to arcjet, ion, andHall thruster systems for various launcher specificGEO spacecraft masses and lifetimes. The data(shown for the Atlas 2AS launcher case) clearlyindicate the value of electric propulsion for typicalmission lifetimes (i.e. > 7 years). In the case of afixed launch vehicle, the savings provided byelectric propulsion can be used to extend satellite

life (currentlya high priority DODgoal) or toincreasepayload.

LEO/MEO SPACECRAFT

Over the past several years, significant attentionhas focussed on the LEO/MEO space sector.Distributed LEO/MEO communications systemsare being developed by several major commercialconcerns and growth in this area is anticipated intothe forseeable future. Growth in small satelliteEarth-science and commercial remote sensingmissions is also anticipated. Mission propulsionfunctions will include orbital insertion, orbit control,

and deorbit. Distributed system concepts willentail both new requirements and constraints.Effective launch strategies, for example, willmaximize the number of spacecraft per launchvehicle and this, in turn, sets specific constraintson spacecraft weight and volume. Assembly lineproduction philosophies will stress thedevelopment of simple, low cost, benignpropulsion systems. Also, deorbit requirementswill be levied on this mission class. These

considerations emphasize the importance of on-board propulsion and provide a uniqueopportunity for the use of advanced electricpropulsion. Both arcjet and Hall technologies arewelt suited for applications such as insertion,maintenance, and deorbit of MEO satellites. Thisis particularly true for the comsat case as thesespacecraft have significant power available forpropulsion functions. In one recent proprietarystudy, the use of electric propulsion for orbitalinsertion was found to reduce propulsion systemmass by a factor of two and volume by a factor ofthree over the proposed chemical baseline withoutchanging the spacecraft power system. For thismission, the time penalty associated with electricpropulsion was between two and three months.Recent mission analyses (Refs. 11, 12) show thatelectric propulsion can greatly benefit even verypower limited Earth-orbital missions. One missionchosen for study was the Total Ozone MappingSpectrometer (TOMS). In this analysis, a lowpower pulsed electric propulsion system wascompared to the hydrazine thruster system actuallyused. Results of this analysis are shown in Figure7 and indicate that the TOMS payload could beincreased by more than 50 percent in the TOMSmission as designed and more than 120 percent ifa deorbit requirement were levied as would be thecase if the mission were designed in todaysenvironment. In addition, the solid propellant-based pulsed system (described below) eliminatessafety and environmental costs/hazards related tothe use of hydrazine thrusters.

SPACE SCIENCE

Fast, cost-effective, high return missions are theclear goal of NASA's planetary explorationprogram. Propulsion is a primary spacecraft massdriver in virtually all planetary-class missions.' Infact, propulsion mass fractions are on the order of50 percent in modest delta-V missions like the oneshown in Figure 1 and can range to more than 70percent for ambitious, high delta-V missions.Figure 4b shows that typical planetary missionsentail both primary and auxiliary propulsion. Todate, propulsion functions in NASA-sponsoredspace science missions have been performedexclusively by chemical systems. Primary electricpropulsion systems can greatly enhance thismission class by reducing launch massrequirements, alleviating time window constraints,and both reducing trip times to and extending staytimes at selected celestial targets. Kakuda, Sercel,and Lee (Ref. 13) recently showed that highperformance ion propulsion systems could deliversubstantial payloads to small bodies such as theasteroids Vesta or Ceres or the comet Kopff in acost effective fashion. While the efficacy of ionpropulsion technology for high delta-V missionshas long been known, it is interesting that evenmoderate specific impulse systems like thehydrazine arcjet can provide significant benefits incertain planetary-class missions. This was shownin a recent proposal to NASA's Discovery programin which arcjets were considered as an alternativeto a conventional hydrazine monopropellantsystem for a sample and return mission to theasteroid Nereus (NEARS). NEARS missionanalyses showed that replacing the SOPmonopropellant system with a 400 second specificimpulse arcjet could both double the stay time(from 70 to 140 days) and more than double themission mass margin (from 10 to 24 percent)without changing the spacecraft power system.

Other space science missions can beenhanced/enabled by electric propulsion. Forexample, precision orbital control/positioning willbe required for the interferometric missions andthis could be provided effectively by pulsedplasma thrusters designed to provide verly smallimpulse bits. Pulsed systems may also be used toeliminate SOP chemical systems for attitudecontrol on planetary missions. Further, spacecraftarrays requiring orbital insertion can benefit fromlow power systems similar to those used in MEOconstellation deployments.

NASA ELECTRIC PROPULSIONPROGRAM DESCRIPTION

Innovative new propulsion technologies will berequired to meet the stringent performance goalsanticipated in evolving mission scenarios such asthose discussed in the preceeding section.NASA's OSAT supports an aggressive On-BoardPropulsion (OBP) program to identify, develop,and transfer high performance propulsiontechnologies for both near- (3 - 5 year) and far- (5 -10 year) term missions. Both electric and chemicalelements are included (Ref. 7) to cover the broadrange of mission requirements and the electricpropulsion element includes efforts in each of thethree major electric thruster classes. Many ofthese technologies cross cut several missions andevery effort is made to assure that the sponsoredtechnologies are capable of performing multiplemissions. To ensure that concepts are carried fromconception to insertion, the program is scopedbroadly and includes fundamental research,technology development, and directedtechnology insertion efforts. The programmaintains flexibility to respond to technologytransfer opportunities as they arise and workscooperatively with all sectors of the areospacecommunity. As noted above, the electricpropulsion element is complemented by a stongpower technology program (Ref. 5). OSAT alsosupports a focused NASA Solar ElectricPropulsion Technology Application Readiness(NSTAR) program, led by the Jet PropulsionLaboratory (JPL) in partnership with LeRC, todevelop and demonstrate a 0.5 - 2.5 kW, 55%efficient ion system (Isp ~ 3100 sec) that willenable launch vehicle class reductions as well as

significant trip time savings for small satelliteplanetary missions. NSTAR was initiated in FY93and has baselined 30-cm ion engine technology

developed under the OBP program. The NSTARsystem has now been chosen for the first missionin NASA's New Millennium program.

The following section provides a description of theelectric propulsion element of the OBP programwith an emphasis on recent progress and programdirections. Near term thrust areas are shown in

Figure 8 for reference.

Electrothermal Systems

As noted above, first generation arcjets are now inoperational in the commercial market. These arcjetsystems were developed through jointOBP/industry efforts which included fundamentalfeasibility demonstrations, contracteddevelopment and validation efforts, and

cooperative arcjet/spacecraft integrationassessments. The arcjet program was recentlyreviewed in detail (Ref. 14). Following the transferof first generation arcjets, a 600 second, 2 kW-class arcjet system development program wasundertaken in response to a known user n_ed(GEO NSSK) and to provide technology foranticipated LEO/MEO satellite insertion anddeorbit requirements. The OBP program-sponsored part of advanced arcjet developmenteffort recently completed a successfulqualification-level demonstration of a flight-typesystem. With the recent acceptance of thistechnology, the OBP program has now focusedattention on the development of low power arcjets(LPATs) for power-limited spacecraft. Over thepast year, sub-kW arcjet systems have beenconsidered for application to LEO/MEO orbitinsertion, NSSK of power limited military GEOcomsats, and for space science missions likeNEARS. Current program targets for firstapplication include both a commercial technologydemonstration spacecraft and a military application.The LPATs program will demonstrate flight-type(0.5 kW, 450 - 500 second Isp) hardware in the1996/1997 timeframe. The OBP program alsosponsors research on the feasibility sub-0.25 kWarcjets for very small spacecraft (Ref. 15).

Electrostatic Systems

The major electrostatic concepts include bothgridded ion and Hall effect thrusters. As noted,gridded ion thruster technology previouslysponsored by the OBP program is now the subjectof focused development. Currently, severalcooperative programs to evaluate Hall thrusters forlow power (sub-2 kW) applications are supported.Both higher power/performance Hall and nextgeneration gridded ion technologies are beingexamined for future high delta-V missions. Overthe next year, the OBP will also initiate an effort toevaluate the fundamental feasibility of a micro-electrostatic system (sub-0.1 kW) formicrospacecraft missions.

Hall thrusters have been extensively developed inRussia (Ref. 16) and have been an area ofsignificant interest in the western aerospacecommunity over the past several years. Twovariations exist, the stationary plasma thruster(SPT) and the thruster with anode layer (TAL).Demonstrated performance characteristics aresimilar for both devices. For the kW-class,demonstrated specific impulse for both devices ison the order of 1600 s at 0.50 efficiency. Both 0.7kW and 1.5 kW SPT's made by Fakel Enterprisesare operational on Russian satellites and the 1.5

4

kWversionis nowbeingreadiedfor commercialuseonwestern commercial GEO comsats (Ref. 4).

Extended, cyclic life (>6000 hours/5000 cycles)was recently demonstrated for the 1.5 kW thruster(Ref. 17) and extensive evaluations of integrationimpacts have been undertaken including severallarge scale tests in OBP testbeds in cooperationwith industry (see, for example, Ref. 18).

Over the past several years, the OBP has acted asan agent for the Ballistic Missile DefenseOrganization's (BMDO) electric propulsionprogram. At present, this program is focused onthe development of an advanced 1.5 kW Hallthruster system "on-a-pallet" in the Russian HallEffect Thruster Test program (RHETT - see Refs.19, 20), and OBP personnel manage this effort.The first flight-like package (RHETT-1, shown inFigure 9) will be demonstrated in ground testing in1995 and a follow on, flight-ready system (RHETT-2) is planned for a near term flight test.

Sub-kW Hall thrusters are being considered forseveral missions including space science. Onehigh potential mission prospect is the EnergeticTransient Array (ETA) mission now beingdeveloped in a Phase A study by theMassachusetts Institute of Technology in NASA'sMIDEX program. In ETA, eight small spacecraftwould be distributed in heliocentric orbit to locate

gamma ray sources as a follow on to the GammaRay Observatory. Existing SPT thrusters, built byFakel and supplied by the Air Force PhillipsLaboratory, are baselined for spacecraft insertions.The OBP program will provide support to the ETAprogram (under a Space Act Agreement) in theform of extensive propulsion systemdemonstrations in ETA's ground test element.

Sub-0o5 kW Hall thrusters may offer very highperformance levels for power limited applicationsbut have not yet been demonstrated. The OBPprogram is currently supportingdevelopment/evaluation of two low power Halltechnologies. One of these, a 0.5 kW-class TAL,was built by Russia's Central Research Institute ofMachine Building (TsNIIMASH), through TexasTech University, and will shortly be delivered fortesting. Similarly, the Moscow Aviation Institute,through the Atlantic Research Corporation, willprovide a 0.25 kW SPT thruster. Both of these Hallthrusters are engineering models and will beevaluated (performance, life, and integrationimpacts) in 1995 and 1996. Further developmentefforts will hinge on the outcome of this research.

For the far term (5 to 10 years), the OBP programhas initiated efforts to develop a very high

efficiency (> 0.6), low-mass plasma propulsionsystem with end-to-end system specific mass(including power) and lifetime goals of 10 kg/kWand 15,000 hours, respectively. These attributesare specified in the integrated Space Power andPropulsion Strategic plan (Ref. 5) and will enabl_ 1)three to five year trip times for complex spacescience missions with small spacecraft and 2)electric orbit transfers (LEO to GEO-class) withhigh payload fractions and relatively short trip times(sub-3 month). At least two electrostatic concepts,an advanced gridded ion system and a high power(> 5 kW) Hall thruster-based system, will beconsidered. For the gridded concept, severalpotential grid technology options will be exploredfor high thrust density applications. Carbon-carbon grid technology (see, for example, Ref. 21)developed under OSAT's Advanced ConceptsProgram has shown great promise for reducinggrid erosion and this technology is currently beingtransitioned to the OBP program. Severalpromising coatings for conventional molybdenumgrids are also being examined. Some initialevaluations of high power Hall technology havebeen initiated in conjuction with the BMDOprogram (see, for example, Ref. 22). Low-masspower systems for these advanced concepts willincorporate new high voltage array, powerconversion, and power distribution technologiesand efforts are underway, with the OSAT SpacePower program, to demonstrate advanced powersystem concepts (Ref 23).

Electromagnetic Systems

For many years the magnetoplasmadynamicthruster (MPD) was the major focus of OBP effortsin the electromagnetic regime. Because of theirlarge power handling capabilities and projectedhigh performance, MPD systems were consideredprime candidates for very ambitious, high powermissions such as those proposed for the SpaceExploration Initiative. The recent trend toward smallsatellites relegates MPD research to the backburner and the OBP retains only a minor effort toexamine the feasibility of MPD thrusters for dualuse applications such as plasmaprocessing/manufacturing. Pulsed plasmathrusters (PPT) are now the focus of the OBPelectromagnetic element for several reasons.These devices utilize solid propellant and provideover 1000 s of specific impulse while operating atpower levels between 2 and 60 watts. Becausethe systems are pulsed, power throttling can beeasily accomplished without changingperformance by varying repetition rate. Impulsebits at least three orders of magnitude below thoseavailable with hydrazine engines (13 mN-s) can be

usedto providefineorbit control. The use of solidfluoropolymer propellant eliminates hazardouspropellant storage and handling concerns andresults in a very simple, low-cost feed system.These attributes make PPTs highly attractive for arange of small spacecraft applications. The OBPprogram is now in the middle of a two phase PPTtechnology development effort which includes in-house, contracted, and university efforts. The firstphase is focused on simultaneously reducing thePPT system mass by a factor of two and doublingtotal impulse capability in order to provide a fourfold increase in propulsion system capability perunit launch mass as compared to SOP PPTsystems. The second phase will further miniaturizethe technology and fundamental research effortstoward this end are already in progress. In thecontracted effort, the Olin Aerospace Company willfirst develop a flight-type system for demonstrationin 1997. The in-house program is focused on thecharacterization of performance, EMI, and plumeimpacts. The academic effort, conducted with theOhio State University (OSU), is building on pastcode development efforts (MACH 2 - Ref. 24) todevelop a high fidelity PPT model to be used inthe design of next generation PPT's. OSU is alsoexploring new propellant options for increasingPPT performance without degrading life (Ref. 25).To date, layered polymer combinations thatprovide higher average specific impulsecharacteristics but avoid electrode carbonizationproblems encountered in previous advanced fueldevelopment efforts are being tested. All of theon-going PPT efforts take advantage of existingOBP testbeds. Recent program outputs include

1) development and demonstration of a newpower converter providing significant reductions involume (3X), weight (2X), parts count (4X), andpower consumption (3.5X) over SOP systems,

2) development and demonstration of a telemetryboard providing a 4X reductions in volume, weight,parts count, and power consumption over SOP,

3) identification and testing of 2 candidatecapacitor technologies with 4X the specific energydensity of SOP technology, and

3) Development and demonstration of a highprecision PPT thrust stand (Ref. 26).

As a final note, the OBP is working cooperativelywith the Air Force and Webber State University inthe joint Air Force/Webber State student satelliteproject (JAWSAT). JAWSAT will fly SOP LES 8/9PPT technology on a 50 kg educational smallsatwhich will use the Global Positioning System (GPS)

for navigation. Under this program, OBPpersonnel are conducting and directing tests inLeRC space propulsion testbeds to quantify andaddress issues related to PPT/spacecraftintegration as illustrated in Figure 10. Figure 10(a)shows two students preparing JAWSAT for a'testto examine the impacts of PPT system EMI onother spacecraft systems in a vacuum chamber atLeRC. Another test of the PPT was recentlyperformed using a small, portable non-conductivevacuum facility, Figure 10(b), to show that PPTfirings did not adversly impact the GPS downlink.Programs such as JAWSAT provide educationalopportunities for students and OBP personnelalike and valuable information on spacecraftintegration to be used in the development of nextgeneration systems.

CONCLUDING REMARKS

On-Board propulsion is a major missionperformance driver for a broad range of spaceapplications. Known and anticipated missionrequirements will require the use of innovative newelectric propulsion systems in both the near- andfar-term. To meet these national requirements,NASA's Office of Space Access and Technology(OSAT) sponsors an aggressive on-boardpropulsion R&D program (OBP) which includes astrong electric propulsion element. Synergisticspace power technologies are address in acomplementary OSAT program. These OBPprograms stress technology transfer and programefforts are directed toward the development ofcommercial technology sources and thedemonstration of program technologies to thelevel required by potential users. The On-BoardPropulsion program is committed to providingcutting edge electric propulsion technologies tothe aerospace community and invites interactionswith the community to help meet this goal.

REFERENCES

1. Smith, R., et al., "Flight Qualification of a 1.8 kWHydrazine Arcjet System," IEPC-93-008,September 1993.

2. Lichon, P. G. and Sankovic, J. M.,"Development and Demonstration of a 600Second Mission Average Arcjet," IEPC-93-087,September 1993.

3. Day, M., Maslennikov, N. A., and Rogers, W. P.,"SPT-100 Subsystem Development Status andPlan," AIAA-94-2853, June 1994.

4. Beattie,J.R.,Williams,J.D.,andRobson,R.R.,"Flight Qualificationof an 18-mNXenonIonThruster,"IEPC-93-106,September1993.

5. Callahan,L., et al., "On-BoardPowerandPropulsionStrategicPlan,"NASAOfficeofSpaceAccessandTechnology,1995.

6. Curran,F.M.,Schreiber,J.G.,andCallahan,L.,"ElectricPowerand Propulsion: The Future,"IECEC-95-366,August1995.

7. Curran,F.M.andCallahan,L.,"TheNASAOn-BoardPropulsionProgram,"AIAA-95-2379,July1995.

8. Oleson,S.R.,etal.,"AdvancedPropulsionforGeostationaryOrbit Insertionand North-SouthStationKeeping,"AIAA-95-2513,July1995.

9. Spores,R. A., et al., "TheAir ForceElectricPropulsionProgram,"AIAA-95-2378,July1995.

10. Riehl,J. P.,Morales,N., andOleson,S.R.,"Benefitsof Ion ElectricPropulsionfor EarthOrbitalApplications,"to bepublishedasa NASATM,1995.

11. Myers,R.M.,Oleson,S.R.,andCurran,F.M.,"SmallSatellitePropulsionOptions,"IECEC-94-4137,August1994.

12. Myers,R.M.,et al.,"PulsedPlasmaThrusterTechnology for Small Satellite Missions,"Presentedat the 9th AnnualAIAA/USUSmallSatellite Conference,Logan, UT, September1995.

13. Kakuda,R.,Sercel,J.,and Lee,W.,"SmallBodyRendezvousMissionUsingSolarElectricPropulsion: Low Cost MissionApproachandTechnologyRequirements,"IAA-I-0710,April1994.

14. Curran, F. M., and Byers, D. C., "NewDevelopmentsand ResearchFindings: NASAHydrazineArcjets,"AIAA-94-2463,June1994.

15. Sankovic, J. M., "Performanceof aMiniaturizedArcjet,"AIAA-95-2822,July1995.

16. Barnett,J. W.,"A Reviewof SovietPlasmaEngineDevelopment,"AIAA-90-2600,July1990.

17. Garner,C., et al., "A 5,730-Hr CyclicEnduranceTestof theSPT-100,"AIAA-95-2667,July1995.

18. Randolf,T.,andPencil,E.J., "Far-FieldPlumeContaminationandSputteringCharacteristicsoftheStationaryPlasmaThruster,"AIAA-95-2855,June1994.

19. Allen,D.M.,et al.,"RHETTandSCARLET:SynergisticPowerandPropulsionTechnologies,"AIAA-95-368,August1995.

20. Caveny,L.H.,"TheBMDOElectricPropulsionFlight Readiness Program," IEPC-95-132,September1995.

21. Mueller,J., Brophy,J. R., and Brown,D.K.,"EnduranceTesting and Fabrication ofAdvanced15-cmand 30-cm Carbon-CarbonCompositeGrids,"AIAA-95-2660.

22. Sankovic,J.M.,Haag,T.W.,andManzella,D.H., "PerformanceEvaluationof a 2.5 KW SPTThruster,"IEPC-95-30,September1995.

23. Hamley,J.A.,DirectDriveOptionsforElectricPropulsionSystems,"AIAA-95-346,July-August1995.

24. Turchi,P.,"Modelingof Ablation-FedPulsedPlasmaThrusters,"AIAA-95-2915,July1995.

25. Leiwike,R.,Myers,R. M., andTurchi,P.,"MultimaterialPropellantsin Ablation-FedPulsedPlasmaThrusters,"AIAA-95-2916,July1995.

26. Haag,T.W.,"PPTThrustStand,"AIAA-95-2917,"July1995.

Table1. EmergingTechnologyDrivers.

• Smaller Spacecraft and Launch Vehicles

• Multiple Deployments per Launch

• Increased Payload Mass/Life

• Reposition and Precision Positioning

• Deorbit Policy

• Reduced Infrastructure and Operations

Table 2. Anticipated On-Board Propulsion Trends.

FUNCTION LEO/MEO GEO SPACE SCIENCE

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EARTH SCIENCE GEO COMSAT PLANETARY

Figure 1. Spacecraft wet mass fractions for Earth-orbit and planetary missions.

Figure2. Highperformance(600s Isp)arcjetsfornextgenerationcommunicationssatellites.

ELECTROTH ERMAI

i GAS HEATED VIA RESISTANCEELEMENT OR ARC ANDEXPANDED THROUGH NOZZLE

ELECTROSTATIC

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ELECTROMAGNETIC

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• RESISTOJETS• ARCJETS

• ION• HALL

• PPT• MPD

Figure 3. Electric propulsion classes.

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Figure 5. Near-term electric propulsion orbit insertion strategy for GEO comsats.

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I

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BASELINE MISSION

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I

PPT

ELECTRIC PROPULSION INCREASES TOMS-EP PAYLOAD BY:

- 57 % IN BASELINE MISSION- 122% IF DEORBIT IS REQUIRED

(1)TOMS-EP MISSION, LAUNCH MASS

80 DAY INSERTION*" DEORBIT TO 500 KM.

OF 287 KG, FINAL ORBIT ALTITUDE OF 955 KM,

Figure 7. Electric propulsion benefits for an Earth science mission (TOMS example).

11

I PROGRAMD!RECT!ONS,ELECTR!C

PULSED PLASMA THRUSTERS

• LEO/MEO INSERTION, MAINTENANCE, DEORBIT

• PRECISION PosmONING & ACS

ARCJETS/HALL THRUSTERS. LEO/MEO INSERTION, MAINTENANCE, DEORBIT

• GEO NSSK FOR POWER LIMITED COMSATS

• APOGEE TOPPING

• MODERTE _V SPACE SCIENCE

NEXT GENERATION PLASMA THRUSTERS

• HIGH _V ORBIT TRANSFERS & SPACE SCIENCE

• NSSK & REPOSITIONING

MICROTHRUSTERSFOR SUB-10 kgSPACECRAFT

Figure 8. Near-term electric propulsion thrust areas.

Figure 9. RHETT-1 demonstration package.

12

Form ApprovedREPORT DOCUMENTATION PAGE OMB No.0704-0188

Publicreportingburdenfor this collectionof informationis esti.rrk.med.to average 1..holJrper r_esponsp.lnc/udin.gthe tin_. for re_'._wi,V.Ins.tzu_. _-_'_|ng e_i__.i____d___SOUn_.L..-gatheringand maintainingthe data needed, and completingarm reviewingthe co,ectmnof inf.orma__ _eno corm r.egar.o|ngm,; oumen e_.imme .or_anyomer la_ffe_,_colisctionof Infomlation, including suggestionsfor reducingthis burden, to WashingtonHea_uarters _e_wlces, Dflectorat.e.tor Inforr_.___2.Ope_ _a_,__Re_oon,_1_:_,_3 _Davis Highway, Suite 1204, Arlington,VA 2220_-4302. and to the Office ot Managementa/to uuaget. Paperwork i.(eOl.l_X_i-'rojea tutu4-ulucDj, wasnmgmm,_ =:u

1. AGENCY USE ONLY (Leave blank) ;?_ REPORTDATE

June 1996

4. TITLE AND SUBTITLE

Electric Propulsion Applications and Impacts

6. AUTHOR(S)

Frank M. Curran and Timothy J. Wickenheiser

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS{ES)

National Aeronautics and Space Administration

Lewis Research CenterCleveland, Ohio 44135-3191

9. SPONSORING/MONITORINGAGENCYNAME(S)ANDADDRESS(ES)

National Aeronautics and Space Administration

Washington, D.C. 20546-0001

3. REPORT TYPE AND DAiP.:_ COVERED

Technical Memorandum

5. FUNDING NUMBE_;S

WU-242-70--02

8. P_Hi_ORMING ORGANIZATIONREPORT NUMBER

E-10295

10. SPONSORING/MONITORINGAGENCY REPORT NUMBER

NASA TM- 107246

IAF--95-S.3.02

11. SUPPLEMENTARYNOTES

Prepared for the 46th International Astronautical Congress sponsored by the International Astronautical Federation, Oslo,Norway, October 2-6, 1995. Responsible person, Frank M. Curran, organization code 5330, (216) 977-7424.

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited

Subject Category 20

This publication is available fzom the NASA Center for AeroSpace Information, (301) 621-0390

12b. DI:_iBUTION CODE

13. ABSTRACT (Maximum 200 words)

Most space missions require on-board propulsion systems and these systems are often dominant spacecraft mass drivers.Presently, on-board systems account for more than half the injected mass for commercial communications systems and

even greater mass fractions for ambitious planetary missions. Anticipated trends toward the use of both smaller spacecraftand launch vehicles will likely increase pressure on the performance of on-board propulsion systems. The acceptance of

arcjet thrusters for operational use on commercial communications satellites ushered in a new era in on-board propulsionand exponential growth of electric propulsion across a broad spectrum of missions is anticipated. NASA recognizes the

benefits of advanced propulsion and NASA's Office of Space Access and Technology supports an aggressive On-BoardPropulsion program, including a strong electric propulsion element, to assure the availability of high performance propul-

sion systems to meet the goals of the ambitious missions envisioned in the next two decades. The program scope rangesfrom fundamental research for future generation systems through specific insertion efforts aimed at near term technology

transfer. The On-Board propulsion program is committed to carrying technologies to levels required for enstomer accep-tance and emphasizes direct interactions with the user community and the development of commercial sources. This paper

provides a disenssion of anticipated missions, propulsion functions, and electric propulsion impacts followed by anoverview of the electric propulsion element of the NASA On-Board Propulsion program.

14. SUBJECT TERMS

Electric propulsion; On-board propulsion; Spacecraft propulsion

17. SECURITY CLASSIFICATIONOF REPORT

Unclassified

NSN 7540-01-280-5500

18. SECURITY CLASSIFICATIONOF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATIONOF ABSTRACT

Unclassified

15. NUMBER OF PAGES

15

16. PRICE CODE

A0320. LIMITATION OF ABreACT

Standard Form 298 (Rev. 2-89)

Pre_d by ANSI Std. 7.39-18298-102

a) Students preparing JAWSAT for PPT integration impacts testing.

b) Tests of PPT impacts on GPS downlink for JAWSAT program.

Figure 10. Pulsed plasma thruster program examples.

13