1805 IEPC-93-198

DEVELOPMENT OF ION THRUSTER SYSTEM FOR INTERPLANETARY MISSIONS

Hitoshi Kuninaka*Institute of Space and Astronautical Science

Yoshinodai, Sagamihara, Kanagawa, Japan

Nobuo Hiroe*, Kazuto Kitaoka*, Yoshio Ishikawa+Nihon University

Narashinodai, Funabashi, Chiba, Japan

Kazutaka Nishiyama**University of Tokyo

Hongo Bunkyo, Tokyo, Japan

andYasuo Horiuchi++

NECIkebe, Midori, Yokohama, Kanagawa, Japan

Abstract systematization and verification. For theabove-mentioned scientific interplanetary

Institute of Space and Astronautical Science probes the electric propulsion would be

has developed the ion thruster system for specified at 500W maximum in electrical

interplanetary missions. It is characterized to power and 20kg maximum in dry weightgenerate simultaneously both plasmas in a including redundant system. The flightplasma source and a neutralizer by a single operation of the interplanetary mission is

microwave generator without thermo-emissive significantly different from that of the

electrodes. A thruster head and a neutralizer geostationary satellite. A single trackinghave been investigated separately. Preliminary center is not able to communicate withtest for the system integration was executed. spacecraft all the time. Telemetry bit rate may

not be enough due to long distance from the

Introduction earth in the order of astronomical unit. Theelectric propulsion, which will take a longer

Institute of Space and Astronautical time to complete a space mission, will be

Science in Japan aims at grading up from M-3 operated automatically without the supervisionto the -5 launcher, which has a capability to of a ground station in some duration at least.to the M-3 launcher, which has a capability to

input about 500kg payload in 'the An onboard computer is required heavy loads

interplanetary space. It stimulates scientists for health check, emergency stop and restart of

planning explorations of planets, asteroids and the electric propulsion, etc. It is reasonable to

comets. High technologies, for example, the develop the electric propulsion with lessgravit assist, the aerobrake, and high tI control parameters, which never confuse thechemical rockets, have been develaerobrake, and high onboard computer. One of the stumbling blockschemical rockets, have been developed too apply the electric propulsion to the spaceenable high delta-V missions. The electric to apply the electric propulsion to the space

mission is its expensive cost, which ispropulsion, which would compete with them for m s o n s i t s expen co st whhthe space missions, is pressed for the urgent originated from complex system and

complicated ground operation. The author

* Research Associate, Space Propulsion, insists that the electric propulsion should aim

Member AIAA, at the simplicity for hardware and operation.

SGraduate Student, Department of It results in light weight, system robustness,Aeronautics and Astronautics, and light load to the computer. In order to

accomplish the above objectives, the ionAssociate Professor, Department of thruster system using microwave discharge hasAeronautics and Astronautics, been developed in Institute of Space and

++ Engineer, Space Development. Astronautical Science.

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ExtractionMicrowave Ion Thruster ropellant Neuralizer

Trank NeutralizerThe microwave discharge is able to Tk

generate plasma without electrodes so that it is -completely free from electrode erosion andcontamination. A part of the thermal electrons Flow eis accelerated by the microwave electric field ontrollerand ionizes collisionally neutral particles. Theprimary electrons with high energy are Microwaveoriginated from the thermal electrons besides Generatorthermo-emissive electrons. The microwavepower is able to ignite plasma quickly withoutthe preignition sequence. Especially, theneedless of the thermo-emissive cathode willsolve several malfunctions on the conventional PlasmaDeceleDC discharge ion thruster system. The plasma Source radonsource is a simple chamber made of soft ironwith permanent magnets. In addition amicrowave generator can feed power to both Accelerationplasmas in the plasma source and theneutralizer because it does not require a Fig. 1 System configuration of microwave ionreference potential. The conventional ion thruster: YOSHINO series.thruster system have seven DC power supplies:those to heater and keeper for the maincathode, discharge, acceleration, deceleration, small one which is isolated electrically fromheater and keeper for the neutralizer. And it the former. The first model demonstrated theintegrates three flow controllers to the main ion propulsion operated by a single microwavechamber, the main cathode and the neutralizer. generator. It was, however, characterized as aOn the other hand, the YOSHINO series ion poor performance of the ion production due tothruster system developed by Institute of low coupling with microwave and plasma. TheSpace and Astronautical Science has a second model (Y-II) was designed as a plasmamicrowave generator and two DC power source with bucket shaped permanentsupplies for the ion acceleration and a flowcontroller as seen in Fig.1. The microwave magnets. The microwave power propagates in apower and propellant are distributed to both plasma and causes the Electron Cyclotronthe discharge chambers by fixed dividers. The Resonance (ECR) discharge near the magnets.theasma srce htegraes ba DC cter in a The magnets not only confines the plasma butplasma source integrates a DC cutter in a also generates the ECR magnetic field. Themicrowave coaxial cable and an isolator in a 5 mrowave rees the plasma cut-offpropellant feed line in order to isolate DC high eect so as to access the R zo. Te io

effect so as to access the ECR zone. The ionpotential. The microwave neutralizer iselectrically grounded without any DC power production performance was drasticallsupplies. This feature makes the ion thruster improved as seen in Fig.2, of which the verticalsystem down-size as contrasted with the axis is expressed by logarithm. In the contrastsystem down-size as contrasted with the

to the Y-II, which has a microwave launcher onconventional system. Microwave power input th the Y-III mcrowave launcher onignites immediately both plasmas in the the side wall, the Y-III model is launched itignites immediately both plasmas in the

plasma source and the neutralizer after from the rear wall through a gradual expanding

propellant injection. wave guide to reduce microwave reflection3

The historical changes of the YOSHINO seriesThe YOSHINO series ion thruster has is summarized in Table 1 including the Y-IV.

several types historically. The first generation The neutralizer with the microwave discharge(model Y-I) generates plasma using the has been investigated independently to the

microwave cavity with 2.4GHz microwave 1 . It thruster head, described in Ref.4.

has two discharge chambers neighboring on thecavity. Ions are extracted from the largechamber and mixed with electrons from the

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1807 IEPC-93-198

/Y-1

Propellant: Xe Efiiny %

Fig. 2 Ci-,iu curves. Fig. 3 Confguration ofY-4 model.

Table 1 Hsocal change of microwave1I00( .-- . L-. Fig.................. "t a o - o l

ion thruster .t m.

-a- me 120 r

model

itm Y-I YI Y-I. Y-IV

plasma

20 40 60 80 100

aropelant Utilization Efficienc,

a e 1 itorica change of microae

Pncator n -toron -con.

Frcqucnc ig .G117z 5.Grvz 5.FGloz o.2Ghmz

trans I Wae sWare chWa e Co xialo

ion thrustero Thtem.

item Y-1 Y-1l Y-ll1 Y-IV

plas madischarge Cavity ECR ECR ECR

microwa Cathodeagne Cathod Semigenerator -toron -con.

frequenc. 2.4Glz 5.9Gilz 5.9GIIz 4.2GIlz

trans Wave Wave Wave Coaxial-mission Guide Guide Guide Cable

rings ofDis Thermo ThermoSamarium-Cobalt permanent magnet.The Y-V mchar-ml is redemissive on the The discharge chamber in 120mm internal

-lizer o the Y-Cathode Ca thode -charge diameter is fed microwave power through a

ooling r ation test, which hWatar f ollowing circular wave guide from its rear wall. The Y-Cooling Cooling Cooling

Fig. 4 Photograph of Y-4 model in operation.

objecties: 1) to integrate the thruster by iron. It has no components to note butwall threerings of Samarium-Cobalt permanent magnet.

The Y-IV model is redesigned on the The discharge chamber in 120mm internalbasis of the Y-Ill in order to conduct the diameter is fed microwave power through aintegration test, which has the following circular wave guide from its rear wall. The Y-objectives: 1) to integrate the thruster by IV plasma source is set facing its outer wall togathering subsystem developed individually, the hexagonal cryogenic panels in the vacuum2) to acquire data of the thrust performance in chamber as seen in Fig.4. Its microwavethe system level, and 3) to get preliminary amplifier is replaced from the electro-data for the endurance test. Figure 3 shows the magnetic tube to the semiconductor. Figure 5cut view of the discharge chamber made of soft represents the diagram of the microwave

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Plasma Source

WaveGuide

Dummy power

Load manitor

Circulator Directional DC CutterCoupler Neutralizer

gas iwave accel accel pwave gas

Osillator r i ttIor Amplifyer Divider Range

on ; : n _ off tff

Circulator Dr ec tional

Coupe Coaal CableCehamber

Dummy r W a ll

Lmad monitor atomosphere vaccum

Fig. 5 Diagram of microwave power generator.

gas gwave accel accel gwave gas

8 o0 o o n

ff ff

BeamCurrent,

mA0,------ ,---------

0

Accel 1Voltage,

kV

00 -

wave - ) Main Plasma SourcePower, -

WNeutralizer

XenonFow,

seem

0 40 80 120Operation Time, sec

Fig. 6 Operation profile of Y-4.

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1809 IEPC-93-198

generator system. The microwave dividerdistributes the amplified microwave power toboth the plasma source and the neutralizer.The plasma source is isolated electrically bythe DC cutter in the coaxial transmission line.The preliminary operation have just beenperformed as seen in Fig.6. The microwavepower injection ignites both the plasmas in theplasma source and the neutralizersimultaneously. And in quick succession theacceleration voltage apply executes ionacceleration and beam neutralization so thatthe signal of beam current is measured inconsistent with the acceleration voltage intime.

Summary

The microwave ion thruster systemYOSHINO series has several advantages incontrast to the conventional DC dischargesystem. It makes the subsystems of the powersupply and the propellant supply down-sizedrastically so that system weight, systemrobustness and computer load would beimproved. Based on the historical achievementsthe thruster operation was demonstrated in thesystem integration test.

Reference

1 H. Kuninaka, H. Miyoshi and K. Kuriki,"Microwave Ion Engine IntegratedNeutralizer", 21st International ElectricPropulsion Conference, July 18-20, 1990,Orlando, AIAA 90-2627.

2 H. Miyoshi, S. Ichimura, H. Kuninaka, K.Kuriki and Y. Horiuchi, "Microwave IonThruster with Electron Cyclotron ResonanceDischarge", 22nd International ElectricPropulsion Conference, Viareggio Italy,October 14-17 1991.

3 H. Kuninaka, S. Ichimura, K. Kuriki and Y.Horiuchi, "Ion Thruster with ElectronCyclotron Resonance Microwave Discharge",Proc. 18th International Symposium on SpaceTechnology and Science, pp.341-345,Kagoshima, May 1992.

4H. Kuninaka, H. Hiroe, K. Kitaoka and Y.Ishikawa, "Microwave Plasma Contactor",23rd International Electric PropulsionConference, September 13-17, 1993, Seattle,IEPC 93-040.

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