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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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IEPC-93-198 1806
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
2
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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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IEPC-92-198 1808
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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