DECIGODECIGO スラスタスラスタ– – 小型マイクロ波イオンエンジン 小型マイクロ波イオンエンジン ––

小泉　宏之國中　均（ ISAS-JAXA ）

Propulsion; RequirementsPropulsion; Requirements

22/30/30

Purpose: Drag-free control

to compensate the solar pressureThrust range: 1 – 100 μN

Quick response & control : > 10 Hzto perform feed-back control

Thrust noise: > 0.1 μN/√Hz not to disturb the measurement

Very unique requirements

Propulsion; RequirementsPropulsion; Requirements

33/30/30

Usual (conventional) propul.

Thrust noise

Response speed

except for recent studies relating to LISA

DECIGO thruster requires the thrust capabilities completely different from usual thrusters.

Specific impulse

Thrust to power ratio

DECIGO (drag-free)

Usually, these parameters are not considered

There has been no studies

44/30/30

About “usual” requirementsAbout “usual” requirements

Allowed power for propul. = 50 WThruster (10 μN/W) with 100 μN x 5 sufficient

Total impulse = 10 kNs

10kg even if Isp: 100 s thruster （ << S/C mass ）

Thrust to power ratio

Specific impulse

DECIGO volume: 5 m3 　　　 10% for thruster ?Weight ＆ Volume

Soft requirements of conventional propulsive capabilities

Challenging issuesChallenging issues

55/30/30

We have to develop…

instruments to evaluate (measure) these parameters

thrusters satisfying DECIGO requirements

µ-Ion thruster using microwave discharge

What is (What is (μμ-wave) ion thrusters ?-wave) ion thrusters ?

66/30/30

Plasma production

Neutralizedion beam

Ionacceleration

Electron emission & Neutralization

Po

ten

tial

Gas

Microwave

Ion

Electron

Neutral

Gas

Electronemitter

µ-Ion thrusterµ-Ion thruster using using µ-wave dischargeµ-wave discharge

77/30/30

Microwave discharge

Simple structure

Ion thruster Thrust is electrically controlled

Acceleration voltage

easily & quickly controllable

suitable for compact plasma source

Microwave power

particle velocity

amount of particle

Electron bombardment typeElectron emitter is necessary in plasma source

Microwave

Outer ring magnet

Inner ring magnetAntenna

Side wallGrid system

10

mm

Back yoke

Gas inlet

Microwave

Ignition

Developed Developed μμ-Ion t-Ion thruster: hruster: μμ11

Vneut

Vac

Vsc

Vneut

Vac

Vsc

Identical plasma sources

Electron emission

Ion beam Electron emission

Ion beam

Switching by electrical connection

Utilization of a plasma source as both ion beam source and neutralizing electron source

Novel Novel μ-μ-Ion Engine SystemIon Engine System

Translation Y-axis rotation(also, inverse rot.)

Z-axis rotation(also, inverse rot.)

Ion engine modeNeutralizer mode

x

y

z

Switching operationTranslation Y-axis rotationZ-axis rotation

What is the benefit of switching operation ?

A lot of motions Multi-function

Switching OperationSwitching Operation

Up-to-date resultsUp-to-date results

1111/30/30

Twin operation & switching operation

Electron extraction from ion engine

Low power & High performance plasma source

Microwave power per head: 1 W

Thrust to power ratio: > 20 µN/W

Total dry weight and power would be < 10 kg & 30 W

with 10 thruster heads (4 at a time)including gas system & PPU

Voltage vs. Ion beam currentVoltage vs. Ion beam current

1212/30/30

0.0

1.0

2.0

3.0

4.0

5.0

0.0 0.5 1.0 1.5

Ion

beam

curr

ent (

mA

)

Screen voltage (kV)

Vac = -506 VVac = -400 VVac = -303 VVac = -202 VVac = -101 VVac = -30 V

Po

ten

tial

Ion beam current can be adjusted by the grid voltage

Simultaneous controlof Vsc & Vac isnecessary (not so difficult)

μμ-wave -wave Power vs. Ion beam currentPower vs. Ion beam current

1313/30/30

0.0

2.0

4.0

6.0

8.0

0.0 2.0 4.0 6.0 8.0

Ion

beam

curr

ent (

mA

)

Input microwave power (W)

0.25 sccm; Down0.2 sccm; Down0.15 sccm; Down0.1 sccm; Down

Ion beam current can be adjusted by the microwave power

Microwave sourceSolid state power amplifier

Careful to plasma quenching near 0 W

How About Thrust Noise ?How About Thrust Noise ?

1414/30/30

We have never measured the thrust noise

Thrust measurement of 10 µN thrust with 10 Hz is difficult.

Ion thruster

Ion beam current = Thrust

Power spectrum of thrust between 0.01 Hz – 100 Hz

not so difficult quite difficult

easily measured there would be no study verified this “equal”under 100 HzBeam(thrust) noise evaluation

How About Thrust Noise ?How About Thrust Noise ?

1515/30/30

?Feed-back control would reduce the noise

Beam current Acceleration voltageor Microwave power

High voltage breakdown would generate impulsive noise

Typically 0.1 – 1 times in a hourBetween grids

During recycling sequences, no thrust.

1616/30/30

SummerySummery

Our current state is

We have developed a novel ion thruster system: µ1for Drag-free control & micro-spacecraft

Small ion engine of 20 mm diameter

Thrust range: 10 – 250 µN

Thrust is adjustable by voltage & µ-wave power

(not yet about minimum thrust)

(not yet about accuracy)

1717/30/30

1818/30/30

Example of thrust noiseExample of thrust noise

JOURNAL OF PROPULSION AND POWERVol. 20, No. 2, March–April 2004

Thrust noise of FEEP for GOCE

μμ-wave -wave Power vs. Ion beam currentPower vs. Ion beam current

1919/30/30

0

200

400

600

800

1000

0.0 0.2 0.4 0.6 0.8 1.0

Ion

prod

uctio

n co

st (W

/A)

Propellant utillization efficiency

0.25 sccm; Down0.2 sccm; Down0.15 sccm; Down0.1 sccm; Down0.05 sccm; Down

2020/30/30

Appendix; Competitive thrustersAppendix; Competitive thrusters ？？

Noise by valve ?Cold gas thruster

10 Hz valve response ?

mono/bi-propellant engine & solid rocket

Chemical thrustersChemical thrusters

Electric Electric propulsionpropulsion

μ-Ion thrusterFEEPColloid thrusterμ-arc jetPPTLaser ablation

quite difficult to control gas flow or combustion reaction with 10 Hz response

10 Hz response is easy for electrical control

2121/30/30

Appendix; FEEP & CTAppendix; FEEP & CT

FEEP＆Colloidthruster

現在、 LISA の Drag-free 制御の有望株要求される性能については、既に結果を出してきている

FEEP・高電圧 (10 kV) が悪影響をおよぼしそうだが？・最大の特徴である高 Isp(>5000s) は全く活かされない　（無駄に高電圧）・セシウムという推進剤も不安（窓へのコンタミ）Colloid thruster・ FEEP に比べると、スラストノイズに不安・低比推力は問題にならない（データが少ない）

2222/30/30

Appendix; μ-Arc jet, PPT, Laser ablationAppendix; μ-Arc jet, PPT, Laser ablation

μ アークジェット・放電電流でどこまで推力制御できるか？・ノズルの耐久性は？

PPT ・パルスの推力発生が大きな短所・ 1 kHz 動作＆ダンパ搭載で擬似定常推力は可能、　しかし、イグナイタ電力および寿命が懸念される

レーザーアブレーション・推進剤の送り機構が”静か”にできるならば、可能性はある