Development of a Miniaturized Ion Development of a Miniaturized Ion

Engine for Drag Free MissionsEngine for Drag Free Missions

Hiroyuki KOIZUMIHitoshi KUNINAKA（ ISAS-JAXA ）

Propulsion; RequirementsPropulsion; Requirements

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 @ 0.1 – 10 Hz not to disturb the measurement

Very unique requirements

22/20/20

Propulsion; RequirementsPropulsion; Requirements

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.

Thrust efficiency

Specific impulse

DECIGO (drag-free)

Usually, these parameters are not considered

There has been no studies

33/20/20

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

Easy requirements for an usual propulsion system

44/20/20

Ho about these unique reqs.?Ho about these unique reqs.?

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 @ 0.1 – 10 Hz not to disturb the measurement

We have to newly evaluate these parameters

55/20/20

: Easy for EP

Challenging issuesChallenging issues

We have to develop…

µ-Ion engine using microwave discharge

66/20/20

What is (What is (μμ-wave) an ion engine ?-wave) an ion engine ?

Plasma production

Neutralizedion beam

Ionacceleration

Electron emission & Neutralization

Po

ten

tial

Gas

Microwave

Ion

Electron

Neutral

77/20/20

Gas

Electronemitter

µ-Ion engineµ-Ion engine using using µ-wave dischargeµ-wave discharge

Microwave discharge

Simple structure

Ion engine Thrust is electrically controlled

Acceleration voltage

Easily controllable with > 10 Hz

suitable for compact plasma source

Microwave power

particle velocity

amount of particle

Electron bombardment typeElectron emitter is necessary in plasma source

Microwave

88/20/20

Outer ring magnet

Inner ring magnetAntenna

Side wallGrid system

10

mm

Back yoke

Gas inlet

Microwave

Ignition

Development of Micro Ion EngineDevelopment of Micro Ion Engine

Cavity for inside-visualization

99/20/20

Up-to-date PerformanceUp-to-date Performance

Microwave power : 1 W

Thrust: 220 µN

Ion acceleration power : 6 W (1.5 kV x 4.0 mA)

Ion production cost: 250 W/A

Specific impulse: 1800 s

15 m

m

1010/20/20

Throttling by ion beam voltageThrottling by ion beam voltage

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 difficult)

1111/20/20

0.0

2.0

4.0

6.0

8.0

0.0 1.0 2.0 3.0

Ion

beam

curr

ent (

mA

)

Input microwave power (W)

Throttling by Throttling by μμ-wave Power-wave Power

Ion beam current can be adjusted by the microwave power

Microwave sourceSolid state power amplifier

Careful to plasma quenching near 0 W

24.4 μg/s

19.5 μg/s

14.6 μg/s

9.7 μg/s

4.9 μg/s

1212/20/20

How About Thrust Noise ?How About Thrust Noise ?

We have never measured the thrust noise

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

Ion engine

Ion beam current = Thrust

Power spectrum of thrust between 0.01 Hz – 100 Hz

not so difficult quite difficult

easily measured there is no study verifying this “equal”with high frequencyBeam(thrust) noise evaluation

1313/20/20

DData analysisata analysis

Ion beam measurement

Sampling points: 217 ptsRecording period: 130 s & 6500 sSampling frequency:1 kHz & 20 HzA/D conversion: 16 bitResolution: 0.3 µA (0.015 µN)FFT

Power spectrum density of ion beam

Thrust noise

Conversion to thrust (54 µN/mA)

1414/20/20

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

0.1 1 10 100

PSD

of i

on b

eam

curr

ent (

mA

^2/H

z)

Frequency (Hz)

Raw PSD data

Graph drawingGraph drawing

Mean and maximum values are used

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

0.1 1 10 100

PSD

of i

on b

eam

curr

ent (

mA

^2/H

z)

Frequency (Hz)

Raw PSD data

Averaged PSD

Maximum PSD

1.E-09

1.E-08

1.E-07

1.E-06

10.0 10.5 11.0

PSD

of i

on b

eam

curr

ent (

mA

^2/H

z)

Frequency (Hz)1515/20/20

Thrust NoiseThrust Noise

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

0.001 0.01 0.1 1 10 100 1000

Thru

st n

oise

(N

/sqr

t(H

z))

Frequency (Hz)

Max Max

Average Average

0.1 µN/√Hz

0.1 – 10 Hz

High frequency noisefrom power source

What causes these noise ??

In this stage, we did not anything to reduce thrust noise

Required thrust noise levelis not accomplished so easily

1616/20/20

How to reduce noise ?How to reduce noise ?

High freq. Electrical noise

Thermal driftLow freq.

Feedback loop using beam current

µ-wave power

PlasmaIon beam

Find out !! Noise causes, and eliminate them !

1717/20/20

NNoise sources oise sources

Screen voltage

Accelvoltage

µ-wave power

AC100 V(50 Hz)

PlasmaAcceleration

Environment

Gas feeding

Ion beam

PlasmaInstability

Measurement

power

power

power

gas

thermal

thermal

electrical

1818/20/20

Rough estimation of system Rough estimation of system

Thruster head assemblyIon beam source 0.4 kg

Power processing unitHigh voltage power source

Microwave power source(including neutralizer power)

Gas feeding systemXenon gas & tank

0.3 kg

0.1 kg

1 kg & 0.2 kg

1 – 2 kg ??Feeding system(valve, regulator, tube)

7 W

7 W

1 W

Neutralizer (electron emitter)

Accel.: 6 W

µ-wave: 1+1W

Pe

r 1

hea

d

Mass Power

Power = (14 W )x operated thrusters + 1 W

Mass = (0.8 kg )x thruster heads + 2 – 3 kg

Thrust = (220 µN )x thruster heads

e.g. ; 4 thruster heads, 2 simultaneous operation

Max 440 µN by 29 W & 5 – 6 kg

1919/20/20

SummerySummery

Our current states are

We have developed a micro ion enginefor Drag-free control & micro-spacecraft

Thrust noise was 0.1 – 1.0 µN/√Hz @ 0.1 – 1.0 Hz & 0.01 – 0.1 µN/√Hz @ 1 – 10 Hz

Thrust : 220 µN by 20 mm diam. thruster

Thrust is adjustable by voltage & µ-wave power

2020/20/20