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