Transcript 宇宙重力波望遠鏡 DECIGO ＆ Drag

Hiroyuki KOIZUMI
Hitoshi KUNINAKA
（ISAS-JAXA）
th 2008
1st LISA-DECIGO workshop, Nov. 12-13
th
ISAS / JAXA, Nov. 13 2008
Propulsion; Requirements
Purpose: Drag-free control
Thrust range: 1 – 100 μN
to compensate the solar pressure
Thrust noise: < 0.1 μN/√Hz @ 0.1 – 10 Hz
not to disturb the measurement
Quick response & control : > 10 Hz
to perform feed-back control
Very unique requirements
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ISAS / JAXA, Nov. 13th 2008
Propulsion; Requirements
DECIGO thruster requires the thrust capabilities
completely different from usual thrusters.
DECIGO (drag-free)
Usual (conventional) propul.
Thrust noise
Thrust efficiency
Response speed
Specific impulse
Usually, these parameters are not considered
There has been no studies
except for recent studies relating to LISA
3/20
ISAS / JAXA, Nov. 13th 2008
About “usual” requirements
Thrust to power ratio
Allowed power for propul. = 50 W
Thruster (10 μN/W) with 100 μN x 5
sufficient
Specific impulse
Total impulse = 10 kNs
10kg even if Isp: 100 s thruster
（<< S/C mass）
Easy requirements for an usual propulsion system
4/20
ISAS / JAXA, Nov. 13th 2008
Ho about these unique reqs.?
Purpose: Drag-free control
Thrust range: 1 – 100 μN : Easy for EP
to compensate the solar pressure
Thrust noise: < 0.1 μN/√Hz @ 0.1 – 10 Hz
not to disturb the measurement
Quick response & control : > 10 Hz
to perform feed-back control
We have to newly evaluate these parameters
5/20
ISAS / JAXA, Nov. 13th 2008
Challenging issues
We have to develop…
Thrusters satisfying DECIGO requirements
µ-Ion engine using microwave discharge
Instruments to evaluate (measure) these parameters
6/20
ISAS / JAXA, Nov. 13th 2008
What is (μ-wave) an ion engine ?
Plasma
Ion
production acceleration
Neutralized
ion beam
Gas
Neutral
Ion
Electron
Potential
Microwave
7/20
Electron emission
& Neutralization
ISAS / JAXA, Nov. 13th 2008
µ-Ion engine using µ-wave discharge
Ion engine
Thrust is electrically controlled
Acceleration voltage
particle velocity
Microwave power
amount of particle
The microwave
discharge
ion engine,
Easily
controllable
with > 10 Hz
called as μ10, was employed to the
Microwave
structure
asteroidSimple
explorer
HAYABUSA
discharge
suitable for compact plasma source
Microwave
Gas
Electron bombardment type
Electron emitter is necessary
in plasma source
Electron
emitter
8/20
ISAS / JAXA, Nov. 13th 2008
Development of Micro Ion Engine
Side wall
10 mm
Back yoke
Grid system
Gas inlet
Microwave
Antenna
Outer ring magnet
Inner ring magnet
Cavity for inside-visualization
9/20
Ignition
ISAS / JAXA, Nov. 13th 2008
Up-to-date Performance
Thruster performance
Microwave power : 1 W
Ion acceleration power : 6 W (1.5 kV x 4.0 mA)
15 mm
Thrust: 220 µN
Ion production cost: 250 W/A
Specific impulse: 1800 s
10/20
ISAS / JAXA, Nov. 13th 2008
Throttling by ion beam voltage
Potential
Ion beam current (mA)
5.0
Ion beam current
can be adjusted
by the grid voltage
4.0
3.0
Simultaneous control
of Vsc & Vac is
necessary
(not difficult)
Vac = -506 V
Vac = -400 V
Vac = -303 V
Vac = -202 V
Vac = -101 V
Vac = -30 V
2.0
1.0
0.0
0.0
0.5
1.0
1.5
Screen voltage (kV)
11/20
ISAS / JAXA, Nov. 13th 2008
Throttling by μ-wave Power
8.0
Ion beam current
can be adjusted
by the microwave power
24.4 μg/s
Ion beam current (mA)
19.5 μg/s
14.6 μg/s
6.0
9.7 μg/s
4.9 μg/s
4.0
Microwave source
Solid state
power amplifier
2.0
0.0
0.0
1.0
2.0
3.0
Careful to plasma
quenching near 0 W
Input microwave power (W)
12/20
ISAS / JAXA, Nov. 13th 2008
How About Thrust Noise ?
Measurement method
We have never measured the thrust noise
Power spectrum of thrust between 0.01 Hz – 100 Hz
not so difficult
quite difficult
Thrust measurement of 10 µN thrust with 10 Hz is difficult.
Ion engine
Ion beam current
= Thrust
easily measured
Beam(thrust) noise evaluation
13/20
there is no study
verifying this “equal”
with high frequency
ISAS / JAXA, Nov. 13th 2008
Data analysis
Ion beam
measurement
FFT
Sampling points: 217 pts
Recording period: 130 s & 6500 s
Sampling frequency:1 kHz & 20 Hz
A/D conversion: 16 bit
Resolution: 0.3 µA (0.015 µN)
Operation in OPEN LOOP
Power spectrum density of ion beam
Conversion to thrust (54 µN/mA)
Thrust noise
14/20
ISAS / JAXA, Nov. 13th 2008
Graph drawing
Mean and maximum values are used
1.E-06
PSD of ion beam current (mA^2/Hz)
PSD of ion beam current (mA^2/Hz)
1.E-05
1.E-06
1.E-07
Huge number
1.E-08Raw PSD
of points
data
Averaged
Raw PSD PSD
data
1.E-09
Maximum PSD
1.E-10
1.E-07
Mean values
1.E-08
1.E-09
0.1
1
10
Frequency (Hz)
15/20
Maximum values
100
10.0
10.5
11.0
Frequency (Hz)
ISAS / JAXA, Nov. 13th 2008
Thrust Noise
Thrust noise (N/sqrt(Hz))
1.E-05
1.E-06
What causes
these noise ??
Max
Max
Average
Average
0.1 µN/√Hz
1.E-07
OVER !!
High frequency noise
from power source
1.E-08
Required thrust noise level
0.1 – 10 Hz
is not accomplished so easily
1.E-09
In this
stage, we did not
0.01thrust0.1
anything0.001
to reduce
noise 1
10
100
1000
Frequency (Hz)
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ISAS / JAXA, Nov. 13th 2008
How to reduce noise ?
Passive noise reduction
Find out !! Noise causes, and eliminate them !
High freq.
Electrical noise
Low freq.
Thermal drift
Active noise reduction
Feedback loop using beam current
µ-wave
power
17/20
Plasma
Ion
beam
ISAS / JAXA, Nov. 13th 2008
Noise sources
thermal
Gas
feeding
Environment
thermal
Measur
ement
gas
Plasma
µ-wave
power
electrical
Accele
ration
Ion
beam
power
Plasma
Instability
There are a lot of noise candidates
Thruster
Screen
voltage
AC100 V
(50 Hz)
18/20
power
power
Accel
voltage
ISAS / JAXA, Nov. 13th 2008
Rough estimation of system
Mass
Power
Accel.: 6 W
Ion beam source
0.4 kg
System
requirement
of a µ-wave:
micro1+1W
ion engine
Neutralizer
(electron
emitter)
= (220
PowerThrust
processing
unit µN )x thruster heads
High
voltage power
source
Power
= (14
W )x
0.3 kg
7W
operated
thrusters
+1W
Microwave power source
0.1 kg
Massneutralizer
= (0.8
kg )x thruster
(including
power)
Per 1 head
Thruster head assembly
7 W + 2 – 3 kg
heads
e.g.system
; 4 thruster heads, 2 simultaneous operation
Gas feeding
Xenon gas & tank Max 4401 µN
kg & by
0.2 kg
29 W & 5 – 6 kg
1W
Feeding system
1 – 2 kg ??
(valve, regulator, tube)
19/20
ISAS / JAXA, Nov. 13th 2008
Summery
We have developed a micro ion engine
for Drag-free control & micro-spacecraft
Our current states are
Thrust : 220 µN by 20 mm diam. thruster
Thrust is adjustable by voltage & µ-wave power
Thrust noise was 0.1 – 1.0 µN/√Hz @ 0.1 – 1.0 Hz
& 0.01 – 0.1 µN/√Hz @ 1 – 10 Hz
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ISAS / JAXA, Nov. 13th 2008