DECIGO????

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DECIGO???? ??????????????
?? ?? ?? ? (ISAS-JAXA)
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Propulsion Requirements
Purpose Drag-free control
Thrust range 1 100 µN
to compensate the solar pressure
Thrust noise gt 0.1 µN/vHz
not to disturb the measurement
Quick response control gt 10 Hz
to perform feed-back control
Very unique requirements
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Propulsion Requirements
DECIGO thruster requires the thrust capabilities
completely different from usual thrusters.
Usual (conventional) propul.
DECIGO (drag-free)
Thrust noise Response speed
Specific impulse Thrust to power ratio
Usually, these parameters are not considered
There has been no studies
except for recent studies relating to LISA
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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
(ltlt S/C mass)
10kg even if Isp 100 s thruster
WeightVolume
DECIGO volume 5 m3 10 for thruster ?
Soft requirements of conventional propulsive
capabilities
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Challenging issues
We have to develop
thrusters satisfying DECIGO requirements
µ-Ion thruster using microwave discharge
instruments to evaluate (measure) these parameters
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What is (µ-wave) ion thrusters ?
Plasma production
Neutralized ion beam
Ion acceleration
Gas
Microwave
Electron emission Neutralization
Potential
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µ-Ion thruster using µ-wave discharge
Ion thruster
Thrust is electrically controlled
Acceleration voltage
particle velocity
Microwave power
amount of particle
easily quickly controllable
Microwave discharge
Simple structure
suitable for compact plasma source
Electron bombardment type
Electron emitter is necessary in plasma source
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Developed µ-Ion thruster µ1
Grid system
Side wall
Back yoke
10 mm
Gas inlet
Microwave
Outer ring magnet
Antenna
Inner ring magnet
Ignition
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Novel µ-Ion Engine System
Identical plasma sources
Electron emission
Ion beam
Vsc
Vsc
Vac
Vac
Electron emission
Ion beam
Vneut
Vneut
Switching by electrical connection
Utilization of a plasma source as
both ion beam source and neutralizing electron
source
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Switching Operation
What is the benefit of switching operation ?
Switching operation
A lot of motions
Multi-function
Translation Y-axis rotation Z-axis rotation
Ion engine mode
Neutralizer mode
Z-axis rotation (also, inverse rot.)
Y-axis rotation (also, inverse rot.)
Translation
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Up-to-date results
Electron extraction from ion engine
Twin operation switching operation
Low power High performance plasma source
Microwave power per head 1 W
Thrust to power ratio gt 20 µN/W
Total dry weight and power would be lt 10 kg 30
W
with 10 thruster heads (4 at a time) including
gas system PPU
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Voltage vs. Ion beam current
Ion beam current can be adjusted by the grid
voltage
Simultaneous control of Vsc Vac is necessary
(not so difficult)
Potential
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µ-wave Power vs. Ion beam current
Ion beam current can be adjusted by the
microwave power
Microwave source
Solid state power amplifier
Careful to plasma quenching near 0 W
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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 thruster
Ion beam current Thrust
easily measured
there would be no study verified this
equal under 100 Hz
Beam(thrust) noise evaluation
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How About Thrust Noise ?
?
Noise of ion thruster
Feed-back control would reduce the noise
Acceleration voltage or Microwave power
Beam current
High voltage breakdown would generate impulsive
noise
Between grids
Typically 0.1 1 times in a hour
During recycling sequences, no thrust.
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Summery
We have developed a novel ion thruster system
µ1 for Drag-free control micro-spacecraft
Our current state is
Small ion engine of 20 mm diameter
Thrust range 10 250 µN
(not yet about minimum thrust)
Thrust is adjustable by voltage µ-wave power
(not yet about accuracy)
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(No Transcript)
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Example of thrust noise
Thrust noise of FEEP for GOCE
JOURNAL OF PROPULSION AND POWER Vol. 20, No. 2,
MarchApril 2004
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µ-wave Power vs. Ion beam current
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Appendix Competitive thrusters?
Chemical thrusters
Noise by valve ?
Cold gas thruster
10 Hz valve response ?
mono/bi-propellant engine solid rocket
quite difficult to control gas flow or combustion
reaction with 10 Hz response
µ-Ion thruster FEEP Colloid thruster µ-arc
jet PPT Laser ablation
Electric propulsion
10 Hz response is easy for electrical control
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Appendix FEEP CT
???LISA?Drag-free??????
FEEP Colloid thruster
?????????????????????????
FEEP ???(10 kV)?????????????? ?????????
Isp(gt5000s)????????? (??????) ?????????????(????
???)
Colloid thruster FEEP???????????????? ??????????
?? (???????)
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Appendix µ-Arc jet, PPT, Laser ablation
µ???????
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?????????????? 1 kHz??????????????????
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PPT
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