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Development of a Miniaturized Ion Engine for Drag Free Missions

Development of a Miniaturized Ion Engine for Drag Free Missions. Hiroyuki KOIZUMI Hitoshi KUNINAKA （ ISAS-JAXA ）. Propulsion; Requirements. Purpose: Drag-free control. Thrust range: 1 – 100 μ N. to compensate the solar pressure. Thrust noise: < 0.1 μN/√Hz @ 0.1 – 10 Hz.

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Development of a Miniaturized Ion Engine for Drag Free Missions

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  1. Development of a Miniaturized Ion Engine for Drag Free Missions Hiroyuki KOIZUMI Hitoshi KUNINAKA （ISAS-JAXA）

  2. 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

  3. Propulsion; Requirements DECIGO thruster requires the thrust capabilities completely different from usual thrusters. DECIGO (drag-free) Usual (conventional) propul. Thrust noise Response speed Thrust efficiency Specific impulse Usually, these parameters are not considered There has been no studies except for recent studies relating to LISA

  4. 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 （<< S/C mass） 10kg even if Isp: 100 s thruster Easy requirements for an usual propulsion system

  5. Ho about these unique reqs.? Purpose: Drag-free control : Easy for EP 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 We have to newly evaluate these parameters

  6. Challenging issues We have to develop… Thrusters satisfying DECIGO requirements µ-Ion engine using microwave discharge Instruments to evaluate (measure) these parameters

  7. What is (μ-wave) an ion engine ? Neutral Plasma production Neutralized ion beam Ion acceleration Ion Electron Gas Ion beam Plasma Microwave Electron emission & Neutralization Potential

  8. 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, called as μ10, was employed to the asteroid explorer HAYABUSA Easily controllable with > 10 Hz Microwave discharge Simple structure suitable for compact plasma source Electron bombardment type Electron emitter is necessary in plasma source

  9. Development of Micro Ion Engine Grid system Side wall Back yoke 10 mm Gas inlet 20 Microwave Outer ring magnet Antenna Inner ring magnet Ignition Cavity for inside-visualization

  10. Up-to-date Performance Thruster performance Microwave power : 1 W Ion acceleration power : 6 W (1.5 kV x 4.0 mA) Thrust: 220 µN Ion production cost: 250 W/A Specific impulse: 1800 s 15 mm

  11. Throttling by ion beam voltage Ion beam current can be adjusted by thegrid voltage Simultaneous control of Vsc & Vac is necessary (not difficult) Potential

  12. Throttling by μ-wave Power Ion beam current can be adjusted by themicrowave power 24.4 μg/s 19.5 μg/s 14.6 μg/s 9.7 μg/s 4.9 μg/s Microwave source Solid state power amplifier Careful to plasma quenching near 0 W

  13. 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 there is no study verifying this “equal” with high frequency Beam(thrust) noise evaluation

  14. Data analysis 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) Ion beam measurement FFT Operation in OPEN LOOP Power spectrum density of ion beam Conversion to thrust (54 µN/mA) Thrust noise

  15. Graph drawing Mean and maximum values are used Maximum values Mean values Huge number of points

  16. Thrust Noise 0.1 µN/√Hz OVER !! High frequency noise from power source What causes these noise ?? Required thrust noise level is not accomplished so easily 0.1 – 10 Hz In this stage, we did not anything to reduce thrust noise

  17. 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 Plasma Ion beam

  18. Noise sources thermal Environment electrical Measurement Gas feeding thermal gas Plasma Acceleration Ion beam µ-wave power power There are a lot of noise candidates Plasma Instability Thruster Screen voltage power power AC100 V (50 Hz) Accel voltage

  19. Rough estimation of system Mass Power Thruster head assembly System requirement of a micro ion engine Ion beam source Accel.: 6 W 0.4 kg Neutralizer (electron emitter) µ-wave: 1+1W Thrust = (220 µN )x thruster heads Power = (14 W )x operated thrusters + 1 W Power processing unit Per 1 head High voltage power source 0.3 kg 7 W Mass = (0.8 kg )x thruster heads + 2 – 3 kg Microwave power source (including neutralizer power) 0.1 kg 7 W e.g. ; 4 thruster heads, 2 simultaneous operation Max 440 µN by 29 W & 5 – 6 kg Gas feeding system Xenon gas & tank 1 kg & 0.2 kg 1 W Feeding system 1 – 2 kg ?? (valve, regulator, tube)

  20. Summery We have developed a micro ion engine forDrag-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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