小泉 宏之 國中 均 （ISAS-JAXA） 6th DECIGO workshop, Apr. 16thth 2008 ISAS / JAXA, Apr. 16 2008 Propulsion; Requirements Purpose: Drag-free control Thrust range: 1 – 100 μN to compensate the solar pressure Thrust noise: > 0.1 μN/√Hz not to disturb the measurement Quick response & control : > 10 Hz to perform feed-back control Very unique requirements 2/30 ISAS / JAXA, Apr. 16th 2008 Propulsion; Requirements DECIGO thruster requires the thrust capabilities completely different from usual thrusters. DECIGO (drag-free) Usual (conventional) propul. Thrust noise Specific impulse Response speed Thrust to power ratio Usually, these parameters are not considered There has been no studies except for recent studies relating to LISA 3/30 ISAS / JAXA, Apr. 16th 2008 About “usual” requirements Thrust to power ratio Allowed power for propul. = 50 W Thruster (10 μN/W) with 100 μN x 5 Specific impulse Total impulse = 10 kNs 10kg even if Isp: 100 s thruster Weight＆Volume DECIGO volume: 5 m3 sufficient （<< S/C mass） 10% for thruster ? Soft requirements of conventional propulsive capabilities 4/30 ISAS / JAXA, Apr. 16th 2008 Challenging issues We have to develop… thrusters satisfying DECIGO requirements µ-Ion thruster using microwave discharge instruments to evaluate (measure) these parameters 5/30 ISAS / JAXA, Apr. 16th 2008 What is (μ-wave) ion thrusters ? Plasma Ion production acceleration Neutralized ion beam Gas Neutral Ion Electron Potential Microwave 6/30 Electron emission & Neutralization ISAS / JAXA, Apr. 16th 2008 µ-Ion thruster using µ-wave discharg 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 Microwave Gas Electron bombardment type Electron emitter is necessary in plasma source Electron emitter 7/30 ISAS / JAXA, Apr. 16th 2008 Developed μ-Ion thruster: μ1 Side wall Gas inlet Microwave Antenna 10 mm Back yoke Grid system Outer ring magnet Inner ring magnet Ignition ISAS / JAXA, Apr. 16th 2008 Novel μ-Ion Engine System Identical plasma sources Electron emission Ion beam Vsc Vsc Vac Vac Vneut Electron emission Ion beam Vneut Switching by electrical connection Utilization of a plasma source as both ion beam source and neutralizing electron source ISAS / JAXA, Apr. 16th 2008 Switching Operation What is the benefit of switching operation ? Switching operation x z y Translation A lot of motions Translation Y-axis rotation Z-axis rotation Neutralizer mode Y-axis rotation (also, inverse rot.) Multi-function Ion engine mode Z-axis rotation (also, inverse rot.) ISAS / JAXA, Apr. 16th 2008 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: > 20 µN/W Total dry weight and power would be < 10 kg & 30 W with 10 thruster heads (4 at a time) including gas system & PPU 11/30 ISAS / JAXA, Apr. 16th 2008 Voltage vs. Ion beam current 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 so 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) 12/30 ISAS / JAXA, Apr. 16th 2008 μ-wave Power vs. Ion beam current Ion beam current (mA) 8.0 6.0 Ion beam current can be adjusted by the microwave power 0.25 sccm; Down 0.2 sccm; Down 0.15 sccm; Down 0.1 sccm; Down 4.0 Microwave source Solid state power amplifier 2.0 Careful to plasma quenching near 0 W 0.0 0.0 2.0 4.0 6.0 8.0 Input microwave power (W) 13/30 ISAS / JAXA, Apr. 16th 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 thruster Ion beam current = Thrust easily measured Beam(thrust) noise evaluation 14/30 there would be no study verified this “equal” under 100 Hz ISAS / JAXA, Apr. 16th 2008 How About Thrust Noise ? ? Noise of ion thruster Feed-back control would reduce the noise Beam current Acceleration voltage or Microwave power High voltage breakdown would generate impulsive noise Between grids Typically 0.1 – 1 times in a hour During recycling sequences, no thrust. 15/30 ISAS / JAXA, Apr. 16th 2008 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) 16/30 ISAS / JAXA, Apr. 16th 2008 17/30 ISAS / JAXA, Apr. 16th 2008 Example of thrust noise Thrust noise of FEEP for GOCE JOURNAL OF PROPULSION AND POWER Vol. 20, No. 2, March–April 2004 18/30 ISAS / JAXA, Apr. 16th 2008 μ-wave Power vs. Ion beam current Ion production cost (W/A) 1000 800 600 400 0.25 sccm; Down 0.2 sccm; Down 0.15 sccm; Down 0.1 sccm; Down 0.05 sccm; Down 200 0 0.0 0.2 0.4 0.6 0.8 1.0 Propellant utillization efficiency 19/30 ISAS / JAXA, Apr. 16th 2008 Appendix; Competitive thrusters？ Chemical thrusters Cold gas thruster Noise by valve ? 10 Hz valve response ? mono/bi-propellant engine & solid rocket quite difficult to control gas flow or combustion reaction with 10 Hz response Electric propulsion 20/30 μ-Ion thruster FEEP Colloid thruster μ-arc jet PPT Laser ablation 10 Hz response is easy for electrical control ISAS / JAXA, Apr. 16th 2008 Appendix; FEEP & CT 現在、LISAのDrag-free制御の有望株 FEEP 要求される性能については、既に結果を出してきている ＆ Colloid FEEP thruster ・高電圧(10 kV)が悪影響をおよぼしそうだが？ ・最大の特徴である高 Isp(>5000s)は全く活かされない （無駄に高電圧） ・セシウムという推進剤も不安（窓へのコンタミ） Colloid thruster ・FEEPに比べると、スラストノイズに不安 ・低比推力は問題にならない （データが少ない） 21/30 ISAS / JAXA, Apr. 16th 2008 Appendix; μ-Arc jet, PPT, Laser ablation μアークジェット ・放電電流でどこまで推力制御できるか？ ・ノズルの耐久性は？ PPT ・パルスの推力発生が大きな短所 ・1 kHz動作＆ダンパ搭載で擬似定常推力は可能、 しかし、イグナイタ電力および寿命が懸念される レーザーアブレーション ・推進剤の送り機構が”静か”にできるならば、可能性はある 22/30 ISAS / JAXA, Apr. 16th 2008
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