2. Electric Propulsion Overview & Hall Thruster

Transcription

1 2. Electric Propulsion Overview & Hall Thruster

2 What is Electric Propulsion? The acceleration of gases for propulsion by electrical heating and/or by electrical and magnetic body forces. (Physics of Electric Propulsion, Robert G. Jahn, 1968) For V e above 10,000 m/s, a propulsion system needs; Extremely high temperature of an insulated gas stream or Direct acceleration by applied body forces EP thrusters are very fuel efficient due to high exhaust velocity V e. 2

3 How to accelerate? Electrothermal Electrostatic Electromagnetic Arcjet thruster (5-10km/s) MPD thruster (50-100km/s) Hall thruster (15-25km/s) Ion thruster (30-50km/s) 3

4 How much mass reduction expected? History of Himawari-5 (Metrological Sat.) 1995 Mar. Launched 2000 Mar. Life-time (5 years)expired 2003 May Taken over by retired GOES Feb. Himawari Feb. Himawari-7 Hydrazine monopropellant thruster Whether satellite Himawari-5 Momo Ion Engine Propellant for NSSK 207kg(28%) 21kg Propellant for OTV 402kg(54%) 40kg Total mass 747kg 199kg 4

5 How Large V mission is possible? Large V = long-range missions (interplanetary flights) long-time missions (maintenance of satellite) Ex. Orbit to Mars V = 14 km/s Typical ion thruster V e = 30 km/s m m Cf. Typical chemical V e = 3 km/s i f e m m exp V V 1.6 i f e exp V V 106 5

6 Electric Propulsion vs Chemical Propulsion Chemical V e = 4.5 km/s Electric V e = 30 km/s 6

7 Power Supply The higher the V e is, The Better? All EP thrusters must have electric power supply on-board the spacecraft. The weight of power supply scales monotonically with the power level, which is directly related to V e. There exists an optimal V e for a given V and thrust level. Total Mass vs. V e ( I sp ). 7

8 Transfer time Final net mass delivered to GEO as a function of LEO-to-GEO trip time for various propulsion options based on a 1550 kg Atlas IIAS-class payload with 10 kw power. (AIAA ) 8

9 Optimum exhaust velocity for OTV by Electric Propulsion (1) Thrust Efficiency th m prop 2P V s 2 e P s : Available Power Specific power of solar cell panels α=p s /m panel (W/kg) β= m panel /P s (kg/w) Typical β=0.05 kg/w Propellant consumption rate m m prop prop : Transfer Time 9

10 Payload ratio Optimum exhaust velocity for OTV by Electric Propulsion (2) 1 mpay P m s 1 m m m prop i i i mprop P s 1 1 m i mprop 2 V V e 1 1 exp 1 Ve 2 th 2 V V e V 0.1 exp 1 exp Ve 2 th Ve 0 V V e,opt 0 th ΔV/V 0 = Ve/Vo Payload ratio and exhaust velocity Ve,opt 10km/s for 30 days, 33km/s for 1 year. 10

11 History of Electric Propulsion

12 Brief History of EP It s An Old Idea. In 1906, R. H. Goddard expressed informally many of the key physical concepts of EP. In 1911, Konstantin Tsiolkovskiy proposed similar concepts as Goddard. In 1929, Herman Oberth included a chapter on EP in his classic book Man into Space. In 1950s, Ernst Stuhlinger summarized his studies in his book Ion Propulsion for Space Flight. In 1960s, EP became a major component of space propulsion development. Ion thrusters in US Hall thrusters in the former Soviet Union 12

13 In the United states in 90s PAS-5 Telstar Intelsat Intelsat( 93-96) :40 Resistjets (Ford Aerospace-SS/Loral) Telstar ( 93-95) 24 Arcjets (GE Aerospace-Lockeed Martin) PanAmSat ( 90-00) 60 Ion thrusters (Hughes-Boeing) Aerojet 550W Arcjet Boeing NSTAR Ion engine 13

14 In Russia and Europe Russia SPT100 D-55 More than 100 Hall thrusters on Cosmos & Meteor series from 70s. Europe PPS1350 SMART-1 Astrium and Alcatel are competing and cooperating for Hall thrusters in 2000s. 14

15 In Japan MELCO Ion thruster ETS-series ISAS Ion Thruster On Hayabsa explorer Ion thrusters No. Operation Satellite NASA NSTAR Ring Cusp 1 16kh DS1 Boeing XIPS13 XIPS25 Type Ring Cusp kh 14kh BS601HP BS702 Astrium UK10 Kaufman 2 0.7kh Artemis RIT10 RF 3 7.7kh Artemis, EURECA MELCO IES Kaufman 8 0.2kh ETS6, COMETS ISAS/NEC μ10 Microwave 4 40 kh HAYABUSA 15

16 Renewed interests in EP in recent years More on-board electric power In-space propulsion for manned asteroid/planet exploration All Electric satellites Courtesy NASA Boeing satellite 16

17 Summary of EP overview

18 So, Do We Really Want an EP System? In general, large V missions are appropriate for using EP systems. Factors in determining a suitable propulsion system: V e, exhaust velocity EP Thrust CP Efficiency EP Power subsystem CP Propellant management subsystem ---- Mission trajectory and time CP/EP Interface with other subsystems CP Reliability (heritage, redundancy) CP Operation of spacecraft (orbit, trajectory) CP/EP Cost CP (advantage for) EP: electric propulsion CP: chemical propulsion 18

19 Operation of a GEO Satellite MBSAT: DBS communications satellite for Japan and Korea built by SS/L, The first US-built satellite with SPT-100. Orbit Control Maneuvering of chemical and Hybrid GEO satellites Propulsion System NSSK time/firing NSSK Cycle EWSK time/firing EWSK Cycle 20-N Bi-prop (x 2 units) A few minutes 1 per two weeks A few seconds 2 per two weeks SPT-100/Biprop 12 hrs. by SPT per day by SPT-100 A few seconds by a Bi-prop 2 per day by a Bi-prop 19

20 Operation of a GEO Satellite (2) For the bi-prop system, 3 maneuvers in 2 weeks. For the EP/Bi-prop hybrid system, 56 maneuvers in 2 weeks. The hybrid system requires orbit control maneuvering every day due to its low thrust SPT-100. One NSSK maneuver takes a few minutes for the bi-prop system and 12 hours for the hybrid system. Orbit control V: 95% for NSSK, 5% for EWSK Large electric power (~ 2 kw) from both the solar cells and batteries is supplied for the hybrid system. Complex battery charging management, especially during the eclipse periods in spring and autumn. 20

21 Cost of EP systems (1) As a simple comparison, the number of orbital maneuvers for a GEO communications satellite by the hybrid system is 18 times that by the bi-prop system. An orbital maneuver is proceeded by a ranging, orbit determination, and control planning and followed by another ranging, orbit determination, and assessment. A rough estimate of cost increase in orbit control operations (with one operator + one orbital engineer) is ~ $8 million in 15 years (orbital lifetime). 21

22 Cost of EP systems (2) MBSAT carries the same number of bi-prop thrusters as the satellite that does not carry SPT-100s. MBSAT: 12 bi-prop thrusters + 4 SPT-100 thrusters Chemical propulsion satellite: 12 bi-prop thrusters ~ $20 million cost increase due to four SPT-100 thrusters plus gimbals, PPU, and PFS Trade-off between the bi-propellant mass and the mass of SPT-related hardware and xenon. The decrease in launch cost is minimal. Having an EP system, with less propellant mass and longer mission lifetime, would NOT REALLY save the total cost when considering actual satellite procurement and operations!! 22

23 EP CAN. can have an advantage with their low thrust level. Extremely small attitude disturbance by their maneuvering. Suitable for satellites with flexible structures. Suitable for missions with fine maneuvering requirement such as co-location and formation flying. can appeal to missions of extremely high V requirements. Impractical to carry the necessary propellant mass of a chemical rocket system Interplanetary missions Deep-space probes can continue to evolve. Higher reliability Lower cost Greater variety of the combinations of thrust, I sp, and power levels. 23

24 Hall Thruster

25 Hall Thruster Principle: Overview Electrostatic acceleration Axial E and radial B Cathode as electron emitter Design criteria: Propellant (Xe) Hall current Acceleration channel Xe + (Larmor radius) (Hall parameter) Anode E B electron Cathode (Ion mean free path) : Channel length 25

26 Anode Cathode side Hall Thruster Principle: Electric Field 100 ~ 1000 V DC Plasma is highly conductive Plasma E field Electric field is shielded Radial magnetic field to confine electron motion r z Φ Channel wall B field Electron gyroradius must be much smaller than channel length B r Electron Larmor radius Anode Channel exit Cathode 26

27 Hall Thruster Principle: Hall Current E x B drift movement of charged particles Electron-induced Hall current E Electron B E x B direction electron motion Hall current For effective confinement of electron motion, electron Hall parameter must be much larger than 1 (Hall parameter) = (Gyrofrequency) x (mean free time) E Collisions contribute to cross B-field transports B Electron motion with collisions 27

28 Hall Thruster Principle: Closed Annular Cavity Hall current B E Operation of Hall thruster Linear Hall-effect ion source

29 Hall Thruster Principle: Ion Generation Electrons are very lightweight Energy loss: Ionization, Wall loss, etc. Φ Energy gain: Joule heating T e Electrons are heated to 20 ev = 232,000 K Ionization region Collisional ionization First ionization energy [ev]: Argon: 15.8 Krypton: 14.0 Xenon: 12.1 Anode Channel exit Cathode Xe + Electron 29

30 Anode Hall Thruster Principle: Ion Acceleration Ions are smoothly accelerated by electric field Little disturbance by magnetic field or collisions Ion Ion Larmor radius Ion mean free path r z Channel wall Exhaust velocity estimation Discharge voltage: Acceleration voltage: Ion mass (Xe): If 90% of is ionized, Elemental charge: 30

31 Hall Thruster Principle: Recap Electrostatic acceleration Axial E and radial B Cathode as electron emitter Design criteria: Propellant (Xe) Hall current Acceleration channel Xe + (Larmor radius) (Hall parameter) Anode E B electron Cathode (Ion mean free path) 31

32 Magnetic Layer vs. Anode Layer Magnetic-layer type Channel length > channel width Dielectric material (BN) to protect ferromagnetic pole pieces Anode-layer type Very short channel length, so that no need for magnetic pole protection Conducting metal at the cathode potential 32

33 Stationary Plasma Thruster (SPT) SPT series specifications Parameter SPT-50 SPT-70 SPT-100 SPT-140 Slot diameter, mm Thrust input power, W Average Isp, s Thrust, mn Thrust efficiency, % >55 Lifetime, h >7000 Status Flight Flight Flight Qualified 33

34 Thruster with anode layer (TAL) TAL series specifications Parameter D-38 D-55 D-100 D-110 D-150 Slot diameter, mm Thrust input power, W Average Isp, s Thrust, mn Thrust efficiency, %

35 Thrust Performances of SPT and TAL Outer diam.: 100mm Power : 1.35 kw I sp : 1600 sec Thrust : 80 mn Efficiency : 50 % Magnetic layer type: SPT-100 Outer diam.: 55mm Power : 2.5 kw I sp : 2000 sec Thrust : 120 mn Efficiency : 55 % Anode layer type: D-55 35

36 Global Exploration Roadmap (GER) GER: Post-ISS international cooperative missions High-power EP (In-space propulsion) is a key tech. 36

37 In-Space Propulsion in US and Europe NASA s 12.5-kW HERMeS thruster 1 Snecma s 5-kW PPS Thrust efficiency : ~ 63% Specific impulse : ~ 3000 s 1 Kamhawi et al., IEPC , Duchemin et al., IEPC ,

38 RAIJIN: All-Japan Collaboration Thruster Head, PPU Plume Interaction Project RAIJIN Mission & Orbit Analyses High-Current Neutralizer 38

39 Development of UT-58 Anode-Layer Thruster UT-58: 2 kw-level TAL developed in UT Magnetic Field Analysis UT-58 3D Model Thermal Analysis 39

40 Performance of UT-58 Xenon Argon Operation of UT-58 with Xenon and Argon Maximum value Xenon (~3.0 Aeq) Argon (~8.0 Aeq) Input power, kw Thrust, mn Anode efficiency, % Exhaust velocity, km/s

41 Comparison: UT-58 and D-series Compared with Russia s D-series, UT-58 achieved 70% of anode eff. with 1-order small input power Anode efficiency vs. Input power of UT-58 and D=series 41

42 Anode Ion Energy Loss to Wall and Wall Erosion Ion collision with wall causes energy losses of ionization and acceleration Channel wall erosion by highenergy ion sputtering limits thruster lifetime r z Ion Channel wall Sputtering Equipotential lines Channel wall Simulation of channel wall recession Magnetic pole piece 42

43 B Field Optimization: Plasma Lens Focusing Plasma Highly conductive E field Metal Electric field lines surrounding conductor B field Plasma lens focusing 43

44 B Field Optimization: Actual Designs ATON thruster Magnetic field geometry using plasma lens focusing 44

45 B Field Optimization: Numerical Simulations 330 h 600 h Calculated space potential distribution. Begin of life and end of life. 1 Cho et al., 48 th Joint Propulsion Conference, AIAA ,

46 Ion Attracting Physics: Presheath Acceleration in presheath Bohm criterion Channel wall Outer channel wall Outer channel wall Equipotential line Ion-loss region Inner channel wall Inner channel wall Convex-shaped magnetic field and ideal ion acceleration direction Deflected equipotential lines and ion-loss region by presheath 46

47 Magnetic Shielding: Theory Magnetic Shielding: Very concave magnetic field geometry Channel wall parallel to magnetic lines High T e Strong presheath Φ T e Low T e Weak presheath Z Anode Channel exit Cathode 47

48 Magnetic Shielding: Numerical Simulation Unshielded configuration 1 Magnetic shielding configuration 1 Calculated space potential distribution 2 1 Hofer et al., Journal of Applied Physics, Mikellides et al., Journal of Applied Physics,

49 Magnetic Shielding: JPL Experiments Measured erosion rate of unshielded (US) and magnetic shielding (MS) configurations 1 1 Hofer et al., Journal of Applied Physics,

50 Strong magnetic shielding Guard-ring current ratio, % UT Experiment: Magnetic Shielding in TAL gap = 14 mm Guard-ring current ratio = Ion wall current Discharge current gap = 19 mm Current tradeoff relation Better New trade-off relation 10 8 gap=14 6 gap=19 gap = 24 mm 4 2 gap=24 Anode Wall Magnetic and wall geometry of UT-58 Better Anode efficiency, % 50

51 Simulation: Magnetic Shielding in TAL Weak magnetic shielding Strong magnetic shielding Calculated space potential distribution in UT-58 51

52 Simulation: Magnetic Shielding in TAL All ions Ions entering channel wall Calculated ion production rate distribution of magnetically shielded UT-58 52

53 Discharge Current Oscillation Inherent oscillation types: 1. Ionization: 10 khz khz 2. Transit-time: 100 khz - 1 MHz 3. Electron-drift: 1 MHz - 10 MHz 4. Electron-cyclotron: 1 GHz 5. Langmuir: 0.1 GHz - 10 GHz Discharge oscillation causes Heavy power processing unit Electromagnetic noise Time history of discharge current 53

54 Number density Ionization Oscillation Ionization rate Frequent ionization Predator-Prey model Neutral depletion Ion, Electron n e Neutral, n n Infrequent ionization Neutral recovery Time Principle of ionization oscillation 54

55 Synchronous Breathing-mode Oscillation Oscillation behavior of plasma 1. 1 Yamamoto et al., Trans. Japan Soc. Aero. Space Sci. (48),

56 Electron Diffusion and Discharge Oscillation Classical diffusion Transition region Anomalous diffusion Classical diffusion Transition region 0.4 Anomalous diffusion 0.01 Typical tendency of discharge current and oscillation vs. magnetic flux density 56

57 Electron Diffusion and Discharge Oscillation Xenon Transition and anomalous diffusion region 60 Argon Classical diffusion region

58 Summary: Hall Thruster Principle: Hall current and electrostatic acceleration High-power thruster for In-space propulsion B-field optimization and magnetic shielding Discharge current oscillation 58