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Electric propulsion

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Electric propulsion

  1. 1. THEORY OF PROPULSION Electric Propulsion
  2. 2. LLiimmiittaattiioonnss ooff CChheemmiiccaall RRoocckkeettss • CChheemmiiccaall rroocckkeett:: eexxhhaauusstt eejjeeccttiioonn vveelloocciittyy iinnttrriinnssiiccaallllyy lliimmiitteedd bbyy tthhee pprrooppeellllaanntt--ooxxiiddiizzeerr rreeaaccttiioonn • LLaarrggeerr vveelloocciittyy iinnccrreemmeenntt ooff tthhee ssppaacceeccrraafftt ccoouulldd bbee oobbttaaiinneedd oonnllyy wwiitthh aa llaarrggeerr eejjeecctteedd mmaassss ffllooww.. • MMiissssiioonn pprraaccttiiccaall lliimmiittaattiioonn:: eexxcceeeeddiinnggllyy llaarrggee aammoouunntt ooff pprrooppeellllaanntt tthhaatt nneeeeddss ttoo bbee ssttoorreedd aabbooaarrdd Theory of Propulsion 2
  3. 3. Electric propulsion “The acceleration of gases for propulsion by electric heating and/or by electric and magnetic body forces.” The general classes of systems for electric propulsion are: •Electrostatic propulsion devices •Electrothermal propulsion devices •Electromagnetic propulsion devices. Theory of Propulsion 3
  4. 4. Advanced ((EElleeccttrriicc)) PPrrooppuullssiioonn FFeeaattuurreess:: • HHiigghh eexxhhaauusstt ssppeeeedd ((ii..ee.. hhiigghh ssppeecciiffiicc iimmppuullssee)),, mmuucchh ggrreeaatteerr tthhaann iinn ccoonnvveennttiioonnaall ((cchheemmiiccaall)) rroocckkeettss • MMuucchh lleessss pprrooppeellllaanntt ccoonnssuummppttiioonn ((mmuucchh hhiigghheerr eeffffiicciieennccyy iinn tthhee ffuueell uuttiilliizzaattiioonn)) • CCoonnttiinnuuoouuss pprrooppuullssiioonn:: aappppllyy aa ssmmaalllleerr tthhrruusstt ffoorr aa lloonnggeerr ttiimmee • MMiissssiioonn fflleexxiibbiilliittyy ((IInntteerrppllaanneettaarryy ttrraavveell,, ddeeffeennssee)) Theory of Propulsion 4
  5. 5. Electric PPrrooppuullssiioonn CCoonncceeppttss • VVaarriieettyy ooff ddeessiiggnnss ttoo aacccceelleerraattee iioonnss oorr ppllaassmmaass • MMoosstt ccoonncceeppttss uuttiilliizzee ggrriiddss oorr eelleeccttrrooddeess:: ppoowweerr aanndd eenndduurraannccee lliimmiittaattiioonnss • IIoonn EEnnggiinnee • HHaallll TThhrruusstteerr • RRFF PPllaassmmaa TThhrruusstteerrss ((EECCRR,, VVAASSIIMMRR,, HHeelliiccoonn DDoouubbllee LLaayyeerr)) • MMaaggnneettooppllaassmmaa DDyynnaammiicc ((MMPPDD)) TThhrruusstteerrss • PPllaassmmooiidd AAcccceelleerraatteedd TThhrruusstteerrss Theory of Propulsion 5
  6. 6. Electrothermal rockets Electrothermal rocket engines are very similar in principle to chemical and nuclear thermal rockets, differing only in using electrical heating to raise the temperature of the propellant prior to accelerating it in a nozzle. •Electric resistance heating, as in the “resistojet” •Heating of the propellant by a high energy arc discharge passing through it, as in the “arc jet” •Heating by passing radio frequency (RF) electromagnetic waves through the propellant to heat it. Fairly high F at reasonably high Isp, but thermal limitations are the same as in chemical and nuclear thermal rocket engines. Theory of Propulsion 6
  7. 7. Resistojet • Propellant: Nitrogen, Xenon,butane & most gases • Thrust: up to 100 mN • Feed pressure: up to 10 bar • Operation temperature to 500°C • Redundant heaters • A resistojet works by super-heating a propellant fluid, such as water or nitrous oxide, over an electrically-heated element and allowing the resulting hot gas to escape through a converging-diverging nozzle. Thrust and specific impulse (a measure of the engine's efficiency) are limited by the material properties of the resistor. Theory of Propulsion 7
  8. 8. Resistojet Valve Heat exchanger Nozzle Theory of Propulsion 8 Electric power supply
  9. 9. Arcjet A simple, reliable form of electrothermal propulsion used to provide brief, low-power bursts of thrust, such a satellite needs for station-keeping. A nonflammable propellant is heated, typically changing state from liquid to gas, by an electric arc in a chamber. It then goes out the nozzle throat and is accelerated and expelled at reasonably high speed to create thrust. Arcjets can use electrical power from solar cells or batteries, and any of a variety propellants. Hydrazine is the most popular propellant, however, because it can also be used in a chemical engine on the same spacecraft to provide high thrust capability or to act as a backup to the arcjet. Theory of Propulsion 9
  10. 10. Arcjet Theory of Propulsion 10
  11. 11. Electrothermal : Arc Jet Propellant tank Pump Accelerated plasma Theory of Propulsion 11 ~ Electric power supply Negative electrode Radiator Positive electrode Pump Circulating nozzle wall coolant Arc Propellant cooled chamber wall
  12. 12. Arcjet nozzle block temperatures Anode attachment zone 2300K 1800K 1900K 2000K 100K 2200K Theory of Propulsion 12 Propellant flow
  13. 13. Arcjet Theory of Propulsion 13 Type Propell ant Energy Isp,vac (s) Thrust (N) Density (g/cc) Resisto jet N2, NH3, N2O4, H2 Resistive heating h=0.9 150- 700 0.005-0.5 0.28, 0.60, 1.0, 0.019 Arcjet NH3, H2, N2H4 Arc heating h=0.3 450- 1500 0.05-5 0.60, 0.019 1.0
  14. 14. Electrostatic rockets The temperature limitations of electrothermal rockets may be avoided if the acceleration of the propellant is achieved by electric body forces. The ion rocket accomplishes this by using - •An ion source to produce a stream of positively charged particles •A negatively charged grid electrode to electrostatically accelerate the ions •An electron source to neutralize the accelerated ions Thus there is no physical nozzle or pressure chamber and the only temperature limitations are on the ion source device. Theory of Propulsion 14
  15. 15. Types Of Electostatic Propulsion Thrusters:: To cause ionization there are mainly 5 different procedures, they are : • electron bombardment • radio frequency • field emission • microwave • ion contact Theory of Propulsion 15
  16. 16. Ion rocket propulsion Def:- A form of electric space propulsion in which ions are accelerated by an electrostatic field to produce a high-speed (typically about 30 km/s) exhaust. An ion engine has a high specific impulse (making it very fuel-efficient) but a very low thrust. Therefore, it is useless in the atmosphere or as a launch vehicle, but extremely useful in space where a small amount of thrust over a long period can result in a big difference in velocity. This makes an ion engine particularly useful for two applications: (1) as a final thruster to nudge a satellite into a higher orbit and or for orbital maneuvering or station-keeping, and (2) as a means of propelling deep-space probes by thrusting over a period of months to provide a high final velocity. The source of electrical energy for an ion engine can be either solar (see solar-electric propulsion) or nuclear Theory of Propulsion 16
  17. 17. Electrostatic: Ion Rocket in space Propellant line Ion source Accelerating electrode Neutralizer: Electron emitter Ions Electrons Theory of Propulsion 17 Battery
  18. 18. IIoonn EEnnggiinnee • SScchheemmee ooff aa ggrriiddddeedd iioonn eennggiinnee wwiitthh nneeuuttrraalliizzaattiioonn Theory of Propulsion 18
  19. 19. Ion rocket capabilities F mU j M U V A q x Theory of Propulsion 19 V=V0 x=0 V=0 x=xa Ion source Accelerating grid Electric field E=dV/dx Ion stream m = NaMUaA 2 0 0 8 a a 9 a e æ ö = = = ç ¸ è ø Ion mass flow Thrust Ua
  20. 20. Electron Bombardment In an electron bombardment thruster, a gas propellant enters a discharge chamber at a controlled rate. A hot, hollow cathode (negative electrode) at the center of the chamber emits electrons, which are attracted to a cylindrical anode (positive electrode) around the walls of the chamber. Some of the electrons collide with and ionize atoms of the propellant, creating positively-charged ions. Theory of Propulsion 20
  21. 21. Hall Thruster Electrons are generated by a hollow cathode (negative electrode) at the downstream end of the thruster. The anode (positive electrode) or "channel" is charged to a high potential by the thruster's power supply. The electrons are attracted to the channel walls and accelerate in the upstream direction. As the electrons move toward the channel, they encounter a magnetic field produced by the thruster's powerful electromagnets. This high-strength magnetic field traps the electrons, causing them to form into a circling ring at the downstream end of the thruster channel. The Hall thruster gets its name from this flow of electrons, called the Hall current. Theory of Propulsion 21
  22. 22. HHaallll TThhrruusstteerr ((IIII)) Theory of Propulsion 22 The Hall thruster scheme
  23. 23. HHaallll TThhrruusstteerr The Hall effect Theory of Propulsion 23
  24. 24. ELECTROMAGNETIC:PPT • PPTs use solid Teflon propellant to deliver specific impulses in the 900 - 1,200 s range and very low, precise impulse "bits" (10-1,000 μNs) at low average power (< 1 to 100 W) • PPTs inherently inefficient (η ~5%) – Simplicity and low impulse bits provide highly useful – Precision-flying of a spacecraft constellation • PPT consists of a coiled spring that feeds Teflon propellant bar, an igniter plug to initiate a small-trigger electrical discharge, a capacitor, and electrodes through which current flows • Plasma is created by ablating Teflon from discharge of capacitor across electrodes • Plasma is then accelerated to generate thrust by Lorenz force that is established by current and its induced magnetic field Theory of Propulsion 24
  25. 25. Pulsed plasma thruster Courtesy NASA GRC Theory of Propulsion 25
  26. 26. MMaaggnneettooPPllaassmmaa AAcccceelleerraattiioonn Theory of Propulsion 26
  27. 27. MagnetoPlasma DDyynnaammiicc TThhrruusstteerr Theory of Propulsion 27
  28. 28. ELECTROMAGNETIC: MPD • Electromagnetic devices pass a large current through a small amount of gas Theory of Propulsion 28 to ionize propellant • Once ionized, plasma is accelerated by electromagnetic body force called Lorentz force which is created by interaction of a current (j) with magnetic field (B): F=j x B • Current provided between energized positive and negative electrodes, while magnetic field is either induced by (created from) current itself, applied externally via an electromagnet or both • Strength of Lorentz force for an MPD thruster with a self-induced magnetic field is roughly proportional to ratio J2 / mdot, where J is total thruster current • While gas-phase propellants like hydrogen and lithium (after vaporization) can be used, solid propellants can also be used in pulsed electromagnetic accelerators called pulsed plasma thrusters (PPTs).
  29. 29. Electromagnetic: MHD engine Propellant tank Pump Magnetic field coils Cathode Electric current Accelerating plasma Electromagnetic force (J X B) J X B Theory of Propulsion 29 ~ Electric power supply Negative electrode Positive electrode Arc Anode J B
  30. 30. ELECTROMAGNETIC: MPD Theory of Propulsion 30
  31. 31. Electric PPrrooppuullssiioonn AApppplliiccaattiioonnss Theory of Propulsion 31 11.. IISSSS 22.. IInntteerrppllaanneettaarryy MMiissssiioonnss 33.. CCoommmmeerrcciiaall//DDeeffeennssee
  32. 32. REFERENCES :: • http://www.daviddarling.info/encyclopedia.hmtl • http://www.mypptsearch.com/index.php • http://www.2dix.com • http://www.jetaerospace.org/ Theory of Propulsion 32
  33. 33. THANK YOU…….. Theory of Propulsion 33

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