Seminar report On

ELECTRIC PROPULSION

Submitted By: Astha Jaiswal

EN-1, Sem-6th

Session: 2008-2012

U.N.R: 0801021031

Certificate

1

This is to certify that Astha Jaiswal (0801021057), student of 2008-2012 Batch of Electrical and Electronics branch in 3rd

Year of United College of Engineering and Research, Naini, Allahabad successfully completed the seminar on ELECTRIC

PROPULSION as per the report submitted by her.

Seminar In-Charge

2

ACKNOWLEDGEMENT

I owe a great many thanks to a great many people who helped and supported me during the writing of this report. I would like to express my special thanks of gratitude to my teacher  Pawan Prakash Gupta    who gave me the golden opportunity to do this wonderful project on the topic Electric propulsion, which also helped me in doing a lot of Research and I came to know about so many new things.I would also thank my Institution and my faculty members without whom this project would have been a distant reality. I also extend my heartfelt thanks to my family and well wishers. Thanks and appreciation to the helpful people at for their support. I am making this project not only for marks but to also increase my knowledge.

Thanking you

3

INDEX

Introduction ……………………………………....... 5 Conceptual Organization ………………………… 6 What is Electric propulsion ……………………… 7 Types of Electric propulsion ……………………… 8 Electrostatic propulsion…………………………… 9-18 Electrothermal propulsion………………………… 19-23 Electromagnetic propulsion…………………….. .. 24-26 Advancements in propulsion……………………… 27-29 Application in other field…………………………… 30

Conclusion ………………………………………… 31

Introduction

The success of a space mission is always linked to the se

The success of a space mission is always linked to the performance of technology. To have a technology ready when a satellites flies research

4

and development must start years in advance. This is the objective of the technology programs of the European Space Agency: to ensure effective preparation for European Space Agency. Electric propulsion is a good example of space technology. This report will give an idea of how it works in spacecraft ,and what challenges it overcomes. Electric propulsion is a generic name encompassing all of the ways of accelerating a propellant using electrical power.

In space there is nothing against which you can push, and so the only way to achieve movement is through reactive forces. It is like being stuck in the middle of a frozen pond with no way to move on the slippery ice. If you are lucky enough to have a heavy rucksack, throwing it away in front of you will push you in the opposite direction, hopefully making you glide to the edge of the pond. Satellites do the same, ejecting matter in one direction and moving in the opposite one.THE SCIENCE AND TECHNOLOGY of electric propulsion (EP)encompass a broad variety of strategies for achieving very high exhaust velocities in order to reduce the total propellant burden and corresponding launch mass of present and future space transportation systems.

CONCEPTUAL ORGANIZATION

A.Motivation

5

The stimulus for development of electrically driven space propulsion systems is nothing less fundamental than Newton s laws of dynamics. Since a rocket propelled spacecraft in free flight derives its only acceleration from discharge of propellant mass, its equation of motion follows directly from conservation of the total momentum of the spacecraft and its exhauststream:mú = mve _(1)where m is the mass of the spacecraft at any given time, ú its acceleration vector, v the velocity vector of the exhaust jet relative to the spacecraft, and mú the rate of change of spacecraft mass due to propellant-mass expulsion. The product mve is called the thrust of the rocket, T, and for most purposes can be treated as if it were an external force applied to the spacecraft. Its integral over any given thrusting time is usually termed the impulse, I, and the ratio ofthe magnitude of T to the rate of expulsion of propellant in units of sea-level weight, mú go, has historically been labeled the specific impulse, Is ve/go. If ve is constant over a given period of thrust, the spacecraft achieves an increment in its velocity, ^v which depends linearly on ve and logarithmically on the amount of propellant mass expended:^v=ve lnmo/m f _ (2)where mo and m f are the total spacecraft mass at the start and completion of the acceleration period. Conversely, the deliverable mass fraction, m f /mo, is a negative exponential in the scalar ratio ^v/ve:m f/mo=e-^v/ve

Inclusion of significant gravitational or drag forces on the flight of the spacecraft adds appropriate terms to Eq. (1) and considerably complicates its integration, but it is still possible to retain relation (3), provided that Z^v is now regarded as a more generalized “characteristic velocity increment,” indicative of the energetic difficulty of the particular mission or maneuver.

What is Electric propulsion?

A form of advanced rocket propulsion that uses electrical energy for heating and/or directly ejecting propellant. Electric propulsion (EP)

6

provides much lower thrust levels than conventional chemical propulsion (CP) does, but much higher specific impulse. This means that an EP device must thrust for a longer period to produce a desired change in trajectory or velocity; however, the higher specific impulse enables a spacecraft using EP to carry out a mission with relatively little propellant and, in the case of a deep-space probe, to build up a high final velocity.

The source of the electrical energy for EP is independent of the propellant itself and may be solar (see solar-electric propulsion) or nuclear (see nuclear-electric propulsion). The main components of an EP system are: an energy source, a conversion device (to turn the source energy into electrical energy at an appropriate voltage, frequency, etc.), a propellant system (to store and deliver the propellant), and one or more thrusters to convert the electrical energy into the kinetic energy of the exhaust material.

Types of Electric propulsion

1.Electrothermal propulsion, wherein the propellant isheated by some electrical process, then expanded

7

through a suitable nozzle

2. Electrostatic propulsion, wherein the propellant is accelerated by direct application of electrostatic forces to ionized particles 3. Electromagnetic propulsion, wherein the propellant is accelerated under the combined action of electric and

magnet . Within each of these categories are several further subdivisions as shown in the table below.

ARCJET

ELECTROTHERMAL RESISTOJET

MICROWAVE PLASMA

IONELECTRON BOMBARDMENT

ELECTRIC ELECTROSTATIC PROPULSION CONTACT ION

FIELD EMISSION

MAGNETOPLASMA

ELECTROMAGNETIC PULSED PLASMA

ELECTROSTATIC PROPULSION

A form of electric propulsion in which the thrust is produced by

8

accelerating charged particles in an electrostatic field. It includes three types of device:

Electron bombardment thrustersContact ion thrusters andField emission/colloid thrusters. Of these, the first two involve the production and acceleration of separate ions and are therefore forms of ion propulsion. The third type involves the production and acceleration of charged liquid droplets. Only electron bombardment thrusters have been used operationally aboard spacecraft.

Ion propulsion

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 (see nuclear-electric propulsion).

Two types of ion propulsion have been investigated in depth over the past few decades:

9

Electron bombardment thrusters Contact ion thrusters.

Of these, the latter remains in the research stage while the former has already been used on a number of spacecraft. Specifically, the variety of electron bombardment thruster known as XIPS (a Hughes/Boeing product) is used for station-keeping by some geosynchronous satellites, while the NSTAR ion engine (developed by NASA and Hughes) propelled the Deep Space 1 interplanetary probe.

One of the most promising new developments in ion propulsion is the DS4G (dual-stage 4-grid) ion engine, developed by the European Space Agency and a group at the Australian National University. This was first tested by ESA in 2005. The DS4G thruster achieves much higher voltages to be used than previously thought possible, resulting in a more powerful post acceleration of the extracted ions. The thruster was tested in a large space simulation chamber in the ESA Technology centre in the Netherlands at a remarkable 30,000 V and produced an ion exhaust plume that travelled at 210 km/s – over four times faster than state-of-the-art ion engine designs achieve.

DS4G ion engine

The dual-stage 4-grid (DS4G) thruster is a new design for a highly efficient ion engine designed and built at the Australian National University and sold to the European Space Agency (ESA) which laid down some basic conceptual requirements. According to the results of tests, announced in January 2006, DS4G achieved an exhaust velocity of 210 kilometers per second – more than 10 times faster than possible with the ion engines used on Deep Space 1 and SMART-1, and four times faster than the latest prototype ion engine design

DS4G ion engine:

10

How it works

Traditional ion engines use three closely separated perforated grids containing thousands of millimeter-sized holes attached to a chamber containing a reservoir of charged particles. These systems effectively extract and accelerate the ions in one stage, which because of physical constraints limits the extraction potential applied between the first and second grids to 5 000 V. The DS4G ion engine solves this limitation by effectively decoupling the acceleration from the extraction process into a two-stage system. This allows for independent throttling of the exhaust velocity but more importantly allows very high accelerating fields to be applied to the second stage without adversely affecting the extraction field. The test model has reached total acceleration potentials as high as 30,000 V, resulting in the high exhaust velocity noted above.

Future missions using DS4G engines

11

"Using a similar amount of propellant as SMART-1, a future spacecraft using our new engine design wouldn't just reach the Moon, it would be able to leave the Solar System entirely," according to an ESA press release. Once developed into full flight ready devices, these engines will propel spacecraft to the outermost planets, the newly discovered planetoids beyond Pluto and further into interstellar space, all with-in the working lifetime of a mission scientist.

Closer to home, these supercharged ion engines could figure prominently in the human exploration of space. With an adequate supply of electrical power, a small cluster of larger, high power versions of the new engine design would provide enough thrust to propel a crewed spacecraft to Mars and back.

Electron bombardment thruster

12

Also known as an electrostatic ion thruster, one of the most promising forms of electric space propulsion and one of only two forms of ion propulsion currently employed aboard spacecraft, the other being the Hall effect thruster.

The two most significant operational forms of electron bombardment thruster are:

NSTAR, developed by NASA, and used aboard Deep Space 1XIPS (xenon-ion propulsion system), developed by Hughes (now part of Boeing), and used for station-keeping on some geosynchronous satellites. NASA is also developing a 20–50 kW electron bombardment thruster, called HiPEP, which will have higher efficiency, specific impulse, and life time than NSTAR

Ions ejected by XIPS travel in a stream at a speed of 30 km/s (62,900 mph), nearly 10 times that of a conventional chemical thruster. The high efficiency of the system leads to a reduction in propellant mass of up to 90% for a satellite designed for 12-15 years operation.

Basic principle of working

13

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. These ions are then drawn toward a high-voltage electric field set up between two closely-spaced grids at the downstream end of the chamber. These grids contain numerous tiny lined-up holes so that they serve as porous electrodes. The ions are drawn through the first grid (the screen grid), are accelerated in the narrow gap between the first and second grid (the accelerator grid), and then pass through the second grid as a fast-moving ion beam. On the downstream side of the accelerator grid, electrons are injected back into the beam before it is expelled in order that the spacecraft remains electrically neutral. If only positively-charged ions were allowed to

escape, the vehicle would become more and more negatively-charged until it prevented the working at all.

XIPS (xenon-ion propulsion system)

14

A commercial electron bombardment thruster (also known as an electrostatic ion thruster) – a form ion propulsion – that is a product of Hughes Space and Communications Company, which, in 2000, became part of Boeing Satellite Systems. XIPS (pronounced "zips") employs the heavy inert gas xenon as a propellant. It was first used operationally aboard the PAS-5 (PanAmSat-5) communications satellite in 1997 and has since been fitted to many other geosynchronous satellites for use primarily in station-keeping.

In a XIPS, xenon atoms are injected into an ionization chamber and ionized by electron bombardment. The propellant is then electrostatically accelerated through a series of biased grids.

Working principle of XIPS:

Hall Effect thruster

15

A small rocket engine that uses a powerful magnetic field to accelerate a low density plasma and so produce thrust. The Hall effect thruster, also called a plasma thruster, is a form of electrostatic propulsion, which in turn is a form ion propulsion (a category of electric space propulsion). Like gridded ion engines, such as XIPS, Hall thrusters are classified as electrostatic thrusters. Both utilize an inert gas, commonly xenon, as a propellant.

Prototype high-voltage Hall thruster developed by NASA Glenn Research Center and the Aero jet Corporation.

Hall thruster:

16

Basic principle of working

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. The propellant, which consists of a inert gas such as xenon or krypton at low pressure, is injected into the thruster's channel. Since

Two diagram showing working of Hall Effect thrusters:

Hall thrusters use inert gas for propellant, there is no risk of explosion as there is with chemical rockets. Some of the trapped electrons in the channel collide with the propellant atoms, creating ions. When the propellant ions are generated, they experience the electric field produced between the channel (positive) and the ring of electrons (negative) and accelerate out of the thruster, creating an ion beam.

17

The thrust is generated from the force that the ions impart to the electron cloud. This force is transferred to the magnetic field, which, in turn, is transmitted to the magnetic circuit of the thruster. The electrons are highly mobile and attracted to the ions in the beam, causing an equal amount of electrons and ions to leave the thruster at the same time. This enables the thruster to remain overall electrically neutral.

Stationary plasma thrusters (SPTs) and anode layer thrusters (ALTs) differ in two main respects:

1. The acceleration region of the SPT is within the thruster itself while in the case of the ALT it is in front of the thruster.

2. The channel wall in the SPT is coated with an insulator (a ceramic material) while the ALT's channel wall is metallic.

Performance

Hall thrusters have a specific impulse typically in the range 1,200 to 1,800 seconds – much higher than the 300 to 400 seconds of chemical rockets. However, they provide a much lower thrust. A modern Hall thruster can deliver up to 3 newtons (0.7 pounds) of thrust, which is equivalent to the force you would feel by holding 54 US quarters in your hand. The high specific impulse enables a spacecraft powered by a Hall thruster to reach a top speed of about 50,000 meters per second (112,000 mph). The low thrust, on the other hand, means that weeks or months are needed to attain this speed.

ELECTRO THERMAL PROPULSION 18

A form of electric propulsion in which electrical energy is used to heat a suitable propellant causing it to expand through a supersonic nozzle and generate thrust. Two basic types of electrothermal thruster are in use today: the resistojet and the arcjet. In both, material characteristics limit the effective exhaust velocity to values similar to those of chemical rockets. A third, experimental type is the microwave plasma thruster which potentially could achieve somewhat higher exhaust velocities.

Resistojet

The simplest form of electric propulsion. 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. Resistojet thrusters, using a variety propellants, are being tested for both low-Earth orbit and deep space missions. For example, the microsatellite UoSAT-12 carries 2.5 kg of nitrous oxide, sufficient for 14 hours running. A 60-minute firing of its resistojet would raise its 650-km orbit by 3 km.

19

FIGURE 1 Photograph and schematic of a flight-ready hydrazine resistojet.

Arcjet

20

A simple, reliable form of electro thermal 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 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.

Microwave plasma thruster

21

An experimental form of electrothermal propulsion that works by generating microwaves in a resonant, propellant-filled cavity, thereby inducing a plasma discharge through electromagnetic coupling. The microwaves sustain and heat the plasma as the working fluid, which is then thermodynamically expanded through a nozzle to create thrust.

Plasma

A low-density gas in which the some of the individual atoms or molecules are ionized (and therefore charged), even though the total number of positive and negative charges is equal, maintaining an overall electrical neutrality. Plasma is considered to be a fourth state of matter.

Picture of plasma:

Plasmas in space

22

Strictly speaking, almost all gas in space is a plasma, though only a tiny fraction of the atoms are ionized when the temperature is below about 1,000 K. The very low densities in space allow the electrons to travel without much obstruction, so paradoxically space is an almost perfect electrical conductor. Although charges can move around freely, averaged over even small volumes (say a million kilometers across) cosmic plasmas are always neutral.

Plasmas in space are permeated by magnetic fields. A good way to think about cosmic magnetic fields is in terms of field lines. These behave like rubber bands embedded in the plasma, so that as the plasma flows the field lines are pulled and stretched along with it. When they are stretched enough they can pull back on the plasma. Individual electrons and ions in the plasma feel a magnetic force, which makes them travel in a helical path around the field lines so that they can only travel long distances in the direction along the field. This binds the plasma together so that it behaves like a continuous medium, even when the individual electrons and ions almost never collide.

23

ELECTROMAGNETIC PROPULSION

A form of electric propulsion in which the propellant is accelerated after having been heated to a plasma state. There are several subcategories of electromagnetic propulsion, including

Magnetoplasmadynamic thrusters, Pulsed-plasma thrusters,

Magnetoplasmadynamic thrusters

A form of electromagnetic propulsion. The MPD's ability to convert megawatts of electric power efficiently into thrust makes this technology a prime candidate for economical delivery of lunar and Mars cargo, outer planet rendezvous, and sample return, and for enabling other new ventures in deep space robotic and piloted planetary exploration. MPDs can process more power and create more thrust than any other type of electric propulsion currently available, while maintaining the high exhaust velocities associated with ion propulsion.

In its basic form, the MPD thruster has two metal electrodes: a central rod-shaped cathode, and a cylindrical anode that surrounds the cathode. Just as in an arc welder, a high-current electric arc is struck between the anode and cathode. As the cathode heats up, it emits electrons, which collide with and ionize a propellant gas to create plasma. A magnetic field is created by the electric current returning to the power supply through the cathode, just like the magnetic field that is created when electrical current travels through a wire. This self-induced magnetic field interacts with the electric current flowing from the anode to the cathode (through the plasma) to produce an electromagnetic (Lorentz) force that pushes the plasma out of the engine, creating thrust. An external magnet coil may also be used to provide additional magnetic fields to help stabilize and accelerate the plasma discharge.

24

Principle of the MPD thruster

Schematic of a magnetoplasmadynamic thruster.

The interaction of the current density vector, J, with the self-induced magnetic field, B, produces a body force density, J × B that accelerates the plasma to high exhaust velocities, producing thrust.

25

Pulsed-plasma thrusters

A type of electromagnetic propulsion system , with a high specific impulse and low power and fuel requirements, that has been used on a number of satellites for station-keeping maneuvers.

A PPT works by ablating and ionizing material from a fuel bar (typically consisting of a chlorofluorocarbon such as Teflon) with the current from a discharging capacitor. The positive ions released are then accelerated between two flat-plate electrodes – one positive, the other negative – arranged in the form of two long parallel rails which are connected across the capacitor. Escaping from the spacecraft, the accelerated ions produce a thrust of some several hundred newtons. The capacitor is then charged up again from a power supply and the pulse cycle repeated.

Principle of the pulsed plasma thruster

Advancements in propulsion26

One heavily researched area is electric propulsion (EP) that includes field emission electric propulsion (FEEP), colloid thrusters and other versions of field emission thrusters (FETs). EP systems significantly reduce the required propellant mass compared to conventional chemical rockets, allowing to increase the payload capacity or decrease the launch mass.

Nanotechnology propulsion technology for space exploration

A new electrostatic thruster technology is under development at the University of Michigan's Plasmadynamics and Electric Propulsion Laboratory, using nanoparticles as propellant with micro- and nano-electromechanical systems (MEMS/NEMS). Termed the nanoparticle field extraction thruster – nanoFET – this highly integrated propulsion concept is a high efficiency, variable specific impulse engine type that can be readily scalable for a large range of future space science and exploration missions ("Nanoparticle Electric Propulsion for Space Exploration";). The nanoFET utilizes highly scalable MEMS/NEMS structures to feed, extract and accelerate nanoparticles through micron-sized thrusters. The nanoparticles to be used as propellant can be of various geometries and materials.

27

nanoFET characteristic size scales (Image: University of Michigan Department of Aerospace Engineering)

Here is how it works:

Conductive nanoparticles would be transported to a small liquid-filled reservoir by a micro-fluidic flow transport system. Particles that come into contact with the bottom conducting plate would become charged and pulled to the liquid surface by the imposed electric field. If the electrostatic force near the surface can cause charged nanoparticles to break through the surface tension, field focusing would quickly accelerate the particles through the surface. Once extracted, the charged nanoparticles would be accelerated by the vacuum electric field and ejected, thus generating thrust. One intriguing aspect of nanoFET is that it uses MEMS/NEMS technology to enable a "flat-panel" thruster design that incorporates power processing as well as nanoparticle manufacture, storage, feed, extraction, and acceleration. This results in a modular and geometrically scale able propulsion system, from watts to megawatts, allowing the decoupling of thruster design from spacecraft design.

Another advantage of this system is that it affords a much broader set of missions with a single engine type – nanoFETs have an unprecedented thrust-to-power ratio for electric propulsion systems; they can adjust specific impulse over a large range from 100s to 10,000s; they show a high efficiency range of over 90% over the entire specific impulse range; they do not have the life-limiting factors common in ion thrusters. The system is also very flexible with regard to the size and type of particles that can be used. Almost any conductive nanoparticle, such as carbon nanotubes, fullerenes, as well as metal nanospheres and nanowires could be used. Currently, the researchers are experimenting with silver, nickel and copper nanoparticles ranging in size from 5 nm to 70 nm. So

28

far, the experimental results have validated the theoretical models and represent a significant step towards proving the fundamental feasibility of nanoFET.

Application in other fields

Vehicle Application

Bombardier Propulsion and Controls Systems

Each vehicle application is uniquely designed to meet customer expectations. The largest supplier of its kind in the world, Bombardier Transportation, has a long track record in satisfying customer requirements. Not only do we provide complete ready-to-commission

29

propulsion systems but also train control and communication applications.

The propulsion system begins at the pantograph and ends with the mechanical drive on the axle bogie. Due to an increased focus on cross-border operations and the gradual shift to private companies, there is an audible demand for complete reliable packages which incorporate multisystem operation, short delivery times and systems that work from the very first day.

Our train control and communication system has the capacity and the modularity to work in parallel with train management systems, hardwired functions, and highly integrated systems with built-in diagnostics.

The intent in facing these technology challenges head-on is to seek out both linear and nonlinear solutions that provide significantly increased capabilities to America’s war fighters. The linear challenges will be met with science and technology efforts maturing before 2020, which are continuations of today’s current technology. These efforts offer lower risk and modest payoff, and they include reusable boost and orbit-transfer vehicles, solid and hybrid expendable launch vehicles, and satellite propulsion. The service’s nonlinear challenges are efforts maturing after 2020 that are new technology breakthroughs involving higher risk but very high payoff. These include space ramjets, magnetohydrodynamics-enhanced propulsion, and directed-energy launches.

Conclusion

When I go through to this technology named Electric propulsion, I discovered that with advancement of this technology we can form the strong base of many new discoveries and technologies, and in this process of advancement electrical engineers also going to have a very significant role.

While these technology developments could lead to many strategic and force-structure implications, the Propulsion Directorate’s goal remains focused on developing new propulsion and power technologies that support the Air Force vision of rapid air and space response. That focus is documented in a mutually supportive and coherent plan for air, space,

30

and an energy technology that covers the next 20 to 50 years. This technology can bring the revolution in many fields in future.

31