Plasma Propelled Rocket Engines

SEMINAR REPORT 2014

PLASMA PROPELLED ROCKET ENGINES

CHAPTER 1 INTRODUCTION Rocket is a device that provides thrust to a vehicle by accelerating some matter (the propellant) and exhausting it from the rocket. Most significant difference between rocket and air breathing engines is that rocket carries all its its own propellant. From the early 19th century onwards scientists have been trying to launch satellites into outer space with the help of rockets. But the success rate of these missions was very low due to lack of technologies and the huge cost involved. Also most fuels get expended in the initial stage of operation which is not practical for deep-space mission’s explorations because they would require huge quantities of fuel. Gravitation boost is also required. The mission conducted by NASA which took off in September 2007, is powered by a kind of space propulsion technology techn ology that is starting to take center stage s tage for long-distance missions- a plasma rocket engine. Such engines, now being developed in several advanced forms, generate thrust by electrically producing and manipulating ionized gas propellants rather than by burning liquid or solid chemical fuels, as conventional rockets do. NASA Jet Propulsion Laboratory selected a plasma engine as the probe’s rocket system because it is highly efficient, requiring only one tenth of the fuel that a chemical rocket motor would have needed to reach the asteroid belt. If project planners had chosen to install a traditional engine, the, vehicle vehic le would woul d have ha ve been able to reach the required destination The benefits afforded by plasma engines become .

most striking in light of the drawbacks of conventional rockets. When people imagine a ship streaking through the dark void toward a distant planet, they usually envision it trailing a long,fiery plume from its nozzles. Yet the truth is altogether different: expeditions to the outer solar system have been mostly rocket less affairs, motor would typically have no fuel left for braking. Such a probe would need the ability to reach its rocket so that it could slow enough to achieve orbit around its target and thus conduct extended scientific observations.

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1.1 LITERATURE SURVEY Konstantin E. Tsiolkovsky on the year (1903) derives the ―rocket equation,‖

which is widely used to calculate fuel consumption for spacemissions. In 1911 he speculates that electric fields could accelerate charged particles to produce rocket thrust.Then after that, during (1954) Ernst Stuhlingera Russian scientist figures out howto optimize the performance of the electric ion rocket engine. Work by researchers in the Soviet Union, Europe and the U.S. leads to the first published description of the Hall thruster, a more powerful class of plasma rocket. NASA’s Jet Propulsion Laboratory’s Deep Space 1 in the year (1999)

demonstrates the first use of an ion engine as the main propulsion system on a spacecraft that escapes Earth’s gravitation from orbit.

Tony Sch¨onherr(2000) studied performance and the plasma created by a pulsedmagnetoplasmadynamic thruster for small satellite application to understand betterthe ablation and plasma propagation processes occurring during the short-time discharge. The results can be applied to improve the quality of the thruster in terms of efficiency and to tune the propulsion system to the needs required by the satellite mission. The word from Houston is that Ad Astra Rocket Co., which has been developing the VASIMR concept, has been making progress with its 200-kw plasma rocket engine prototype. VASIMR(Variable Specific Impulse Magnetoplasma Rocket) offers constant power throttling (CPT), which would allow it to vary its exhaust for thrust and specific impulse while maintaining a constant power level. A (2015) flight prototype prototype is in the works, a VASIMR VASIMR drive that could reach an exhaust velocity of up to 500 kilometers per second, corresponding to a specific impulse of 50,000 seconds, which translates into an Alpha Centauri Centa uri crossing in 2200 years

.

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CHAPTER 2 HISTORY The fall of 2012 marks humankind's 55th year as a space-faring society. Our world changed irreversibly on October 4, 1957, when the Soviet Union successfully launched Sputnik I, the world's first artificial satellite. Sputnik I was about the size of a basketball, weighed only 183 pounds and took about 98 minutes to orbit the Earth. This marked the start of the Space Age and the US-USSR space race that ultimately led to the piloted Moon landings between 1969 and 1972. Some 30 years after humans last walked on the Moon, access to space has become almost routine. On any given day, hundreds of spacecraft orbit our planet, relaying television images, tracking weather patterns, and enabling us to pay for our gasoline at the pump. We now have a space station the size of an airliner constantly inhabited with a three person crew and have sent space probes to every planet in our solar system except Pluto. We see wondrous images of distant planets, quasars and galaxies from our orbiting space telescopes. While the list of wondrous stories associated with space travel is almost endless, it is hard to imagine that a little over 100 years ago, no human had flown even one foot off the ground in a powered vehicle. In fact, scientists of the day debated whether space travel would even be possible since, as some argued, "There was no air for the rocket motor propellant to push against to impart thrust." We now realize as Sir Isaac Newton did centuries earlier how specious this argument was. However, it is important to realize how rapidly the field of rocket propulsion developed from a largely ineffective weapon to what it is today. As early as the first decade of the 20th century, rocket pioneers speculated about using electricity to power spacecraft. But the late Ernst Stuhlingera member of Wernher von Braun’s legendary team of German rocket scientists that spearheaded

the U.S. space program-finally turned the concept into a practical technology in the mid-1950s. A few years’ later engineers at the NASA Glenn Research Center (then known as Lewis) built the first operating electric rocket. That engine made a

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suborbital flight in 1964 onboard Space Electric Rocket Test 1, operating for half an hour before the craft fell back to Earth. In the meantime, researchers in the former Soviet Union worked independently on concepts for electric rockets. Since the 1970s mission planners have selected the technology because it can save propellant while performing such tasks as maintaining the attitude and orbital position of telecommunications satellites in geosynchronous orbit.

CHAPTER 3 ROCKET EQUATION Space missions are characterized by the kinetic energy (velocity) a vehicle must achieve to reach a destination. For example, an object must reach a velocity of roughly 8 km/s (18,000 mph) to reach Earth orbit. If an object is to escape from the Earth's gravitational influence and enter interplanetary space (e.g., for a trip to Mars), the object must be accelerated to a velocity of at least 11 km/s (25,000 mph). Therefore, when NASA sends probes to deep space, these vehicles must be accelerated to velocities in excess of 11 km/s. Today, large rockets are used to propel probes to these speeds. However, the faster the desired speed of the probe (e.g., to reach a distant planet such as Pluto in a "reasonable" amount of time), the smaller the probe must be. To understand the reason behind this, one must consider the so-called Rocket Equation, perhaps first developed by Ziolkovsky in Russia.

 

 



 

The Rocket Equation relates the vehicle mass prior to engine operation (initial mass, M i ), when the vehicle is full of the propellant it will use to accelerate to its final velocity (ΔV ), the final mass of the vehicle ( M f ), and the exhaust velocity of

the propulsion system (U e). The equation shows that the mass ratio (M f /M ) i decreases

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exponentially with the ratio of ΔV over the propellant exhaust velocity, which means that for ΔV s larger than U e, most of the initial mass of the vehicle is propellant.

CHAPTER 4 COMPARISON OF ELECTRIC AND CHEMICAL ROCKETS $10,000 is roughly what it costs to send a pound (0.45 kilogram) of payload Earth orbit with conventional rocket boosters. This high price tag is one reason engineers go to great lengths to shave as much mass from spacecraft as is feasible. The fuel and its storage tank are the heaviest parts of a vehicle powered by a chemical rocket.

Fig. 1: Velocity comparison( [1] )

To travel to Mars from low-Earth orbit requires a delta-v of about 4.5 km/s. The rocket equation says that a conventional chemical rocket would require that more than two thirds of the spacecraft’s mass be propellant to carry out such an

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interplanetarytransfer. For more ambitious trips-such as expeditions to the outer planets, which have delta requirements that range from 35 to 70 km/s- chemical rockets would need to be more than 99.98 percent fuel. That configuration would leave no space for other hardware or useful payloads. As probes journey farther out into the solar system, chemical rockets become increasingly useless-unless engineers can find a way to significantly raise their exhaust speeds.

CHAPTER 5 PLASMA PROPULSION A plasma propulsion engine is a type of Ion thruster which uses plasma in some or all parts of the thrust generation process. Even though less powerful than conventional rocket engines, plasma engines are able to operate at higher efficiencies and for longer periods of time. Plasma engines are better suited for longdistance interplanetary space travel mission. Plasma propulsion systems, in contrast, offer much greater exhaust speeds. Instead of burning chemical fuel to generate thrust, the plasma engine accelerates plasmas-clouds of electrically charged atoms or moleculesto very high velocities. Plasma is produced by adding energy to a gas, for instance, by radiating it with lasers, microwaves or radio-frequency waves or by subjecting it to strong electric fields. The extra energy liberates electrons from the atoms or molecules of the gas, leaving the latter with a positive charge and the former free to move freely in the gas, which makes the ionized gas a better electrical conductor than copper metal. Because plasmas contain charged particles, whose motion is strongly affected by electric and magnetic fields, application of electric or electromagnetic fields to plasma can accelerate its constituents and send them out the back of a vehicle as thrust-producing exhaust. The necessary fields can be generated by electrodes and magnets, using induction by external antennas or wire coils, or by driving electric currents through the plasma.

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The electric power for creating and acceleratingthe plasmas typically comes from solar panels that collect energy from the sun. But deep-space vehicles going past Mars must rely on nuclear power sources, because solar energy gets too weak at long distances from the sun. Today’s small robotic probes use thermoelectric devices

heated by the decay of a nuclear isotope, but the more ambitious missions of the future would need nuclear fission (or even fusion) reactors. Any nuclear reactor would be activated only after the vessel reached a stable orbit at a safe distance from Earth. Its fuel would be secured in an inert state during liftoff. Three kinds of plasma propulsion systems have matured enough to be employed on longdistance missions.

5.1ION DRIVE An ion

thruster is

a

form

of electric

propulsion used

for spacecraft

propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and accelerate the ions in the direction of the electric field. Electromagnetic ion thrusters use the Lorentz force to accelerate the ions. The term "ion thruster" by itself usually denotes the electrostatic or gridded ion thrusters. In its most common incarnation, the ion engine gets its power from the photovoltaic panels. Gridded electrostatic ion thrusters commonly utilize xenon gas. This gas has no charge and is ionized by bombarding it with energetic electrons. These electrons can be provided from a hot cathode filament and when accelerated in the electrical field of the cathode, fall to the anode. Alternatively, the electrons can be accelerated by the oscillating electric field induced by an alternating magnetic field of a coil, which results in a self-sustaining discharge and omits any cathode (radiofrequency ion thruster).

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The positively charged ions are extracted by an extraction system consisting of 2 or 3 multi-aperture grids. After entering the grid system via the plasma sheath the ions are accelerated due to the potential difference between the first and second grid (named screen and accelerator grid) to the final ion energy of typically 1-2 keV, thereby generating the thrust.

Fig. 2: Ion thruster( [1] )

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Ion thrusters emit a beam of positive charged xenon ions only. To avoid charging-up the spacecraft, another cathode is placed near the engine, which emits electrons (basically the electron current is the same as the ion current) into the ion beam. This also prevents the beam of ions from returning to the spacecraft and thereby cancelling the thrust. Dozens of ion drives are currently operating on commercial spacecraft mostly communication satellites, in geosynchronous orbit for orbital station-keeping and attitude control. They were selected because they save millionsof dollars per spacecraft by greatly shrinkingthe mass of propellant that would berequiredfor chemical propulsion.

5.2 HALL THRUSTER The essential working principle of the Hall thruster is that it uses an electrostatic potential to accelerate ions up to high speeds. In a Hall thruster the attractive negative charge is provided by electron plasma at the open end of the thruster instead of a grid. A radial magnetic field of a hundred gauss (about 100 – 300 G, 0.01 – 0.03 T) is used to confine the electrons, where the combination of the radial magnetic field and axial electric field cause the electrons to drift azimuthally, forming the Hall current from which the device gets its name. An electric potential between 150 and 800 volts is applied between the anode and cathode. The central spike forms one pole of an electromagnet and is surrounded by an annular space and around that is the other pole of the electromagnet, with a radial magnetic field in between. The propellant, such as xenon gas, is fed through the anode, which has numerous small holes in it to act as a gas distributor. Xenon propellant is used because of its high atomic weight and low ionization potential. As the neutral xenon atoms diffuse into the channel of the thruster, they are ionized by collisions with high energy circulating electrons (typically 10 – 40 eV, or about 10% of the discharge

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voltage). Once ionized, the xenon ions typically have a charge of +1, though a small fraction (~20%) is +2.

Fig. 3: Hall thruster (Wikipedia)

The xenon ions are then accelerated by the electric field between the anode and the cathode. For discharge voltages of 300 V, the ions reach speeds of around 15 km/s for a specific impulse of 1,500 seconds (15 kN·s/kg). Upon exiting, however, the ions pull an equal number of electrons with them, creating a plume with no net charge. Compared to chemical rockets, the thrust is very small, on the order of 83 mN for a typical thruster operating at 300 V, 1.5 kW. For comparison, the weight of a coin like the U.S. quarter or a 20-cent Euro coin is approximately 60 mN. As with all forms of electrically powered spacecraft propulsion, thrust is limited by available power, efficiency, and specific impulse. Hall thrusters operate at the high specific impulses that are typical of electric propulsion. This allows for much smaller thrusters compared to gridded ion

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thrusters.Another advantage is that these thrusters can use a wider variety of propellants supplied to the anode, even oxygen, although something easily ionized is needed at the cathode.

5.3 MAGNETOPLASMADYNAMIC THRUSTER The Magnetoplasmadynamic (MPD) thruster (MPDT) is a form of electrically powered spacecraft propulsion which uses the Lorentz force (the force on a charged particle by an electromagnetic field) to generate thrust. It is sometimes referred to as Lorentz Force Accelerator (LFA) or (mostly in Japan) MPD arc jet. Generally, a gaseous fuel is ionized and fed into an acceleration chamber, where the magnetic and electrical fields are created using a power source. The particles are then propelled by the Lorentz force resulting from the interaction between the current flowing through the plasma and the magnetic field (which is either externally applied, or induced by the current) out through the exhaust chamber. Unlike chemical propulsion, there is no combustion of fuel. As with other electric propulsion variations, both specific impulse and thrust increase with power input, while thrust per watt drops. There are two main types of MPD thrusters, applied-field and self-field. Applied-field thrusters have magnetic rings surrounding the exhaust chamber to produce the magnetic field, while self-field thrusters have a cathode extending through the middle of the chamber. Applied fields are necessary at lower power levels, where self-field configurations are too weak. Various propellants such as xenon, neon, argon, hydrogen, hydrazine, and lithium have been used, with lithium generally being the best performer. An MPDT consists of a central cathode sitting within a larger cylindrical anode. A gas, typically lithium, is pumped into the annular space between the cathode and the anode. There it is ionized by an electric current flowing radially from the cathode to the anode. This current induces an azimuthal magnetic field (one that encircles the central cathode), which interacts with the same current that induced it to generate the thrust-producing Lorentz force.

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Fig. 4: Magnetoplasmadynamic thruster( [1] )

A single MPD engine about the size of an average household pail can process about a million watts of electric power from a solar or nuclear source into thrust (enough to energize more than 10,000 standard light bulbs), which is substantially larger than the maximum power limits of ion or Hall thrusters of the same size. An MPDT can produce exhaust velocitiesfrom 15 to 60 km/s. This design also offers the advantage of throttling; its exhaust speed and thrust can be easily adjusted by varying the electric current level or the flow rate of the propellant. Throttling allows a mission planner to alter a spacecraft’s engine thrust and exhaust velocity as needed to optimize its trajectory.

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In theory, MPD thrusters could produce extremely high specific impulses (I sp) with an exhaust velocity of up to and beyond 110,000 m/s, triple the value of current xenon-based ion thrusters, and about 20 times better than liquid rockets. MPD technology also has the potential for thrust levels of up to 200 newtons (N) by far the highest for any form of electric propulsion, and nearly as high as many interplanetary chemical rockets. This would allow use of electric propulsion on missions which require quick delta-v maneuvers (such as capturing into orbit around another planet), but with many times greater fuel efficiency. Due to imperfect acceleration and phenomena like late-time ablation and particulate emission, pulsed MPD thrusters often suffer from low thrust efficiency. A better understanding of the ablation processes, especially the ionization, might yield valuable information to improve the propulsion system in terms of efficiency, thus enabling

more

payloads

on

the

satellite.

To

investigate the

phenomena

occurringwithin the plasma during the discharge and the influence of the thruster properties, high-speed camera observations were used.

5.3.1 EXPERIMENTAL SETUP AND EQUIPMENTS Pulsed MPD thruster Experiment was conducted using the pulsed MPD thrustercalled ADD SIMP LEX (Advanced

Stuttgart

ImpulsingMagnetoPlasmadynamicthruster

for

Lunar

Exploration) shown in Fig. 5.

Fig. 5: Setup of ADD SIMP-LEX( [2] )

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A total capacitance of 80 μF at a maximum voltage of 1300V allow for a

maximum stored energy of 68 J. Solid Teflonis used as propellant in the so-called side-fed configuration. The main discharge is triggered by a semiconductor spark plugmounted in the cathode. After the initial spark, the energy stored in the ca pacitors isreleased forming a high-current arc across the surface of the propellant thereby creating Tefloplasma. Vacuum conditions for near-space environments areachieved by a vacuum chamber with a pump system capableof a throughput of 2.2 ×10-3 Pa m3/s at 0.01 Pa. Discharge voltage and current measurements are conductedin parallel to link the oscillation behavior of the thrusterscircuit to the plasma observations Fig. 7 shows typicaldischarge progressions of the two properties whereas a picture of the plasma in the visible spectrum is given in Fig. 6.

Fig. 6: Exemplary image of the discharge plasma( [2] )

Fig. 7: Typical progression of discharge voltage and current( [2] )

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Measuring the discharge current and voltage gives information about the oscillation behavior and thepeak currents occurring during the breakdown. These information are evident, as they enable a judgment,whether a plasma propelled thruster is well optimized and efficiently working. For the sake of better visibility, only selected voltages are shown. It is obvious that an increase in discharge voltage yields a less-damped oscillation. This is linked to a second or even third plasma creation and acceleration. As energy increases, the current density in the discharge space varies, and further plasma can be created. Introducing more capacitors increases not only the capacitance, but also changes the circuit resistance and inductance of the thruster. Hence, a more damped oscillation can be observed in this configuration. Due to the higher damping, the peak value of the discharge current increases only by a factor of 2.5 than compared to the 4-times higher energy stored in the capacitor bank, leading to a maximum value of 25 kA at the 68 J configuration. Introducing more capacitors is not only affecting the capacitance of the system, but also introduces inductance and resistance influencing the damping coefficient and the plasma creation. Here the voltage tends to become negative which means that there is a change in polarity. This phenomenon is caused due to oscillating behavior of the thruster. The negative part of the current waveform does not significantly contribute to the thrust creation as almost no charged particles are created and accelerated, but only a neutral plasma fraction is formed.

High-speed camera experimentation To enable an insight into the plasma propagation during theshort-time discharge, a DRSHadland Ltd. Ultra-8 high-speedcamera together with a Nikon 85mm f/1.8 lens was applied.With this setup, eight pictures having a resolution of 520 ×520 pixel are taken with a typical exposure time of 100 ns andframe speed of 5

Mfps. As brightness of the emission changestremendously during the discharge due to the strong variationin discharge current, adjustments in aperture of the lens, andgain of the CCD camera sensor are done to keep brightnessalmost constant.The camera is triggered by a photo detector, i.e., recordingof the pictures takes place after the initial

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spark of the igniter.Due to hardware delays, the initial few 100 ns of the dischargecannot be visualized with this system. However, as the viewon the plasma creation is blocked by the opaque propellantbars, no information on the actual plasma propagation is lost. Pictures of the propagating plasma were taken for discharge voltages of 500, 900 and 1300 V respectively. 8 frames could be recorded per pulse and were triggered in a time difference of 200 ns. As pulses and triggering of the camera are reproducible, the delay of the camera was adjusted to register the entire plasma phenomenon. Fig.8shows a benchmark selection of these plasma pictures. Colour was added to the usually black-and-white images for the sake of visibility. In all three cases, the propagation of thecreated plasma can be seen during the first few microseconds whereas the brightness and the illumination decrease rapidly after the peak in discharge current and, thus, at 4 to 5 μs after plasma creation most part of the

inter- electrode space is not strongly illuminated. After the first 5 μs, almost no light is emitted anymore because the discharge

current has already past its maximum at that time, and the following current density is not sufficient to yield ionized particles. Nevertheless, neutral particles are ablated and propagated by thermal expansion, and light is then emitted by the excited matter even after the discharge current ceases. A distinct current sheet of about 2 mm thickness could be observed for this part of the plasma, as acceleration forces do not distort the sheet to a diffuse one.The pictures further show clearly a strong plasma canting effect, observed in other thrusters before. The current sheet itself is not distinguishable in the images,however, as no plasma is created in front of the current sheet, the border of plasma illumination can be estimated as being the current sheet position.As the plasma is not uniform, several points were traced throughout the pictures of the first few microseconds to derive an estimation of the velocity.

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Fig. 8. Pictures captured with high-speed camera at 3 voltage levels (ctd.) . ( [2] )

Fig. 8: Pictures captured with high-speed camera at 3 voltage levels.( [2] )

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Fig. 9: Propagation positions for different points for 500 V ( [2] )

Fig. 9 shows the results for the tracing within the 500 V images.From this propagation information a velocity of the plasma, and, hence, the current sheet can be drawn, and the results are summarized in Table 1.

Volt (V)

500

900

1300

Km/s

43.1

55.4

25.7

Table. 1: CurrentSheet Propagation Velocities, In KM/S( [2] )

The configuration using 900 V as a discharge voltage showed the highest velocity in the experiments whereas the highest energy input yielded the lowest current sheet velocity. This may be due to following reasons: a) Due to more capacitors (4 capacitors used for 1300V), more damped oscillation of voltage takes place. In the case of 1300V, as more number of capacitors are introduced, it not only affects the capacitance of the system,but also introduce inductance and resistance influencing the damping coefficient and also the plasma creation.Thus the energy required for the creation of plasma is more which results in difference in energy exchange within plasma.While anincrease in voltage to 900 V ameliorates this exchange, the

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additional plasma creation during the 1300 V case reduces the velocity again as more energy is going towards the ablation, dissociation and ionization of the propellant rather than accelerating the plasma out. Furthermore, it may be due to the electrical internal behavior of the plasma.Voltage difference is the driving force of electric propulsion, but it will not indicate propagation velocity as maximum when voltage has a maximum value. There will be an optimum potential difference above which if voltage tends to increase, the value of the velocity tends to decrease. b) As voltage is applied, temperature and energy of molecules increases. Around 900-940V, there will be a non-uniform distribution of temperature. Thus molecules have different states of energy and random collision takes place and thus the velocity increases. In a thruster it is always important to have the V/D ratio (V is the applied voltage and D is the distance between the electrode and anode) constant. Due to oscillation behavior and high plasma creation, there will be small change in D in terms of microns. When this distance increases to a level, the intensity of discharge decreases thereby reducing the density of plasma formation hence thrust decreases thereby the velocity decreases.

A maximum current sheet velocity was found for an energy level different to the highest bank energy, but the mean exhaust velocity, as an average of all accelerated particles independent of their charge, crests at maximum energy. Estimations of the degree of ionization and the relative number densities might yield to a full picture of the plasma creation process. As for the satellite mission, the results suggest the application of the highest energy level to consume the propellant most efficiently.The results of these studies can eventually be used to obtain a numerical model suitable for performance prediction and thruster optimization.

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CHAPTER 6 LATEST DEVELOPMENTS Much as the fabled slow and steady tortoise beats out the intermittently sprinting hare, in the marathon flights that will become increasingly common in the present era of deep-space exploration. So far the most advanced designs could impart a delta-v of 100 km/s — much too slow to take a spacecraft to the far-off stars but plenty enough to visit the outer planets in a reasonable amount of time. One particularly exciting deepspace mission that has been proposed would return samples from Saturn’s largest moon, Titan, which space scientists believe has an

atmosphere that is very similar to Earth’s eons ago. A sample from Titan’s surface would offer researchers a rare chance to search for signs of chemical precursors to life. The mission would be impossible with chemical propulsion. And with no incourse propulsion, the journey would require multiple planetary gravity assists, adding more than three years to the total trip time. A probe fitted with the little plasma engine that would be able to do the job in a significantly shorter period.

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CHAPTER 7 CONCLUSION Ion, Hall and MPD thrusters are but three variants of electric plasma rocket technology. During the past few decades researchers have developed many other promising related concepts to various degrees of readiness.Some are pulsed engines that operate intermittently; others run continuously. Some generate plasmas through electrode-based electric discharge; others use coil-based magnetic induction or antenna-generated radiation. The mechanisms they apply to accelerate plasmas vary as well, some use Lorentz forces; others accelerate the plasmas by entraining them in magnetically produced current sheets or in traveling electromagnetic waves. One type even aims to exhaust the plasma through invisible ―rocket nozzles‖ composed of

magnetic fields. In all cases, plasma rockets will get up to speed more slowly than conventional rockets. And yet, in what has been called the ―slower but faster paradox,‖ they can often make their way to distant destinations more quickly by

ultimately reaching higher spacecraft velocities than standard propulsion systems can using the same mass of propellant. They thus avoid time-consuming detours for gravity boosts.

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REFERENCES [1] Edgar Y. Choueiri-“Efficient electric plasma engines are propelling the next generation of space probes to the outer solar system”. -SCIENTIFIC

AMERICAN 2011, INC, 58-65. [2] Tony Sch¨onherr, KimiyaKomurasaki, and Georg Herdrich-“Study on Plasma

Creation

and

Propagation

in

a

Pulsed

MagnetoplasmadynamicThruster”-WORLD ACADEMY OF SCIENCE,

ENGINEERING AND TECHNOLOGY 74 2011, 563-569. [3] DanM. Goebel and Ira Katz. Wiley , -“ Fundamentals of Electric Propulsion: Ion and Hall Thrusters.” 2008,124-131.

[4] Tony Schönherr et al.,- Evaluation of discharge behavior of pulsed “

plasma thruster SIMP-LEX ‖July 2010, 25-28.

[5] http://www.stanford.edu/group/pdl/EP/EP.html [6] http://www.nasa.gov [7] http://en.wikipedia.org [8] http://www.princeton.edu/~achaney/Magnetoplasmadynamic_thruster

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Plasma Propelled Rocket Engines

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