Seminar Report - Copy Xenon Ion As A Fuel In Rocket Engine .docx

Mahatma Gandhi Mission’s College of Engineering and Technology Noida, U.P., India

Seminar Report On

" Recent Development In Xenon Ion As A Fuel In Rocket Engine" As

Part of B. Tech Curriculum Submitted by: Anupam kumar Singh V Semester 1509540014 Under the Guidance of: Mr. Ram Prakash Associate Professor MGM COET, Noida

(Seminar Coordinator) Mr. Ram Prakash Department,

Submitted to: HOD Mechanical Engineering MGM COET, Noida

Mahatma Gandhi Mission’s College of Engineering and Technology Noida, U.P., India

Department of Mechanical Engineering

CERTIFICATE

This is to certify that Mr. Anupam kumar singh B. Tech. Mechanical Engineering, Class TT-ME and Roll No.

1509540014

seminar on the topic "Recent Development

has delivered

In Xenon Ion As A

Fuel In Rocket Engine". His seminar presentation and report during the academic year 2016-2017 as the part of B. Tech Mechanical Engineering curriculum was good.

(Guide)

(Seminar coordinator)

(Head of the Department)

Acknowledgement I would like to express my deep sense of gratitude to my supervisor Mr. Ram Prakash sir, Professor, Mechanical Engineering Department, M.G.M. College of Engineering and Technology, Noida, India, for his guidance, support and encouragement throughout this project work. Moreover, I would like to acknowledge the Mechanical Engineering Department, M.G.M. College of Engineering and Technology, Noida, for providing me all possible help during this project work. Moreover, I would like to sincerely thank everyone who directly and indirectly helped me in completing this work.

(Anupam kr Singh )

Abstract Ion propulsion is one of the latest advances in spaceflight propulsion. Rather than ejecting a relatively large amount of mass over a short period of time to create thrust, an ion propulsion engine ejects individual atoms at velocities 5-30 times higher s, over a much longer period of time (days, weeks, or longer). This type of thrust eventually will propel the spacecraft to much larger velocities than that obtained by traditional engines. Ion propulsion is currently one of the best answers to long distance missions, and, ironically, is also very well suited for small attitude adjustment thrusting, because of the extremely low impulse of the thrust. This project compares a mission to Saturn using traditional propulsion with an identical mission using ion propulsion. It was determined that for this mission, ion propulsion used 98% less fuel than conventional propulsion, but took nearly 50% longer. Solar powered ion propulsion engines use energy from the sun (gathered through solar panels) to accelerate the ejected atoms. Using specifications from Deep Space 1 (DS1), NASA’s first ion propelled spacecraft, it was found that DS1 was must remain with 630 million km of the sun if it is to receive enough solar energy to power its ion drive.

CONTENTS PAGES Certificate Acknowledgements Abstract

ii iii iv

Table of Contents List of figure CHAPTER 1. INTRODUCTION 1.1- History

v vi

CHAPTER 2. ION PROPULSION SYSTEM 2.1- Ion propulsion system 2.1.1 - working of ion propulsion engine 2.1.2 - problem of interest 2.1.3 - range of ion propulsion CHAPTER 3. ION PROPULSION TYPES 3.1 - current ion propulsion 3.2 - future ion propulsion CHAPTER 4. ION THRUSTER 4.1 - performance 4.2 - tests 4.3 - status CHAPTER 5 NASA's innovative ion space thruster sets endurance world record CHAPTER 6 Ion propulsion : farther, faster, cheaper CHAPTER 7. ION THRUSTER OPERATION Conclusion References

LIST OF FIGURE

CHAPTER 1 . INTRODUCTION Electric blue, that's the colour of NASA's latest high-tech spaceship engine, which uses xenon ions instead of a rocket blast. The stunning blue glow comes from photons released by the ions as they lose energy upon leaving the engine. The solar-electric propulsion thruster ditches burning chemical fuel for xenon ions accelerated by an electric field generated using solar panels. This provides a steady stream of ions that can slowly nudge a spacecraft to high speeds with minimal fuel, making it a good choice for long-range missions. NASA Explains "Since the ions are generated in a region of high positive and the accelerator grid's potential is negative, the ions are attracted toward the accelerator grid and are focused out of the discharge chamber through the

apertures, creating thousands of ion jets. The stream of all the ion jets together is called the ion beam. The thrust force is the force that exists between the upstream ions and the accelerator grid. The exhaust velocity of the ions in the beam is based on the voltage applied to the optics".xenon-ion propulsion engine, and instead of using rocket fuel, it harnesses magnetic fields to create thrust. Ion engines will be fuel-efficient and more suited for space travel. And indeed, NASA plans to launch an ion-powered unmanned spacecraft to capture a small asteroid and re-locate it in the moon’s neighborhood. Afterwards, a spacewalking team will get to it via the Orion space capsule currently under development. NASA hopes to retrieve the asteroid in 2019 and explore it in 2021. This is all in preparation of larger, more important missions, including a trip to Mars. In addition, ion engines could be power spacecraft capable of redirecting incoming asteroids. Also called a solar-electric ion propulsion engine or Hall effect thruster, it’s powered by an inert and odorless xenon gas. Space is the only frontier where man’s exploration is limited by speed. Even if all other hurdles to life in space are overcome, such as unfriendly atmospheres, changes in gravity, irate aliens, etc, the immense distances of space will still require large amounts of time to travers. time that may span multiple human lifetimes. Consider a trip to Mars- With current chemical propulsion and a simple Hohmann-type transfer, the voyage would take nine months! And what about a truly distant planet? It takes LIGHT over five hours to reach Earth from Pluto- a trip that could take a current spacecraft decades. It is obvious that “time is of the essence” in space exploration, but what can be done? Short of mathematicians and physicists “folding” time and space, our best bet is to create spacecraft that can travel faster. And faster. And faster.

Unfortunately, increasing flight speed through space is not as easy as just “stepping on the gas”- we are limited by the laws of physics. The law of conservation of momentum and Newton’s 3 rd law tell us that the mass of a spacecraft’s exhaust (M se) multiplied by the velocity of that exhaust (V e ) must equal the mass of the rocket (or spacecraft) (M s ) multiplied by the velocity of the spacecraft (V s ). Simply put, the force required to push the exhaust out the back of the spacecraft is the same force that pushes the spacecraft forward. Conventional rockets exhaust large masses at relatively slow velocities- the Saturn V rocket used for launching the Apollo missions burned 16000 kilograms of fuel every second, with an exhaust velocity of approximately 3000 m/s. An ion propulsion engine, however, emits individual ions at speeds approaching 30000 m/s. However, because the actual mass exhausted is very small, the spacecraft accelerates very slowly. As an example, consider Deep Space 1, which is the first spacecraft to use ion propulsion as its main propulsion source. Its ion engine provides a thrust which can vary between 20 and 92 milli-newtons, which is about as much force as the weight of a piece of paper on one’s hand! Because of this low thrust, ion engines are obviously impractical for launching from Earth- in practice, ion engines begin thrusting only after the spacecraft is in space. Over time (a period of months, or even years) however, the ion thrusters can propel the spacecraft to speeds far greater than that reached by traditional chemical propulsion. Ion engines have another key application- because of their low thrust, they work wonderfully for attitude corrections. They can orient a spacecraft very slowly, taking less of a toll on the onboard instruments, and allowing for very precise attitude adjustments. CHAPTER 2 . ION PROPULSION SYSTEM 2.1- Ion propulsion system 2.1.1- How does an ion propulsion system work? Ions must be created before they can be expelled. To do this, a plasma (typically xenon, because it is relatively stable and is over 4 times heavier than air) is bombarded with electrons emitted from a cathode. When an electron strikes a xenon atom, it knocks away one of the atom’s electrons, resulting in a positively charged xenon ion. An electric field is created in the rear of the xenon chamber using a pair of positively and negatively charged metal grids. The xenon atom accelerates through this electric field, and is ejected from the spacecraft- imparting an equal and opposite force to the spacecraft as it leaves. To prevent the ion from being attracted back to the spacecraft (and therefore negating any thrust it provided) a stream of electrons is directed into the exhaust to neutralize the ions.

2.1.2- PROBLEMS OF INTEREST Ion propulsion seems to be the propulsion of the future but how much of an improvement is it really. To find out, compare two missions to Saturn- one using conventional chemical rockets; the other using ion propulsion. As the goal of this project is to compare the two propulsion systems over a long distance, not to design the quickest or most elegant mission possible, a simple Hohmann transfer from the Earth’s orbit to Saturn’s will be used. This will simplify calculations considerably. Another benefit of comparing Hohmann transfers is that a Hohmann transfer is the most efficient transfer possible (in terms of fuel used). If ion propulsion can accomplish the same mission in less time, using even less fuel than that used in a chemically- propulsed Hohmann transfer, it will be a breakthrough indeed. The orbit determination was done through Satellite Tool Kit (STK). The semimajor axis of the initial orbit of the satellite was chosen to be 180,000,000 km. Because ion propulsion does not produce enough thrust for launch, the satellite must be launched into a “parking” orbit with chemical rockets before it can use the ion propulsion system. A 180,000,000 km orbit was chosen because it gets the satellite far enough away from the earth that it does not need to orbit Earth many times before it gains enough velocity to head to Saturn (more on this later). The Targeting feature in STK was used to determine the transfer orbit. Using the ΔV as the control variable, and the semi-major axis of Saturn’s orbit as the constraint, STK’s numerical integrator found the impulsive ΔV without any problem. Determining the orbit when the ion propulsion was used (a finite maneuver) was not so simple. The perturbation technique used by STK to determine an orbit through the Targeting feature requires a very accurate initial guess (or nominal value) for the control variable. As the ion drive was to be modeled as a constant thrust over a variable amount of time, the time thrusting was used as the perturbation. After determining the impulsive ΔV necessary for the transfer, the estimated burn time (as reported by STK) was used as the initial guess for the burn time in the finite transfer. This guess was close enough for STK to converge and solve the orbit… provided the engine used was the same as that used in the impulsive ΔV burn! As the ion engine has a thrust 4 orders of magnitude smaller than that of the engine used in the impulsive ΔV burn, a guess-and-check method was adopted to find initial burn time values for the ion engine. A different engine was created, with half the thrust and twice the specific impulse (Isp) of the Impulsive ΔV engine, and a burn time was guessed for this new engine. This “halving” of the engines was done eight times, until the values for the ion engine were reached (the guess for the burn time was generally about twice the burn time of the previous engine). The orbit, burn time, and fuel consumed was calculated for each intermediate engine by STK. The values are in Table 2. For the engines 1-3, a fuel mass of

above 5000kg was needed- nearly 15000 kg for the impulsive ΔV engine 1 (which is the type of engine typically used today). The spacecraft left the parking orbit on 1 January 2001. It can be seen from Table 2 that nearly all of the engines reached Saturn in approximately 7.5 years, except for the ion engine, which took almost 3 years longer. Bear in mind that chemical engines typically only attain an Isp of 3000, so engines 5-8 are only theoretical. Engine 8 looks to be the best bet- it arrives at Saturn within a month of the chemically propulsed spacecraft, but requires less than 2 % as much fuel as the traditional chemical rockets! (Engines 1 and 2). Though ion propulsion is not yet this “powerful”, Deep Space 4 is planned to have four ion propulsion drives, which will bring the total thrust capability closer to that of Engine 8. It is obvious that ion propulsion may not be the best way to transport people to Mars- its real benefit comes with truly “deep space” missions. The faster a spacecraft goes, the more energy is needed to accelerate it- i.e. it takes much less energy to accelerate a satellite from 9 to 10km/s than it does to accelerate the same satellite from 29 to 30 km/s. This was especially apparent when propagating the orbit in STK for Engine 1, which is a traditional chemical engine. The satellite was initially given 10000kg of fuel, but STK determined that the satellite needed just 200 more kg to complete the orbit. Therefore, the fuel was increased to 11000 kg- but that added another 1000kg that had to pushed through space until it was used, so the satellite now needed 11100 kg to complete the transfer. After giving the satellite 12000 kg, it was determined to need just a little more- and on and on up to 15000kg, which barely satisfied the fuel needs. The diminishing returns of a kg of fuel are due largely to the amount of fuel still left, which must be accelerated along with the spacecraft. This inefficiency is minimized by carrying less fuel mass- a task which ion propulsion performs admirably. To go the same distance, ion propulsion needed only 25kg of fuel, vs. the 15000 required for chemical propulsion. This is a fuel savings of 98%, not including the enormous costs to launch 15000kg from Earth! Compare the orbit pictures from Engine 1 (the traditional propulsion) with that of Engine 9 (ion propulsion). In the case of the ion propulsion, the satellite nearly completes an entire orbit around the sun (about 1 year) before it has enough velocity to head for Saturn. This is typically how low thrust orbits will look - they orbit for long periods of time, gradually building speed and increasing the radius of their orbit, before reaching escape velocity. The following links show this happening. They represent a spacecraft orbiting the earth with a radius of 10080km, before undergoing a ΔV over a period of time to increase the radius of orbit to 11080 (a 1000km change). The orbit is green initially, yellow while the engine is burning, and magenta after the engines have stopped. Note - how the spacecraft slowly gains velocity and spirals outward toward its intended orbit. For “deep space” missions, this time “wasted” while the satellite

goes ‘round and ‘round is made up for over great distances by the vastly increased velocity obtained. 2.1.3 - What Is The Range Of Ion Propulsion? As mentioned in the introduction, ion propulsion engines accelerate atoms by first ionizing them, then accelerating them through an electric field. There are currently two ways for the engines to get the power necessary for these tasks- by solar arrays or nuclear power. Solar arrays convert energy from the sun into electricity to be used by the engine, while nuclear powered engines use radiation energy from a nuclear plant onboard the spacecraft. Nuclear power is potentially harmful (radioactive fallout from a spacecraft explosion above a densely populated residential area is, of course, the greatest fear!) but they have the benefit of being able to provide energy even after the spacecraft is so far away that it can no longer receive enough energy from the sun. CHAPTER 3. NASA -ION PROPULSION Ion thrusters are being designed for a wide variety of missions—from keeping communications satellites in the proper position ( station -keeping) to propelling spacecraft throughout our solar system. These thrusters have high specific impulses—ratio of thrust to the rate of propellant consumption, so they require significantly less propellant for a given mission than would be needed with chemical propulsion. Ion propulsion is even considered to be mission enabling for some cases where sufficient chemical propellant cannot be carried on the spacecraft accomplish the desired missions.so It also is inert and has a high storage density; therefore, it is well suited for storing on spacecraft. In most ion thrusters, electrons are generated with the discharge cathode by a process called thermionic emission. Electrons produced by the discharge cathode are attracted to the dis- charge chamber walls, which are charged to high positive potential by the voltage applied by the thruster’s discharge power supply. Neutral propellant is injected into the discharge chamber, where the electrons bombard the propellant to produce positively charged ions and release more electrons. High-strength magnets prevent electrons from freely reaching the discharge channel walls. lengthens the time that electrons reside in the discharge chamber and increases the probability of ion. The positively charged ions migrate toward grids that contain thousands of very precisely aligned holes ( apertures ) at the aft end of the ion thruster. The first grid is the positively charged electrode (screen grid). A very high positive voltage is applied to the screen grid, but it is configured to force the discharge plasma to reside at a high voltage. As ions pass between the grids, they are accelerated toward an accelerator grid ) to very high speeds (up to 90,000 mph).The positively charged ions

are accelerated out of the thruster as an ion beam, which produces thrust. The neutralizer, another hollow cathode, expels an equal amount of electrons to make the total charge of the exhaust beam neutral. Without a neutralizer, the spacecraft would build up a negative charge and eventually ions would be drawn back to the spacecraft, reducing thrust and causing The primary parts of an ion propulsion system are the ion thruster, power processing unit (PPU),propellant management system (PMS), and digital control and interface unit (DCIU). The PPU converts the electrical power from a power source—usually solar cells or a nuclear heat source—into the voltages needed for the hollow cathodes to operate, to bias the grids,and to provide the currents

needed to produce the ion beam. The PMS may be divided into a high-pressure assembly (HPA) that reduces the xenon pressure from the higher storage pressures in the tank to a level that is then metered with accuracy for the ion thruster components by a low-pressure assembly (LPA). The DCIU controls and monitors . The NASA Glenn Research Center has been a leader in ion propulsion technology development since the late 1950s, with its first test in space— the Space Electric Rocket Test 1— flying on July 20, 1964. From 1998 to 2001, the NASA Solar Technology Application Readiness (NSTAR) ion propulsion system enabled the Deep Space 1 mission, the first spacecraft propelled primarily by ion propulsion, to travel over 163 million miles and make flybys of the asteroid Braille and the comet Borelly. 3.1 - Current Ion Propulsion Ion thrusters (based on a NASA design) are now being used to keep over 100 geosynchronous Earth orbit communication satellites in their desired locations, and three NSTAR ion thrusters that utilize Glenn-developed technology are enabling the Dawn spacecraft (launched in 2007) to travel deep into our solar system. Dawn is the first spacecraft to orbit two objects in the asteroid belt between Mars and Jupiter: the protoplanets Vesta and Ceres. 3.2 - Future Ion Propulsion As the commercial applications for electric propulsion grow because of its ability to extend the operational life of satellites and to reduce launch and operation costs, NASA is involved in work on two different ion thrusters: the NASA Evolutionary Xenon Thruster (NEXT) and the Annular Engine. NEXT, a high-power ion propulsion system designed to reduce mission cost and trip time, operates at 3 times the power level of NSTAR and was tested continuously for 51,000 hours (equivalent to almost 6 years of operation) in ground tests without failure, to demonstrate that the thruster could operate for the required duration of a range of missions. NASA Glenn recently awarded a contract to Aerojet Rocketdyne to fabricate two NEXT flight systems (thrusters and power processors) for use on a future NASA science mission. In addition to flying the NEXT system on NASA science missions, NASA plans to take the NEXT technology to higher power and thrust-to-power so that it can be used for a broad range of commercial, NASA, and defense applications. NASA Glenn’s patented Annular Engine has the potential to exceed the performance capabilities of the NEXT ion propulsion system and other electric propulsion thruster designs. It uses a new thruster design that yields a total (annular) beam area that is 2 times greater than that of NEXT. Thrusters based on the Annular Engine could achieve very high power and thrust levels, allowing ion thrusters to be used in ways that they have never been used before. The objectives are to reduce system cost, reduce system complexity, and enhance performance (higher thrust-to-power capability).

CHAPTER 4 . ION THRUSTER The NASA Evolutionary Xenon Thruster ( NEXT ) project at Glenn Research Center aims to build an ion thruster about three times as powerful as the NSTAR used on Dawn and Deep Space 1 spacecraft. NEXT affords larger delivered payloads, smaller launch vehicle size, and other mission enhancements compared to chemical and other electric technologies for Discovery, New Frontiers , Mars Exploration , and Flagship outer-planet exploration missions. Glenn Research Center manufactured the test engine's core ionization chamber, and Aerojet Rocketdyne designed and built the ion acceleration assembly. The first two flight units will be available in early 2019. 4.1 - Performance The NEXT engine is a type of solar electric propulsion in which thruster systems use the electricity generated by the spacecraft's solar panel to accelerate the xenon propellant to speeds of up to 90,000 mph (145,000 km/h or 40 km/s). NEXT can produce 6.9 kW thruster power and 236 mN thrust .It can be throttled down to 0.5 kW power, and has a specific impulse of 4190 seconds (compared to 3120 for NSTAR ). The NEXT thruster has demonstrated a total impulse of 17 MN·s; which is the highest total impulse ever demonstrated by an ion thruster. A beam extraction area 1.6 times that of NSTAR allows higher thruster input power while maintaining low voltages and ion current densities, thus maintaining thruster longevity. 4.2 - Tests In November 2010, it was revealed that the prototype had completed a 48000 hours (5.5 years) test in December 2009. Thruster performance characteristics, measured over the entire throttle range of the thruster, were within predictions and the engine showed little signs of degradation and is ready for mission opportunities. 4.3 - Status NASA was considering offering this ion thruster for the next Discovery Program mission to be chosen in September 2016.Proposed missions include placing an orbiter up to 4000 kg into Saturn orbit,or performing a sample return from Mars'

moon Deimos .But the first two flight units will not be available until early 2019, in time for use on a New Frontiers-4 mission. After that, it will be a commercial product for purchase by NASA and non-NASA customers. Aerojet Rocketdyne, and their major sub-contractor ZIN Technologies retain the rights to produce the system, known as NEXT-C for future commercialization. Dawn's futuristic, hyper-efficient ion propulsion system allows Dawn to go into orbit around two different solar system bodies, a first for any spacecraft. Meeting the ambitious mission objectives would be impossible without the ion engines. Ion propulsion was proved on NASA's Deep Space 1 mission, which tested it and11 other technologies while journeying to an asteroid and a comet. Each of Dawn's three 30-centimeter-diameter (12- inch) ion thrust units is movable in two axes to allow for migration of the spacecraft's center of mass during the mission. This also allows the attitude control system to use the ion thrusters to help control spacecraft attitude. Two ion propulsion engines are required to provide enough thruster lifetime to complete the mission, and the third engine serves as a spare. Since launch the spacecraft has used each of the three ion engines, operating them one at a time. Dawn will use ion propulsion with interruptions of only a few hours each week to turn to point the spacecraft's antenna to Earth. Total thrust time to reach the first science orbit will be 979 days, with more than 2,000 days of thrust through entire the mission. This surpasses Deep Space 1's 678 days of ion propulsion operation by a long shot. The thrusters work by using an electrical charge to accelerate ions from xenon fuel to a speed 7-10 times that of chemical engines. The electrical power level and xenon fuel feed can be adjusted to throttle each engine up or down in thrust. The engines are thrifty with fuel, using only about 3.25 milligrams of xenon per second (about 10 ounces over 24 hours) at maximum thrust. The Dawn spacecraft carried 425 kilograms (937 pounds) of xenon propellant at launch. Xenon was chosen because it is chemically inert, easily stored in a compact form, and the atoms are relatively heavy so they provide a relatively large thrust compared to other candidate propellants. At launch, the gaseous xenon stored in the fuel tank was 1.5 times the density of water. At maximum thrust, each engine produces a total of 91 millinewtons—about the amount of force involved in holding a single piece of notebook paper in your hand. You would not want to use ion propulsion to get on freeway — at maximum throttle, it would take Dawn's system four days to accelerate from 0 to 60 MPH. As slight as that might seem, over the course of the mission the total change in velocity from ion propulsion will be comparable to the push provided by the Delta II rocket that carried it into space — all nine solid-fuel boosters, plus the Delta's first, second and third stages. This is because the ion propulsion system will operate for thousands of days, instead of the minutes during which the Delta performs.

As the commercial applications for electric propulsion grow because of its ability to extend the operational life of satellites and to reduce launch and operation costs, NASA is involved in work on two different ion thrusters: the NASA Evolutionary Xenon Thruster (NEXT) and the Annular Engine. NEXT, a highpower ion propulsion system designed to reduce mission cost and trip time, operates at 3 times the power level of NSTAR and was tested continuously for 51,000 hours (equivalent to almost 6 years of operation) in ground tests without failure, to demonstrate that the thruster could operate for the required duration of a range of missions. NASA Glenn recently awarded a contract to Aerojet Rocketdyne to fabricate two NEXT flight systems (thrusters and power processors) for use on a future NASA science mission. In addition to flying the NEXT system on NASA science missions, NASA plans to take the NEXT technology to higher power and thrustto-power so that it can be used for a broad range of commercial, NASA, and defense applications. NASA Glenn’s patented Annular Engine has the potential to exceed the performance capabilities of the NEXT ion propulsion system and other electric propulsion thruster designs. It uses a new thruster design that yields a total (annular) beam area that is 2 times greater than that of NEXT. Thrusters based on the Annular Engine could achieve very high power and thrust levels, thrusters to be the objectives are to reduce system cost, reduce system complexity, and enhance performance (higher thrust-to-power capability). NASA Glenn’s continuing advancements will adapt ion thrusters for a broad range of missions to efficiently and reliably provide propulsion for NASA, commercial, and defense applications. Could ion propulsion work on Earth or does it work only in space? Basically, propulsion works by throwing stuff, usually hot gases, out of the back of something like a rocket or jet airplane that you are trying to speed up. The thrust, or how much something is pushing you, is equal to the amount of stuff

you are throwing out the back multiplied by how fast you are throwing those things. Then F= m*a propulsion is that in ion propulsion you are throwing little tiny amounts of stuff out the back at very high speeds but in conventional propulsion you are throwing huge amounts of stuff out the back at a slower speed. Ion rocket: Force = little tiny mass x BIG

ACCELERATION Normal rocket: Force = HUGE MASS x less acceleration Does that fact alone stop us from using ion propulsion on Earth? No, because you can speed up (accelerate) the little mass enough to produce enough force. The problem of getting a rocket into space is a different problem which engineers call power density . Power density is the amount of power an engine has divided by the weight of the engine. For example, the space shuttle's main engines have a power density of about 70 lbf/lb (70 pounds of force per pound) which means that for each pound of the engine it can lift 70 times its weight. On the other hand, the entire ion propulsion in DS1 can produce 92 mN of force which is "roughly" equivalent to the pulling power of a large beetle, like a cockroach, and DS1 weighs 489.5 kg. This is much less than 1 lbf/lb. The reason why ion engines work in space is because of two reasons: there is no friction in the vacuum of space to cause resistance and being far from planets limits the influence of gravity.

Because there is no friction then the small continuous pushes over long times will eventually speed up the ship. Gravity, which does exist in space, doesn't work to slow or stop the ship in the way it would on Earth. CHAPTER 5 5.1 - NASA’s NEXT ion drive breaks world record, will eventually power interplanetary missions Proving yet again that Star Trek was scarily prescient, NASA has announced that its NEXT ion drive NASA’s Evolutionary Xenon Thruster — has operated continually for over 43,000 hours (five years). This is an important development, as ion thrusters are pegged as one of the best ways to power long-term deep-space missions to other planets and solar systems. With a proven life time of at least five years, NEXT engines just made a molecules) out of a nozzle at high speed (pictured above). In the case of NEXT, operation is fairly simple. Xenon (a noble gas) is squirted into a chamber. An electron gun (think cathode ray tube TV) fires electrons at the xenon atoms, creating a plasma of negative and positive ions. The positive ions diffuse to the back of the chamber, where high-charged accelerator grids grabs the ions and propel them out of the engine, creating thrust. The energy to power the electron gun can either come from solar panels, or from a radioisotope thermoelectric generator (i.e. a nuclear battery, just like Curiosity ). The downside of ion thrusters, though, is that the amount of thrust produced is minuscule: State-of-the-art ion thrusters can deliver a grand total of 0.5 newtons of thrust (equivalent to the force of a few coins pushing down on your hand), while chemical thrusters (which power just about every spacecraft ever launched) on a satellite or probe deliver hundreds or thousands of newtons. The flip side of this, though and the reason ion thrusters are so interesting is that they have a fuel efficiency that’s 10 to 12 times greater than chemical thrusters. Obviously, for long trips through space, fuel efficiency is very important. With such puny thrust, a NEXT-based ion drive would need to run for 10,000 hours just over a year to reach a suitable speed for space travel. Dawn, a NASA probe that’s powered by previous-generation NSTAR ion thrusters, accelerated from 0 to 60 mph in four days. As a corollary, ion thrusters only work at all because of the near-vacuum of space; if there was any friction at all, like here on Earth, an ion drive would be useless. The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph). Moving forward, it now remains to be seen if NASA will use the NEXT on an actual spacecraft.

In 2011, NASA put out a request-for-proposals for a test mission that will likely use a NEXT engine, and presumably, following this successful engine test, we might soon hear more news about that. Other space agencies, including the ESA, are also working on spacecraft propelled by ion thrusters. 5.2 - NASA's Innovative Ion Space Thruster Sets Endurance World Record The next generation of ion engines have a fuel efficiency 10 to 12 times greater than traditional chemical thrusters. NASA A five-year test of NASA's latest ion drive for future spacecraft has set a new world record for the longest single space engine test. The space agency's Evolutionary Xenon Thruster (NEXT) project completed a continuous test the ion engine for more than 48,000 hours — over five and a half years — longer than any other space propulsion system ever tested. With low fuel weight and long-running efficiency, ion engines have become strong contenders for deep space missions. Spacecraft traveling through miles of space require energy to keep moving. Ion propulsion engines can help to minimize the bulkiness of fuel, allowing for increased scientific exploration in smaller packages.

Over the course of nearly six years, NEXT consumed only 1,900 pounds (860 kilograms) of fuel, compared to the 22,000 pounds (10,000 kg) a conventional rocket would burn to create the same momentum. Part of a class of solar electric propulsion (SEP) engines, NEXT bombards xenon with electrons, ionizing it. The ionized propellant is then focused out the back of the engine, creating a stream of ion jets known as an ion beam. The movement creates the thrust that moves the craft. Ion engines win out over traditional engines much like the tortoise defeated the hare. Though it takes more time to speed up, it is able to run longer than its competition. Charged particles from NEXT reached speeds of up to 90,000 miles per hour (144,841 km/h), making it ideal for deep space missions in particular. "SEP uses electricity, generated by solar panels, to power an electric thruster to propel spacecraft," principle investigator Michael Patterson of NASA's Glenn Research Center said in a statement. "Because it reduces the amount of propellant needed for a given mission, it greatly reduces the weight of the vehicle."

Less weight means less traditional propellant required to launch the craft into space — or more room for science.

Ion engines on NASA's Dawn mission , which traveled to the asteroid Vesta and is now headed toward the dwarf planet Ceres, enabled its team to include more scientific equipment than they would have managed on a traditionally-powered craft. Once the staple of science fiction, ion propulsion engines have made a slow influx in military, commercial, and civilian space programs. An ion engine propelled NASA's Deep Space 1 mission, launched in October 1998, demonstrating the engine's long duration. "The bottom line in space is to maximize the payload we deliver including potential missions in support of human operations and scientific payload," Patterson said. "We don't want to spend all our resources pushing propellant around. NEXT can fly huge payloads deep into space with super fuel efficiency." CHAPTER 6 6.1 - Ion Propulsion: Farther, Faster, Cheaper Ion thrusters, the propulsion of choice for science fiction writers have become the propulsion of choice for scientists and engineers at NASA. The ion propulsion system's efficient use of fuel and electrical power enable modern spacecraft to travel farther, faster and cheaper than any other propulsion technology currently available. Chemical rockets have demonstrated fuel efficiencies up to 35 percent, but ion thrusters have demonstrated fuel efficiencies over 90 percent. Currently, ion thrusters are used to keep communication satellites in the proper position relative to Earth and for the main propulsion on deep space probes. Several thrusters can be used on a spacecraft, but they are often used just one at a time. Spacecraft powered by these thrusters can reach speeds up to 90,000 meters per second (over 200,000 mph). In comparison, the Space Shuttles can reach speeds around 18,000 mph. The trade-off for the high top speeds of ion thrusters is low thrust (or low acceleration). Current ion thrusters can provide only 0.5 newtons (or 0.1 pounds) of thrust, which is equivalent to the force you would feel by holding 10 U.S. quarters in your hand. These thrusters must be used in a vacuum to operate at the available power levels, and they cannot be used to put spacecraft in space because large amounts of thrust are needed to escape Earth's gravity and atmosphere. To compensate for low thrust, an ion thruster must be operated for a long time for the spacecraft to reach its top speed. Acceleration continues throughout the flight, however, so tiny, constant amounts of thrust over a long time add up to much shorter travel times and much less fuel used if the destination is far away. Deep Space 1 used less than 159 pounds of fuel in over 16,000 hours of thrusting. Since much less fuel must be carried into space, smaller, lower-cost launch vehicles can be used.

6.2 - Propulsion Sir Isaac Newton's third Law states that every action has an equal and opposite reaction. This is like air escaping from the end of a balloon and propelling it forward. Conventional chemical rockets burn a fuel with an oxidizer to make a gas propellant. Large amounts of the gas push out at relatively low speeds to propel the spacecraft. Modern ion thrusters use inert gases for propellant, so there is no risk of the explosions associated with chemical propulsion. The majority of thrusters use xenon, which is chemically inert, colorless, odorless, and tasteless. Other inert gases, such as krypton and argon, also can be used. Only relatively small amounts of ions are ejected, but they are traveling at very high speeds. For the Deep Space 1 probe, ions were shot out at 146,000 kilometers per hour (more than 88,000 mph). 6.3 - Making Ions and Plasma Ion thrusters eject ions instead of combustion gases to create thrust: the force applied to the spacecraft that makes it move forward. An ion is simply an atom or molecule that has an electrical charge because it has lost (positive ion) or gained (negative ion) an electron. With ion propulsion, the ions have lost electrons, so they are positively charged. A gas is considered to be ionized when some or all the atoms or molecules contained in it are converted into ions. Plasma is an electrically neutral gas in which all positive and negative charges-from neutral atoms, negatively charged electrons and positively charged ions-add up to zero. Plasma exists everywhere in nature (for example, lightning and fluorescent light bulbs), and it is designated as the fourth state of matter (the others are solid, liquid and gas). It has some of the properties of a gas but is affected by electric and magnetic fields and is a good conductor of electricity. Plasma is the building block for all types of electric propulsion, where electric and/or magnetic fields are used to accelerate the electrically charged ions and electrons to provide thrust. In ion thrusters, plasma is made up of positive ions and an equal amount of electrons. by a hollow cathode, called the discharge cathode, located at the center of the thruster on the upstream end. The electrons flow out of the discharge cathode and are attracted (like hot socks pulled out of a dryer on a cold day) to the discharge chamber walls, which are charged highly positive by the thruster's power supply.

CHAPTER 7 7.1 - Ion thruster operation: the thruster pushes out the needed electron Step 1--Electrons (shown as small, pale green spheres) are emitted by the discharge hollow cathode, traverse the discharge chamber, and are collected by the anode walls. Step 2--Propellant (shown in green) is injected from the plenum and travels toward the discharge cathode. Step 3--Electrons impact the propellant atoms to create ions (shown in blue). Step 4--Ions are pulled out of the discharge chamber by the ion optics. Step 5--Electrons are injected into the beam for neutralization. When a high-energy electron (negative charge) from the discharge cathode hits, or bombards, a propellant atom (neutral charge), a second electron is released, yielding two negative electrons and one positively charged ion. High-strength magnets are placed along the discharge chamber walls so that as electrons approach the walls, they are redirected into the discharge chamber by the magnetic fields. Maximizing the length of time that electrons and propellant atoms remain in the discharge chamber, increases the chances that the atoms will be ionized. NASA also is researching electron cyclotron resonance to create ions. This method uses high-frequency radiation (usually microwaves) coupled with a high magnetic field to add energy to the electrons in the propellant atoms. This causes the electrons to break free of the propellant atoms and create plasma. Ions can then be extracted from this plasma. In a gridded ion thruster, ions are accelerated by electrostatic forces. The electric fields used for this acceleration are generated by two electrodes, called ion optics or grids, at the downstream end of the thruster. The greater the voltage difference between the two grids, the faster the positive ions move toward the negative charge. Each grid has thousands of coaxial apertures (or tiny holes). The two grids are spaced close together (but not touching), and the apertures are exactly aligned with each other. Each set of apertures (opposite holes) acts like a lens to electrically focus ions through the optics. NASA's ion thrusters use a two-electrode system, where the upstream electrode (called the screen grid) is charged highly positive, and the downstream electrode (called the accelerator grid) is charged highly negative. Since the ions are generated in a region that is highly positive and the accelerator grid's potential is negative, the ions are attracted toward the accelerator grid and are focused out of the discharge chamber through the apertures, creating thousands of ion jets. The stream of all the ion jets together is called the ion beam. The thrust is the force that exists between the upstream ions and the accelerator grid. The exhaust velocity of the ions in the beam is based on the voltage applied to the optics. Whereas a chemical rocket's top speed is limited by the heatproducing capability of the rocket nozzle, the ion thruster's top speed is limited by the voltage that is applied to the ion optics, which is theoretically unlimited. Because the ion thruster ejects a large amount of positive ions, an equal amount of negative charge must be ejected to keep the total charge of the exhaust beam

neutral. Otherwise, the spacecraft itself would attract the ions. A second hollow cathode called the neutralizer is located on the downstream perimes.

7.2 - Electric Propulsion System The ion propulsion system consists of five main parts: the power source, the power processing unit, the propellant management system, the control computer, and the ion thruster. The power source can be any source of electrical power, but solar or nuclear are usually used. A solar electric propulsion system (like that on Deep Space 1) uses sunlight and solar cells to generate power. A nuclear electric propulsion system (like that planned for the Jupiter Icy Moons Orbiter) uses a nuclear heat source coupled to an electric generator. ion thruster being tested at 20 kilowatts in Glenn's Vacuum Facility 6. For comparison, a household microwave operates at about 1 kilowatt. The power processing unit converts the electrical power generated by the power source into the power required for each component of the ion thruster. It generates the voltages required by the ion optics and discharge chamber and the high currents required for the hollow cathodes. The propellant management system controls the propellant flow from the propellant tank to the thruster and hollow cathodes. It has been developed to the point that it no longer requires moving parts. The control computer controls and monitors system performance. The ion thruster then processes the propellant and power to propel the spacecraft. The first ion thrusters did not last very long, but the ion thruster on Deep Space 1 exceeded expectations and was used more than 16,000 hours during a period of over 2 years. The ion thrusters being developed now are being designed to operate for 7 to 10 years.

7.3 - Next-generation ion engine sets new thrust record The NEXT ion engine fires at peak power during testing at NASA’s Glenn Research Center By David Shiga. An ion engine has smashed the record for total thrust in a NASA test. The successful test means the engine could be used in future NASA missions.

Ion engines work by accelerating electrically charged atoms, or ions, through an electric field, thereby pushing the spacecraft in the opposite direction. The thrust they provide at any given moment is very small, roughly equal to the force needed to hold up a sheet of paper against Earth’s gravity. But they can operate continuously in space for years using very little fuel, ultimately providing a much bigger boost than a chemical rocket. Advertisement The Dawn mission, which launched on Thursday, is equipped with NASA’s first generation of ion engines, called NSTAR. Dawn’s three NSTAR engines will

allow it to reach the asteroid belt and park in orbit around two different asteroids. The agency has also been testing a more advanced ion engine, called NASA’s Evolutionary Xenon Thruster (NEXT), which generates 2.5 times as much thrust as an NSTAR engine. Now, NEXT has broken a record, providing more “total impulse” than any previous ion engine. Total impulse is a measure of the overall acceleration that an engine would provide to a spacecraft. It is the result of multiplying the engine’s thrust by how long it fires. Record fuel The NEXT engine has now been fired for over 12,000 hours (500 days), providing more than 10 million Newton-seconds of impulse, more than any ion engine has ever achieved. During this time, it has processed more than 245 kilograms of fuel in the form of xenon gas, a record amount for an ion engine. The amount of fuel an ion engine can handle before wearing down is critical, since ion engines on spacecraft need to fire for years at a time. Previous estimates have suggested NEXT engines could safely handle 450 kilograms of fuel in their lifetime. NSTAR is rated for only 150 kilograms of fuel throughput, although one NSTAR engine has processed 235 kilograms of fuel in a previous test. “This test validates NEXT technology for a wide range of NASA solar system exploration missions, as well as the potential for Earth-space commercial ventures,” says NEXT principal investigator Mike Patterson of NASA’s Glenn Research Center in Cleveland, Ohio, US. NEXT could power a mission to Saturn’s moon, Titan. It would require about 20 kilowatts of engine power to get there if the mission included both an orbiter and a lander. . “We could do that with an array of three thrusters, plus a spare,” NEXT project manager Scott Benson of Glenn told New Scientist .

Star Wars Although NSTAR and NEXT both use xenon gas as a propellant, NEXT accelerates the xenon ions more efficiently, providing up to 236 milliNewtons of thrust compared to NSTAR’s maximum of 92 mN. The ion engines used on Japan’s Hayabusa spacecraft to the asteroid Itokawa use 22 mN, while those used on the European Space Agency’s SMART-1 Moon probe operated at 70 mN. NEXT can also vary its thrust by a factor of 11, as compared with NSTAR’s factor of five.

This means it can throttle down to lower levels as it travels farther from the Sun and receives less sunlight, allowing it to operate at greater distances than NSTAR. Although ion engines are just beginning to see regular use on scientific probes, they have been a common sight in science fiction for many years. Dawn spacecraft engineer Marc Rayman of NASA’s Jet Propulsion Laboratory in Pasadena, California, US, reminded journalists at a recent press conference of the ion engines used in the Star Wars movies. Conclusion This project explored some of the strengths and weaknesses of ion propulsion. It was found that ion propulsion requires much less fuel than conventional propulsion, (98% in this test) although it is not the fastest mode of transportation in the inner solar system, especially for large masses. The results of the fictional Engine 8 in this test are promising- achieving a thrust of 1 newton with an Isp of 30000 seems attainable in the near future. Today’s use of ion propulsion to propel small satellites far and fast seems the best application for this technology. A very real limitation of DS1’s ion propulsion is the spacecraft’s dependency on solar power- 630 million km is really not that far in space. For a true “deep space” mission, nuclear power seems the best option, but NIMBY… In addition to these lessons, this project has piqued my interest in ion propulsion, and provided me with countless hours (actually, about 50) of practice in STK. References http://www.qrg.ils.nwu.edu/projects/vss/docs/Propulsion/subzoompropulsion.html http://nmp.jpl.nasa.gov/ds1/ http://nmp.jpl.nasa.gov/ds1/arch/mrlog66.html http://www.space.com/scienceastronomy/solarsystem/deepspace_propulsion_000 816.html http://whyfiles.org/shorties/ion_thruster.html http://www.space.com/scienceastronomy/solarsystem/deepspace_propulsion_000 816.htm l