ANTIMATTER PROPULSION

Transcription

1 ANTIMATTER PROPULSION Huma has nkind been exploring space for four decades, and in that time our reach has extended throughout the solar system with the use of unmanned probes. Finally, what about the exploration of other solar systems? INTRODUCTION Humankind has been exploring space for four decades, and in time our reach has extended throughout the solar system with the use of unmanned probes. Finally, what abut the exploration of our solar systems? A.I.S.S.M.S. s 1

2 These issues are being addressed by the NASA Advanced Space Transportation Program (ASTP), which is currently investigating new ways to propel a unmanned spacecraft to Alpha Centauri in the span of a human lifetime of 50 years Both tasks suffer the same dilemma: chemical propellants simply will not work. For the first case, chemical propellants lack the energy needed to boost a space probe up to 10% the speed of light. The overall mass of such a booster would be unthinkable. For the latter case, the spacecraft only needs to obtain the velocity necessary to get to Mars within 3-6 months; however, the mass of a manned payload once again places a burden on the size of the booster engine. Many concepts have been devised. For years, scientists have suggested nuclear fission as an alternative approach for sending a manned spacecraft to Mars. Although the specific impulse (Isp) is still too low for interstellar missions, it does open new avenues near the vicinity of Earth. Unfortunately, environmental issues have all but "grounded" the use of nuclear fission as a propulsion source. Nuclear fusion is cleaner, and it is a more exciting prospect with its higher energy density and specific impulse. However, scientists are still developing such a device that offers beyond break-even energy (more energy output than input), let alone making the same device small enough to be sent into deep space. Last, electric propulsion, as used for Deep Space I, cannot accelerate a spacecraft fast enough for the tasks mentioned above due to its low thrust-to-weight ratio. A.I.S.S.M.S. s 2

3 It is here that antimatter addresses attention. Upon annihilation with matter, antimatter offers the highest energy density of any material currently found on Earth. As shown in the table below, this indicates that antimatter offers the greatest specific impulse of any propellant currently available or in development, and its thrust-to-weight ratio is still comparable with that of chemical propulsion. Simply put, it would take only 100 milligrams of antimatter to equal the propulsive energy of the Space Shuttle. Propulsion Specific Thrust-to- Type Impulse [sec] Weight Ratio Chemical Bipropellant Electromagnetic Nuclear Fission Nuclear Fusion Antimatter Annihilation Antimatter is one of the most recognized and attractive words in science fiction. It's the stuff that drives fictional starships from one side of the universe to the other. Now NASA is giving it serious consideration as a rocket propellant to get around the solar system. A gram of antimatter would carry as much potential energy as 1,000 Space Shuttle external tanks carry. The rockets will employ the ages old action-reaction principle in an interesting meeting of Albert Einstein (E=mc 2 ) and Isaac Newton (F=ma). What is Antimatter? A.I.S.S.M.S. s 3

4 Antimatter is exactly what you might think it is -- the opposite of normal matter, of which the majority of our universe is made. Until just recently, the presence of antimatter in our universe was considered to be only theoretical. In 1928, British physicist Paul A.M. Dirac revised Einstein's famous equation E=mc2. Dirac said that Einstein didn't consider that the "m" in the equation -- mass -- could have negative properties as well as positive. Dirac's equation (E = A.I.S.S.M.S. s 4

5 + or - mc2) allowed for the existence of anti-particles in our universe. Scientists have since proven that several anti-particles exist. These anti-particles are, literally, mirror images of normal matter. Each anti-particle has the same mass as its corresponding particle, but the electrical charges are reversed. Positrons Electrons with a positive instead of negative charge. Discovered by Carl Anderson in 1932, positrons were the first evidence that antimatter existed. A.I.S.S.M.S. s 5

6 Anti-protons Protons that have a negative instead of the usual positive charge. Anti-atoms Pairing together positrons and antiprotons, scientists at CERN, the European Organization for Nuclear Research, created the first anti-atom. Nine anti-hydrogen atoms were created, each lasting only 40 nanoseconds. Annihilation The complete conversion of matter into energy-releases the most energy per unit mass of any known reaction in physics. When antimatter comes into contact with normal matter, these equal but particles collide to produce an explosion emitting pure radiation, which travels out opposite the point of the explosion at the speed of light. Both particles that created the explosion are completely annihilated, leaving behind other subatomic particles. The explosion that occurs when antimatter and matter interact transfers the entire mass of both objects into energy. Scientists believe that this energy is more powerful than any that can be generated by other propulsion methods. So, why haven't we built a matter-antimatter reaction engine? The problem with developing antimatter propulsion is that there is a lack of antimatter existing in the universe. If there were equal amounts of matter and antimatter, we would likely see these reactions around us. Since antimatter doesn't exist around us, we don't see the light that would result from it colliding with matter.. A.I.S.S.M.S. s 6

7 Matter-Antimatter Engine Scientists announced early designs for an antimatter engine that could generate enormous thrust with only small amounts of antimatter fueling it. The amount of antimatter needed to supply the engine for a one-year trip to Mars could be as little as a millionth of a gram. Matter-antimatter propulsion will be the most efficient propulsion ever developed, because 100 percent of the mass of the matter and antimatter is converted into energy. When matter and antimatter collide, the energy released by their annihilation releases about 10 billion times the energy that chemical energy such as hydrogen and oxygen combustion, the kind used by the space shuttle, releases. Matter-antimatter reactions are 1,000 times more powerful than the nuclear fission produced in nuclear power plants and 300 times more powerful than nuclear fusion energy. So, matter-antimatter engines have the potential to take us farther with less fuel. There are three main components to a matter-antimatter engine: Magnetic storage rings Antimatter must be separated from normal matter so storage rings with magnetic fields can move the antimatter around the ring until it is needed to create energy. A.I.S.S.M.S. s 7

8 Feed system When the spacecraft needs more power, the antimatter will be released to collide with a target of matter, which releases energy. Magnetic rocket nozzle thruster Like a particle collided on Earth, a long magnetic nozzle will move the energy created by the matter-antimatter through a thruster. The storage rings on the spacecraft will hold the antimatter. The popular belief is that an antimatter particle coming in contact with its matter counterpart yields energy. That's true for electrons and positrons (anti-electrons). They'll produce gamma rays at 511,000 electron volts. But heavier particles like protons and anti-protons are somewhat messier, making gamma rays and leaving a spray of secondary particles that eventually decay into neutrinos and low-energy gamma rays. And that is partly what Schmidt and others want in an antimatter engine. The gamma rays from a perfect reaction would escape immediately, unless the ship had thick shielding, and serve no purpose. But the charged debris from a proton/anti-proton annihilation can push a ship. Production of Antimatter Antimatter does not exist in nature or at least certainly nowhere near us, which is just as well. If it did it would immediately annihilate with matter and explode with more force than we have ever experienced. This means we have to manufacture it and then very carefully store it; it is only produced at certain high-energy laboratories around the world (probably most famously at CERN in Geneva). The actual manufacturing is achieved in a particle accelerator creating extremely high-energy collisions. Over the past 20 years scientists at CERN A.I.S.S.M.S. s 8

9 have been using antiparticles in many different ways for their daily work. Electrons and positrons (anti electrons) do a neat job of it, but protons and antiprotons are messy. They yield three types of pions that 1) decay to produce gamma radiation 2) decay to produce muons and neutrinos plus electrons and positrons that make more gamma rays. Electrons are lightweight and tough to store in a magnetic model, so scientists have been working on antiprotons whose greater mass makes them easier to handle. (Even anti-atoms that might be stored at near absolute zero are a possibility.) Billionths of a gram of antiprotons are created each year in high-energy particle accelerators high in the Alps. A billion antiprotons are produced every 10 minutes, but only 1,000 of those are captured and stored. Antiparticles can be generated by colliding subatomic particles. Before being delivered to the various physics experiments, they must be isolated, collected and stored in order to tune their energy to the appropriate level. Until now, each of these steps has been carried out by a dedicated machine with the main purpose of providing high-energy antiparticles. But now the first "self-contained antiproton factory", the Antiproton Decelerator (or AD), is operational at CERN. It will produce the low energy antiprotons needed for a range of studies, including the synthesis of antihydrogen atoms - the creation of antimatter. A.I.S.S.M.S. s 9

10 Making Antiprotons Antimatter in the form of antiprotons is being made today, albeit in small quantities. The antiprotons are generated by sending a high-energy beam of protons into a metal target. When the relativistic protons strike the dense metal nuclei, their kinetic energy, which is many times their rest-mass energy, is converted into a spray of particles, some of which are antiprotons. A magnetic field focuser and selector separates the antiprotons from the resulting debris and directs the antiprotons into a storage ring. These collecting rings have stored as many as antiprotons for day sat a time. To give some scale as to what has already been accomplished at these research facilities, antiprotons have a mass of 1.7 pg. When this amount of antimatter is annihilated with an equivalent amount of normal matter, it will release300 J, an engineering significant amount of energy. A.I.S.S.M.S. s 10

11 STORING ANTIMATTER In a recent experiment, a team of scientists took the low energy antiprotons in one of these rings, slowed them down to almost zero velocity, and captured a few hundred antiprotons in a small electromagnetic ion trap. Other experiments planned for late 1987 will attempt to capture many millions of antiprotons in a trap no bigger than a thermos bottle. The electromagnetic trap will be made portable so the antiprotons can be transported to other laboratories for experiments. In order to use antiprotons as a propulsion fuel, it will be necessary to find a more compact method of storage than an ion trap, which is limited to relatively low ion densities. Another Air Force sponsored research program is looking into adding positrons to the antiprotons in the ion traps and slowly building up "cluster ions" of antihydrogen. These cluster ions are large agglomerations of neutral antihydrogen atoms clustered around a single antiproton ion. The net negative electric charge of the cluster ion allows it to be kept in the ion trap, yet the mass of each ion can be increased until we have an ice crystal with enough charge that it can be electrostatically levitated without touching the walls of the cryogenically cooled trap Antimatter does not exist in nature - or at least certainly nowhere near us, which is just as well. If it did it would immediately annihilate with matter and explode with more force than we have ever experienced. This means we have to manufacture it and then very carefully store it; it is only produced at certain high-energy laboratories around the world (probably most famously at CERN in Geneva).The actual manufacturing is achieved in a particle accelerator creating extremely high-energy collisions, which results in the kinetic energy being converted to matter (subatomic particles), some of which is antimatter. A.I.S.S.M.S. s 11

12 Storage is possible because it may be controlled in magnetic fields, thereby avoiding the obvious problem of trying to store it in structural containers. The Penning trap has been developed; it is a portable antiproton trap, which is capable of storing (10^10) antiprotons for one week using the superposition of electric and magnetic fields. The next stage is an improvement to (10^12) antiproton storage. For complete antimatter propulsion it is thought that (10^20) anti-protons will need to be stored. A.I.S.S.M.S. s 12

13 Storage is possible because it may be controlled in magnetic fields, thereby avoiding the obvious problem of trying to store it in structural containers. APPLICATION TO PROPULSION Because of the long lifetime and interaction length of the charged pions that result from the annihilation of antiprotons with protons, it is relatively easy to collect the charged pions in a thrust chamber constructed of magnetic fields and to obtain propulsion from them. A.I.S.S.M.S. s 13

14 As is shown in Figure the energy in the pions can then either be used to heat a working fluid, such as hydrogen, to produce thrust, or the highspeed pions themselves can be directed by a magnetic nozzle to produce thrust. Even after the charged pions decay, they decay into energetic charged muons, which have even longer lifetimes and interaction lengths for further conversion into thrust. Thus, if sufficient quantities of antiprotons could be made, captured, and stored, then presently known physical principles show that they can be used as a highly efficient propulsion fuel. Since antimatter does not exist naturally, it must be made, one particle at a time. It is a synthetic fuel. It will always require much (~l0 4 times) more energy to produce antimatter than can be extracted from the annihilation process. Its major advantage is that it is a highly concentrated form of energy storage. A tenth of a milligram, about the size of a single grain of salt, contains the energy of 2 tonnes of the best rocket fuel known, liquid oxygen/liquid hydrogen. A study that compared antihydrogen propulsion systems with chemical propulsion systems found that antiproton propulsion could possibly be cost effective for space propulsion. More importantly, it was mission enabling, in that it would allow missions to be performed that are essentially impossible to perform with chemical fuels. A.I.S.S.M.S. s 14

15 There are four main designs for an antimatter rocket; they are listed here in increasing specific impulse: Solid Core - Annihilation occurs inside a solid-core heat exchanger, the reaction superheats hydrogen propellant that is expelled through a nozzle. High efficiency and high thrust, but due to the materials the specific impulse is only 1000secs at best. Gas Core - Annihilation occurs in the hydrogen propellant. The charged pions are controlled in magnetic fields and superheat the hydrogen; there is some loss in the form of gamma rays that cannot be controlled. Specific impulse of 2500secs. Plasma Core - Annihilation of larger amounts of antimatter in hydrogen to produce hot plasma. Plasma contained in magnetic fields, again some loss in form of gamma radiation, and the plasma is expelled to produce thrust. There are no material constraints here so higher specific impulse is possible (anywhere from 5,000 to 100,000secs). A.I.S.S.M.S. s 15

16 Beam Core - Direct one to one annihilation, magnetic fields focus the energetic charged pions that are used directly as the exhausted propellant mass. These pions travel close to speed of light. ADVANTAGES: 1. Antimatter is hundred percent efficient. When Antimtter comes in contact with Matter it annihilates and the whole is converted into Energy. 2. For propulsion of spacecraft the amount of Antimatter required will be very less. A ten-gram of Antimatter would be enough to send manned spacecraft to Mars. 3. Specific impulse of Antimatter is very high. The specific impulse could be greater than 10,000,000secs. 4. Speed of Antimatter particles is about 94% that of speed of light. The spacecrafts with fuel as Antimatter will almost travel at the speed of light. A.I.S.S.M.S. s 16

17 DISADVANTAGES: 1. Problem with developing Antimatter is that it does not exists naturally. 2. Production of Antimatter is a problem.a few gram of Antimatter will take many years. Large-scale production techniques are not yet developed. 3. Storing Antimatter is very difficult. It requires special vessels to store. 4. Time of existence of Antimatter is very less. When scientist made Antiatoms, each of which lasted for about 40 billionths of second. 5. Energy from matter-antimatter reaction is released in the form of particles moving about one third speed of light. Speed is very high. 6. Antimatter is the most expensive substance on Earth about $62.5 trillion a gram. OTHER APPLICATIONS: 1. Antimatter can be used in medicine for scanning. 2. It can be used for medical diagnosis where positrons are used to identify diseases with positron emission Tomography or PET-scan. 3. Antimatter can be used to propel the future cars. 4. It is possible to built Antimatter weapon. 5. By beaming Anti-protons through large metal structure to detect flaws A.I.S.S.M.S. s 17

18 and even to cure flaws internally. PLANS FOR ANTI-MATTER PROPULSION: Because antiproton propulsion promises a major advance in Space propulsion capability, the recently completed Air Force Systems Command Project Forecast II study recommended that their Force start a new program in antimatter propulsion. As a direct result of the Project Forecast II recommendations, the Air Force Astronautics Laboratory at Edwards AFB in California has reorganized its advanced propulsion activities and formed a new project called ARIES (Applied Research In Energy Storage). The project has two major thrusts - chemically bound excited states and antimatter. The Air Force Office of Scientific Research has initiated a new program on antimatter research in the Physical and Geophysical Sciences Branch under Col. Hugo Weichel. The Program Manager for Antimatter is Maj. John Prince, who evaluates unsolicited proposals for research on antimatter sciences. In Europe, an Antimatter Research Team (ART) has been formed attelespazio, SpA per I.e. Communication Spaziali in Italy. Their research work will cover antiproton and positron production and storage, and engine simulations, leading ultimately to technology demonstrations. A.I.S.S.M.S. s 18

19 CONCLUSION: After analyzing the whole topic, it can be concluded that the Antimatter propulsion even though it is under development,but it will certainly bring revolutionary change in conventional propulsion systems. Now mankind can think about the journey beyond the Galaxy. Scientist believe that the speed of an Matter-Antimatter powered spacecrafts would allow man to go where no man has gone before in space. A.I.S.S.M.S. s 19

20 BIBLIOGRAPHY: Various internet sites A.I.S.S.M.S. s 20