_____________________________________________________________Antimatter propulsion ANTIMATTER PROPULSION Huma nkind has 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? ______________________________________________________________1 A.I.S.S.M.S.’s C.O.E. _____________________________________________________________Antimatter propulsion 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. ______________________________________________________________2 A.I.S.S.M.S.’s C.O.E. _____________________________________________________________Antimatter propulsion 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 200 - 410 .1 - 10 Bipropellant Electromagnetic 1200 - 5000 10-4 - 10-3 Nuclear Fission 500 - 3000 .01 - 10 Nuclear Fusion 10+4 - 10+5 10-5 - 10-2 Antimatter 10+3 - 10+6 10-3 - 1 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=mc2) and Isaac Newton (F=ma). What is Antimatter? ______________________________________________________________3 A.I.S.S.M.S.’s C.O.E. _____________________________________________________________Antimatter propulsion 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 = ______________________________________________________________4 A.I.S.S.M.S.’s C.O.E. _____________________________________________________________Antimatter propulsion + 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. ______________________________________________________________5 A.I.S.S.M.S.’s C.O.E. _____________________________________________________________Antimatter propulsion 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. ______________________________________________________________6 A.I.S.S.M.S.’s C.O.E. _____________________________________________________________Antimatter propulsion 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. ______________________________________________________________7 A.I.S.S.M.S.’s C.O.E. _____________________________________________________________Antimatter propulsion 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