ALTERNATE FORM OF PROPULSION USING AND PLASMA

1T. UDAYCHANDH, 2VISHNU CHANDAR, 3SIVA SANKAR, 4MANOJ PRABHAKAR, 5ARAVINDAKSHAN. R, 6SANDEEP NARAYANAN, 7YESHWANTH NAPOLEAN

1,2,3,4,5,6,7 Undergraduate students (B.Tech), Department of Aerospace Engineering, Srm University, Chennai

Abstract- Matter antimatter propulsion system is one of the few ways to do fast interstellar rendezvous mission. This paper discusses the general mission requirements and system technologies that would be required to implement an antimatter propulsion system where a magnetic nozzle (superconducting magnet) is used to direct charged particles (from the annihilation of protons and ) to produce thrust. A gas core engine is used for propulsion. The disadvantage of a gas core is that plasma may be created. Using a plasma core can eliminate this. Magnetic fields would serve to contain the plasma and the propellant (which would also be a plasma by the time it had exited the ). Antiprotons would be injected into the plasma core, annihilating and heating the plasma. Heat would be rapidly transferred to the propellant, which would be expelled from the drive at high velocity. Excess plasma is redirected to the ion thruster for additional thrust.

I. INTRODUCTION and Projectile (1865) and the Apollo Saturn V and Command Module (1969). One of mankind’s oldest dreams has been to visit the tiny pinpoints of light visible in the night sky. Over the last 40 years we have visited most of the major bodies in our solar system, reaching out far beyond the orbit of Pluto with our robotic spacecraft. And yet this distance, which strains the limits of our technology, represents an almost negligible step towards the light-years that must be traversed to travel to the nearest stars. For example, even though the Voyager spacecraft is one of the fastest vehicles ever built, traveling at 17 km/s or 3.6 AU/year, it would still require almost 74,000 years for it to traverse the distance to our nearest stellar neighbour. Verne was impossibly wrong in his prediction of the Thus, travel to demanding stretch goal of a fast launch vehicle, yet he was remarkably right in interstellar rendezvous mission, only beamed energy predicting the crew capsule. In part, this is because of Laser Sail, matter-antimatter, and fusion ramjet the quantum leaps in technological capability made concepts were viable candidates. by the launch vehicle (e.g., cannons versus )? By contrast, the need to support three crew members II. TECHNOLOGY PREDICTIONS in a trip to the Moon is somewhat technology- independent (i.e., they need a certain amount of living Predicting the types of systems and technologies to be volume, food, oxygen, etc.), so it is perhaps not used for an interstellar mission some 50-100 years surprising that the crew capsules are so similar. from now is, somewhat by definition, virtually impossible. This is made obvious by considering the The specific objectives of our work here is to create a state of knowledge in 1903 versus 2003. For example, conceptual design of an alternate form of propulsion in 1903, Newton and Maxwell represented the that incorporates an antimatter rocket and an ion reigning models of nature; advanced transportation thruster. technology was represented by Steam Locomotives (which at that time held the world speed record). By There are three types of antimatter rockets contrast, 100 years later, Quantum Mechanics and Solid core – Energy is transferred to a propellant in Relativity rule physics; we have rockets, lasers, tungsten metal matrix heated by annihilation gamma transistors, high-temperature (100K) super- rays. conductors, and so on. What technology might do? Perhaps the most famous example is the difference Advantages – Well understood technology. between the dream of Jules Verne’s From the Earth to Disadvantages – Performance limited by melting the Moon (1865) and Apollo 11 (1969) as illustrated temperature of tungsten. in Table 1. Gas core – Energy is transferred to liquid/gas Table 1. Comparison between Jules Verne’s Cannon propellant directly heated by annihilation gamma rays.

Proceedings of International Conference on Advances in Engineering & Technology, 20th April-2014, Goa, India, ISBN: 978-93-84209-06-3 21 Alternate Form of Propulsion Using Antimatter and Plasma Advantages – Improvement over solid core, not density of the proton- reaction of “only” limited by melting temperature. 64% of the ideal limit, or 5.8~10’J/~kg. Disadvantages – Flowing multi-fluid is unstable at boundaries, may ionise and create plasma. One serious issue is the gamma radiation produced in the annihilation reaction. Because of the short Solid Ablation – Energy is transferred to a material (relativistic) lifetime of the neutral , it only that ablates off surface of a pusher plate. moves 0.06 micrometers before decaying into Advantages – Simplicity in design, no obvious gammas. In practical terms, this means that the technology limits. neutral promptly decay into very high-energy Disadvantages - Half of the gamma rays do not strike gamma rays (ca. 200 MeV each) at the annihilation the pusher plate, maximum efficiency 50%. point. By contrast, the charged pions move 21 m and their decay products, charged muons, move another One of the disadvantages of gas core rockets, creation 1.85 km before decaying. of plasma can be eliminated by routing the plasma thus created to an ion thruster for additional thrust. Thus, one major systems consideration in designing a proton-antiproton annihilation propulsion system is We choose the gas core rocket as its performance is the need to shield spacecraft systems against an not limited by factors like melting point and intense (e.g., 38% of the propellant mass), high- efficiency with which gamma rays strike a plate. energy flux of gamma radiation. (By comparison, the electron- annihilation gammas, at 0.511 III. MATTER-ANTIMATTER ANNIHILATION MeV each, are negligible.) Finally, we have treated the annihilation mass-energy distribution as if it were Matter-antimatter annihilation offers the highest possible to separate out rest mass from kinetic possible physical of any known energy; in fact, of course, we must deal with the reaction substance. The ideal energy density relativistic mass-energy content (e.g., rest mass plus (E/M=c2) of 9 ~ 1 0 J’/~kg is orders of magnitude relativistic mass “increase” due to traveling of the greater than chemical (lx107 J/kg), fission (8 ~ 1 0 pions, etc. Thus, for example, the total mass-energy ’J/~kg), or even fusion (3 ~ 1 0J’nC~g) reactions. content of the neutral pion is converted into gammas, Additionally, the matter- antimatter annihilation not just its rest mass. reaction proceeds spontaneously, therefore not requiring massive or complicated reactor systems. These properties (high energy density and spontaneous annihilation) make antimatter very attractive for propulsive ambitious space missions (e.g., ).

Antimatter for Propulsion Applications Note that for a propulsion application, proton- antiproton annihilation is preferred over electron- positron (anti-electron) annihilation because the products of proton-antiproton annihilation are charged particles that can be confined and directed magnetically. (The antiproton is identical in mass to the proton but opposite in electric charge and other quantum numbers.) By contrast, electron-positron Source: annihilation produces only high-energy gamma rays, “To build an antimatter rocket for interstellar which cannot be directed to produce thrust and do not missions, systems level consideration in designing “couple” their energy efficiently to a working fluid advanced propulsion technology vehicles”, (and also require significant shielding to protect the vehicle and its payload). This is the primary reason Robert H. Frisbee, Jet Propulsion Laboratory, for selecting the annihilation of a proton (p’) and California Institute of Technology antiproton (p-); the products include neutral and charged pions (no, n+C), and the charged pions can For these reasons, antimatter for propulsion be trapped and directed by magnetic fields to produce applications is typically assumed to be in the form of thrust. However, the pions produced in the antiprotons, neutral anti- atoms (an annihilation reaction do possess (rest) mass (about antiproton with a positron), or anti-molecular 22% of the initial proton- antiproton annihilation pair hydrogen (anti-H,). Antiprotons do not exist in nature rest mass for charged pions, 14% for the neutral and currently are produced only by energetic particle pions), so not all of the proton- antiproton mass is collisions conducted at large accelerator facilities converted into energy. This results in an energy (e.g., Fermi National Accelerator Laboratory,

Proceedings of International Conference on Advances in Engineering & Technology, 20th April-2014, Goa, India, ISBN: 978-93-84209-06-3 22 Alternate Form of Propulsion Using Antimatter and Plasma FermiLab, in the U.S., CERN in Geneva Switzerland, or IHEP in Russia). This process typically involves accelerating protons to relativistic velocities (very near the speed of light) and slamming them into a metal (e.g., tungsten) target. The high-energy protons are slowed or stopped by collisions with nuclei of the target; the relativistic kinetic energy of the rapidly moving antiprotons (more correctly the relativistic mass increase due to traveling near the speed of light) is converted into matter in the form of various subatomic particles, some of which are antiprotons. The antiprotons are electromagnetically separated from the other particles.

Note that antiprotons annihilate spontaneously when brought into contact with normal matter; thus, they must be contained by electromagnetic fields in high vacuums. This greatly complicates the collection, storage and handling of antimatter.

IV. HIGH-TEMPERATURE (L00K) SUPERCONDUCTOR MAGNET MAGNETIC NOZZLE

Source: The magnetic nozzle consists of a single-loop high- temperature (100K) superconductor coil. This “To build an antimatter rocket for interstellar geometry was chosen so as to make use of prior missions, systems level consideration in designing modelling of a similar system in the VISTA (Vehicle advanced propulsion technology vehicles”, for Interplanetary Space Transportation Applications) Robert H. Frisbee, Jet Propulsion Laboratory, inertial confinement fusion (ICF) study. The overall California Institute of Technology geometry has a magnet coil centreline radius (R) that is twice the standoff distance (X) from the ICF implosion or, in our case, the annihilation region.

This geometry was also assumed in a Monte-Carlo modelling of the proton-antiproton reaction that was used to determine the “effective” Isp the antimatter rocket. As can be seen, there is imperfect reflection of the charged pions; some of them even travel “upstream” from the annihilation point because of the finite capability of the magnet to turn the ions and direct them “downstream” to produce thrust.

Figure 1 : Schematic of antimatter propulsion system Thus, the effective Isp is less than the relativistic velocity of the charged pions. The above figure is a basic representation of a beam core propulsion system. In this figure a ring shaped V. RADIATION SHIELDS magnet is used to generate the magnetic field for the nozzle. A radiation shield is placed between the A radiation shield is required to protect the magnetic nozzle and the engine to protect the engine superconductors, main radiator, electronics, from the gamma rays produced by the antiproton- propellant tanks, payload, etc. from the intense flux proton annihilation and the decay of neutral pions. of gamma rays produced in the annihilation process. A shadow shield is placed between the magnetic We assumed a tungsten shield because of its excellent nozzle and the rest of the vehicle to protect the gamma shielding properties, and because it can be vehicle from exposure to radiation. Antiprotons operated at a high temperature (1500K assumed here) would be injected into the plasma core, annihilating to minimise the radiator needed to reject the gamma and heating the plasma. Heat would be rapidly energy absorbed by the shield. Properties for the transferred to the propellant, which would be expelled shield and representative allowable radiation doses from the drive at high velocity. The excess plasma is are listed in Tables 3 and 4, respectively. then diverted to an ion thruster to provide additional thrust.

Proceedings of International Conference on Advances in Engineering & Technology, 20th April-2014, Goa, India, ISBN: 978-93-84209-06-3 23 Alternate Form of Propulsion Using Antimatter and Plasma antimatter that we use for propulsion. Creation of antimatter can be called a work in progress.

Positronics Research in Santa Fe, New Mexico are working on production of in large uantities. They have also found the pathway to long-term storage of large amounts of positrons. It involves making electrically neutral positronium (neutral atom of an electron and positron) atoms, thenstabilising them in magnetic and electric fields.

REFERENCES

[1]. “To build an antimatter rocket for interstellar missions, systems level consideration in designing advanced Figure 2: Schematic of Ion Thruster propulsion technology vehicles”, Robert H. Frisbee, Jet Propulsion Laboratory, California Institute of Technology CONCLUSION [2]. http://ffden2.phys.uaf.edu/213.web.stuff/Scott%20Kircher/p lasmacore.html The initial inspiration for this idea was drawn from [3]. http://courses.ae.utexas.edu/ase333t/past_projects/03fall/anti the movie franchise “Star Trek”. There is a diversion matter/applications_of_antimatter.htm mechanism like a plasma pump connected to the annihilation chamber so that the excess plasma is [4]. “Antimatter Production for Near-term Propulsion Applications” by G.R. Schmidt, H.P.Gerrish and J.J. Martin, siphoned off and is provided as input for the Ion NASA Marshall Space Flight Center Huntsville, AL ,G.A. thruster. Thus more thrust can be obtained. Smith and K.J. Meyer,Pennsylvania State University University Park, PA . The main problems associated with antimatter are its [5]. “Antimatter plasmas and antihydrogen”,R. G. Greaves and creation and its containment. Here we employ a pre C. M. Surko ,Department of Physics, University of existing mechanism called the Penning trap to contain California, San Diego, California.

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Proceedings of International Conference on Advances in Engineering & Technology, 20th April-2014, Goa, India, ISBN: 978-93-84209-06-3 24