AFAL TR-87-070 AD-A189 218 Final Report for the period 1 May 1986 to 30 June 1987 October 1987 Author: R. L. Forward Hughes Research Laboratories 3011 Malibu Canyon Road Malibu, CA 90265 Contract No. F04611-86-C-0039 Approved for Public Release; Distribution is unlimited. Prepared for: Air Force Astronautics Laboratory, Air Force Space Technology Center, Space Division, Air Force Systems Command, Edwards Air Force Base, California 93523-5000 Title: Advanced Space Propulsion Study--Antiproton and Beamed Power Propulsion (U) Abstract: The contract objective was to monitor the research at the forefront of physics and engineering to discover new spacecraft propulsion concepts. The major topics covered were antiproton annihilation propulsion, laser thermal propulsion, laser-pushed lightsails, tether transportation systems, solar sails, and metallic hydrogen. Five papers were prepared and are included as appendices. They covered (1) pellet, microwave, and laser beamed power systems for interstellar transport; (2) a design for a near-relativistic laser-pushed lightsail using near-term laser technology; (3) a survey of laser thermal propulsion, tether transportation systems, antiproton annihilation propulsion, exotic applications of solar sails, and laser-pushed interstellar lightsails; (4) the status of antiproton annihilation propulsion as of 1986, and (5) the prospects for obtaining antimatter ions heavier than antiprotons. Two additional appendices contain the first seven issues of the Mirror Matter Newsletter concerning the science and technology of antimatter, and an annotated bibliography of antiproton science and technology. TABLE OF CONTENTS INTRODUCTION AND SUMMARY - Page 1 ANTIPROTON ANNIHILATION PROPULSION - Page 4 - Properties of Antimatter - Page 4 - Application to Propulsion - Page 6 - Making Antiprotons - Page 7 - Storing Antimatter - Page 8 - Antimatter Engines - Page 8 - Future Plans for Antiproton Annihilation Propulsion - Page 10 BEAMED POWER PROPULSION - Page 12 OTHER PROPULSION CONCEPTS - Page 14 - Renewing Research on Metallic Hydrogen - Page 14 - Tether Space Transportation Systems - Page 16 - Unconventional Missions Using Solar Sails - Page 20 REFERENCES - Page 28 APPENDICES A. BEAMED POWER PROPULSION TO THE STARS - Page A-1 B. LASER WEAPON TARGET PRACTICE WITH GEE-WHIZ TARGETS - Page B-1 C. EXOTIC PROPULSION IN THE 21ST CENTURY - Page C-1 D. PROSPECTS FOR ANTIPROTON PRODUCTION AND PROPULSION - Page D-1 E. PRODUCTION OF HEAVY ANTINUCLEI: REVIEW OF EXPERIMENTAL RESULTS - Page E-1 F. MIRROR MATTER NEWSLETTER - ISSUES 1 THROUGH 7 - Page F-1 G. ANTIMATTER SCIENCE AND TECHNOLOGY BIBLIOGRAPHY - Page G-1 LIST OF ILLUSTRATIONS Figure 1: Normal Matter and Mirror Matter - Page 5 Figure 2: Schematic of Antiproton Annihilation Propulsion - Page 6 Figure 3: Present Method of Making Antiprotons - Page 7 Figure 4: Polar Levitated Geostationary Orbit - Page 23 Figure 5: Eclipsat - Page 25 Figure 6: Sunwatcher sail system - Page 26 The objective of this contract was to monitor the research at the forefront of physics and engineering in order to discover new technology and scientific phenomena that might have application to spacecraft propulsion; and based on these latest developments, to propose new spacecraft propulsion concepts. The effort was to include an emphasis on the study of antiproton annihilation propulsion and to present approaches for promoting the scientific and technology issues of this concept. During the contract a series of separate studies on possible advanced space propulsion concepts were carried out. Some of these studies were successful in adding to the knowledge about present propulsion concepts or in inventing new space propulsion concepts. Other studies were unproductive and were dropped. The successful studies resulted in a number of written reports and briefings, as well as five papers prepared for presentation and publication in the proceedings of meetings or in scientific journals. The first paper (reprinted in Appendix A), "Beamed Power Propulsion to the Stars," was presented at the AAAS Symposium on Interstellar Communication and Travel at the AAAS Annual Meeting, held in Philadelphia, Pennsylvania (25-30 May 1986). In the paper I discuss three different beamed power propulsion systems capable of achieving the very difficult advanced space propulsion mission of sending payloads over interstellar distances: pellet-stream-pushed, microwave-beam-pushed, and laser-beam-pushed. The second paper (reprinted in Appendix B), "Laser Weapon Target Practice with Gee-Whiz Targets," was contributed to the Laser Propulsion Workshop held at Lawrence Livermore National Laboratory, Livermore, California (7-18 July 1986). In the paper I discuss a new concept for a very high performance laser-pushed lightsail that uses near-term high power laser systems to boost very light payloads to terminal velocities approaching 0.01 c. The third paper (reprinted in Appendix C), "Exotic Propulsion in the 21st Century," was an invited keynote paper at the American Astronautical Society 33rd Annual Meeting held in Boulder, Colorado (26-29 October 1986). In the paper I review laser thermal propulsion, tether transportation systems, antiproton annihilation propulsion, exotic missions using solar sails, and laser-pushed lightsails for interstellar transport. The fourth paper (reprinted in Appendix D), "Prospects for Antiproton Production and Propulsion," was an invited keynote paper at the Cooling, Condensation, and Storage of Hydrogen Cluster Ions Workshop held at SRI International, Menlo Park, California (8-9 January 1987). In the paper I review the history of antiproton annihilation propulsion and point out critical areas of antihydrogen storage technology. The fifth paper (reprinted in Appendix E), "Production of Heavy Antinuclei: Review of Experimental Results," dated 23 April 1987, surveyed the literature on producing heavier antimatter ions (antideuterium, antitritium, antihelium-3) for potential use in nucleating or stabilizing antihydrogen ion clusters. To promote the science and technology of antiproton annihilation propulsion, seven issues of the Mirror Matter Newsletter were prepared and distributed to over 500 scientists and engineers (Appendix F), and an extensive bibliography was compiled (Appendix G). A major new form of propulsion has just graduated from the never-never land of science fiction and has now become a serious topic for scientific and engineering investigation. In the past it was called antimatter propulsion, but to emphasize the difference between past fiction and present reality, I prefer to call it antiproton annihilation propulsion, for the use of antiprotons as the form of the antimatter is crucial to the use of antimatter for propulsion. PROPERTIES OF ANTIMATTER For every particle known to exist, there is a mirror image twin particle that has its charge, spin, and quantum states reversed from that of normal particles. The stable particles that make up atoms--electrons, protons, and neutrons--have mirror twins called positrons, antiprotons, and antineutrons. Conceptually, these could be combined to form antiatoms, such as antihydrogen. When a particle comes near its antiparticle, they attract each other and annihilate each other, totally converting all of their rest mass into energy. When positrons and electrons annihilate they produce gamma rays, which are difficult to convert to thrust. On the contrary, when antiprotons annihilate with protons, the annihilation process does NOT produce gamma rays immediately. Instead, the products of the annihilation are from three to seven particles called pions. On the average there are three charged pions and two neutral pions. The neutral pions have a very short lifetime and almost immediately convert into two high energy gamma rays. The charged pions have a normal half-life of 26 ns. Because they are moving at 94% of the speed of light, however, their lives are lengthened to 70 ns. Thus, they travel an average of 21 m before they decay. These charged pions contain 60% of the annihilation energy. 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. The energy in the pions can then either be used to heat a working fluid, such as hydrogen, to produce thrust, or the high speed 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. 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. MAKING ANTIPROTONS Antimatter in the form of antiprotons is generated by sending a high-energy beam of protons into a metal target. Relativistic protons convert kinetic energy into a spray of particles, some of which are antiprotons. Collecting rings have stored as many as 10^12 antiprotons for days at a time (mass of 1.7 pg, releasing 300 J upon annihilation). STORING ANTIMATTER Experiments have captured antiprotons in Penning ion traps. Research programs explore adding positrons to build 'cluster ions' of antihydrogen around a single antiproton ion, which can be electrostatically levitated as ice crystals. ANTIMATTER ENGINES One simple design replaces the nuclear reactor core of a NERVA engine with a tungsten heat exchanger core. Using 13 micrograms/s of antiproton fuel produces an Isp of 1100 s at 4.4x10^5 N thrust (power level 2.7 GW), enabling a 100-tonne payload roundtrip to Mars in 6 months. Magnetic bottle reaction chambers operate with pure hydrogen plasma in an optically thick regime (density 3x10^19 ions/cm^3, temperature 2 eV / 23,000 K, magnetic field 5 T, pressure 1000 psi / 67 atm). BEAMED POWER PROPULSION In beamed power propulsion, the propellant, energy source, and engine are left on the ground or in orbit, while the payload and lightweight structure carry out the mission. Examples include pellet-stream-pushed, microwave-beam-pushed (Starwisp), and laser-beam-pushed systems. METALLIC HYDROGEN Metallic hydrogen is a postulated high-energy propellant with an estimated specific impulse of 1700 s and density 1.15 g/cm^3. Static pressures of 0.21 to 0.55 TPa (2.1 to 5.5 Mbars) have been reached using diamond anvil presses, indicating research should be renewed. TETHER SPACE TRANSPORTATION SYSTEMS Skyhooks and rotating Rotavators can lift payloads into space or transfer orbital velocity. A graphite skyhook cable requires high-strength materials (tensile strength ~2.1x10^6 N/cm^2). A 4000-km-long rotating Rotavator could touch the upper atmosphere every 20 minutes, boosting payloads to Mars (72 days) or Venus (41 days). A Mars-Phobos-Deimos tether system could provide low-energy interplanetary launch. UNCONVENTIONAL MISSIONS USING SOLAR SAILS Solar sails operate by photon pressure (force F = 2P/c). Perforated ultrathin aluminum films (areal density 0.11 g/m^2) allow solar sails to achieve high acceleration (~0.01 g). Applications include: 1. Polar Levitated Geostationary Orbit: Displacing a geostationary orbit 13,000 km northward from the equatorial plane using constant solar pressure to cover polar regions. 2. Eclipsat: Hovering indefinitely in Earth's shadow cone at 217 Earth radii to continuously observe the solar corona. 3. Sunwatcher Sail System: Artificial 25-day solar-synchronous orbits or polar hovering orbits around the Sun. Appendix A: Beamed Power Propulsion to the Stars (AAAS Symposium Proceedings reprint on pellet, microwave Starwisp, and laser lightsails). Appendix B: Laser Weapon Target Practice with Gee-Whiz Targets (Proposal for testing high-power SDI lasers using ultra-thin multilayer and diamond lightsails accelerated to >100 km/s and near-relativistic speeds). Appendix C: Exotic Propulsion in the 21st Century (AAS Preprint 86-409 covering laser thermal, tethers, antiproton engines, and lightsails). Appendix D: Prospects for Antiproton Production and Propulsion (Detailed technical analysis of antiproton production efficiency, linac drivers, magnetic collection, Penning trap containment, and antihydrogen cluster ions). Appendix E: Production of Heavy Antinuclei: Review of Experimental Results (Survey of antideuteron, antitritium, and antihelium-3 production rates in high-energy collisions). Appendix F: Mirror Matter Newsletter (Issues 1 through 7 covering worldwide antiproton and low-energy physics activities). Appendix G: Antimatter Science and Technology Bibliography (Comprehensive annotated bibliography covering 10 categories including antiproton production, trapping, annihilation, biomedical applications, and propulsion).