DOW-UAP-D123, AAWSAP DIRD, Positron Aerospace Propulsion, March 2010

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UNCLASSIFIED//POI\ OFFICIAL USE Oiltt Positron Aerospace Propulsion Prepared by: Acquisition Support Division (DW0-3) Defense Warning Office Directorate for Analysis Defense Intelligence Agency AAP Person 69 Administrative Note COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one in a series of advanced technology reports produced in FY 2009 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapon System Applications (AAWSA Pro ram. Comments or uestions pertaining to this document should be addressed to AAP Person 1 , AAWSA Program Manager, Defense Intelligence Agency, ATTN: CLAR/DWO-3, Bldg 6000, Washington,

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Positron Air-Breathing Propulsion.......................................................................... 2 Unmanned Aerial Vehicle (UAV) ......................................................................... 5 Ramjet-Assisted Missile (RAM) .......................................................................... 7 The Solid-Core Positron Rocket ........................................................................ 12 The Gas-Core Positron Rocket .......................................................................... 14 The Sanger Photon Positron Rocket ................................................................. 16 Positron Rocket System Comparison ................................................................ 17 Positron Energy Conversion for Onboard Power............................................... 18 Positrons for a Manned Mars Mission ................................................................... 19 Positron Production.............................................................................................. 22 Formation of Positronium in Porous Media ....................................................... 25 Long-Term Storage of Positronium .................................................................. 25 Figure 1. Specific Energy for Chemical, Nuclear and Antimatter Materials............. 1 Figure 2. Tory-IIC Ready for Testing ...................................................................... 3 Figure 3. PTRE Turbojet and Turbo-Ramjet Modes ................................................. 3 Figure 4. Details of the PTRE Engine.......................,............................................... 4 Figure 5. Combustion Turbo-Ramjet....................................................................... 4

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UNCLASSIFIED/J FOR OFFICIAL USE ONLY Figure 8. BOMARC and Talos Ramjet-Assisted Missiles........................................... 8 Figure 10. Artist's Rendition of a Four-Engine Positron SSRV............................... 11 Figure 11. Solid-Core Positron Rocket Engine With a Hot-Bleed Configuration..... 12 Figure 13. Modified Sanger Photon Rocket Concept ............................................. 17 Figure 14. Closed Brayton Cycle Using Positron Annihilation ............................... 18 Figure 15. Conceptual 110 Watt Positron Closed Cycle Generator Based on the NASA Glenn Research Center Stirling Radioisotope Generator (SRG) .. 18 Figure 16. Mars Trajectories (X-Coordinates Defined in Direction of Aries) ......... 20 Figure 17. Spacecrafts Using Positron Engines..................................................... 21 Figure 18. Proposed Undulator-Based Positron Source for the International Figure 22. TEM of Silica Aerogel ........................................................................... 26 Table 4. Comparison of Space Propulsion and Power Systems - Solid Core ......... 13 Table 5. Comparison of Three Positron Propulsion Concepts for Mars Mission ..... 17 Table 6. Positron and Antiproton Expected Costs in the Next 10 Years ................ 23

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Positron Aerospace Propulsion Antimatter is considered an extremely attractive fuel for aerospace propulsion because of its enormous advantage in energy density over all other known sources of energy. However, because antimatter does not occur naturally and is unstable in the presence of matter, no vehicles have ever flown using it. After a short overview of the various aerospace applications of antimatter, this paper provides a detailed analysis of air-breathing turbojets and turbo-ramjet missiles, as well as rockets for manned interplanetary missions. It discusses new methods of producing and storing large numbers of antielectrons, or positrons, and compares their costs with those of antiprotons. Finally, the paper considers the prospects for the first, modest demonstration of positron propulsive flight within the next 10 years. Interplanetary missions on positron-propelled spaceships are described in detail, with estimates of positron requirements for each mission. Standalone positron power systems are described briefly. Studies of positrons as a fuel for aerospace propulsion applications have been sponsored by the Air Force Research Laboratory, Eglin Air Force Base, Florida, and the NASA Institute for Advanced Concepts, Atlanta, Georgia. This paper is an anthology of that work and not a general review of antimatter propulsion. The positron was predicted by Dirac in 19291 and discovered by Anderson in 1932.2 Along with the antiproton, which was discovered in 1954,3 the positron has the largest specific energy of any known material. Because aerospace propulsion performance is ultimately limited by specific power, this advantage was immediately appreciated. However, compared with chemical sources of energy, positrons presented new and serious production and storage Antimatter has a long history of appearing in science fiction literature, dating to a 1942 short story in Astounding Science Fiction and the 1949 book Seetee. It later appeared in the Star Trek television and film series and continues to be an appealing subject for contemporary books and films, such as Angels and Positron aerospace propulsion is now entering a critical period owing to new technologies that bear on production and storage issues. To their advantage, positrons, unlike nuclear fission and antiprotons, present no radiation or environmental safety problems.

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Antimatter appears in the form of fundamental particles that have their sign of electric charge reversed from their matter counterpart. For example, the positron, e+, is the antiparticle to the electron, e·. According to the CPT theorem,4 properties of matter and their counterpart antimatter particles are identical. This has been tested in the laboratory to an accuracy of roughly 1 part in 10 million. Antimatter is appealing for aerospace uses because its specific energy by annihilation is 180 MJ/µg, or 10 orders of magnitude larger than chemical energy, as shown in Figure Olerrical Fission Fusion Fbsitron Figure 1. Specific Energy for Chemical, Nuclear, and Antimatter Materials In the presence of matter, the positron binds with an electron to form a short-lived atom called positronium (Ps). Depending on the relative spin orientations of the positron and electron, Ps has a mean lifetime in a vacuum of 125 picoseconds (para-Ps, spins antiparallel), or 142 nanoseconds (ortho-Ps, spins parallel). From quantum number conservation, para-Ps decays into two gamma rays of equal energy, 511 kiloelectronvolts (keV), whereas ortho-Ps decays into three gamma rays whose energies add up to 1022 keV. Hence, when Ps self-annihilates, there is 100 percent conversion of mass into electromagnetic energy given by Einstein's famous equation, E = mc2, where c is the speed of light. Although the energies of positron annihilation gamma rays are on the nuclear scale, they have none of the undesirable features associated with nuclear energy. First, the annihilation evolves rapidly (nanoseconds) and is controllable under predictable electromagnetic forces. There is no long-term inertia as with nuclear reactors. Consequently, positron-generated thrust can be throttled.

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Second, low-energy gamma rays from positron annihilation cannot make residual radioactivity in surrounding air and containment vessels. In contrast, antiprotons