Journal of the British Interplanetary Society VOLUME 72 NO.4 APRIL 2019 General interstellar issue POSITRON PROPULSION for Interplanetary and Interstellar Travel Ryan Weed et al. SPACECRAFT WITH INTERSTELLAR MEDIUM MOMENTUM EXCHANGE REACTIONS: the Potential and Limitations of Propellantless Interstellar Travel Drew Brisbin ARTIFICIAL INTELLIGENCE for Interstellar Travel Andreas M. Hein & Stephen Baxter Subscriber copy www.bis-space.com ISSN 0007-084X PUBLICATION DATE: 30 MAY 2019 Submitting papers International Advisory Board to JBIS JBIS welcomes the submission of technical Rachel Armstrong, Newcastle University, UK papers for publication dealing with technical Peter Bainum, Howard University, USA reviews, research, technology and engineering in astronautics and related fields. 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JBIS Vol 72 No.4 April 2019 109 JBIS VOLUME 72 2019 PAGES 110–115 POSITRON PROPULSION for Interplanetary and Interstellar Travel RYAN WEED1, BALA RAMAMURTHY1, JOSH MACHACEK1, DANTE SBLENDORIO1, MASON PECK2 1Positron Dynamics Inc, Livermore, California, USA; 2Sibley School of Mechanical and Aerospace Engineering, Cornell University, New York City, USA Email [email protected] Current state of the art in-space propulsion systems fail to meet requirements of 21st century space missions. Antimatter propulsion has been identified as a candidate mechanism that could safely transport humans and/or robotic systems with drastically reduced transit times, providing quicker scientific results, increasing the payload mass to allow more capable instruments and larger crews, and reducing the overall mission cost. Propulsion systems based on antimatter have been considered in several manifestations. Despite the substantial performance advantages, significant technical barriers have kept the cost of usable antimatter well outside the realm of propulsion applications. Each design is a trade-off between mass and complexity, but they all share high specific impulse (Isp) well above those obtained from even the most ambitious electric ion-propulsion. We describe a positron-based propulsion system utilizing radioisotope positron sources combined with annihilation-catalyzed fusion and include a basic design for a propulsion demonstration employing the CubeSat architecture as well a scaled propulsion system that utilizes an ‘on-board’ radioisotope breeding technique. Keywords: Antimatter, Positrons, Fusion propulsion 1 INTRODUCTION thrust levels and transit times required for interplanetary and interstellar travel. We present initial analysis of a positron The primary challenge of an antimatter propulsion system is source generation concept based on Deuterium-Deuterium conversion of the annihilation products into propulsive force. (DD) fusion neutron capture reaction 78Kr(n,γ)79Kr [8, 9, 10]. One way to do this is by catalyzing a fusion reaction(s), re- This type of radioisotope ‘breeder’ fuel cycle would allow for sulting in fast charged particle products that can be guided to much higher positron source intensities and thrust levels re- produce thrust [1]. Traditional laser or particle fusion-driver quired for an interstellar mission. systems have high mass and power requirements that are not practical for any near-term space applications [2]. 1.1 Why Positrons? PositronsSubscriber are the easier form of antimatter to obtain - over Antiprotons have been thecopy antimatter particle of choice for the past 20 years the cost of usable positron production has de- most propulsion system studies over the last several decades creased, and the techniques have become more widely known [11,12,13]. While antiproton annihilation does release approx- [3]. Our solution to antimatter propulsion is based on using imately 2,000 times more energy per annihilation, a large accel- electron/positron annihilation induced fusion reactions, first erator (e.g. CERN, FermiLab) is required to reach the energies proposed in the 1990s [4], but never experimentally meas- required for pair production of antiprotons. Such large systems ured. Recent advances in cold positron production [5], cre- are unrealistic in a spacecraft, therefore, antiproton propulsion ation of dense deuterium clusters on metallic substrates [6], concepts rely on storage of these