Journal of the British Interplanetary Society VOLUME 72 NO.2 FEBRUARY 2019 General interstellar issue DIRECT FUSION DRIVE for Interstellar Exploration S.A. Cohen et al. INTERMEDIATE BEAMERS FOR STARSHOT: Probes to the Sun’s Inner Gravity Focus James Benford & Gregory Matloff REALITY, THE BREAKTHROUGH INITIATIVES and Prospects for Colonization of Space Edd Wheeler A GRAVITATIONAL WAVE TRANSMITTER A.A. Jackson and Gregory Benford CORRESPONDENCE www.bis-space.com ISSN 0007-084X PUBLICATION DATE: 29 APRIL 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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Registered Charity No: 250556. Printed by Latimer Trend & Company Ltd, Estover Road, Plymouth, PL6 7PY, England. © 2019 British Interplanetary Society. No part of this magazine may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying or recording by any information storage or retrieval system without prior permission from the Publishers. CONTENTS VOLUME 72 NO.2 FEBRUARY 2019 38 DIRECT FUSION DRIVE for interstellar exploration S.A. Cohen et al. 51 INTERMEDIATE BEAMERS FOR STARSHOT: Probes to the Sun’s Inner Gravity Focus James Benford & Gregory Matloff 56 REALITY, THE BREAKTHROUGH INITIATIVES and Prospects for Colonization of Space Edd Wheeler 62 A GRAVITATIONAL WAVE TRANSMITTER A.A. Jackson and Gregory Benford 70 CORRESPONDENCE OUR MISSION STATEMENT The British Interplanetary Society promotes the exploration and use of space for the benefit of humanity, connecting people to create, educate and inspire, and advance knowledge in all aspects of astronautics. JBIS Vol 72 No.2 February 2019 37 JBIS VOLUME 72 2019 PAGES 37–50 DIRECT FUSION DRIVE for interstellar exploration S.A. COHEN1, C. SWANSON1, N. MCGREIVY1, A. RAJA3, E. EVANS1, P. JANDOVITZ1, M. KHODAK3, GARY PAJER2, T.D. ROGNLIEN4, STEPHANIE THOMAS2, MICHAEL PALUSZEK2 1Princeton Plasma Physics Laboratory, Princeton NJ, USA; 2Princeton Satellite Systems, Plainsboro, NJ, USA; 3Princeton University, Princeton, NJ, USA; 4Lawrence Livermore National Laboratory, Livermore, CA, USA. Email [email protected] (corresponding author) The Direct Fusion Drive rocket engine (DFD), based on the Princeton Plasma Physics Laboratory’s Princeton Field Reversed Configuration machine, has the potential to propel spacecraft to interstellar space and to nearby solar systems. This paper discusses a design for a starship that would be well suited to a variety of solar system and interstellar missions. DFD employs a unique plasma heating system to produce nuclear fusion engines in the range of 1 to 10 MW, ideal for human solar-system exploration, robotic solar-system missions, and interstellar missions. This paper gives an overview of the physics of the engine. Its innovative radiofrequency (RF) plasma heating system and the fuel choice are explained. The thrust augmentation method is described along with results of multi-fluid simulations that give an envelope of expected thrust and specific impulse. The power balance is described and the subsystems needed to support the fusion core are reviewed. The paper gives the latest results for the system design of the engine, including just-completed work done under a NASA NIAC study. A mass budget is presented for the subsystems. The paper then presents potential interstellar missions. The first are flyby missions. One is the proposed 550-AU mission that would use the Sun as a gravitational lens for exoplanet research. This mission can be done without a deceleration phase. Next, flyby missions – requiring major technological advances – to the nearest star are described. Finally we sketch a mission to orbit a planet in either the Alpha Centauri A or Alpha Centauri B systems. The mission analyses include a communications system link budget. DFD can operate in an electric-power-only mode, allowing a large fraction of the fusion power to be used for the payload and communications, enhancing the scientific return. All of the missions start in low Earth orbit. Keywords: Interstellar Mission, Solar Sail Spacecraft, Post-Newtonian Gravitational Theory 1 INTRODUCTION NOMENCLATURE The idea to use fusion power for spacecraft propulsion has a B = magnetic field long history [1, 2], with its support arising from the high ener- β = ratio of plasma pressure to magnetic-field energy density gy density of the fuel and the high velocity of the fusion prod- c = speed of light ucts. Early proponents of fusion rockets that provided steady – rather than pulsed or explosive – propulsion based their de- cs = ion sound speed signs on the fusion devices that were then in vogue, tokam- E = ratio of plasma FRC plasma core length to diameter aks [3, 4], mirror machines [5] and levitated dipoles [6]. The γLH = Lower-hybrid drift instability growth rate experimental results of that period in fusion history indicated Ip = plasma current that the plasma’s anomalous transport, meaning poor plasma energy confinement, and instability would necessitate low β, Isp = specific impulse D-T burning,