JBIS - Journal of the British Interplanetary Society VOLUME 72 NO.2 FEBRUARY 2019 General interstellar issue CONTENTS: 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. ISSN 0007-084X | PUBLICATION DATE: 29 APRIL 2019 www.bis-space.com Submitting papers to JBIS: JBIS welcomes the submission of technical papers for publication dealing with technical reviews, research, technology and engineering in astronautics and related fields. Editor: Roger Longstaff Deputy Editor: Duncan Law-Green Associate Editors: Stephen Ashworth, Keith Cooper, Stephen Gamble, Paul Gilster, Rob Swinney Production: MP3 Media Promotion: Gill Norman JBIS Office: British Interplanetary Society, Arthur C. Clarke House, 27-29 South Lambeth Road, London, SW8 1SZ, United Kingdom International Advisory Board includes: Rachel Armstrong, Peter Bainum, Stephen Baxter, James Benford, James Biggs, Anu Bowman, Gerald Cleaver, Charles Cockell, Ian A. Crawford, Adam Crowl, Eric W. Davis, Kathryn Denning, Martyn Fogg, Raghavan Gopalaswami, Lamartine Guimarães, Mark Hempsell, Takuto Ishimatsu, Les Johnson, Terry Kammash, Kelvin F. Long, Inoue Makoto, Gregory L. Matloff, Koichi Mori, Richard Obousy, Robert Parkinson, George Schmidt, Paul Schuch, Tabitha Smith, Andreas Tziolas, Chris Welch, Friedwardt Winterberg. DIRECT FUSION DRIVE for interstellar exploration S.A. COHEN, C. SWANSON, N. MCGREIVY, A. RAJA, E. EVANS, P. JANDOVITZ, M. KHODAK, GARY PAJER, T.D. ROGNLIEN, STEPHANIE THOMAS, MICHAEL PALUSZEK Email: [email protected] ABSTRACT: 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 NOMENCLATURE: B = magnetic field β = ratio of plasma pressure to magnetic-field energy density c = speed of light cs = ion sound speed E = ratio of plasma FRC plasma core length to diameter γLH = Lower-hybrid drift instability growth rate Ip = plasma current Isp = specific impulse MT = metric tonne, 10^3 kg q = plasma safety factor rs = FRC core plasma radius s = 0.3 rs/ρi S* = rs ωpi/c Th = Thrust τA = Alfvén time ~ rsE/cs ωpi = ion plasma frequency 1. INTRODUCTION The idea to use fusion power for spacecraft propulsion has a long history, with support arising from the high energy density of the fuel and the high velocity of the fusion products. Early steady-state concepts required massive Tokamaks or mirror machines burning D-T fuel. New Field-Reversed Configuration (FRC) designs provide high beta (over 10x higher than tokamaks), compact size, lower magnetic field requirements, and enable aneutronic fuels such as D-3He. 2. THE DFD ROCKET ENGINE CORE The core operates at ca. 100 keV and moderate density (~5 x 10^14 cm^-3) confined inside a magnetic separatrix. Odd-parity Rotating Magnetic Field (RMFo) heating provides stable plasma current drive without tilt instability, keeping the device small (radius ~ 30 cm) and kinetic rather than fluid-like. 3. FUEL CHOICE, NEUTRON PRODUCTION, AND POWER BALANCE D-3He fuel is selected. Fast fusion products passing through the cool Scrape-Off Layer (SOL) experience electron drag (airbrake-like effect) rapidly cooling them and preventing excessive D-D side-reaction neutron production. Increasing the 3He to D ratio to 2:1 reduces neutron flux by orders of magnitude. Table 1 Parameters for a 2-MW DFD rocket engine: - rs: 0.3 m - Elongation E: 6 - Ba: 4.3 T - Ip: 8.0 MA - Fuel: D-3He (2:1 ratio) - ne: 3 x 10^20 m^-3 - Te: 50 keV, Ti: 100 keV - <β>: 0.84 - PRMF: 0.5 MW - Fusion Power Pf: 2.13 MW - Specific Impulse Isp: 2.3 x 10^4 s - Thrust: 12.5 N - Engine Mass: 1700 kg 5. MISSIONS - 550-AU Mission: Deliver a 1-m optical telescope to 550 AU using solar gravitational lensing to image exoplanets with 3-km surface resolution at 30 parsecs. Transit takes 13 years. - Interstellar Rendezvous & Flyby: Missions to Alpha Centauri at 100 MW power level can achieve rendezvous in ~325-500 years with staged jettisoning of modules and high specific power (5 to 100 kW/kg). INTERMEDIATE BEAMERS FOR STARSHOT: Probes to the Sun's Inner Gravity Focus JAMES BENFORD & GREGORY MATLOFF Email: [email protected] / [email protected] ABSTRACT: The Starshot technology development program will build a modular Beamer system that will incrementally achieve steadily higher launch speeds. We examine what an intermediate-level Starshot Beamer system would be like and the relative merits of Beamer technologies in nearer-term missions. We quantify one such intermediate destination for robotic probes, the Sun's Inner Gravity Focus. A constellation of such probes would each see a "pixel" of the image plane. We describe cost-minimized Beamers driving probes to ~100km/sec using laser, millimeter-wave and microwave sources and antennas/optics. Such systems would cost roughly $1 billion at present costs. Substantial progress on driving down laser and/or millimeter-wave costs is essential to near-term system cost reductions. Power density in the sail varies substantially among the Beamers, with lasers giving the lowest sail temperatures. Key Findings: - Investigates launching 4-gram sails (1.5-gram payload, 5-m diameter) to 100 km/s to reach the solar gravitational focus (550–600 AU) in ~30 years. - Comparison of Beamer technologies: * Present-day Laser Beamer: 21 MW power, 52 m aperture, capital cost ~$4.25B, sail temp ~1,000 K. * Optimistic Laser Beamer: 36 MW power, 30 m aperture, capital cost ~$0.73M (assuming radical cost reduction to $0.01/W). * Millimeter-Wave (with economies of scale): 1.5 GW power, 3.7 km aperture, capital cost ~$2B, sail temp ~2,900 K. * Microwave Beamer: 29 GW power, 1.9 km aperture, capital cost ~$0.58B, sail temp ~6,000 K. - Conclusion: Laser systems yield the lowest thermal strain on sails, but power cost reductions are crucial. REALITY, THE BREAKTHROUGH INITIATIVES and Prospects for Colonization of Space EDD WHEELER Email: [email protected] ABSTRACT: Although Einstein considered truth as independent of human beings, reality for us is tied to human experience and the five senses. It is the context in which lives, aspirations, and plans develop or fail. Understanding reality is essential in laying markers for progress or lapse in momentous undertakings such as the Breakthrough Initiatives begun in 2015 and in man's possible attempt to colonize space. This article examines the progress made in these two endeavors in context of reality and dangers. Breakthrough Initiatives to date has resulted at best in moderate success, but has yet to run half its at least decade-long course. Emphasis has switched from its unfocused Breakthrough Message program to the "Starshot" space probe, intended to launch by 2050 scores of tiny sail-craft, propelled by coordinated emissions from a field of lasers, to unprecedented velocity of .192 c. In a 22-year journey to nearest star system, Alpha Centauri, nanocraft will investigate if exoplanet Proxima Centauri b is habitable or has identifiable life. Among the challenges is whether craft can withstand the many thousands of g (gravitational) forces exerted during acceleration. Sustaining public interest for 26 years between launch and receipt of data may be difficult. A brief and compelling statement by the Initiatives to the public is needed on why space exploration is in their interest and how it could be decisive in the future of mankind. Sections discuss: - Epistemological definitions of reality (Davies, Hawking, Tegmark, Penrose, Dawkins, James). - Breakthrough Listen, Breakthrough Message, and Starshot initiatives. - Hostile radiation environment around Proxima Centauri b and Trappist-1. - Challenges of sail durability under 60,000 g acceleration. - Debates on space colonization featuring Hawking, Wilson, Dyson, O'Neill, Musk, and Eiseley. A GRAVITATIONAL WAVE TRANSMITTER A. A. JACKSON & GREGORY BENFORD Email: [email protected] / [email protected] ABSTRACT: We consider how an advanced civilization might build a radiator to send gravitational waves signals by using small black holes. Micro black holes on the scale of centimeters but with masses of asteroids to planets are manipulated with a super advanced instrumentality, possibly with very large electromagnetic fields. The machine envisioned emits gravitational waves in the GHz frequency range. If the source to receiver distance is a characteristic length in the galaxy, up to 10000 light years, the masses involved are at least planetary in magnitude. To provide the energy for this system we posit a very advanced civilization that has a Kerr black hole at its disposal and can extract energy by way of super-radiance. Background gravitational radiation sets a limit on the dimensionless amplitude that can be measured at interstellar distance using a LIGO-like detector. Key Concepts: - Kardashev Type II / III civilizations sending communications via high-frequency (~1-3 GHz) gravitational waves. - Zoom-Whirl Orbit Mechanism: A 0.1 Earth mass black hole orbiting a 1.0 Earth mass black hole at relativistic speeds near the critical radius (rp ~ 3-5 rs), radiating ~10^47 ergs per orbit in pulses. - Power Source: A Kerr black hole power plant exploiting superradiance (the "black hole bomb" effect) inside a reflective cavity to generate the 10^48 - 10^49 ergs needed to manipulate orbital dynamics. - Motivations for gravwave beacons: Longevity, legacy memorials ("Kilroy Was Here", "High Church", "Ozymandias"), and intentional electromagnetic silence to avoid aggressive civilizations. CORRESPONDENCE: Letter from Dr. David G. Stephenson (Merrickville, Ontario, Canada) clarifying the historical origin of the term 'Fermi's Paradox' in archival literature, originating from discussions at the British Interplanetary Society during the summer of 1976 and published in JBIS in March 1977. ANNOUNCEMENTS: - Call for Papers: One-day technical symposium "Putting Astronauts in Impossible Locations" on Wednesday 27th November 2019 at BIS HQ, London. - Vacancy Announcement: Society seeking replacement Editor for JBIS following Roger Longstaff's tenure.