Nuclear Fusion Options for Interstellar Flight

Published January 22, 2019

The subject of my book is confined primarily to discussing how we can employ nuclear fission to enable human missions to the ends of our solar system. This kind of nuclear fission rocket technology was already ground tested in both the United States and the USSR during the 1950s and 1960s and is available today. It is a technology robust enough to transform our entire solar system into a virtual human lake having resources capable of sustaining our species for the next few centuries. I explain in my book how it enables us to make the transition into an interplanetary species.

In contrast, human interstellar travel will require even higher energy densities only available from highly advanced advanced nuclear fusion or matter-antimatter propulsion systems. We do not yet know how to build these kinds of systems but good theoretical work on the problem has been underway for several decades. An international workshop on the Foundations of Interstellar Studies held on June 13-15, 2017 at New York City College of Technology of the City University of New York (CUNY) explored some of these topics. Several papers presented at the conference have just been published in a special issue of the Journal of the British Interplanetary Society Volume 71, No. 8, 2018. I would like to call my readers’ attention to one of these papers that was presented by Robert G. Kennedy entitled “The Interstellar Fusion Fuel Resource Base of Our Solar System” appearing on pp. 298-305. Mr. Kennedy details the various types of nuclear fusion options that have been considered over the years and explores the benefits and shortcomings of each. These include tritium-tritium, , deuterium-helium3, helium3-lithium6, helium3-helium3, , deuterium-deuterium, deuterium-lithium6, proton-lithium6, and proton-boron11. He makes the case for why proton-boron11 is the most robust of these options from a theoretical standpoint but that our solar system holds only very limited reserves of boron11. After exploring the possibility of artificially creating boron 11 by bombardment of other nuclides he also acknowledges that this would prove to be very expensive. In his conclusion he pithily observes that “if we ever meet someone’s worldship fueled with boron-11, we’ll know that they’re either very rich or desperate.” (p. 305).

While we can probably send robotic flyby missions to some of our nearest stellar neighbors using either nuclear fission or very basic nuclear fusion building true interstellar space cruisers capable of slowing down at their destination remains at present a dream for the remote future. Solar sails and beamed propulsion have also been suggested but each presents their own technological challenges. I nonetheless recommend this special issue of the Journal that also contains such articles as “First Stop on the Interstellar Journey: The Solar Gravity Lens Focus” by Louis Friedman and Slava G. Turyshev, “Experimental Simulation of Dust Impacts at Starflight Velocities” by Andrew J. Higgins, “Plasma Dynamics in Firefly’s Z-pinch Fusion Engine” by Robert M Freeland II, “Gram-Scale Nano-Spacecraft Entry Into Star Systems” by Albert Allen Jackson IV, and “Tests of Fundamental Physics in Interstellar Flight” by Roman Ya Kezerashvili.