The Future of Space Propulsion

A paper presents an overview of state of the art of space propulsion, oriented toward attempting to understand recent history in order to make some predictions about future developments. As used here, “space propulsion” refers generally to what are now called “spacelift” and “spacecraft propulsion.” Further, as used here, “spacelift” refers generally to large rockets, associated equipment, and other resources for launching spacecraft into outer space, while “spacecraft propulsion” refers generally only to systems for propelling spacecraft once they are in outer space. The paper includes a summary of recent history of spacecraft propulsion, with greatest emphasis on spacelift systems, from the perspective of striving to maintain the military superiority and economic competitiveness of the United States in the face of the rapid international evolution of space technology. Advantages and disadvantages of various engine designs and propellant substances, and considerations of cost and development time, are discussed. Trends in spacelift (and, to a lesser extent, trends in spacecraft propulsion) are discussed. An attempt is made to predict the general nature of future developments by extrapolating the trends into the foreseeable future.