Interstellar propulsion opportunities using near-term technologies

Interstellar transportation over periods shorter than the human lifetime requires speeds in the range of 0.2-0.3c. These speeds are not attainable using rockets, even with advanced fusion engines. Anti-matter engines are theoretically possible but current physical limitations would have to be suspended to get the mass densities required. Interstellar ramjets have not proven practicable, so this leaves beamed momentum propulsion as the remaining candidate. This paper reviews the state of beamed-momentum in-space propulsion and presents a point design system suitable for human exploration of nearby stars using today's physics and resources known to exist in the solar system. The total beam energy requirement for an interstellar probe mission is roughly 10(20) J, which would require the complete fissioning of one thousand tons of uranium assuming 35 percent power plant efficiency. This is roughly equivalent to a recurring cost per flight of 3.0 billion dollars in reactor grade enriched uranium using today's prices. Therefore, interstellar flight is an expensive proposition, but not unaffordable, if the nonrecurring costs of building the power plant can be minimized. (C) 2003 International Astronautical Federation. Published by Elsevier Ltd. All rights reserved.