In this paper we discuss the advantages and challenges of utilizing Fission
Fragment Rocket Engines (FFREs) to dramatically reduce transit time in space
travel, for example, traveling to Mars. We discuss methods to decrease the size
and weight of FFREs. These include utilizing metallic deuterides as moderators,
driving the engines with electron beam bremsstrahlung, and operating the FFREs
as subcritical assemblies, not as nuclear reactors. We discuss these and other
new innovations based upon improved materials and technology that may be
integrated into a revolutionary nuclear rocket technology.Comment: 10 pages, 2 figures, 2 table