Nuclear Propulsion Systems: An Introduction
Nuclear propulsion systems offer massive comparative advantages over electric propulsion systems in terms of both thrust and Isp. Two categorical types of nuclear propulsion systems are outlined; first, direct thrust propulsion, which utilizes the products of a nuclear reaction for direct propulsion, and secondly, nuclear thermal propulsion, which uses thermal expansion as thrust. Currently, however, no direct nuclear or nuclear thermal propulsion system has flown; testing, including full operation of a nuclear thermal thruster has occurred, and research with more advanced nuclear systems is currently being conducted. Therefore, this webpage considers nuclear propulsion systems inherently unviable; the subsequent sections detail theoretical viability of various nuclear propulsion systems, but a full analysis is restricted due to current developmental stage.
Direct Nuclear Thrust Systems
Figure 13: A conceptual design for a fission fragment thruster. A indicates the exhaust nozzle on the thruster, B indicates the interior fragment confinement and radiofrequency bombardment chamber, C denotes the deceleration chamber for accelerated particles, d shows the confinement electromagnets, e indicates the radiofrequency coupler, and f is the individual radiofrequency antennae. (Duckysmokton, Dusty plasma bed reactor, 2007).
A direct nuclear thrust system uses the products of a nuclear reaction as propellant; three conceptual types are analyzed with an assessment on current development, theoretical performance, and conceptual design. While these technologies are currently theoretical, assessment of viability is vital for the continuation of current developmental strategies and research investment. An overall conclusion states this report’s recommendation for the technology that best accomplishes the mission parameters based upon theoretical application and functionality.
Nuclear Thermal Thrust Systems
Figure 20: Diagram denoting the operation of an active nuclear thermal propulsion system (CommiM, 2007).
Contrasting with the operating principle of direct nuclear thrust systems, nuclear thermal thrust systems do not rely upon the products of a nuclear reaction for direct thrust; instead, nuclear thermal thrust systems rely upon the heat generated during a reaction to expand and expel particles for propulsion. Although no nuclear thermal propulsion system is flight tested, several extensive governmental projects developed and ground tested preliminary nuclear thermal thrusters. Two primary categories of nuclear thermal thrusters are briefly examined, with an analysis of the current and future viability for each of the developing conceptual technologies.
Nuclear Propulsion Systems: Conclusion
Of the two primary nuclear propulsion categories, direct and thermal, this report recommended the most potentially viable propulsion system based upon both current and foreseeable development and research. Nuclear propulsion systems for space-based applications are currently unimplemented, and this report cannot fully consider any aforementioned technology viable until it has reached an acceptable level of research and development. Several technologies within the nuclear propulsion category are tested, but this report cautions an incorrect assessment of validity for systems not extensively tested and adequately applied. Based upon conclusions reached by this paper in the preceding sections, the conceptual nuclear thermal propulsion technology with the highest potential viability is the NSWR thruster. High Isp and thrust ranges are conducive to the potential viability of this propulsion method. A significant negative aspect of the NSWR reactor is the untested theoretical basis of operation; significant debate over the functionality of the reaction method creates significant viability concerns. While a highly promising technology, the current stage of conceptualization restricts it to a partial recommendation for validity. Selected as potentially most viable from the direct nuclear propulsion category, the NPP system shows an extremely high potential for fulfilling the required constraints; outperforming the NSWR reactor with extremely high thrust and Isp levels, the NPP system is also in a higher stage of development and testing. A significant concern with the NPP system is the United Nations treaty banning nuclear tests in outer space; as NPP relies upon fusion explosions to propel the spacecraft, significant proliferation concerns could restrict its use (United Nations, 1963). Although both propulsion methods offer significant advantages over other alternatives in fulfilling the mission constraints, the NPP system receives this reports recommendation based upon a higher stage of development and improved overall performance; this technology is considered viable pending application and further testing.