In-space nuclear power as an enabling technology for exploration of the outer heliopause

Deep space missions, both for scientific and human exploration and development, are as weight limited today as they were 35 yr ago. Right behind the weight constraints is the nearly equally important mission limitation of cost. Launch vehicles, upper stages, and in-space propulsion systems also cost about the same today with the same efficiency as they have had for many years (excluding impact of inflation). These dual mission constraints combine to force either very expensive, megasystem missions or very light weight, but high risk/low margin planetary spacecraft designs, such as the recent unsuccessful attempts for an extremely low cost mission to Mars during the 1998-99 opportunity (Mars Climate Orbiter and Mars Polar Lander). When one considers spacecraft missions to the heliopause, the enormous weight and cost constraints will impose even more daunting concerns for mission cost, risk, and the ability to establish adequate mission margins for success. This paper will address the benefits of using a safe in-space nuclear reactor as the basis for providing both sufficient electric energy and high performance space propulsion that will greatly reduce mission risk and significantly increase weight initial mass in low-Earth orbit (IMLEO) and cost margins. Weight and cost margins are increased by enabling much higher payload fractions and redundant design features for a given launch vehicle (higher payload fraction of IMLEO). This paper will also discuss and summarize the recent advances in nuclear reactor technology and safety of modem reactor designs and operating practices and experience, as well as advances in reactor control coupled with high power generation and high performance nuclear thermal and electric propulsion technologies. It will be shown that these nuclear propulsion and power technologies are major enabling capabilities for higher reliability, higher margin and lower cost deep space missions designed to reliably reach the heliopause for scientific exploration.