Comparison of Radioisotope Power Systems to Enable the Endurance Mission Concept

NASA has a long history of using Radioisotope Power System (RPS) technologies to enable space missions. Today, NASA's RPS Program, working with the Department of Energy, deliver RPS to NASA missions to enable the exploration of cold, dark, dusty, and harsh environments. The RPS Program manages the investments made to develop RPS products to enable future missions. To better understand what technologies could most benefit current and future missions, the RPS Program conducts mission and systems studies. This study was undertaken to understand the impact of different RPS technologies on a lunar surface rover mission concept. The Endurance mission concept is one of the mission concept studies for the 2023-2032 Planetary Science and Astrobiology Decadal Survey. It would be an autonomous rover mission enabled by the RPS to traverse 2,000 km on the lunar surface collecting and delivering samples to the Artemis basecamp near the south pole. The baseline RPS used in the design concept for the four-year mission is the Next Gen RTG (NGRTG). To gain insight into the power requirements of a lunar rover mission concept, the RPS Program Office and the Jet Propulsion Laboratory's (JPL's) Team-X conducted a study comparing the impact of various RPS technology options using the Endurance rover concept as a baseline. The study generated parametric point-designs that analyzed one of two different thermal subsystem designs and, notably for the power system, one of four RPS products: MMRTG, NGRTG, plutonium oxide-based Stirling RPS, and an americium-based variant of Stirling RPS. From the RPS Program's perspective, the MMRTG is the current state-of-the-art, the NGRTG is a planned next generation product, and both Stirling RPS variants are potential future product offerings. The rover's thermal and mechanical design and configuration were altered to accommodate the RPS; other variables were kept constant throughout the study, facilitating the comparison of different point-designs. This paper provides a summary of the results of the Team-X study for the seven point-design that were evaluated. The metrics for evaluation were the estimated mass of the rover and the estimated mission duration; these metrics were selected to track the viability of rover delivery via a Commercial Lunar Payload Service (CLPS) lander, and in meeting the four-year mission duration requirement. Overall, the results showed that achieving mission closure for the Endurance rover mission is possible with any of the specified power systems and either of the heater architectures (depending on the power system implemented).