Design Reference Mission Set for RPS Enabled Missions in Support of NASA's SSE Roadmap

Abstract

NASA's 2006 Solar System Exploration (SSE) Strategic Roadmap identified a set of small, medium and large missions, to address exploration targets, set out by the National Research Council (NRC) in the SSE Decadal Survey. Large size Flagship class missions are proposed to target Europa, Titan / Enceladus, Venus, and the Neptune system. Under the current candidate architectures, all of these Flagship class missions would require Radioisotope Power Systems (RPSs), as enabling technologies. Medium size New Frontiers (NF) class missions could also consider RPSs, although the ones targeting the 3rd NF opportunity would not likely utilize them. To constrain costs, small size Discovery class missions are not allowed to use RPSs. The proposed SSE Roadmap missions represent the highest priority subset of a broader collection of mission concepts, called NASA's SSE Design Reference Mission (DRM) set. In line with the SSE DRM set, the RPS DRM set includes a collection of potential future missions, which could be enabled or enhanced by the use of RPS technologies. Currently, NASA has proposed the development of the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), with static power conversion; and the Stirling Radioisotope Generator (SRG), with dynamic conversion. Advanced RPSs under consideration for possible development target increased specific power levels, consequently increasing electric power generation for the same amount of fuel, or reducing fuel requirements for the same power output, compared to the proposed MMRTG or SRG. It is expected that the RPSs will need modifications to operate in the extreme environments of Titan or Venus. An RPS on the proposed Titan Explorer would use smaller fins to minimize heat rejection in the extreme cold environment; while the Venus Mobile Explorer long-lived in situ mission would require the development of a new RPS, in order to tolerate the extreme hot environment, and to provide active cooling to the payload and other electric components. This paper discusses NASA's SSE RPS DRM set in line with the SSE DRM set, and gives a qualitative assessment of the impact of various RPS options on the potential mission architectures. The assessment could aid NASA with RPS technology development planning, and with the understanding of fuel needs over the next three decades.