NASA Radioisotope Power System Program - Technology and Flight Systems

Abstract

NASA sometimes conducts robotic science missions to solar system destinations for which the most appropriate power source is derived from thermal-to-electrical energy conversion of nuclear decay of radioactive isotopes. Typically the use of a radioisotope power system (RPS) has been limited to medium and large-scale missions, with 26 U,S, missions having used radioisotope power since 19' 61. A research portfolio of ten selected technologies selected in 2003 has progressed to a point of maturity, such that one particular technology may he considered for future mission use: the Advanced Stirling Converter. The Advanced Stirling Radioisotope Generator is a new power system in development based on this Stirling cycle dynamic power conversion technology. This system may be made available for smaller, Discovery-class NASA science missions. To assess possible uses of this new capability, NASA solicited and funded nine study teams to investigate unique opportunities for exploration of potential destinations for small Discovery-class missions. The influence of the results of these studies and the ongoing development of the Advanced Stirling Radioisotope Generator system are discussed in the context of an integrated Radioisotope Power System program. Discussion of other and future technology investments and program opportunities are provided.I. Introduction Solar system exploration is a mainstay of the scientific program of robotic spacecraft missions conducted by NASA. To enable certain missions, power must be generated without the use of conventional photovoltaic methods. Use of radioisotope power systems has been finnl y established since 1961 as a means to fulfill the need for such power among a variety of missions. Twenty-six missions have taken advantage of the investments of radioisotope power systems development to allow scientific exploration of destinations such as the moon, Mars, Jupiter, Saturn, and Pluto. Because of the longevity of radioisotope power systems, some of these missions have even continued to perform extended mission operations beyond the farthest reaches of the solar system.The contemporary method of energy conversion for flight radioisotope power uses the Seebeck effect, in a thennoelectric (TE) energy conversion process. This method was first used in flight in 1961 , and continues today as the means to power the Mars Science Lab rover. MSL uses the Multi-Mission Radioisotope Thennoelectric Generator (MMRTG), and is scheduled for launch in 2011. Thennoelectric energy conversion technology investments over the years have yielded more robust components that have a longer life. IE power systems have now been seen to demonstrate over 30 years of spaceflight operation on the two Voyager spacecraft, for example. While thermoelectric technology is well proven. it also has fairly poor conversion efficiency.Investments seeking alternative energy conversion methods have been made over the years at both NASA and DOE. Most recently, NASA invested in a radioisotope power conversion technology program. A gas...

NASA’s Radioisotope Power Systems Program Status

“…Other investments in energy conversion R technologies have been made to identify and improve performance of particular approaches of both static and dynamic methods. 3,4,5 In 2010, NASA established the RPS Program. 1 The Program is chartered to provide flight systems, develop supporting technologies and promote operational efficiencies.…”

Power for Science and Exploration: Upgrading the General-Purpose Heat Source Radioisotope Thermoelectric Generator (GPHS-RTG)

“…In 2007, NASA directed that the new OPFM would use the MMRTG. 11 Separately, NASA's Jet Propulsion Laboratory (JPL) pursued development of an Advanced Radioisotope Thermoelectric Generator (ARTG) with plans to provide BOM powers in the range 250 We to 270 We at a system efficiency of 8% to 9% and a specific power of about 7 We/kg. 12,13,14 Beginning-of-life (BOL) power is defined at the time of RPS fabrication by DOE.…”

“…2 American Institute of Aeronautics and Astronautics In the world of "faster, cheaper, better" and smaller, U.S. radioisotope power source (RPS) efforts naturally have focused on the lower powered (~125 We BOL) Multi-Mission RTG (MMRTG) for the Mars Science Lander (MSL) and the Advanced Stirling Radioisotope Generator (ASRG) (~140 We BOL). 10,11 In parallel, there has been some technology development aimed at producing a higher power (~250 We -270 We) Advanced RTG (ARTG). 12,13,14 (It should be noted that with work both the MMRTG and ASRG technologies could be upgraded to produce higher powers.)…”

“…14,15 NASA and DOE are pursuing an aggressive program to address these issues, including a flight test to provide added confidence in the ASRG. 11 The ARTG, which has attractive performance goals, was not selected because it was "judged too risky and immature for the either the 2015 or 2017 launch opportunities" evaluated in the Europa Explorer study. 14 It was estimated to have a "longer development schedule and higher development risk" and to be "still in its infancy in concept development".…”

Space Nuclear Power and Propulsion at USNC-Tech

“…VENNERI and EADES • SPACE NUCLEAR POWER AND PROPULSION AT USNC-TECH probes such as the Cassini and the Voyager utilized 238 Pu power systems because of game-changing capabilities to enable the science goals of those missions. While 238 Pu radioisotope power sources are enabling due to their extremely high performance and reliability, 21,22 the cost and availability of 238 Pu have by necessity prevented their implementation beyond flagship and new frontiers missions. 23 This is not to say that lower-budget missions wouldn't benefit tremendously from using a radioisotope power system.…”