Advanced Stirling radioisotope generator

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Cutaway diagram of the advanced Stirling radioisotope generator.

The advanced Stirling radioisotope generator (ASRG) was a radioisotope power system under development for NASA. It would have used a Stirling power conversion technology, to convert radioactive-decay heat into electricity for use on spacecraft. The development was cancelled in 2013.


Development was undertaken under joint sponsorship by the United States Department of Energy and NASA for potential future space missions. The development was cancelled in 2013 after the cost had risen to over 260 million US dollars, 110 million more than originally expected.[1]


The higher conversion efficiency of the Stirling cycle compared with that of radioisotope thermoelectric generators (RTGs) used in previous missions (Viking, Pioneer, Voyager, Galileo, Ulysses, Cassini, New Horizons, and Mars Science Laboratory) would have offered an advantage of a fourfold reduction in PuO2 fuel, at half the mass of an RTG. It would have produced 140 watts of electricity using a quarter of the plutonium an RTG or MMRTG needs.[2]

NASA got a final design for the ASRG, plus a partially completed qualification unit, which was shipped to NASA's Glenn Research Center. Glenn Research Center will continue development and testing of Stirling technology for potential use by future space exploration missions.[3][4] However, while NASA is pressing on with some basic technology development for the ASRG, there are no longer plans to produce a flight unit.[2]

The finished prototype generator has these specifications:[5]

Flight proposals[edit]

A spacecraft proposed to use this generator was the TiME lander mission to Titan, the largest moon of the planet Saturn, with a launch intended for January 2015.[6][7] In February 2009 it was announced that NASA/ESA had given Europa Jupiter System Mission (EJSM/Laplace) mission priority ahead of the Titan Saturn System Mission (TSSM), which could have included TiME.[8][9] In August 2012, TiME also lost the 2016 Discovery class competition to the InSight Mars lander.[10]

The HORUS mission was proposing to use three ASRG to power an orbiter for the Uranian system.[11] The Jupiter Europa Orbiter mission proposed using four ASRG to power an orbiter in the Jovian system. Another possibility was the Mars Geyser Hopper

See also[edit]


  1. ^ The ASRG Cancellation in Context Future Planetary Exploration
  2. ^ a b Leone, Dan (11 March 2015). "U.S. Plutonium Stockpile Good for Two More Nuclear Batteries after Mars 2020". Space News. Retrieved 2015-03-12. 
  3. ^ Stirling Converter Technology. NASA, 2014
  4. ^ Closing out the ASRG program. Author: Casey Dreier. 23 January 2014.
  5. ^ NASA's Planetary Science Division Update (June 23, 2008).
  6. ^ Stofan, Ellen (25 August 2009). "Titan Mare Explorer (TiME): The First Exploration of an Extra-Terrestrial Sea" (PDF). Archived (PDF) from the original on 24 October 2009. Retrieved 2009-11-03. 
  7. ^ Titan Mare Explorer (TiME): The First Exploration of an Extra-Terrestrial Sea
  8. ^ "NASA and ESA Prioritize Outer Planet Missions". NASA. February 18, 2009. 
  9. ^ Rincon, Paul (February 18, 2009). "Jupiter in space agencies' sights". BBC News. 
  10. ^ Vastag, Brian (August 20, 2012). "NASA will send robot drill to Mars in 2016". Washington Post. 
  11. ^ Smith, R.M.; Yozwiak, A.W.; Lederer, A.P.; Turtle, E.P. (2010). "HORUS—Herschel Orbital Reconnaissance of the Uranian System". 41st Lunar and Planetary Science Conference: 2471. Bibcode:2010LPI....41.2471S. 

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