Advanced Stirling Radioisotope Generator

The advanced Stirling radioisotope generator (ASRG) is a radioisotope power system first developed at NASA's Glenn Research Center. It uses a Stirling power conversion technology to convert radioactive-decay heat into electricity for use on spacecraft. The energy conversion process used by an ASRG is about four times more efficient than in previous radioisotope systems to produce a similar amount of power, and allows it to use about one quarter of the plutonium-238 as other similar generators.

Despite termination of the ASRG flight development contract in 2013, NASA continues a small investment testing by private companies. Flight-ready Stirling-based units are not expected before 2028.

Development

Development was undertaken in 2000 under joint sponsorship by the United States Department of Energy (DoE), Lockheed Martin Space Systems, and the Stirling Research Laboratory at NASA's Glenn Research Center (GRC) for potential future space missions.

In 2012, NASA chose a solar-powered mission (InSight) for the Discovery 12 interplanetary mission, negating the need for a radioisotope power system for the 2018 launch.

The DOE cancelled the Lockheed contract in late 2013, after the cost had risen to over $260 million, $110 million more than originally expected.

Specifications

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, Mars Science Laboratory, and Mars 2020) 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.

The two finished units had these expected specifications:
*≥14-year lifetime
*Nominal power: 130 W
*Mass:
*System efficiency: ≈ 26%
*Total mass of plutonium-238-dioxide:
*Plutonium housed in two General Purpose Heat Source (“Pu²³⁸ Bricks”) modules
*Dimensions: 76 cm × 46 cm × 39 cm (2.5 ft × 1.5 ft × 1.3 ft)

Flight proposals

ASRGs could be installed on a wide variety of vehicles, from orbiters, landers and rovers to balloons and planetary boats. A spacecraft proposed to use this generator was the TiME boat-lander mission to Titan, the largest moon of the planet Saturn, with a launch intended for January 2015, or 2023. 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. In August 2012, TiME also lost the 2016 Discovery class competition to the InSight Mars lander.

The Herschel Orbital Reconnaissance of the Uranian System (HORUS) mission was proposing to use three ASRGs to power an orbiter for the Uranian system. Another Uranus probe concept using the ASRG was MUSE which has been evaluated as both an ESA L-Class mission and New Frontiers enhanced mission. The Jupiter Europa Orbiter mission proposed using four ASRG to power an orbiter in the Jovian system. Another possibility was the Mars Geyser Hopper.

It was proposed in 2013 to fly three ASRG units on board the FIRE probe to study Jupiter's moon Io for the New Frontiers program Mission 4.

See also

* Nuclear power in space
* Radioisotope heater unit
* Stirling engine
* Stirling radioisotope generator

References

External links

Advanced Stirling Technology Development at NASA Glenn Research Center
at NASA, 2015 (PDF)
ASRG Technical Interchange Meeting
at NASA, 2015 (PDF)
Advanced Stirling {{sic, Conv, ertor, nolink=y Development for NASA Radioisotope Power Systems
Sunpower, Inc. & GRC. April 1, 2015.

Nuclear technology
Electrical generators
Nuclear power in space
Stirling engines