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Radioisotope Power Systems: Power to Explore
Color illustration of spacecraft flying above Saturn's rings.
Artist's view of NASA's Voyager 2 spacecraft passing Saturn in 1981.

For more than four decades, Radioisotope Power Systems (PDF, 1.08 MB) (RPS) have played a critical role in the exploration of space, enabling missions of scientific discovery to destinations across the solar system. These pioneering voyages have helped reveal the composition and nature of Earth's Moon, allowed us to witness icy geysers and sulfur volcanoes on moons of the outer planets and sustained long journeys to the outer reaches of our sun's influence. NASA and the United States Department of Energy (DOE) are working together to ensure that space nuclear power technologies will be available to enable or enhance ambitious solar system exploration missions in this decade and beyond.

What is RPS technology and why does NASA use it?

Color photo of astronaut removing component from lunar module.
Astronaut Alan Bean unloads the plutonium fuel core that powered the Apollo Lunar Science Experiment Package, or ALSEP, which was deployed on five of the U.S. manned missions to the Moon.

One of the most important components for any space mission is a robust and reliable electrical power supply. For most space exploration missions where sunlight is abundant, solar power has been the preferred choice. But as the environments at chosen destinations grow harsher, and missions evolve to be more demanding, it becomes more likely that effective power and heating for a spacecraft would require the use of a radioisotope power system (RPS).

An RPS converts the heat generated by the natural decay of the radioactive isotope plutonium-238 into electricity; this material is not used in weapons and cannot explode like a bomb. A portion of this decay heat often has an important secondary use in helping to keep spacecraft subsystems warm in cold environments. RPS are designed and built with multiple layers of protective material designed to contain its plutonium dioxide fuel in a wide range of potential accidents, verified through impact testing. In addition, the plutonium used in an RPS is manufactured in a ceramic form, which limits its ability to become a health risk.

RPS offer the key advantage of operating continuously, independent of unavoidable variations in sunlight. Such systems can provide power for long periods of time (significantly longer than chemical batteries), and at vast distances from the sun. Additionally, an RPS has little sensitivity to temperature, radiation, dust or other space environmental effects. They are ideally suited for missions involving autonomous, long-duration operations in the most extreme environments in space and on planetary surfaces.

Targets of Exploration RPS-enabled NASA Missions
Sun Ulysses (1990-2009)
Moon Apollo Lunar Surface Experiment Package (1969-1977)
Mars Viking 1 and 2 (landers) (1976-1982)
+Mars Pathfinder (1997)
+Mars Exploration Rovers (MER) (2004-)
Mars Science Laboratory (Scheduled arrival 2012)
Jupiter and its moons Pioneer 10 and 11 (1972-1973)
Voyager 1 and 2 (1979)
Galileo (1995-2003)
Saturn and its moons Pioneer 11 (1973) Voyager 1 and 2 (1980)
Cassini-Huygens (2004-)
Uranus Voyager 2 (1986)
Neptune Voyager 2 (1989)
Pluto and the Kuiper Belt New Horizons (2015-)
+Solar powered missions enabled by radioisotope heater units (RHUs)


Color illustration of rover examining a rock on Mars.
An RPS called a Multi-Mission Radioisotope Thermoelectric Generator is planned for use on the Mars Science Laboratory mission.
As part of an ongoing partnership with the DOE, NASA is conducting a mission-driven RPS Program whose purpose is to develop the next generation of reliable radioisotope power systems. These technologies could enable a broad range of science missions to operate more widely and efficiently than their predecessors. This program is developing and validating two basic RPS units: the Multi-Mission Radioisotope Thermoelectric Generator (PDF, 378 KB) (MMRTG) and the Advanced Stirling Radioisotope Generator (PDF, 687 KB) (ASRG).

In the future, radioisotope power systems could continue to support missions to some of the most extreme environments in the solar solar system, probing the secrets of Jupiter's ocean moon Europa, the liquid lakes of Saturn's moon Titan or the brutally hot atmosphere of Venus.

Additional information

For more information about NASA's use of radioisotope power systems, contact Radioisotope Power Systems Program.

News Release, August, 2011:"Power to Explore: 50 Years of Nuclear Space Power".

RPS information from the US Department of Energy:http://www.ne.doe.gov/space/neSpace2a.html.


Radioisotope Power Source Fact Sheets:

Last Updated: 17 February 2012

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Last Updated: 17 Feb 2012