Department of Energy

To Pluto and Beyond: Powering New Horizons’ 3-Billion-Mile Journey

July 15, 2015

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This image of Pluto, taken by New Horizons after a 9 1/2-year journey, is our highest-resolution photo of the dwarf planet since its discovery by Clyde Tombaugh in 1930. | Photo courtesy of NASA.

This image of Pluto, taken by New Horizons after a 9 1/2-year journey, is our highest-resolution photo of the dwarf planet since its discovery by Clyde Tombaugh in 1930. | Photo courtesy of NASA.

NASA’s New Horizons spacecraft just accomplished one of the most exciting feats in the history of space exploration. After a 9 1/2-year, 3-billion-mile journey, the mission’s historic flyby of Pluto has provided us with our first-ever closeup views of the frozen world at the edge of the solar system. It’s a remarkable achievement, one that wouldn’t have been possible without careful planning, ingenuity -- and a little help from the Department of Energy.

In 2006, when NASA engineers were designing New Horizons, they knew that it would need a long-lasting, compact and incredibly reliable power source to survive the cold, dark reaches of outer space.

Solar power was out of the question. The spacecraft’s itinerary would take it billions of miles from the center of the solar system into the realm of Pluto and the Kuiper Belt. That far out, the Sun shines with just a tiny fraction of the intensity we see here on Earth -- scarcely brighter than the stars in the night sky. Other options like batteries or fuel cells wouldn’t last long enough.

Surface of Pluto

New close-up images of Pluto's surface reveal mountains rising as high as 11,000 feet. | Photo courtesy of NASA.

For New Horizons, the answer lay in the power of plutonium. Specifically, in a radioisotope thermoelectric generator (RTG). This simple form of nuclear power, developed by the Energy Department, takes heat from the radioactive decay of plutonium-238 and converts it into electricity using devices called “thermocouples.” The RTG provides about 200 Watts of electricity to the spacecraft.

Used by the United States in space exploration since the 1960s, RTGs are rugged and reliable, with no moving parts to wear out or break. That durability made an RTG the perfect candidate to power a deep-space mission like New Horizons. To build it, NASA turned to the Energy Department’s National Labs.

The heat-producing ceramic “fuel pellets” of plutonium dioxide for the RTG -- designed and safety-tested by Energy Department scientists -- were manufactured at Los Alamos National Laboratory in New Mexico, with special iridium and graphite shielding provided by Oak Ridge National Laboratory in Tennessee. The plutonium-238 itself came from the Savannah River Site in South Carolina, which produced nuclear fuel for NASA's space missions for nearly three decades.

The final product was assembled at Idaho National Laboratory in September 2005, just three years after the Energy Department decided to relocate its RTG program there in 2002. That’s especially impressive when you consider that an entirely new facility needed to be constructed before the team could even begin to build and test the RTG for New Horizons.

Pluto's moon Charon

Pluto’s largest moon Charon is seen in remarkable detail in this July 13, 2015, image from New Horizons. | Photo courtesy of NASA.

New Horizons has now captivated the world with its breathtakingly detailed images of Pluto’s surface, but it isn’t done exploring. Through the Kuiper Belt and beyond, its RTG will keep it warm and watchful as it ventures into the outer reaches of our solar system.

The Energy Department is thrilled to be part of this momentous journey and to witness these groundbreaking discoveries. We’re ready to support NASA’s exploration of our universe wherever it takes us.

To learn more about the Energy Department’s role in the U.S. space program, check out our interactive timeline of nuclear-powered NASA missions through history.