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RPS: Radioisotope Power Systems
New Horizons
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Artist's rendering of the New Horizons during its Pluto flyby.

The Power to Explore...Pluto!

  • Launched on January 19, 2006
  • Performed gravity assist flyby of Jupiter in 2007
  • Spacecraft en route to Pluto and the Kuiper Belt, passing Pluto in July 2015

Powered by: one GPHS-RTG

Goals: NASA's New Horizons spacecraft is designed to make the first close-up study of Pluto and its moons and other icy worlds in the distant Kuiper Belt. The spacecraft has seven scientific instruments to study the atmospheres, surfaces, interiors and intriguing environments of Pluto and its distant neighbors.

Accomplishments: The spacecraft is closing in on its primary science target, and started a long-distance observation campaign of the Pluto system in January 2015. On the way to Pluto, New Horizons completed a thrilling study of the Jupiter system during its gravity assist flyby of the giant planet in 2007. The spacecraft took pictures of the planet and its moons, and detected clumps in Jupiter's rings and lightning near its poles. As it departed Jupiter, New Horizons observed a unique space environment, traveling a long distance down the tadpole-shaped tail of Jupiter's magnetic field.


About the Radioisotope Thermoelectric Generator

Electrical power for the New Horizons mission to Pluto is furnished by a single radioisotope thermoelectric generator (RTG), which transforms the heat from the natural radioactive decay of plutonium dioxide into electricity. The compact, rugged General Purpose Heat Source (GPHS)-RTG aboard New Horizons, developed and provided by the U.S. Department of Energy, carries approximately 11 kilograms (24 pounds) of plutonium dioxide fuel.

By the time of the Pluto flyby in July 2015, the GPHS-RTG aboard New Horizons will supply 202 watts of power, down from 240 watts at launch. Onboard systems manage the spacecraft's power consumption (at 30 volts of direct current) so that the load does not exceed the output from the RTG, which slowly decreases by about four watts per year.

The GPHS-RTG has a rich history in space exploration, serving as the power system for the Cassini mission to Saturn, the Galileo mission to Jupiter, the Ulysses mission to polar orbit around the Sun.

As with several of these past outer planet missions powered by RTGs, New Horizons does not carry a battery for storing power. The spacecraft's shunt regulator unit maintains a steady input from the RTG and dissipates power the spacecraft cannot use at a given time. New Horizons can ease the strain on its limited power source by cycling science instruments on and off during planetary encounters.

An RTG has no moving parts. The power system transforms the heat emitted by the plutonium dioxide fuel directly into electricity using solid-state thermoelectric converters, which generate electricity using the flow of heat from the large temperature difference between the hot nuclear fuel and the cold environment of space outside the generator.

Radioisotope power systems enable spacecraft to operate at significant distances from the Sun or in other locations where solar power systems would not be feasible or effective; for example, sunlight is 1,000 times fainter at Pluto and in the Kuiper Belt compared to its brightness in Earth orbit. Used in space for more than 50 years, such power systems are reliable and durable, well matched to the challenging needs of New Horizons on its long, four billion-mile journey from Earth.


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Last Updated: 26 Sep 2012