TABLE E.1 Radioisotope Power Systems for Space Exploration

Name and Model

Used on (Number of RTGs per User)

Maximum Output

Maximum Fuel Used (kg)

RPS Mass (kg)

Electrical (W)

Heat (W)


Transit-4A/B (1)






Transit 5BN-1/2/3 (1)






Nimbus B1 (2)






Nimbus III (2)






Pioneer 10/11 (4)





Modified SNAP-19

Viking 1/2 (2)






Apollo 12-17 ALSEP (1)






LES-8/9 (2)






Voyager 1/2 (3)






Galileo (2)






Ulysses (1)






Cassini (3)






New Horizons (1)





NOTE: ALSEP, Apollo Lunar Surface Experiments Package; GPHS, General Purpose Heat Source; LES, Lincoln Experimental Satellite; MHW, Multi-hundred Watt; SNAP, Systems for Nuclear Auxiliary Power.

SOURCES: Data from G.L. Bennett, “Space Nuclear Power: Opening the Final Frontier,” AIAA 2006-4191, pp. 12-13, presentation at 4th International Energy Conversion Engineering Conference and Exhibit (IECEC), San Diego, Calif., June 26-29, 2006; G.K. Ottman and C.B. Hersman, “The Pluto-New Horizons RTG and Power System Early Mission Performance,” AIAA-2006-4029, 4th International Energy Conversion Engineering Conference, San Diego, Calif., June 26-29, 2006; R.D. Cockfield, “Preparation of RTG F8 for the Pluto New Horizons Mission,” AIAA-2006-4031, 4th International Energy Conversion Engineering Conference, San Diego, Calif., June 26-29, 2006; R.R. Furlong and E.J. Wahlquist, “U.S. Space Missions Using Radioisotope Power Systems,” Nuclear News, April 1999, p. 29.

instruments to map the surface geology and composition of Pluto and its three moons, investigate Pluto’s atmosphere, measure the solar wind, and assess interplanetary dust and energetic particles. After it passes Pluto, NASA plans to fly the spacecraft by one or two Kuiper Belt objects. Since sunlight at the Kuiper Belt is more than 1,000 times less intense than at Earth, New Horizons relies on a GPHS RTG for power (Ottman and Hersman, 2006).

Table E.1 lists key parameters for U.S. RPSs that have been used in space, the missions on which they were used, and the fuel, mass, and output. All have been fueled by 238Pu.


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