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RTG Cutout
RTG Cutout

On October 15, 1997 the Cassini spacecraft was successfully launched on its mission to Saturn. Electrical power for the Cassini spacecraft and instruments is provided by three radioisotope thermoelectric generators (RTGs) and thermal control is provided by a number of small radioisotope heater units. RTGs are used for missions which cannot use solar power.

The size of the Cassini spacecraft, and the distance to its destination, Saturn, required the use of a Titan IV/Centaur launch vehicle. Even with this powerful launch vehicle, there was not enough energy to send the spacecraft directly to Saturn. So the mission analysts designed a unique trajectory which involved gravity-assists from Venus, Earth, and Jupiter. The spacecraft arrived at Saturn in July 2004.

NASA and the Cassini program have made nuclear safety a top priority. As part of this, NASA has sought to inform the public about Cassini's use of RTGs by publishing an extensive Environmental Impact Statement (EIS).

Following are several documents related to Cassini safety:

Spacecraft Power for Cassini - NASA fact sheet 07/1999 PDF/44 K
Department of Energy Facts: Radioisotope Heater Units (RHUs) 12/1998 PDF/72 K
Why the Cassini Mission Cannot Use Solar Arrays 11/1996 PDF/44 K

For answers about Cassini's nuclear safety not contained here, please contact JIa-Rui Cook ( at the JPL Media Relations Office.

For more information about Radioisotope Thermoelectic Generators, visit: