English: Jet Propulsion Laboratory (JPL) workers use a borescope to verify pressure relief device bellows integrity on a radioisotope thermoelectric generator (RTG) which has been installed on the Cassini spacecraft in the Payload Hazardous Servicing Facility. The activity is part of the mechanical and electrical verification testing of RTGs during prelaunch processing. RTGs use heat from the natural decay of plutonium to generate electric power. The three RTGs on Cassini will enable the spacecraft to operate far from the Sun where solar power systems are not feasible. They will provide electrical power to Cassini on its 6.7-year trip to the Saturnian system and during its four-year mission at Saturn. The Cassini mission is scheduled for an Oct. 6 launch aboard a Titan IVB/Centaur expendable launch vehicle. Cassini is built and managed for NASA by JPL.