A documentary focussing on the structure and safety of RTGs [radioactive isotope thermoelectric generators], as used in the joint ESA/NASA Huygens/Cassini mission launched in November 1997. Organised as follows: animation of the solar system; RTGs, as used on the Voyager, Galileo and Ulysses missions; presentation of a prototype RTG to Eisenhower [still]; animations to show the radioactive decay of Plutonium 238; ESA and NASA's work on photovoltaic solar cells; safety testing of RTGs; Cassini construction; animation of the Huygens mission; animation showing the impracticality of using solar arrays for interplanetary probes; animation Galileo at Jupiter, Galileo's trajectory to Jupiter; list of missions on which RTGs have been used, along with some footage and animations of these missions; cutaway view of an RTG; heat source modules; list of probable accident environments; explosion blast overpressure test, projectile impact bullet test; rocket sled test for face-on and edge-on fragment collisions; impact test