The aim of the Cassini-Huygens mission, a joint venture of NASA, the ESA (European Space Agency), and the ASI (Italian Space Agency), is to study Saturn and its moons. The Cassini spacecraft was launched on October 1997 and entered into orbit around Saturn in mid 2004. One of the largest spacecrafts ever built – at 6.8 m (22.3 ft.) high, and more than 4 m (13.1 ft.) wide, the Cassini weighed 5.6 tons. One of the most interesting features of the spacecraft is its power source, based on radioisotope thermoelectric generators (RTGs). These are necessary since the spacecraft operates at such a long distance from the sun where solar energy is not sufficient to effectively power its instrumentation.