NASA said its fiscal 2011 budget provides a $60 million-per-year extension for continued study of the ringed planet.
"This is a mission that never stops providing us surprising scientific results and showing us eye popping new vistas," said Jim Green, director of NASA's planetary science division. "The historic traveler's stunning discoveries and images have revolutionized our knowledge of Saturn and its moons."
Cassini was launched in October 1997 with the European Space Agency's Huygens probe. The spacecraft arrived at Saturn in 2004. The probe was equipped with six instruments to study Titan, Saturn's largest moon.
NASA said Cassini's 12 instruments have returned a daily stream of data from Saturn's system for nearly six years. The project was scheduled to end in 2008, but the mission received a 27-month extension to Sept. 2010.
Scientists said the newly announced second extension will enable researchers to study seasonal and other long-term weather changes on the planet and its moons, as well as continue observations of Saturn's rings and the magnetic bubble around the planet known as the magnetosphere.
The Cassini-Huygens mission is a cooperative project of NASA and the European and Italian space agencies.