The Flagship-class robotic spacecraft comprised both NASA's Cassini space probe and ESA's Huygens lander, which landed on Saturn's largest moon, Titan.

[16] Scientists and individuals from 27 countries made up the joint team responsible for designing, building, flying and collecting data from the Cassini orbiter and the Huygens probe.

ESA continued with its own study in 1986, while the American astronaut Sally Ride, in her influential 1987 report NASA Leadership and America's Future in Space, also examined and approved of the Cassini mission.

NASA officials and advisers involved in promoting and planning Cassini–Huygens attempted to correct this trend by stressing their desire to evenly share any scientific and technology benefits resulting from the mission.

Cassini–Huygens came under fire politically in both 1992 and 1994, but NASA successfully persuaded the United States Congress that it would be unwise to halt the project after ESA had already poured funds into development because frustration on broken space exploration promises might spill over into other areas of foreign relations.

Its bus was a dodecagonal prism atop a conical frustum connecting it to a cylinder containing the propellant tanks, to which the RTGs and Huygens were attached.

[64] To gain momentum while already in flight, the trajectory of the Cassini mission included several gravitational slingshot maneuvers: two fly-by passes of Venus, one more of the Earth, and then one of the planet Jupiter.

[65] NASA's risk analysis to use plutonium was publicly criticized by Michio Kaku on the grounds that casualties, property damage, and lawsuits resulting from a possible accident, as well as the potential use of other energy sources, such as solar and fuel cells, were underestimated.

But analysis of Cassini imagery showed that individual storm cells of upwelling bright-white clouds, too small to see from Earth, pop up almost without exception in the dark belts.

On October 10, 2003, the mission's science team announced the results of tests of Albert Einstein's general theory of relativity, performed by using radio waves transmitted from the Cassini space probe.

Previous tests using radiowaves transmitted by the Viking and Voyager space probes were in agreement with the calculated values from general relativity to within an accuracy of one part in one thousand.

[81] The first close-up images were received on June 12, 2004, and mission scientists immediately realized that the surface of Phoebe looks different from asteroids visited by spacecraft.

Images taken through special filters (able to see through the moon's global haze) showed south polar clouds thought to be composed of methane and surface features with widely differing brightness.

[89] During the first two close flybys of the moon Enceladus in 2005, Cassini discovered a deflection in the local magnetic field that is characteristic for the existence of a thin but significant atmosphere.

The data returned helped create a detailed and high resolution mosaic image of the southern part of the moon's Saturn-facing hemisphere.

On April 3, 2014, nearly ten years after Cassini entered Saturn's orbit, NASA reported evidence of a large salty internal ocean of liquid water in Enceladus.

[94][95][96] On June 30, 2014, NASA celebrated ten years of Cassini exploring Saturn and its moons, highlighting the discovery of water activity on Enceladus among other findings.

[97] In September 2015, NASA announced that gravitational and imaging data from Cassini were used to analyze the librations of Enceladus' orbit and determined that the moon's surface is not rigidly joined to its core, concluding that the underground ocean must therefore be global in extent.

[98] On October 28, 2015, Cassini performed a close flyby of Enceladus, coming within 49 km (30 mi) of the surface, and passing through the icy plume above the south pole.

[99] On December 14, 2023, astronomers reported the first time discovery, in the plumes of Enceladus, of hydrogen cyanide, a possible chemical essential for life as we know it, as well as other organic molecules, some of which are yet to be better identified and understood.

According to the researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life".

In images captured September 5, 2005, Cassini detected spokes in Saturn's rings,[102] previously seen only by the visual observer Stephen James O'Meara in 1977 and then confirmed by the Voyager space probes in the early 1980s.

[103][104] Radar images obtained on July 21, 2006, appear to show lakes of liquid hydrocarbon (such as methane and ethane) in Titan's northern latitudes.

[90] On March 13, 2007, the Jet Propulsion Laboratory announced that it had found strong evidence of seas of methane and ethane in the northern hemisphere of Titan.

[112] Data from the composite infrared spectrometer (CIRS) instrument indicated a powerful discharge from the storm that caused a temperature spike in the stratosphere of Saturn 83 K (83 °C; 149 °F) above normal.

Scientists have also determined that the storm witnessed was the largest, hottest stratospheric vortex ever detected in the Solar System, initially being larger than Jupiter's Great Red Spot.

[114][115] The imaging team said they wanted people to smile and wave to the skies, with Cassini scientist Carolyn Porco describing the moment as a chance to "celebrate life on the Pale Blue Dot".

[124] On November 29, 2016, the spacecraft performed a Titan flyby that took it to the gateway of F-ring orbits: This was the start of the Grand Finale phase culminating in its impact with the planet.

In September 2018, NASA won an Emmy Award for Outstanding Original Interactive Program for its presentation of the Cassini mission's Grand Finale at Saturn.

In January 2019, new research using data collected during Cassini's Grand Finale phase was published: The spacecraft operation was organized around a series of missions.