Cassini retirement

The Cassini space probe was deliberately disposed of via a controlled fall into Saturn's atmosphere on September 15, 2017, ending its nearly two-decade-long mission. This method was chosen to prevent biological contamination of any of the moons of Saturn now thought to offer potentially habitable environments. Factors that influenced the mission end method included the amount of rocket fuel left, the health of the spacecraft, and funding for operations on Earth. Some possibilities for Cassini later stages were aerobraking into orbit around Titan, leaving the Saturn system, or making close approaches and/or changing its orbit. For example, it could have collected solar wind data in a heliocentric orbit. During planning for its extended missions, various future plans for Cassini were evaluated on the basis of scientific value, cost, and time. Some of the options examined included collision with Saturn atmosphere, an icy satellite, or rings; another was departure from Saturn orbit to Jupiter, Uranus, Neptune, or a centaur. Other options included leaving it in certain stable orbits around Saturn, or departure to a heliocentric orbit. Each plan required certain amounts of time and changes in velocity. Another possibility was aerobraking into orbit around Titan. This table is based on page 19 of Cassini Extended Missions (NASA), from 2008. On July 4, 2014, the Cassini science team announced that the proximal orbits of the probe would be named the "Grand Finale". This would be immediately preceded by a gradual shift in inclination to better view Saturn's polar hexagon, and a flyby of Enceladus to more closely study its cryovolcanism. This was followed by a dive into Saturn's atmosphere. There was budgetary drama in 2013–14 about NASA receiving U.S. government funding for the Grand Finale. The two phases of the Grand Finale ended up being the equivalent of having two separate Discovery Program-class missions in that the Grand Finale was completely different from the main Cassini regular mission. The U.S.