A unique mission: Cassini-Huygens, the Orbiter, the descent Probe and the cruise science

The Cassini-Huygens mission has characterized the Solar System exploration scenario for more than 30 years, from when it was conceived until the completion of its long life. Its legacy is an enormous amount of high quality scientific data and astonishing images of the Saturn system and its moons, Titan first. Also, the mission has been the gymnasium where new technologies and procedures have been discussed, developed and after adopted by many other missions. Cassini-Huygens also played a great role in allowing a new generation of scientists and engineers to increase their knowledge and skills, merging the already matured experience of a generation, formed on previous missions as Voyager, with a new generation belonging to many different countries. The international scenario that allowed the realization of the mission is the other distinguishing character of this adventure, led by the partnership of three space agencies, NASA with the Jet Propulsion Laboratory first, the European Space Agency-ESA for Huygens and the Italian Space Agency-ASI. This cooperative environment allowed both ESA and ASI to enter at best in the environment of the deep-space planetary missions and also provided the opportunity for other 15 nations to have their scientist on board and contributing to the mission. A cooperative effort, well guided and harmonized by the Project Science Group, lasted till the very end of the mission when the Cassini Grand Finale was played with the last plunge into the Saturn atmosphere. Hereafter, the mission is described including some details on the technical aspects of the Cassini spacecraft, the Huygens probe, the science instruments part of their payload and the science results are summarized with a special emphasis on the Italian contribution. This paper focuses on the science results in the cruise phase, where radio science experiments testing different aspects of relativistic gravity were performed. In particular, we describe the use of the novel Cassini radio system (based on Ka band frequencies, 32–34 GHz) to test the space components of the metric in the Solar System and a search of low-frequency gravitational waves, with a set of extensive observations in 2001 and 2002. The Cassini radio signal was tracked just prior to the final plunge into Saturn’s atmosphere (15 September 2017) from a new configuration of the Sardinia Radio Telescope called “Sardinia Deep Space Antenna”. The Venus and Jupiter fly-bys offered the opportunity to calibrate the VIMS instrument and to carry out new science observations.