Cassini was the first spacecraft ever to orbit Saturn, thanks to a complex maneuver that allowed it to slip through the giant planet's rings and become captured by the planet's gravity. Cassini, the largest interplanetary spacecraft ever launched by NASA, also successfully launched the European Space Agency's Huygens probe. The probe dropped through the atmosphere of Saturn's biggest moon, Titan, returning photos of a surface that had never before been seen by humans.
Launched in October 1997, Cassini picked up speed by using the gravity of other planets, swinging by Venus twice, then Earth, then Jupiter. Cassini needed the gravitational assists to make it far out into the solar system. Cassini's life far exceeded the four years originally planned for its mission at Saturn. After arriving at Saturn in July 2004, Cassini's mission sent back loads of data on Saturn until its mission ended with operators sending it on a deliberate plunge into Saturn's atmosphere in September 2017.
When launched, Cassini was made up of two parts: the Cassini orbiter and the Huygens probe. The orbiter was the main part of the craft, and it carried 12 scientific experiments along with the Huygens probe which had been attached to its side prior to being jettisoned into the atmosphere of Saturn’s largest moon, Titan. On the way to Saturn, Cassini searched for gravitational waves throughout the solar system and photographed any planets and moons that it passed. While Cassini was at Saturn, it collected an immense amount of measurements, including:
- Examining the gravitational field of Saturn, its rings and moons using radio waves
- Taking photos in visible, near-ultraviolet (UV) and near-infrared (IR) light
- Mapping the surface of Titan using radar
- Studying particles around Saturn and its moons to learn about their atmospheres and ionospheres
- Determining the structure and chemical composition of surfaces and atmospheres of Saturn, its moons and rings
- Recording temperatures from the rings, atmospheres and surfaces of Saturn and its moons
- Studying ice and dust grains in the Saturn system
- Investigating plasma waves and how they interact with Saturn's magnetic field
- Discovering how the solar wind interacts with Saturn's magnetosphere
- Studying Saturn's magnetic field and how it interacts with Saturn's rings, moons and solar wind
- Measuring ultraviolet energy from atmospheres, surfaces and rings
The Huygens probe, contributed by the European Space Agency, carried eight more experiments. The probe was released from the main Cassini spacecraft on December 24, 2004, and reached Titan on January 14, 2005, where it dropped through the thick atmosphere to land on the surface. The Huygens experiments allowed the probe to:
- Take pictures of Titan's atmosphere and surface
- Measure particle temperatures
- Examine the physical properties, chemical composition and structure of Titan's atmosphere
- Study clouds, winds and particles in Titan's atmosphere
- Explore the physical properties of the surface of Titan
During the missions of Cassini and Huygens, Cassini communicated with Earth using three microwave antennas. The large white dish on top of Cassini is the high-gain antenna—it could send and receive data a lot faster than the other antennas on board. The dish also doubled as a shield to protect Cassini from the heat when the spacecraft was close to the sun during the period shortly after its launch. As Cassini got closer to Saturn, cold temperatures became a much bigger problem, so Cassini carried heaters and was wrapped in an insulating blanket. Cassini ran on about 700 watts of electrical power, produced by radioisotope thermoelectric generators (RTGs). The generators were powered by the heat given off by a small amount of plutonium as it naturally decays. RTGs were chosen to power the instruments on board because they will last for at least 11 years, which gave Cassini plenty of time to reach Saturn and complete its mission.