Projected Mission:
After launch, Cassini proceeded to Venus, where it received two gravity assists*, return to Earth for one, then fly by Jupiter for its last gravity assist to Saturn. It is expected to arrive at Saturn on July 1, 2004.
When it arrives, Cassini must perform complex maneuvers in order to come to a stable orbit around Saturn.
Then, in November of 2004, it will release Huygens, and the Huygens atmospheric probe will travel into Titan, and three weeks later will drop into Titan's atmosphere, and will relay data for about three hours. The Huygens probe, supplied by the European Space Agency, carries a well-equipped robotic laboratory which it will utilize to study the clouds, atmosphere, and the surface of Titan. As the 8.9 foot (2.7 m) diameter probe enters the atmosphere, it will begin to take measurements in the upper stratosphere. As it descends, first on a main parachute and later on a drogue chute for stability, various instruments will measure the temperature, pressure, density, and energy balance in the atmosphere.
The Cassini orbiter must travel to Titan so it can collect the data from Huygens and relay it back to Earth. The probe will measure the organic chemicals in the atmosphere, as well as take many panoramic pictures of Titan's surface. Instruments will be used to study the surface indirectly, and perhaps directly when the probe lands.
Data gathered by the probe will be downloaded twice from the Cassini orbiter in order to check the transmission. After verification, the Huygens probe mission will be considered completed.
The Cassini orbiter will continue to gather data about Saturn and its moons for a maximum of four years. After those four years, all of its scientific goals must have been met. It is expected to make thirty-five fly-bys of Titan, and also fly by Iapetus, Dione, Mimas, Rhea, and Enceladus. One reason that it will fly-by Titan so much is because NASA plans to use Titan for gravity assists, just as it used Venus and will use Earth and Jupiter. The Cassini orbiter will not only use Titan for gravity assists; NASA plans to conduct many mapping experiments, measure its magnetic field, measure its gravitational field, and study atmospheric dynamics.
Overall, NASA about 60 orbits of Saturn, with orbital periods ranging
from over a hundred days to less than ten. NASA plans that the closest approach to Saturn will be about 110,000 miles (180,000 km), and that the farthest orbit will take Cassini to 260,000 (420,000 km) miles away from Saturn. Orbital inclinations (how far above or below the equator) should provide good opportunities for ring imaging, occultations of Saturn and the ring system by the Earth and the Sun, and observations of a wide range of activity in Saturn's magnetic field.
After Cassini's official mission ends in 2008, NASA has several ideas for an extended mission. The most probable extended mission would be to continue to study the Saturn system. Cassini might find new moons or rings that would merit further study. Another possibility is that NASA will put Cassini into orbit around Titan, to continue to study this moon further. A third possibility is that NASA will attempt to pull Cassini out of Saturn's orbit, and send it to study more planets or asteroids. This isn't as likely, for it would take Cassini a long time and several fly-bys of Titan and Saturn to go very far (unless it had a lot of fuel left over). A fourth possible extended mission would be to study Saturn's rings more closely. The Voyagers found evidence of braided rings and ring spokes that scientists have yet to explain.
* A gravity assist is when a probe enters close enough to a planet (or large body) for it to begin to feel the tug of its gravity. Under the influence of the planet's gravity, the craft will speed up. Then, at the right moment, the craft fires maneuvering jets in order to avoid hitting the planet, but still retain its speed. This is commonly used by space probes to save fuel.
Important Dates:
| Date | What Happened/Will Happen |
|---|---|
| October 15, 1997 | Probe launched |
| February 26, 1998 | First Venus gravity assist |
| June 24, 1999 | Second Venus gravity assist |
| August 18, 1999 | Earth gravity assist |
| December 30, 2000 | Jupiter gravity assist |
| July 1, 2004 | Arrival at Saturn |
| November 6, 2004 | Titan probe separation |
| November 27, 2004 | Titan probe entry |
| June 25, 2008 | End of primary mission |