After a seven year journey beginning in late 1997, Cassini will enter orbit around Saturn and for four years intensively investigate its structure, atmosphere, chemical composition, rings, magnetic fields, and several moons.

The mission has involved more than 4,300 engineers and scientists from around the world and will cost more than $3.2 billion. The sophisticated spacecraft will provide the most complete exploration of another planet. Attached to the main vehicle is a small probe, built by the European Space Agency, that will detach and glide through the dense, smoggy atmosphere of Titan, one of 21 known moons in the Saturnian system, which scientists believe may be analogous to Earth during its infancy billions of years ago.

800 Million Miles Away

Saturn lies some 800 million miles from Earth -- about 3,300 times the average distance of Earth to the Moon. The Cassini spacecraft will be launched by a giant Titan IV/Centaur rocket. Even with its immense thrust, it is not powerful enough to send Cassini directly to Saturn. Consequently, it will be jettisoned on an indirect route that uses "gravity assists" to catapult the spacecraft to its destination.

Cassini will whip past Venus twice, gaining momentum, then shoot by Earth in 1999, then Jupiter, finally arriving at Saturn in July of 2004. The alignment of the planets to allow this roundabout course occurs only once every 175 years.

Titan

After insertion into orbit around Saturn, Cassini will detach a probe to explore Titan, a moon larger than Mercury with an atmosphere that is four times more dense than Earth. The craft, dubbed Huygens [Hoy-gehns] (after Christiaan Huygens, who discovered Titan in 1655), will descend though the clouds, taking measurements of the atmosphere to determine its chemical composition. It will measure winds and global temperatures and, with a radar imager take pictures of the surface area, which may have icy continents with seas of liquid ethane and methane. (The gases liquify at very low temperatures.)

Recent images made by the Hubble Space Telescope reveal a bright area, about the size of Australia, which may be a solid surface.

Titan's atmosphere is composed mainly of nitrogen (the same as Earth) and is extremely cold (-289¿ Fahrenheit). The moon orbits Saturn every 16 days, with the same face always pointing toward the planet (similar to Earth's Moon.) By investigating Titan, scientists hope to find clues to understanding the origin of life on Earth.

Scientific Goals

Voyager 2, the last mission to Saturn, swept past the ringed planet on August 25, 1981. It briefly surveyed the Saturnian system, then steered toward Uranus. Cassini, by contrast, will enter orbit around Saturn, collecting scientific data over a four year period. The 4,750 pound spacecraft contains a battery of scientific instruments to study the planet's chemical composition, magnetic field, atmosphere, surfaces, rings, and several moons.

By intensively studying Saturn and comparing its physical and chemical processes with other planets, scientists hope to understand the origin and evolution of our solar system. Through comparative planetology, they seek to learn how planets and moons came into existence and evolved, as well as how life developed.

Cassini's Power System

Saturn lies nearly 900 million miles from the Sun -- ten times the distance of Earth from the Sun -- making power through solar arrays and solar cells impossible. Cassini is powered by a Radioisotope Thermoelectric Generator (RTG), which has been employed successfully on 23 missions over the past three decades. Cassini's RTG uses a radioactive material (plutonium 238) to produce heat, which is converted to electricity. The RTG uses only decay heat, meaning there are no nuclear reactions involved and also that the radioactive material can be encapsulated to prevent release into the atmosphere.

Because the plutonium is molded into ceramic pellets and protected by iridium and graphite encasements, it is extremely unlikely that, in the event of an accident resulting in release, they would shatter into tiny particles that could be inhaled. There is less than a one in a million chance of a major accient involving Cassini that would result in release. The expected radiation dosage a person might receive is only one millirem. To put this in perspective, we receive an average of 360 millirems each year just by living on Earth.

New Technology

Spacecraft have rigorous engineering requirements. Components must be lightweight, highly reliable, operate with minimal power for long durations, communicate extreme distances, withstand wrenching vibrations during launch, and survive the bombardment of solar radiation while transiting the deep freeze of space.

Not surprisingly, Cassini has generated numerous spin-offs that have commercial applications. Among the high-tech innovations, engineers developed a solid-state data recorder that has no moving parts, a new-generation gyro (also with no moving parts), a new solid-state power switch, and a new-generation radio receiver.

They also developed a very high-speed integrated circuit that is ten times more powerful than those used on the Galileo spacecraft. Each chip replaces about 100 traditional components. The technologies boost reliability and will enhance future space missions, as well as improve the performance of commercial satellites and consumer electronic devices.