The planet Saturn, its famous icy rings, and its enigmatic moon, Titan, are the prime scientific targets of the international Cassini mission, the most ambitious and far-reaching planetary exploration ever mounted. Final preparation of Cassini is now underway for a launch from Cape Canaveral, FL, in October 1997.

The mission marks the first time a space probe has attempted to land on the moon of another planet, providing the first direct sampling of the Earth-like atmosphere of Titan and the first detailed pictures of its previously hidden surface. Titan is Saturn's largest moon, nearly the size of Mars and bigger than either Mercury or Pluto.

Cassini, in development since October 1989, is a cooperative endeavor of NASA, the European Space Agency (ESA) and the Italian Space Agency, or Agenzia Spaziale Italiana. The mission will send a sophisticated robotic spacecraft equipped with 12 scientific experiments to orbit Saturn for a four-year period and study the Saturnian system in detail. The ESA-built Huygens probe that will parachute into Titan's thick atmosphere carries another six scientific instrument packages.

"With its bright, complex rings, 18 known moons and magnetic environment, Saturn is a lot like a solar system in miniature form," said Dr. Wesley T. Huntress, NASA's associate administrator for space science. "Saturn's family of rings and moons is a one- stop treasure trove, offering countless clues to the history of planetary and solar system evolution. Cassini and the Huygens probe represent our best efforts yet in our ongoing exploration of the solar system."

The launch period for Cassini's nearly seven-year journey to Saturn opens on Oct. 6 at 5:39 a.m. EDT and closes Nov. 15, 1997. A U.S. Air Force Titan IVB/Centaur launch system, the most powerful launch vehicle in the U.S. fleet, will loft Cassini onto the interplanetary trajectory that will deliver the spacecraft to Saturn almost seven years later on July 1, 2004. Cassini's primary mission concludes in July 2008.

Saturn is the second-largest planet in the solar system and is made up mostly of hydrogen and helium. Its placid-looking, butterscotch-colored face masks a windswept atmosphere where jet streams blow at 1,100 miles per hour and swirling storms roil just beneath the cloud tops. Spacecraft passing by Saturn found a huge and complex magnetic environment, called a magnetosphere, where trapped protons and electrons interact with each other, the planet, rings, and surfaces of many of the moons.

Saturn's best known feature -- its bright rings -- consists not just of a few rings but of hundreds of rings and ringlets broad and thin, composed of ice and rock particles ranging in size from grains of sand to boxcars. "Shepherd moons" found orbiting near the edges of some of the rings gravitationally herd in ring particles that would otherwise spread out into deep space.

Although it is believed to be too cold to support life, haze- covered Titan is thought to hold clues to how the primitive Earth evolved into a life-bearing planet. It has an Earth-like, nitrogen-based atmosphere and a surface that many scientists believe probably features chilled lakes of ethane and methane. Scientists believe that Titan's surface is probably coated with the residue of a sticky brown organic rain.

On Nov. 6, 2005, Huygens will descend by parachute into Titan's sky, providing our first direct sampling of Titan's atmosphere and the first detailed photos of its hidden surface.

The Cassini spacecraft is the most complex interplanetary spacecraft ever built. Because of Cassini's challenging mission, the long distance Cassini must travel, and the value of its scientific return, each component and the system as a whole has undergone an unprecedented program of rigorous testing for quality and performance.

"Every phase of the mission has been reviewed and validated internally and externally by NASA and independent experts," said Huntress.

Because of the very dim sunlight at Saturn's orbit, Cassini could not conduct its mission to Saturn on solar power. Electrical power is supplied to Cassini by a set of radioisotope thermoelectric generators (RTGs) which convert the heat from the natural decay of plutonium. RTGs have been used on 23 previous U.S. missions. Plutonium dioxide also is used in 117 radioisotope heater units placed on Cassini and Huygens to keep electronics systems at their operating temperatures. These units were most recently used on the Mars Pathfinder mission's Sojourner rover to keep the system from failing during cold Martian nights.

The mission is named for two 17th century astronomers: Italian-French astronomer Jean-Dominique Cassini made several key discoveries about Saturn, and Dutch scientist Christian Huygens discovered Titan.

Development of the Huygens probe was managed by an ESA team located at the European Space Technology and Research Center (ESTEC) in Noordwijk, The Netherlands. The Cassini orbiter was designed, developed and assembled at NASA's Jet Propulsion Laboratory (JPL), located in Pasadena, CA. JPL is a division of the California Institute of Technology. The overall mission is managed by JPL for NASA's Office of Space Science, Washington, DC.

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