FACT SHEET: THE CASSINI MISSION **CALL THE NASA SPACE LINK BBS** THIS GOVERNMENT BBS IS THE OFFICIAL SYSTEM OF THE NATIONAL SPACE ANS AERONAUTIC ADMINSTRATION. (205) 895-0028! SPACELINK NOTE: The February 1991 launch manifest shows December, 1995 asthe launch date for Cassini. The ringed planet Saturn, its major moon Titan andcomplex system of at least 16 other satellites will be thedestination for NASA's and the European Space Agency'sCassini Mission. Named for the Italian-French astronomer who discovered several of Saturn's moons, Cassini is under study at the Jet Propulsion Laboratory as one of two initial projects in the Mariner Mark II series of missions to the outer solar system. Early during the spacecraft's four-year tourorbiting Saturn, it will launch a parachuted probe descendingthrough Titan's dense atmosphere to the surface of thesatellite -- which boasts unique organic-like chemistry thatcould provide clues to the origin of life on Earth. On its way to Saturn, Cassini will also execute anencounter with an asteroid and will fly down the magnetotailof Jupiter, performing studies complementing NASA's CometRendezvous Asteroid Flyby (CRAF) mission and the Galileomission to Jupiter. Recommended by NASA's Solar System ExplorationCommittee in its report to the space agency in the early1980s, the Mariner Mark II series will use shared designconcepts and advanced manufacturing techniques to build anumber of unmanned spacecraft to explore the solar systembeyond the orbit of Mars. CRAF and Cassini are the first twomissions proposed in the series. MISSION OVERVIEW As currently planned, Cassini would be launched inApril 1996 on an expendable rocket. NASA would provide theTitan-Centaur launch vehicle and the Cassini orbiterspacecraft; the European Space Agency (ESA) would contributethe Titan probe. NASA and ESA member countries would providescience instruments for both the orbiter and probe. In order to reach Saturn, Cassini will firstexecute flybys of the Earth and of Jupiter in order to gain"gravity assist" boosts in velocity to send it on its way.The first flyby of Earth will take place 26 months afterlaunch, followed by the Jupiter flyby some 19 months later.Cassini would then arrive at Saturn in October 2002. During the first leg of its trip -- after launchand before its first Earth flyby -- Cassini will navigatethrough part of the asteroid belt and could perform anencounter with the asteroid Maja in March 1997. After flyingby the Earth at a distance of 300 kilometers (about 190miles), the spacecraft will be flung out through the asteroidbelt where it may be possible to encounter another asteroid. Maja is a carbonaceous, or "C" type, asteroid 78kilometers (about 50 miles) in diameter. Two small asteroidsare being considered as possible additional targets (only oneof the two asteroids could be visited). Cassini's final encounter before proceeding toSaturn will be with Jupiter, which it will pass at a distanceof about 3.6 million kilometers (about 2.2 million miles),some 50 times the radius of Jupiter itself. Cassini's flightpath will take it for 130 days down through a region that nospacecraft has explored more than briefly -- the giantplanet's magnetotail, a long tube of Jupiter's energy fieldtrailing many millions of miles away from the Sun. Upon reaching Saturn the spacecraft will swingwithin 1.8 Saturn radii of the planet to begin the first ofsome three dozen highly elliptical orbits during theremainder of its mission. Eighty-five days after reachingSaturn -- traveling back in toward the planet as it completesit’s first orbit -- Cassini will release its instrumentedprobe to begin descent to Titan. Eleven days later the probe will enter Titan'sdense atmosphere, buffered at first by a heat shield.Throwing off that protection, the probe will then deploy itsparachute for final descent to the surface. After relaying to Earth data uplinked from theTitan probe, Cassini will continue with orbits of Saturn andflybys of most of the planet's 16 or more other moons. Planscall for 40 targeted flybys including 36 close encounters ofTitan, two of the major moon Iapetus, and one each ofEnceladus and Dione. Cassini will make 26 non-targeted flybysof the Saturnian moons. In addition, the spacecraft's orbitswill allow it to study Saturn's polar regions after examiningthe planet's equatorial zone. SATURN AND ITS MOONS: UNRESOLVED QUESTIONS Much has been learned about the ringed planet sinceRenaissance astronomers first turned their telescopes on itin the 17th century. Many questions remain, however, whichcould provide clues to how the solar system evolved and howlife began on Earth. One of the bright planets known to the ancients,Saturn was first studied via telescope by Galileo Galilei(1564-1642) and, in the generation following him, by suchEuropean astronomers as the mission's namesake, Cassini.Glimpsing the planet's famous rings through an earlytelescope, Galileo first thought them to be two smallerplanet-like bodies flanking the main planet Saturn; onlyobservations by others with later, better telescopesrevealed their true nature. The greatest wealth of information on the planethas come from unmanned spacecraft. Initially reconnoitered by NASA's Pioneer 11, the planet was encountered by Voyager 1and Voyager 2 during flybys in 1980 and 1981, respectively. Those missions showed Saturn to be a giant gaseousglobe of hydrogen and helium 95 times more massive than theEarth, buffeted by winds of up to 500 meters per second(1,100 miles per hour). The ring system proved to be muchmore complex than previously realized, with intricate"braiding" in some parts of the system. Small moons were alsodiscovered by the spacecraft, bringing the total of Saturnianmoons to at least 17. Because of the brief nature of those flybys, manyquestions remain for Cassini to explore. In studying Saturn'smagnetosphere -- the pocket of energy enveloping the planet,much like Earth's radiation belts -- scientists hope tounderstand the configuration and dynamics of themagnetosphere; the nature, source and fate of its energyparticles; how it interacts with the solar wind, satellitesand rings; and how Titan interacts with the solar wind andSaturnian magnetosphere. At the planet itself, topics of study includecloud properties and composition of the atmosphere; winds andtemperatures; Saturn's internal structure and rotation; theplanet's ionosphere; and Saturn's origin and evolution.Science objectives in respect to Saturn's rings includestudies of their structure and composition, dynamicprocesses, interrelations of the rings and Saturniansatellites, and the dust/micrometeoroid environment at therings. Because of the dense atmosphere shrouding the moonTitan, little is known of its surface -- whether it is solidor covered with liquid oceans. At Titan, scientists hope togain a better understanding of abundances of elements andcompounds in its atmosphere; distribution of trace gases andaerosols; winds and temperatures; surface state andcomposition; and the satellite's upper atmosphere. Saturn's other major moons are ice-covered bodies.Scientists wish to use Cassini to study their characteristicsand geological histories; how their surfaces are modifiedover time; composition and distribution of materials on theirsurfaces; overall composition and internal structure of thesatellites; and how they interact with Saturn'smagnetosphere. To carry out those studies, the Cassini orbiterwill carry 15 science experiments, with nine more on theTitan probe.
The orbiter will house several instruments on its
directable, high-precision scan platform: a solid-state
