NASA/Spacelink FACT SHEET: CRAF -- COMET RENDEZVOUS/ASTEROID FLYBY SPACELINK NOTE: The February 1991 launch manifest shows February, 1996 as the launch date for CRAF. The Jet Propulsion Laboratory is planning a new exploratory mission for NASA to send a Mariner Mark II spacecraft to encounter an asteroid, and then to rendezvous with a comet and fly alongside it for nearly three years. The mission is called Comet Rendezvous Asteroid Flyby (CRAF). The spacecraft will closely examine the comet during part of its orbit around the Sun. CRAF will launch a heavily instrumented penetrator/lander into the comet's nucleus to measure temperatures and chemical composition. CRAF's other instruments will collect data on the comet's nucleus, its coma, and its dust and ion cloud and tail. CRAF will also provide the first close-up look at how a comet's coma and its tail of dust and ions form. The mission will use the Mariner Mark II class spacecraft being developed for NASA by JPL. Mariner Mark II is a new design approach advocated by NASA's Solar System Exploration Committee and is intended for flights in the 1990s to the outer planets and primitive bodies, such as comets and asteroids. CRAF will be the first Mariner Mark II mission. The second mission, called Cassini, will orbit Saturn and place a probe into the atmosphere of the ringed planet's largest satellite, Titan. CRAF and Cassini use identical Mariner Mark II spacecraft, but each will carry unique science instruments. Mariner Mark II will use hardware and designs from previous missions in conjunction with selected new hardware designs to reduce significantly the costs of planetary exploration. CRAF will be launched aboard a Titan IV-Centaur expendable launch vehicle in August 1995. The trajectory will carry CRAF out to the asteroid belt, where a propulsion maneuver will send the spacecraft back toward Earth for a gravity-assist boost. CRAF will fly past Earth in July 1997 to take up its final flight path. (By using gravity assist, NASA can launch spacecraft aboard rockets that have less thrust than would be needed for a direct flight.) The spacecraft would encounter an asteroid named 449 Hamburga in January 1998 en route to the comet. CRAF would take photographs and other scientific measurements during the encounter period. Asteroid 449 Hamburga is about 88 kilometers (55 miles) in diameter and is a carbonaceous type asteroid. CRAF's cometary target is called Kopff. It is named for August Adalbert Kopff, who discovered it on August 22, 1906, during an observing session at Koenigstuhl Observatory near Heidelberg, Germany. Ninety-four years after Kopff's discovery, CRAF will arrive at the rendezvous point with Comet Kopff -- in August 2000. Comet and spacecraft will be at the distance of Jupiter's orbit, and 850 days before closest approach to the Sun, or perihelion. CRAF will fire its penetrator/lander at the comet in August 2001, then will continue to fly beside Kopff. The spacecraft will take data for a total of two and two-thirds years, until about 109 days after they pass closest to the Sun and are outward bound again. It will be the first time a spacecraft will have flown in formation with a comet, though a U.S. spacecraft, International Cometary Explorer (ICE), flew by Comet Giacobini-Zinner in 1985 and spacecraft from several countries encountered Comet Halley in 1986. The comet rendezvous will allow study of matter that scientists think is the original, relatively unchanged material left behind when a cloud of dust and gas collapsed to form the solar system 4.6 billion years ago. Scientists believe comets now reside in a distant region of the solar system called the Oort Cloud. Current theory holds that gravitational nudges from stars in the Sun's neighborhood send some comets from the Oort Cloud falling toward the Sun. Later, in what has been called a gravitational accident, a long-period comet may pass so close to a planet that the gravitational interaction between them changes the comet's orbit once more. The comet may become trapped, at least temporarily, in the inner solar system and thus become a short-period comet. Comet Kopff is one of those short- period comets. Its closest approach to the Sun is 1.58 AU. (An AU, or astronomical unit, is 93 million miles, the average distance between Earth and the Sun.) Comet Kopff's orbit carries it once around the Sun in 6.46 years. Comet Kopff travels between a region from just inside the orbit of Jupiter inward to perihelion near the orbit of Mars, 220 million kilometers (140 million miles) from the Sun. Kopff is apparently a fairly normal short-period comet whose nucleus probably has a diameter of about 8 to 12 kilometers (about 5 to 7.5 miles). When it is most active (near perihelion) it spews out about a ton of gas and dust every second. The gas and dust form a cloud called a coma that boils off the nucleus as the comet approaches the Sun. A growing tail streams away from the coma as the solar wind and light pressure from the Sun push the material away. The CRAF spacecraft will fly extremely close to the comet's nucleus, within 10 kilometers (6 miles). The close-up exploration will take place before the coma and tail begin to build. Later the spacecraft will move in and out through the coma and down the tail to study their properties and the complex processes occurring in them, and to collect samples of dust for detailed analysis onboard the spacecraft. All the phenomena associated with comets will be the target of CRAF's instruments. And the long duration of the rendezvous -- almost three years -- is expected to fill in many of the major gaps in scientific understanding of the strange objects. The mission's scientific payload was selected in October 1986. It will include: * Cameras to photograph the nucleus, coma and tail, and changes that occur as Kopff orbits the Sun. Photos also would help scientists determine the comet's size and structure, the location of its poles, its rotation rate and geological structure. * A surface penetrator-lander to be fired into Kopff's nucleus. The instruments aboard the penetrator- lander would collect a sample of cometary ices, study how they change when heated, and perform a chemical analysis of the gases released from the ice. The penetrator would bury its tip, which will contain a gamma-ray spectrometer measuring abundances of as many as 20 chemical elements, up to one meter (three feet) below the comet's surface. The penetrator wil carry accelerometers to determine Kopff's surface strength and its resistance to puncture, and thermometers to measure temperatures beneath the surface. The penetrator/lander will radio its findings to the spacecraft, which will then relay them to Earth. * Mass spectrometers to study composition of gases released by the nucleus and the cloud of plasma (ionized gas) surrounding the nucleus. * Dust counters, collectors and analyzers to capture samples of the comet's dust and study them onboard. The information would help scientists determine the chemical elements that make up the dust and ice. In addition, the mass, size, shape and composition of individual dust grains will be measured. * A visual and infrared mapping spectrometer to study chemical composition of the coma and the surface of the nucleus as they change with time. * A magnetometer and a plasma-wave analyzer to measure interactions between the coma and electrically charged particles streaming from the Sun. The magnetometer will also measure the comet's intrinsic magnetic field, if it has one. In December 2002 the spacecraft and the comet will make their closest approach to the Sun. They will then head outward again toward aphelion near Jupiter's orbit. On March 31, 2003, the Comet Rendezvous Asteroid Flyby, first primary mission of Mariner Mark II, will end. At that time the Cassini mission, with the second Mariner Mark II spacecraft, will be in its Saturnian-tour phase.