|One of the Most Complex and Ambitious Ventures in the History of Space Exploration|
A robot explorer named Cassini is outbound from Earth on a seven-year trip to the faraway planet Saturn and its moon Titan. On-the-spot chemical analysis and photography by robots like Cassini tell us a lot about the makeup of our Solar System's planets. Will Cassini find ethane waterfalls, methane icebergs, or lakes of organic compounds on Titan?
Click to enlarge Cassini's first test image of the giant ringed planet showing Saturn's shadow falling across its rings on October 21, 2002. The dot at upper left in this NASA image is the planet's largest moon, Titan, some 177 million miles from Saturn.
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. Cassini was launched from Cape Canaveral, Forida, on October 15, 1997.
Titan is Saturn's largest moon, nearly as big as the planet Mars and bigger than either of the planets Mercury and Pluto. The Cassini 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.
Cassini, in development since October 1989, is a cooperative endeavor of U.S. National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Italian Space Agency (Agenzia Spaziale Italiana).
Robot with twelve jobs. Cassini is a sophisticated robot spacecraft equipped with twelve scientific experiments. It will orbit Saturn for four years and study the Saturnian system in detail.
A smaller, ESA-built probe, named Huygens, attached to Cassini, parachuted into Titan's thick atmosphere carrying another six scientific instrument packages.
The Cassini orbiter dropped Huygens via parachute to the surface of Titan where it landed January 14, 2005, and reported on the moon's atmosphere and produced a panoramic photograph of the moon.
"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."
Saturn is 930 million miles away from the Sun, and consequently, about 746 million miles away from Earth.
A U.S. Air Force Titan IV-B/Centaur launch system, the most powerful launch vehicle in the U.S. fleet, lofted Cassini onto the interplanetary trajectory that will deliver the spacecraft to Saturn almost seven years later on July 1, 2004. Cassini's main job will end in July 2008.
Second largest planet. 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 earlier found a huge, complex magnetic environment -- a magnetosphere -- where trapped protons and electrons interact with each other, and with the planet, the planet's rings, and the 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. The rings are composed of ice and rock particles ranging in size from grains of sand to boxcars.
So-called "shepherd moons" have ben found orbiting near the edges of some of the rings. The shepherd moons gravitationally herd in the ring particles that would otherwise spread out into deep space.
Lakes of methane. 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 Titan's surface is coated with the residue of a sticky brown organic rain.
Cassini released Huygens on December 24, 2004. On January 14, 2005, Huygens descended by parachute through Titan's sky, providing our first direct sampling of Titan's atmosphere and the first detailed photos of its hidden surface.
Most complex spacecraft. 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.
Click to enlarge ESA artist concept of Cassini flying into orbit around Saturn.
"Every phase of the mission has been reviewed and validated internally and externally by NASA and independent experts," said Huntress.
Nuclear power. 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.
Namesakes. The spacecraft are named for two 17th century astronomers, the Italian-French astronomer Jean-Dominique Cassini who made several key discoveries about Saturn, and the Dutch scientist Christian Huygens who discovered Titan.
Development of the Huygens probe was managed by an ESA team 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.
The Road to Saturn
The flight team at NASA's Jet Propulsion Laboratory (JPL), Pasadena, California, directed Cassini's trek to Saturn from 1997 to 2004. Here's the path they used to take the spacecraft and its piggy-back rider, Huygens, to the outer Solar System:
The first color picture from the surface of Titan by Huygens on January 14, 2005.
The Cassini mission is a joint effort of NASA, the European Space Agency and the Italian Space Agency.
- 1997 October 15 — Cassini was launched from Cape Canaveral Air Force Station in Florida.
- 1998 April 26 — Cassini gained momentum in a Venus flyby.
- 1999 June and August — Cassini flew by Venus on June 24 and Earth on August 18. Cassini used the pull of the planets' gravity to boost its speed and fling it on toward the outer planets of our Solar System. During the Earth flyby, several of Cassini's science instruments recorded data, which were sent to Earth through NASA's Deep Space Network of large sensitive antennas at stations in Spain, Australia and California.
- 2000 end of the 20th century — Cassini's odometer showed 1.25 billion miles of travel across space as it was amidst the rocks of the Asteroid Belt, a seldom-traversed ring of small bodies between Mars and Jupiter.
- 2000 December 30 — Cassini gained additional speed in a Jupiter flyby on December 30. That last gravity-assist maneuver gave Cassini the final thrust of energy it needed to project itself all the way to Saturn. The Cassini mission and science teams made observations and tested Cassini's science instruments as the spacecraft flew within 6.2 million miles of Jupiter. With Galileo still orbiting Jupiter, it was the first time two spacecraft had explored that gas giant simultaneously.
- 2002 year end — the Cassini spacecraft was travelling at about 17,491 mph and was some 677 million miles from Earth. So far on its journey, Cassini had travelled almost 2 billion miles. The spacecraft was about 408 million miles from Jupiter with its ultimate target, Saturn, which was a mere 173 million miles ahead.
- 2003 June 25 — telemetry received by NASA's Deep Space Network Canberra, Australia, tracking station showed the spacecraft was in excellent health and operating normally enroute to Saturn. June 24 was the four-year anniversary of Cassini's Venus 2 flyby.
- 2004 June 11 — Cassini flies by and photographs Saturn's moon Phoebe. The tiny mysterious object is a mere 136.7 miles in diameter.
- 2004 July 1 — carrying twelve science experiments, Cassini entered orbit around the giant ringed planet for a four-year tour of Saturn's system of moons and rings. The spacecraft will fly close to Saturn 76 times and visit the moon Titan 45 times. The Huygens probe gave us the closest view ever of Titan.
- 2005 January 14 — the European Space Agency's Huygens probe descended through the atmosphere of Saturn's large moon Titan to the surface.
- 2004 October 26 — Cassini makes its first close flyby of the big moon Titan.
- 2005 August 1 — Cassini flies by the moon Mimas.
- 2005 September 23 — Cassini flies by the moon Tethys.
- 2005 September 25 — Cassini flies by the moon Hyperion.
- 2005 October 10 — Cassini flies by the moon Dione flyby.
- 2005 November 25 — Cassini flies by the moon Rhea.
- 2007 December 3 — Cassini flies by the moon Epimetheus.