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Science & Space

Cassini races toward Saturn orbit

By Michael Coren

This image of Saturn was captured by Cassini as it approached the planet.
This image of Saturn was captured by Cassini as it approached the planet.
Gallery: Saturn and moon Lord of the Ringsexternal link

• Interactive: Cassini spacecraft
• NASA: Cassini-Huygensexternal link
• ESA: Cassini-Huygensexternal link
• Closing in on Titanexternal link
National Aeronautics and Space Administration (NASA)
Space Exploration
Science and Technology
Cassini-Huygens mission to Saturn and its moon Titan:

  • SATURN: Planet second in size to Jupiter with a diameter of 74,898 miles (120,511 km). Seven rings of ice and rock particles with 31 known moons. Visited by Pioneer 11 (1979), Voyager 1 (1980), Voyager 2 (1981).

  • TITAN: Largest Saturnian moon. May harbor organic compounds similar to those predating life on Earth. Temperature is minus 290 degrees Fahrenheit.

  • CASSINI ORBITER: Launched Oct. 15, 1997. Spacecraft is 22 feet long and weighs 12,593 pounds (5,667 kg). Runs on nuclear power. Will orbit Saturn 76 times over four years.

  • HUYGENS PROBE: Spacecraft is 8.9 feet in diameter and 705 pounds (317 kg). Will be released from Cassini on Dec. 24 and enter Titan's atmosphere on Jan. 14.

  • MISSION COST: $3.3 billion, shared by NASA, ESA, Italian Space Agency.
  • (CNN) -- NASA's Cassini probe has threaded through a gap between two of Saturn's rings and fired its engine in a critical maneuver towards becoming the first spacecraft ever to orbit the giant planet about 930 million miles (1.44 billion km) away from Earth.

    "The spacecraft is just really looking solid," Cassini program manager Robert Mitchell said as officials in mission control cheered when the maneuver began.

    Cassini has been programmed to fire its rocket for 96 minutes to slow it down and place it into orbit.

    The craft risked shooting past Saturn if the burn failed.

    "This is not a slam dunk by any means...(But) confidence in the spacecraft is high, Mitchell said.

    Cassini has spent the last seven years making a 2.2 billion-mile journey to study Saturn's atmosphere, magnetic field and weather patterns -- including its lightning and stormy ammonia clouds.

    "It's going to be the star of the show for the next four years," Mitchell said.

    Saturn, the second largest planet in our solar system, has intrigued scientists for centuries. Its unique atmosphere and the wild chemistry on its many moons could shed light on how the planets -- and possibly life -- formed in our solar system.

    The $3.3 billion craft will train its 12 scientific instruments on the planet and moons over the next four years. In December, it will deploy a probe, called Huygens, to land on Saturn's largest moon, Titan. That moon may hold chemical clues to how life began on Earth.

    But first, Cassini must navigate a hazardous passage through Saturn's rings and insert itself into orbit, at times passing just 12,000 miles above the clouds of Saturn.

    Mission controllers will know if the maneuver is successful by about 12:12 EDT (0412 GMT) when the spacecraft transmits a signal through a gap in Saturn's rings. Mission leaders said they would be "holding their breath" until Cassini sent word to controllers, but did not expect a problem.

    "The spacecraft has performed flawlessly to date and once we see the signal come back everything will be all right," said Julie Webster, a lead spacecraft engineer. "I have full faith in this spacecraft. We've performed 17 burns and the burns have all gone flawlessly."

    Cassini scientists said a receiving antennae in Australia might be inoperable during the maneuver because of high winds. But Cassini, fully capable of operating autonomously for a time, would be unaffected. Other antennas could pick up the signal later.

    Through the rings

    The craft will send back the closest images ever taken of the ice, rock and dust orbiting the gas-giant. To ward off dust-size particles, Cassini's main antenna will act as a shield during the 90-minute, 98,500-mile (158,000-km) transit of the rings.

    Afterward, Cassini will fire its main engine for 96 minutes and slow down to slide into orbit around Saturn.

    On December 24, it will deploy Huygens, a saucer-shaped probe now attached to the spacecraft. That 705-pound probe will plunge through Titan's atmosphere, one of Saturn's 31 moons, and reach the surface before shutting down.

    Huygens will peer beneath layers of smog that shroud the moon with an atmosphere surprisingly similar to Earth's -- 4 billion years ago. Titan's nitrogen-rich atmosphere, possible seas of liquid ethane and tar-like permafrost are thought to resemble conditions on early Earth.

    Scientists hope Titan will have the same organic compounds that led to life on primordial Earth and will shed new light on how the planets and life evolved.

    "We may find some highly complex molecules that may have been on Earth long before there was life here," said Jean-Pierre Lebreton, project scientist for the European Space Agency's Huygens probe. "Going to Titan now is like going to Earth and going back in time."

    Reaching the planets

    The Cassini mission is one of the most advanced and ambitious ever attempted. The interplanetary spacecraft was designed to be the most "sophisticated and reliable...spacecraft ever built for exploration of the planets," NASA said.

    An artist's deptiction of the surface of Titan as the Huygens probe makes its descent.
    An artist's deptiction of the surface of Titan as the Huygens probe makes its descent.

    At 22 feet long and 13 feet wide, weighing nearly 12,600 pounds loaded with fuel and the Huygens probe, it is also one of the largest. Its propellant load alone has more mass than both Voyager I and II combined, two craft that preceded Cassini's visit to Saturn about 20 years ago.

    The electronic brain of Cassini, a sophisticated computer directing its movements, is now a standard feature on spacecraft. It uses a relatively new family of integrated circuits -- the first civilian application of this technology -- that is 10 times more efficient than previous spacecraft at just a fraction of the size.

    These computer chips, along with the radio transponders from Cassini, were pulled from the spacecraft's production line for use on NASA's Mars Pathfinder and the Near Earth Asteroid Rendezvous, or NEAR, missions

    First steps

    Cassini's journey to Saturn began at a meeting between European and American scientists in 1982. The Saturn orbiter and Titan probe were conceived as a mission that would benefit the scientific and, technological sectors of the scientists' respective countries.

    Seven years later, the U.S. Congress approved funding for the Cassini mission and Cassini-Huygens was launched in 1997.

    However, the original design process -- aimed at producing multiple spacecraft with standardized components -- was dramatically scaled back. Engineers eliminated most of Cassini's moving parts in favor of simplicity.

    The designers replaced tape recorders with solid-state recorders, installed gyroscopes without spinning components and dropped an articulated antenna arm for one bolted to the spacecraft.

    This reliance on nonmoving components meant Cassini must rotate its entire body in order to communicate with Earth or collect data by aiming its instruments. These acrobatics are accomplished with two main engines (one as a backup) and 16 smaller thrusters controlling the craft's orientation. But it also lessens the risk of problems on the spacecraft.

    NASA also designed Cassini to be independent because the time lag of one hour and 24 minutes -- the time for light to travel 930 million miles from Saturn to Earth -- means controllers on Earth cannot immediately react to unexpected problems.

    Instead, Cassini operates on its own.

    "The spacecraft has been programmed to continue even in the event of an emergency," said Mitchell in a statement. "We don't want Cassini to call home if a problem arises, we want it to keep going."

    That forced engineers to give Cassini an 'inner ear,' or computer software, that recognizes the spacecraft's orientation at all times. It gauges its position in space, as well as its location relative to the Earth, sun, Saturn and stars.

    To stay warm, Cassini also sports nuclear-powered heaters for cold interplanetary nights. More than two-dozen layers of insulation wrap the spacecrafts sensitive innards from frigid space and meteorites.

    The spacecraft also carries a DVD record of 616,400 handwritten signatures from 81 countries around the globe, including the mission's namesakes, Jean-Dominique Cassini and Christiaan Huygens, lifted from 17th-century letters.

    On Cassini's four-year mission, it will make 52 close encounters with a handful of Saturn's 31 moons and orbit Saturn 76 times.

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