The destination is within clear view, and a beckoning sight it is. Saturn and its creamy pastel bands of thick atmosphere shimmer in pale sunlight, and the majestic rings of dust and rock set it apart from the sun's other worlds.
Dancing about in rhythmic orbits are 31 known satellites, of which the most mysterious and inviting is the planet-size Titan.
After a nearly seven-year voyage from Earth, the Cassini spacecraft is fast approaching the moment that scientists have dreamed of and planned for over the better part of their careers. The spacecraft is scheduled to swing into orbit around Saturn on the evening of June 30.
Expectations are high for the US$3.3 billion American-European mission, which is planned to last at least four years and could keep going for as much as a decade.
"The Saturn system represents an unsurpassed laboratory, where we can look for answers to many fundamental questions about the physics, chemistry and evolution of the planets and the conditions that give rise to life," Edward Weiler, associate administrator for science at NASA, said in a statement.
Scientists dare not predict the discoveries waiting to be made as the spacecraft focuses its cameras and instruments repeatedly on Saturn and its signature rings and takes the measure of the icy moons during at least 76 orbits.
"Prepare to be amazed," Carolyn Porco, chief of the mission's imaging team, said in an interview last week.
Anxiety also is rising, though a compensating air of optimism seems to prevail. The spacecraft's performance over the 4.34 billion-kilometer flight so far has been virtually trouble free.
"There's not a single thing to point to and say, `I'm worried about that,"' said Robert Mitchell, the project manager at the Jet Propulsion Laboratory in Pasadena, California, where the mission is being directed.
Still, when the time comes for the Cassini to thread the gap between two dust rings, and the main engine to kick on and burn 96 minutes, slowing for capture by Saturn's strong gravity, Mitchell confessed, "I'll be in mission control with my fingers crossed."
The spacecraft has already had its first Saturn encounter, passing by Phoebe, the planet's small dark outermost moon last Friday. Scientists theorize that in Phoebe they may be getting their first close examination of an object from the outer reaches of the solar system. Everything about its appearance and motions suggests that the 220km-diameter Phoebe originated far beyond the outer planets and that it was flung toward Saturn, which captured it into its orbit.
Saturn itself, second to Jupiter in size, now looms so large with respect to Cassini that it's the planet's full girth no longer fits inside the frame of the craft's narrow-angle camera. The Cassini's two cameras are expected to take as many as 500,000 pictures in the next four years.
If all continues to go well, the spacecraft -- the 2,131kg Cassini orbiter and the attached 317kg Huygens, to be released in December to investigate the atmosphere and surface of Titan -- will arrive at Saturn below the plane of the spreading rings. It is to pass through the gap between the F and G rings.
Recent photography, including observations by the Hubble Space Telescope, shows no sign of hazardous debris in Cassini's path, Mitchell said. Three previous spacecraft have flown through the region without harm.
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