Arrival at Saturn

Surviving seven years in space and a treacherous passage through the rings of Saturn, the Cassini spacecraft is now in Saturn’s orbit, ready to begin a four-year study of the giant gaseous planet and its moons.

At the end of a white-knuckled interplanetary roller-coaster ride last Wednesday, jubilant mission control scientists at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., broke into cheers and high-fived and hugged each other as they received all the hoped-for signals from the spacecraft.

Cassini executed the delicate and dangerous “orbit insertion” maneuver without any apparent hitch. Reaching speeds of over 60,000 miles per hour, the craft used Saturn’s gravity to pull itself through a gap in the planet’s rings, over the top of the planet, and back down through the rings again. To brake itself, the craft fired its engine for 95 minutes—“a long, long time,” noted Edward J. Weiler, associate administrator of NASA.

“It feels awfully good to be in orbit around the ‘lord of the rings,’” JPL Director Charles Elachi remarked.

The international Cassini team also used the opportunity to capture the closest ever images of the icy rocks that make up the planet’s rings, and is already marveling at the rings’ density waves, scalloped edges, and wispy areas. Carolyn Porco, imaging team leader at the Space Science Institute in Boulder, Colo., said the photos’ clarity was “so shocking, I thought I was seeing a simulation.”

In the coming months, Cassini’s 12 instruments will begin monitoring Saturn’s atmosphere, magnetic structure, and moons.

The craft faced numerous dangers during the orbit insertion. Though previous surveys showed that the gap in the rings that it sailed through contained nothing more than dust, a particle not much larger could have derailed the mission. “Something the size of a marble could do a lot of damage,” said Robert T. Mitchell, Cassini program manager at JPL.

Engineers turned the craft so that its high-gain antenna, made of a tough graphite epoxy, functioned as a shield against small particles.

The 6-ton spacecraft’s next big task will be to dispatch a probe to Saturn’s giant moon, Titan, on Dec. 25. The probe will plunge through Titan’s nitrogen-and-methane atmosphere to land on the surface.

The $3 billion project is the largest and most complex of its kind in NASA’s history. The Cassini Saturn orbit insertion is the most recent in a number of successes for NASA. Two rovers have been traversing the surface of Mars for months, confirming, among other things, that the planet was once wet. And last month, NASA’s Stardust spacecraft flew close to a comet, gathering samples to return to Earth.