Mission scientists at NASA's Jet Propulsion Laboratory are preparing for an all-nighter as the Cassini spacecraft heads into orbit around Saturn for its planned four-year tour. The Cassini orbiter and the attached Huygens probe blasted off from Earth on October 15, 1997, and have spent the past seven years traveling through space toward the gas giant. At 10:36 EDT tonight, the spacecraft is scheduled to begin a set of maneuvers that will slow it down and allow the planet's gravitational field to capture it.

Cassini is set to approach Saturn and pass through a large gap between two of its rings, known as F and G. During this time its main antenna dish, which measures four meters across, will shield the craft against dust particles (a secondary antenna will continue to transmit a monotone signal for tracking purposes). The main engine will then fire for 96 minutes, acting as a brake and slowing the ship by 626 meters a second. The spacecraft has been programmed to continue even in the event of an emergency, explains Cassini-Huygens program manager Robert T. Mitchell. With a one-way light time of one hour and 24 minutes, we had to teach the spacecraft to take care of itself.

During the so-called Saturn Orbit Insertion (SOI) Cassini will come within 19,980 kilometers of Saturn's cloud cover--closer than any other probe in history. Some of its 12 onboard instruments will be collecting data throughout the burn, whereas others will be turned on shortly after it is complete. Cassini should start sending data from the SOI back to Earth around 3 a.m. EDT on July 1, with the first images expected by 8 a.m. In a sense, Cassini and the Huygens probe are like time machines that will take us back to examine a world we've never seen before, a world that may resemble what our own world was like 4.5 billion years ago, says Jean-Pierre Lebreton of the European Space Agency. If all goes according to plan, Cassini will begin its first of 76 orbits of Saturn, including 52 close encounters with seven of the planet's 31 known moons. And in January of next year, the Huygens probe will touch down on the surface of Titan, becoming the first probe to reach another planet's moon.