Cassini used Titan’s gravity during the Titan 125 (T-125) flyby to put the spacecraft into its history-making Ring-Grazing Orbits. The spacecraft will be in an elliptical (egg-shaped) orbit inclined about 60 degrees from Saturn’s ring plane. On each orbit, Cassini will swoop down through the ring plane just outside Saturn’s F ring. Each of Cassini’s orbits, known as Revs, or revolutions, begins when the spacecraft is at its most distant from Saturn, a position known as apoapse, and each of the ring-plane crossings happen around when Cassini is around its nearest point to Saturn, known as periapse.
The first Ring-Grazing Orbit begins on Nov. 30 with a ring plane crossing five days later on Dec. 4. The spacecraft will repeat this feat 20 times, with only about a week between each ring-plane crossing. Those orbits end with the spacecraft’s final close Titan flyby, T-126 in April, at which point Cassini enters a series of even more daring Grand Finale Orbits.
The summaries posted on this page for each ring-grazing orbit include only a few highlights of the many unparalleled science investigations that Cassini performs during these ambitious orbits.
Ring-Grazing Orbits Countdown
On this ring-grazing orbit, Cassini will cross Saturn’s ring plane within 6,867 miles (11,051 kilometers) of Saturn’s F ring.
To calibrate Cassini’s magnetometer for later, the spacecraft will roll for part of its second ring-grazing orbit. The sun will be between Earth and Saturn in what’s called a conjunction, during which the sun’s solar wind/plasma interferes with normal radio communications and radio science experiments. Cassini will take advantage of the alignment by using its radio science instrument to study that interference for the benefit of future missions.
Cassini will also practice for its Grand Finale Orbits, in which the spacecraft passes in the unexplored narrow space between the planet and its rings. Inward and outward from Saturn’s dense, visible rings, a less-dense population of hard-to-see particles reside in the ring plane and can pose a hazard to the spacecraft. To minimize the hazard from ring particles, the spacecraft will orient its high-gain antenna toward the direction the spacecraft is traveling (called RAM position) like a snow plow. Only a few of Cassini’s instruments extend beyond the diameter of the spacecraft’s high-gain antenna. So during the first Grand Finale Orbit, the dish will serve as a shield when Cassini punctures Saturn’s ring plane at thousands of miles per hour. As a result, most instruments should be relatively safe from ring particles.
Cassini will practice that positioning during its ring-plane crossing on Rev 252. As part of the exercise, the spacecraft’s Radio and Plasma Wave Science instrument will “listen” to particle collisions, and the Cosmic Dust Analyzer will scoop up and analyze particles. Scientists will use data from the two instruments during this pass to calibrate them for the first ring-plane crossing of Cassini’s Grand Finale Orbits, which will happen during Rev 271.
For the complete list of F Ring orbits, visit our Ring-Grazing Orbits Quick Reference.