Spaceflight Insider

Cassini prepares to graze Saturn’s rings

Cassini: Saturn rings order of discovery animation

Saturn’s rings were named alphabetically in the order they were discovered. The narrow F Ring marks the outer boundary of the main ring system. Image & Caption Credit: NASA/JPL-Caltech/Space Science Institute

NASA’s robotic Cassini spacecraft will begin a grand tour of Saturn’s ring system starting this week as the mission enters into its final stages.

The mission is scheduled to conclude on Sept. 15, 2017, when spacecraft controllers plan to direct Cassini into Saturn’s atmosphere in order to prevent it from impacting and potentially contaminating any of the planet’s moons when the craft runs out of fuel.

The Cassini spacecraft has been in orbit since 2004. Since that time, it has revolutionized our understanding of the ringed planet. Image Credit: James Vaughan / SpaceFlight Insider

The Cassini spacecraft has been in orbit since 2004. Since that time, it has revolutionized our understanding of the ringed planet. Image Credit: James Vaughan / SpaceFlight Insider

The end of the mission will require gradually bringing the Cassini spacecraft the closest to Saturn it has been since arriving in 2004, providing scientists with an opportunity to study the planet’s atmosphere and ring system in unprecedented detail.

On Nov. 29, Cassini will receive a gravitational boost as it passes close to Titan, setting the spacecraft on a trajectory to have a Dec. 4 encounter with Saturn’s diffuse F Ring at a distance of 4,850 miles (7,800 kilometers). This pass through of the planet’s ring plane will be the first of 20 encounters scheduled to happen between Nov. 30 and April 22.

“We’re calling this phase of the mission Cassini’s Ring-Grazing Orbits, because we’ll be skimming past the outer edge of the rings,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “In addition, we have two instruments that can sample particles and gases as we cross the ring plane, so in a sense Cassini is also ‘grazing’ on the rings.”

Cassini’s instruments will attempt to sample the rings during many of these orbits, measuring the composition and properties of the particles, molecules, and gases that make up the ring material. A few hours after the ring plane crossing, Cassini’s Radio Science Subsystem (RSS) instrument will transmit a radio signal to Earth through Saturn’s rings in order to measure the distribution of dust and gas across the ring plane.

Additionally, the spacecraft’s Visual and Infrared Mapping Spectrometer will make a nine-hour movie of the Saturn’s north polar region while several other instruments will measure the boundaries of Saturn’s upper atmosphere. The extent of Saturn’s atmosphere has previously been observed to fluctuate over the seasons, so these measurements will be used by the mission team to navigate the spacecraft into future orbits that will safely skim the upper reaches of the atmosphere for direct sampling.

During Cassini’s Dec. 4 pass through the ring plane, it will conduct an engine burn that will refine its trajectory for future orbits.

“This will be the 183rd and last currently planned firing of our main engine,” said Earl Maize, Cassini project manager at JPL. “Although we could still decide to use the engine again, the plan is to complete the remaining maneuvers using thrusters.”

The upcoming orbital maneuver will also include observations of the geologically active south polar region of Enceladus as well as Tethys to study the red-striped terrain on its surface.

The Cassini spacecraft was launched in 1997 from Cape Canaveral Air Force Station in Florida. It is operated by NASA through the Jet Propulsion Laboratory in Pasadena, California.

Video Courtesy of NASA Jet Propulsion Laboratory



Paul is currently a graduate student in Space and Planetary Sciences at the University of Akransas in Fayetteville. He grew up in the Kansas City area and developed an interest in space at a young age at the start of the twin Mars Exploration Rover missions in 2003. He began his studies in aerospace engineering before switching over to geology at Wichita State University where he earned a Bachelor of Science in 2013. After working as an environmental geologist for a civil engineering firm, he began his graduate studies in 2016 and is actively working towards a PhD that will focus on the surficial processes of Mars. He also participated in a 2-week simluation at The Mars Society's Mars Desert Research Station in 2014 and remains involved in analogue mission studies today. Paul has been interested in science outreach and communication over the years which in the past included maintaining a personal blog on space exploration from high school through his undergraduate career and in recent years he has given talks at schools and other organizations over the topics of geology and space. He is excited to bring his experience as a geologist and scientist to the Spaceflight Insider team writing primarily on space science topics.

Reader Comments

Victor H. Middleton

Great stuff! Thank you. It’s an amazing time to be living in. I hope it results in positive results for our grand children and future generations.

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