Spaceflight Insider

Cassini prepares for sixth ring-grazing orbit

Cassini at Saturn

This artist’s rendering shows NASA’s Cassini spacecraft above Saturn’s northern hemisphere, heading toward its first dive between Saturn and its rings on April 26, 2017. Image & Caption Credit: NASA/JPL-Caltech

NASA’s Cassini spacecraft is currently completing its fifth ring-grazing orbit of Saturn as it conducts its Grand Finale nearing the end of its mission. The probe will reach its orbital apoapsis on May 25 at 08:50 UTC (4:50 a.m. EDT), at which point its sixth ring-grazing orbit will begin. The sixth ring crossing of the Grand Finale will occur on May 28 at 14:22 UTC (10:22 a.m. EDT).

The fifth ring-crossing occurred at 03:11 UTC on May 22 (11:11 p.m. EDT, May 21), during which time the spacecraft was actively transmitting to Earth using its Radio Science Subsystem (RSS) to conduct radio occultation measurements of the rings as well as to help measure the planet’s gravitational field. Cassini also imaged and mapped Saturn’s atmosphere using its Imaging Science Subsystem (ISS) and two spectrometers to study the temperature and composition of the atmosphere.

In addition to the RSS experiment and imaging campaign, Cassini’s Cosmic Dust Analyzer (CDA) sampled the composition of small particles along the ring plane to help further refine the composition and age of the rings. Results are still being analyzed, but more particle strikes on the CDA would be indicative of an older age for the rings and fewer strikes would indicate a younger age. Cassini passed within 3,120 miles (5,010 kilometers) of the innermost portion of Saturn’s D ring.

The sixth ring-grazing orbit will see Cassini pass within 2,370 miles (3,810 kilometers) of Saturn’s D ring – its closest pass of the mission. Cassini will point its High Gain Antenna in the direction of its flight path to help shield the spacecraft from larger particles it may encounter in the ring plane. During this closest phase of the ring-plane crossing, the Radio and Plasma Wave Science (RPWS) instrument will be used to ‘listen’ for the impact of ring particles, which produce a detectable plasma cloud when they strike the instrument and spacecraft.

As Cassini approaches and recedes away from the rings, it will direct its ISS to image the edge of the A, B, C, and F rings, and the space in between them to better understand the structure of the rings as well as how ring particles interact with the region. Cassini will also use its RADAR instrument to measure the rings in the first of a series of three related experiments.

RADAR is a synthetic aperture radar that has previously been used to map the surface of Titan, which is hidden beneath a veil of clouds and haze. Its use during the sixth ring crossing orbit represents the first time radar measurements have been taken of Saturn’s rings from close-range.

Cassini’s Grand Finale of 22 ring-grazing orbits is leading up to the conclusion of the mission later this year on September 15 when the spacecraft will enter Saturn’s atmosphere.

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.

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