Saturn Plunge Nears for Cassini Spacecraft

Cassini end of mission

After more than a decade of exploring Saturn, the Cassini spacecraft will soon commit suicide by plunging into the planet it has been documenting for years.

The spacecraft launched nearly 20 years ago and took about seven years to make it to Saturn’s orbit. Since 2004, Cassini has completed more than 290 orbits of the planet, sending back thousands of stunning images and making discoveries about Saturn, its rings, and its moons. On Sept. 15, Cassini will die by diving into Saturn’s atmosphere. Here’s what to know about its mission and final days:

–What is Cassini’s last mission?

Before Cassini makes its fatal plunge into Saturn’s clouds, the spacecraft will complete what NASA calls a “Grand Finale.” The final mission started in April and will end in September as the spacecraft transmits as much data as it can from Saturn before it dies in the clouds. After doing a close flyby of Titan, one of Saturn’s moons, Cassini will complete a series of weekly dives between Saturn and its rings, offering a never-before-seen look at one of the solar system’s most unique regions.


Source: NASA

–What has it found?

Throughout the course of its time documenting Saturn, Cassini has uncovered a trove of new knowledge. Scientists managing the spacecraft have seen through Cassini how the seasons on Saturn change, witnessed a massive storm on the planet and more. The discovery of methane lakes on the moon Titan and oceans on the moon Enceladus have shown scientists “how prevalent and common life beyond Earth may truly be,” said Curt Niebur, a Cassini program scientist, during a NASA press conference on Tuesday.

NASA hopes that the last few days of Cassini’s life will allow scientists to “understand Saturn from the inside out,” according to Linda Spilker, a Cassini project scientist. This includes obtaining more information on the composition of Saturn’s atmosphere, the interior of the planet and the age and size of its rings. Cassini’s dives between Saturn and its rings has revealed to scientists that there’s a complex interaction between the planet’s atmosphere and ring particles and that Saturn’s rings are slightly less massive than expected.

–Why will Cassini die on Saturn?

According to NASA, Cassini is running out of rocket fuel, which will eventually prevent mission operators from being able to control where the spacecraft goes. Left to its own devices, the spacecraft could collide with one of Saturn’s moons. Because Enceladus was revealed through Cassini’s findings to have the potential to carry a habitable environment, NASA wants to avoid a potential situation in which the spacecraft collides with the moon and interferes with a future search for life there. Therefore, NASA has decided to have Cassini die safely on Saturn.

In its final week, Cassini will pass several milestones en route to its science-rich Saturn plunge.

— Sept. 9 — Cassini will make the last of 22 passes between Saturn itself and its rings — closest approach is 1,044 miles (1,680 kilometers) above the clouds tops.

— Sept. 11 — Cassini will make a distant flyby of Saturn’s largest moon, Titan. Even though the spacecraft will be at 73,974 miles (119,049 kilometers) away, the gravitational influence of the moon will slow down the spacecraft slightly as it speeds past. A few days later, instead of passing through the outermost fringes of Saturn’s atmosphere, Cassini will dive in too deep to survive the friction and heating.

— Sept. 14 — Cassini’s imaging cameras take their last look around the Saturn system, sending back pictures of moons Titan and Enceladus, the hexagon-shaped jet stream around the planet’s north pole, and features in the rings.

— Sept. 14 (5:45 p.m. EDT / 2:45 p.m. PDT) — Cassini turns its antenna to point at Earth, begins a communications link that will continue until the end of the mission, and sends back its final images and other data collected along the way.

— Sept. 15 (4:37 a.m. EDT / 1:37 a.m. PDT) — The “final plunge” begins. The spacecraft starts a 5-minute roll to position INMS for optimal sampling of the atmosphere, transmitting data in near real time from now to end of the mission.

— Sept. 15 (7:53 a.m. EDT / 4:53 a.m. PDT) — Cassini enters Saturn’s atmosphere. It’s thrusters fire at 10 percent of their capacity to maintain directional stability, enabling the spacecraft’s high-gain antenna to remain pointed at Earth and allowing continued transmission of data.

— Sept. 15 (7:54 a.m. EDT / 4:54 a.m. PDT) — Cassini’s thrusters are at 100 percent of capacity. Atmospheric forces overwhelm the thrusters’ capacity to maintain control of the spacecraft’s orientation, and the high-gain antenna loses its lock on Earth. At this moment, expected to occur about 940 miles (1,510 kilometers) above Saturn’s cloud tops, communication from the spacecraft will cease, and Cassini’s mission of exploration will have concluded. The spacecraft will break up like a meteor moments later.


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