APOD: Cassini Approaches Saturn (2016 Apr 10)

[APOD Robot]

Cassini Approaches Saturn

Explanation: Cassini, a robot spacecraft launched in 1997 by NASA, became close enough in 2002 to resolve many rings and moons of its destination planet: Saturn. At that time, Cassini snapped several images during an engineering test. Several of those images were combined into the contrast-enhanced color composite featured here. Saturn's rings and cloud-tops are visible toward the image bottom, while Titan, its largest moon, is visible as the speck toward the top. When arriving at Saturn in July 2004, the Cassini orbiter began to circle and study the Saturnian system. A highlight was when Cassini launched the Huygens probe that made an unprecedented landing on Titan in 2005, sending back detailed pictures. Now nearing the end of its mission, Cassini is scheduled to embark on a Grand Finale phase in late 2016 where it will repeatedly dive between the giant planet and its innermost rings.

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[heehaw]

Boy, way back in 2002!

[Case]

Now nearing the end of its mission, Cassini is scheduled to embark on a Grand Finale phase in late 2016 where it will repeatedly dive between the giant planet and its innermost rings.

Exerpt from transscript of Coming Attractions movie closed captioning:
“... And then of course the mission end itself is completely unique. Starting in 2016 ending in 2017, these orbits will take us up and over the north and south poles of the planet. We’re actually going to dive in between the innermost edge of the D ring and the upper atmosphere of the planet itself. From that we’re going to learn how is Saturn constructed from inside out. We’ll also get the magnetic field of the planet, the mass of the rings, for the very first time and get to sample a place that no spacecraft has ever flown before ... ”

[Chris Peterson]

Explanation: Cassini, a robot spacecraft launched in 1997 by NASA...

Launched by NASA, but to be clear, a joint American-European mission.

[Guest]

Based on the description, it sound very brave and daring to 'risk' the space craft by passing between the planet and the rings. But is it really just a maneuver to use the planets outer atmosphere as a means of braking in preparation to a final plunge into the planet? All part of a suicide plan but collecting data all the way in?

[heehaw]

Why, why, would they not end the mission with a slow glide "onto" a ring, so we would get close up images of a portion of a ring, showing (presumably) a stately procession of snowballs of various sizes all moving in parallel and never colliding; except they can't all move in parallel at the same speed, as the ones that are a bit farther from Saturn must move a bit slower: it is amazing that collisions never ever occur which would scatter stuff out of the ring plane.

[Chris Peterson]

Why, why, would they not end the mission with a slow glide "onto" a ring, so we would get close up images of a portion of a ring, showing (presumably) a stately procession of snowballs of various sizes all moving in parallel and never colliding; except they can't all move in parallel at the same speed, as the ones that are a bit farther from Saturn must move a bit slower: it is amazing that collisions never ever occur which would scatter stuff out of the ring plane.

Because getting that close to a ring is just too risky. The last thing anybody wants is fragments of Cassini orbiting Saturn.

[Jim Leff]

" The last thing anybody wants is fragments of Cassini orbiting Saturn"

Due to exo-ecological concerns?

[Chris Peterson]

" The last thing anybody wants is fragments of Cassini orbiting Saturn"

Due to exo-ecological concerns?

Yeah. Contamination from the probe could really mess up future research. That's why they burn up outer planet probes at the end of missions.

[neufer]

Why, why, would they not end the mission with a slow glide "onto" a ring, so we would get close up images of a portion of a ring, showing (presumably) a stately procession of snowballs of various sizes all moving in parallel and never colliding; except they can't all move in parallel at the same speed, as the ones that are a bit farther from Saturn must move a bit slower: it is amazing that collisions never ever occur which would scatter stuff out of the ring plane.

Because getting that close to a ring is just too risky.
The last thing anybody wants is fragments of Cassini orbiting Saturn.

One of the interesting options for "Cassini's retirement" would have been to fly out to a stable orbit outside(/of?) Phoebe near the distant Phoebe ring. However, it was the least favorite option for a number of reasons not the least of which was that it would require a delta velocity impulse of ~120m/s.

To have gone instead to a stable orbit outside(/of?) Pandora near the outer F ring would require a delta velocity impulse of ~7,000m/s. There just isn't enough fuel left for that sort of maneuver.

[heehaw]

Well I think that reasoning is just silly and wrong. That Cassini, tiny Cassini, would contaminate the rings of Saturn! Pathetic! And the close-up of a portion of a ring would have been wonderful.

[geckzilla]

Well I think that reasoning is just silly and wrong. That Cassini, tiny Cassini, would contaminate the rings of Saturn! Pathetic! And the close-up of a portion of a ring would have been wonderful.

It's not the rings, it's the potentially life-bearing moons surrounding Saturn. If Cassini gets splattered in that system, little bits of it are going to fall on every single one of them.

[Chris Peterson]

Well I think that reasoning is just silly and wrong. That Cassini, tiny Cassini, would contaminate the rings of Saturn! Pathetic! And the close-up of a portion of a ring would have been wonderful.

It's not the rings, it's the potentially life-bearing moons surrounding Saturn. If Cassini gets splattered in that system, little bits of it are going to fall on every single one of them.

And probably of even greater concern is simply contaminating other moons, without consideration for their life-bearing potential. We study other bodies in our solar system with instruments that measure things at the parts per billion level, and instrument sensitivities improve all the time. Cassini could produce more than enough contamination to mess up future measurements and interfere with our ability to understand natural processes and materials.