Grand Finale part 1, F ring orbits Options

[Daniele_bianchin...]

Cassini mission was best for me. See so 'many different bodies.
I did not think we would see Pan so 'close. I would have preferred mission like this around Jupiter (Juno never liked). Spectacular cliffs pan. Strange her album. A shape similar to get if launches a ball of clay at high rotation; the ball-clay equator is crushed (perhaps by gravity 'or by the concentration of water). Pan could be in fast-rotation during its formation, before cooling?

[Phil Stooke]

No, the equatorial ring must be some kind of accretion from the surrounding rings. No idea how that works yet, but Atlas also has an equatorial ridge, and soon we will get closer images of that to help us.

Galileo was supposed to be a Cassini-like mission for Jupiter, but its antenna problem resulted in less than 1% of the data return we could have expected. To be fair, it's a miracle we got anything from it at Jupiter.

Phil

[Paolo]

there was a paper in Science a few years ago explaining how Atlas and Pan got their flying saucer shape
http://ciclops.org/media/sp/2008/5168_11571_0.pdf

[jasedm]

Atlas also has an equatorial ridge, and soon we will get closer images of that to help us.

Fingers crossed on this. The encounter with Atlas back in December 2015 at ~26,000km came close to missing Atlas due to uncertainties in its orbital perameters. This encounter I'm guessing will be a deal closer, with those uncertainties being magnified in the camera boresights.

It will be a triumph if the team catch Atlas up-close.

[Explorer1]

Can't distant observations right now pin the location down better? Like optical navigation for any approach to a small body...

[Phil Stooke]

Yes, and they do it all the time, but there are many effects which modify the little satellite orbits so they remain difficult to predict precisely.

Phil

[jasedm]

Can't distant observations right now pin the location down better? Like optical navigation for any approach to a small body...

Cassini doesn't operate like this (i.e. onboard autonomous navigation) during a flyby. The observation sequences are written weeks (months?) in advance based on opnav images previously obtained, plus an exquisite knowledge of the spacecraft's trajectory.
The fly-in-the-ointment with the smaller ring moons is a not-quite-perfect knowledge of their masses, the effects of drag by nearby rings, and the gravitational effects and resonances with nearby moons. During a close-encounter (say less than 40,000km) small discrepancies may cause the moons to start to slide out of the field-of-view of the narrow-angle camera depending on the trajectory of the approach. This has happened with imaging plans for Helene, Atlas, Daphnis and Aegaeon (Aegaeon was missed completely during its very close encounter) I imagine it's as challenging as looking through a pea-shooter at night and trying to keep a firefly in view.

This said, I think all would agree that an incredibly comprehensive reconnaissance of the Saturn system has been achieved in no small part by those responsible for writing the imaging sequences and those controlling Cassini's trajectory through the Saturn system.

[Explorer1]

Thanks for the explanation, jasedm. I suppose closest approach probably gives so little time to make a large mosaic and be lucky enough to catch the moon. Near the periapse of Saturn orbit is a pretty different situation from the leisurely pace of Rosetta approaching 67P or Habausa and Itokawa...

On a related note, does the spacecraft still use the HGA as a shield whenever crossing the ring-plane, like during SOI in 2004? Is that why the Pan encounter movie has a break just before/after the ridge would be edge-on?

[jasedm]

Yes, I believe so.

[belleraphon1]

This SpaceFlightNow report by Stephen Clark mentions using the High Gain in ram mode during the Grand Finale portion staring in April


Perils and discoveries lie ahead for long-lived Saturn orbiter
https://spaceflightnow.com/2017/03/11/peril...saturn-orbiter/

[wildespace]

A nice closeup of the rings taken on March 8th with Narrow Angle camera and red, green, and blue filters (with some colour adjustment from me to better approximate true colours):



As we're getting closer to the rings and start seeing large-scale clumps of material, I wonder how hard it will be to clean those images of artifacts while trying to preserve the graininess of the actual rings.

[ngunn]

That is one impressive cloud streak in today's Titan images: https://saturn.jpl.nasa.gov/raw_images/409517
It was mentioned in Looking Ahead that these full phase images would be good for observing any opposition surge from Titan. I wonder if that's what the clouds in particular are showing here.

[titanicrivers]

Very impressive cloud streaks indeed! There may be some cloud streak movement if one animates the first image taken at 8:05 am and the last one taken at 9:21 am. There is some space craft movement as well, but I think there's some counterclockwise movement of the streaks as well in a similar direction as noted last October on the 29th and 30th and beautifully shown here: http://photojournal.jpl.nasa.gov/archive/PIA21051.gif

[wildespace]

That's some impressive clouds! What I find interesting is that they are visible in the visible part of spectrum, and have a reddish colour:

A quick RGB stack with some colour adjustment



CB3/MT1 combo:

[JRehling]

Might the clouds appear reddish because they are truly white but are above a significant fraction of the atmosphere's methane, which absorbs red? In other words, are they perhaps less-blue rather than more-red?