Rev 128 - Mar 12-29, 2010 - Icy moons occultations Options

[Adam Hurcewicz]

12 Mar. 2010 Cassini starts 128 orbit around Saturn.

"Cassini will not fly by any moons during this orbit, it will take advantage of its position near Saturn's ring plane to image a number of mutual events between two or more moons."

http://ciclops.org/view/6260/Rev128

[jasedm]

Thanks as ever to Volcanopele for the very informative looking 'ahead article' at Ciclops. A couple of questions:

Does Cassini not approach Polydeuces to within 35,000km on the upcoming rev? I would have thought that this was a good opportunity to improve on the best imaging to date for the tiny moon. (I'm assuming that Daphnis and Prometheus are both in eclipse when Cassini passes by at reasonable distances just prior to periapse)

Also, excuse my ignorance, but icy moon occultations seem to get quite a bit of attention from the Cassini team - is there a particularly valuable reason for observing these (aside from the beautiful images they present)

Interestedly,

Jase

[elakdawalla]

Jason can correct me if I'm wrong but I think occultations provide really valuable data for determining the orbits of the icy moons, more precise than op nav images that align moons with the starry background.

[volcanopele]

From Celestia, it looks like Cassini is doing some ring observations at the time of the Polydeuces C/A, and might be crossing the ringplane at the time... the HGA is pointed up...

Emily, that sounds about right.

[pat]

O.K., so why aren't there observations to take advantage of the ~30,00 km flyby of Polydeuces? They were requested for DOY 80 between about 03:00 and 07:00. The problem was that CDA had identified the time from ~DOY 78 15:50:00 to ~DOY 81 06:00 as being ideal for an equatorial ring scan and they had pretty much been promised this entire peripase "day" to do exactly that. I think this is the only time CDA were allocated a peripase "day" for ring plane dust observations during the XM. Unfortunately Polydeuces lost out, the CDA observations were considered to be more important. However VIMS Saturn atmosphere occultations of Betelgeuse and Sirius and a UVIS solar occultation were considered to be important enough to carve time out of the CDA observation.

Thats just the way that the negotiations go. A ~30,000 km flyby of a rock simply wasn't compelling enough to justify taking time away from the long CDA ringplane dust observation but the star and solar occs by Saturn's atmosphere were. I think that the rev 128 periapse period had been allocated to the Rings Target Working Team in the first place solely because of that CDA observation.

[jasedm]

Ah the fine-tuning of orbital characteristics - that makes a lot of sense.

Pat - re: Polydeuces, thanks for the insider's take on this - there are obviously a great many demands on the spacecraft's time, especially at periapse. I understand there are a couple of closer passes to Polydeuces in 2015, so with luck, a few images may be able to be factored-in then.

Thanks for the responses.

Jase

[Adam Hurcewicz]

Occultation Titan and Dione,
I use 27 images in this animation

[S_Walker]

This one turned up on the raw images site this morning... its serene beauty beckoned me to put it together. Anyone know which moons they are?

Sean W.

[Adam Hurcewicz]

This one turned up on the raw images site this morning... its serene beauty beckoned me to put it together. Anyone know which moons they are?

Sean W.

Very nice image.

Up is Mimas, low is Tethys images taken about 18:50 UTC (15 Mar. 2010)

[Juramike]

Dione and Titan still image from March 13, 2010:



('bout halfway point in Adam's animation above)

[ugordan]

*cough* there's color data available *cough*

[Juramike]

Ahhh, but sometimes there is a stark and pure beauty in a black and white image.

(+ laziness on my part to deal with all the bodies in motion and color balance.)

[ugordan]

Titan, March 16, distance 1.9 million km, phase angle about 156 deg. Red/green/UV3 composite to bring out the high altitude haze.

[ElkGroveDan]

Nice. Thanks for that Gordan.

[Juramike]

Here is a color version of the Titan Dione occultation (so I can hold my head high again):



Details of the extensive processing are here.