Adam Hurcewicz
Mar 11 2010, 11:40 AM
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
Mar 11 2010, 08:42 PM
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
Mar 11 2010, 09:27 PM
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
Mar 11 2010, 10:23 PM
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
Mar 12 2010, 07:55 PM
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
Mar 13 2010, 05:16 PM
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
Mar 14 2010, 10:53 AM
Occultation Titan and Dione,
I use 27 images in this animation
Click to view attachment
S_Walker
Mar 17 2010, 07:27 PM
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.
Click to view attachment
Adam Hurcewicz
Mar 17 2010, 09:20 PM
QUOTE (S_Walker @ Mar 17 2010, 08:27 PM)
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
Mar 17 2010, 10:23 PM
Dione and Titan still image from March 13, 2010:
Click to view attachment('bout halfway point in Adam's animation above)
ugordan
Mar 17 2010, 10:28 PM
*cough* there's color data available *cough*
Juramike
Mar 17 2010, 10:49 PM
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
Mar 18 2010, 05:07 PM
Titan, March 16, distance 1.9 million km, phase angle about 156 deg. Red/green/UV3 composite to bring out the high altitude haze.
Click to view attachment
ElkGroveDan
Mar 18 2010, 06:36 PM
Nice. Thanks for that Gordan.
Juramike
Mar 19 2010, 01:12 AM
Here is a color version of the Titan Dione occultation (so I can hold my head high again):
Click to view attachmentDetails of the extensive processing are
here.
Bill Harris
Mar 19 2010, 11:22 AM
> a stark and pure beauty in a black and white image.
Well-spoken by an Ansel Adams of Planetary photography...
ugordan
Mar 25 2010, 05:43 PM
nprev
Mar 26 2010, 01:44 AM
Just can't get enough of them mutuals.
Beautiful, Gordan.
jasedm
Mar 26 2010, 07:23 PM
LOVE the Rhea/Epimetheus combo. Phenomenal!
Ian R
Mar 27 2010, 06:26 AM
Y'know, there comes a time when a lone emoticon just seems so woefully inadequate...
Great stuff as usual, Gordan!
ngunn
Mar 28 2010, 10:13 AM
ugordan
Mar 28 2010, 11:38 AM
QUOTE (ngunn @ Mar 28 2010, 12:13 PM)
Neat! There's actually 3 moons visible, can you spot the 3rd one?
Click to view attachment
ngunn
Mar 28 2010, 11:55 AM
Superb Gordan! Would that be one of the F ring shepherds just right of centre? BTW which is the near edge of the rings in that view?
ugordan
Mar 28 2010, 12:04 PM
Heh, it's not superb, Titan's limb isn't aligned to sub-pixel accuracy making it appear reddish here. Based on the moon location within the ring, yes, and I'd guess it's Prometheus. Since this is the unlit side of the rings, it's from below the ring plane so the upper edge is nearer to Cassini.
EDIT: Ah, just checked - make that the lit side of the rings, so the near edge is the lower edge.
ugordan
Mar 28 2010, 12:22 PM
Titan and Janus, brightened for visibility:
Click to view attachment
Juramike
Mar 31 2010, 12:56 AM
Rhea against the rings, March 28, 2010:
Click to view attachment
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