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Rev 56 observations
jasedm
post Jan 15 2008, 06:13 PM
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I feel a bit like a caretaker sweeping up in the background, what with all this Messenger Mercury activity, but here goes wink.gif :
The Ciclops looking-ahead detail has been posted for Cassini's Rev 56, disappointingly, no Methone observations are slated (closest we get from here on in) but I'm sure there's a good reason.
Interestingly, they list two 'calibration sequences' for the NAC just prior to apoapse when there will be a 'stare' into the (relative) blackness of space to determine camera sensitivity, and any damage to the optics. I presume that this is so that any lens anomalies can be subtracted from subsequent images. Strikes me as good housekeeping what with the lull in Titan observations until 22nd Feb.
Ok, as you were, back to my sweeping (GO MESSENGER!!!!)
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ugordan
post Jan 15 2008, 06:17 PM
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QUOTE (jasedm @ Jan 15 2008, 07:13 PM) *
I presume that this is so that any lens anomalies can be subtracted from subsequent images.

Sounds like dark current characterization to me; seeing how it builds up after prolonged exposure to space environment, characterizing "hot" pixels and such. I always found the term "dark space" interesting, is there really any region in the sky where you wouldn't pick up at least several stars in your FOV if you stared for several seconds?


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ngunn
post Jan 15 2008, 08:05 PM
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QUOTE (jasedm @ Jan 15 2008, 06:13 PM) *
the lull in Titan observations until 22nd Feb.


Just so nobody's misled there are two distant flybys of Titan before then. The first, on Jan 20th, promises 'the best view so far of Menrva' impact feature (other than the T3 RADAR veiw of course).
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Holder of the Tw...
post Jan 15 2008, 08:22 PM
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QUOTE (jasedm @ Jan 15 2008, 12:13 PM) *
... no Methone observations are slated ...


I hope this is not the case.
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volcanopele
post Jan 15 2008, 08:46 PM
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Unfortunately, it is.


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jasedm
post Jan 15 2008, 09:13 PM
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Holder of the two leashes, I share your regret re: Methone, (If only Methone)
Perhaps a privileged insider (Volcanopele, Tallbear?) can shed some light on future possibilities for imaging of this little rock - I understand (based on information on this forum and a couple of similar ones) that Cassini will buzz Methone reasonably closely a handful of times between now and the end of the XM.
Ranges vary from ~18,000km to 88,000km between now and the end of 2010. The lower end equates to 25 pixels or so in the NAC FOV - enough to discern some large craters.
What are the odds............
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elakdawalla
post Jan 15 2008, 09:36 PM
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Here's the specifics on the closest upcoming encounters with Methone. Most of them are quite high phase, unfortunately; today's was extremely high phase at 142 degrees.

56 2008-015T21:11 Inbound 15517 km flyby, speed = 13.7 km/s, phase = 142
62 2008-083T11:24 Inbound 102556 km flyby, speed = 17.0 km/s, phase = 114
67 2008-130T23:36 Inbound 95865 km flyby, speed = 15.2 km/s, phase = 138
68 2008-138T23:35 Inbound 79224 km flyby, speed = 20.1 km/s, phase = 105
72 2008-168T05:18 Outbound 114262 km flyby, speed = 23.3 km/s, phase = 100
73 2008-175T08:04 Inbound 56806 km flyby, speed = 21.9 km/s, phase = 77
74 2008-182T09:04 Inbound 85994 km flyby, speed = 22.6 km/s, phase = 92
75 2008-189T10:02 Outbound 117044 km flyby, speed = 23.4 km/s, phase = 102
80 2008-224T20:41 Inbound 60489 km flyby, speed = 18.4 km/s, phase = 127
83 2008-247T00:26 Outbound 91222 km flyby, speed = 19.2 km/s, phase = 127
91 2008-305T16:02 Inbound 116146 km flyby, speed = 18.8 km/s, phase = 102
119 2009-287T03:19 Inbound 85902 km flyby, speed = 11.8 km/s, phase = 39
124 2010-011T02:26 Inbound 27175 km flyby, speed = 8.0 km/s, phase = 145
125 2010-027T01:40 Inbound 72123 km flyby, speed = 14.0 km/s, phase = 60
128 2010-079T23:33 Outbound 54797 km flyby, speed = 11.1 km/s, phase = 99
131 2010-138T08:20 Inbound 18453 km flyby, speed = 4.3 km/s, phase = 75

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Holder of the Tw...
post Jan 15 2008, 10:23 PM
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QUOTE (volcanopele @ Jan 15 2008, 02:46 PM) *
Unfortunately, it is.


(Temper tantrum edited out - 2/13)

Well, Nereid made it into the Neptune family album with fewer pixels, as did Himalia into Jupiter's (courtesy of Cassini, no less), but this page looks to be blank for Saturn.

Just academically, I'm wondering if it would have stayed at high phase (142 degrees) the whole time it was in close proximity. Depending on the orbit, I've seen satellite encounters vary from almost constant phase, to ones that quickly sweep through angles. The programs I use (JPLs Solar System Simulator and Mark Showalters' Saturn Viewer) don't show Methone.
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jasedm
post Jan 15 2008, 10:27 PM
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Thanks Em for the clarification. This means that the two remaining Methone closest approaches are:
1) 11th January 2010 - Altitude 27,175, Phase 145 degrees
2) 18th May 2010 - Altitude 18,453, Phase 75 degrees (27 NAC pixels assuming image taken at C/A)
The latter is comparable to the best current image of Calypso (31 pixels) and has a good phase angle to highlight topography.
Here's hoping that an allowance has been made to image this moon at or near closest approach on that date.
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ugordan
post Jan 15 2008, 10:30 PM
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You can probably scratch 1) off the list, too, jasedm. That's a really high phase angle.


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tallbear
post Jan 16 2008, 10:48 PM
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The Methone Flyby today occurred over an RSS RING OCC.....

I'm sure that if it had not been sitting right on top of what amounts to
what is the highest prioirty Ring Observation that Rings would have found
some time for this.... *If there had been an ISS request in the system*

but an RSS OCC opportunity trumps anything else around unless we have
a series off RSS Occs lined up where we can pick N of M to do.

T
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tallbear
post Jan 16 2008, 10:56 PM
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QUOTE (ugordan @ Jan 15 2008, 03:30 PM) *
You can probably scratch 1) off the list, too, jasedm. That's a really high phase angle.



Actually .... The phase at C/A is pretty meaningless...... with close flybys we come in
practically on an impact course..... so you can have low phase incoming and high phase
at C/A and beyond..... and the opposite sometimes occurs but not that often

We... and that is several people ... have combed over all the Rock flybys.... particularly
the Ring Rocks .... to pick out the most useful flybys.......but I will say that in some circles
there is less interest in the non-ring rocks..... but getting good in-close looks at the rocks
in and near the rings is a priority ... but it has been a difficult one to achieve....

T
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jasedm
post Jan 18 2008, 06:49 AM
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Tallbear - thanks for the insights. It's interesting to hear about some of the hard decisions that are made as regards trading-off different priority observations.
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edstrick
post Jan 18 2008, 08:16 AM
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If Cassini had retained a simple 1-degree of freedom (fore-and-aft) scan platform, a roll maneuver and platform slew could have permitted imaging while the antenna was on Earth for the RSS occultation. Another victim of NASA and JPL's total failure to contain costs during the "Mariner Mark II" development of a new "low cost" multi-mission outer solar system vehicle.
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jasedm
post Jan 18 2008, 09:27 PM
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QUOTE (tallbear @ Jan 16 2008, 10:56 PM) *
We... and that is several people ... have combed over all the Rock flybys.... particularly
the Ring Rocks .... to pick out the most useful flybys.......
T


Very interesting T, so can you confirm whether Daphnis and Pan are actually included in future sequences for some close attention from ISS?
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