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Posted by: jasedm Jan 15 2008, 06:13 PM

I feel a bit like a caretaker sweeping up in the background, what with all this Messenger Mercury activity, but here goes :
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!!!!)

Posted by: ugordan Jan 15 2008, 06:17 PM

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?

Posted by: ngunn Jan 15 2008, 08:05 PM

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).

Posted by: Holder of the Two Leashes Jan 15 2008, 08:22 PM

I hope this is not the case.

Posted by: volcanopele Jan 15 2008, 08:46 PM

Unfortunately, it is.

Posted by: jasedm Jan 15 2008, 09:13 PM

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............

Posted by: elakdawalla Jan 15 2008, 09:36 PM

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

--Emily

Posted by: Holder of the Two Leashes Jan 15 2008, 10:23 PM

(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.

Posted by: jasedm Jan 15 2008, 10:27 PM

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.

Posted by: ugordan Jan 15 2008, 10:30 PM

You can probably scratch 1) off the list, too, jasedm. That's a really high phase angle.

Posted by: tallbear Jan 16 2008, 10:48 PM

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

Posted by: tallbear Jan 16 2008, 10:56 PM

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

Posted by: jasedm Jan 18 2008, 06:49 AM

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.

Posted by: edstrick Jan 18 2008, 08:16 AM

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.

Posted by: jasedm Jan 18 2008, 09:27 PM

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

Posted by: rlorenz Jan 20 2008, 02:44 PM

RSS occs are pretty power-consuming. Even if there were a scan platform there might not be power
to run it and its instruments as well as all the RF downlinks near the end of the nominal mission as the RTGs
run down

I don't disagree scan platforms add enormously to flexibility during the fleeting geometric opportunities
that present themselves on a mission like Cassini, but
a) 'simple..scan platform' may define the null set
as future outer solar system Flagships are being considered and costed, people are wondering how
Cassini was as cheap as it (apparently) was

MMII would have been a bargain if implemented as originally intended - a platform designed once and
re-used for multiple missions - 2 missions for the price of 1.5, 3 missions for the price of 2 maybe.... but
as so often happens with multiple missions (remember how Pathfinder was Mesur Pathfinder....?)
budget got squeezed, CRAF got killed, and Cassini is what it is.

Posted by: ugordan Jan 20 2008, 02:53 PM

Isn't the HGA transmitter limited to something about 20 watts? Is the TWTA the power hungry part in the equation?

Posted by: tallbear Jan 20 2008, 08:46 PM

RSS Occs are preferably done using 3 frequencies S , X , Ka which give Cassini Occs more info than anything
Voyager could do ... If I recall correctly that's something like 80 watts ... and for any occs after Rev 28 we have had
to 'borrow' power to get 3 frequency RSS Occs .....( RTG power decay ) .... that means that other instruments
have to be put to sleep in order to get the power for the RSS Occ.... In the XM we are trying to keep 3 frequencies
for the RSS Occs in the first handful of Revs... but for occs in 2009 and later we have to basically do the occs
Voyager style...

While we all wish for a scan platform ..... besides the budget decision .... It turns out that as launch plans evolved
and Cassini ended up going up off a Titan IV that the S/C would not have fit in the vehicle if the Scan Platform
had been in place.....

and on a final note .... For RSS Occs.... we need the S/C to be absolutely stable.... nothing on the S/C is allowed to
be moving during an RSS Occ ... so the scan platform wish would lose out to practical matters..... the trades are always
to get the best science possible

T

Posted by: tedstryk Feb 13 2008, 07:10 PM

Some great images have been posted from February 8. I never remember seeing these in the latest images, but if you do the actual search for the targets, they are there.
Here are a few example shots.

Dione

Great multispectral set (Feb 8)
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=142851
Another set. (Feb 10)
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=142860

Rhea

Sequence of Rhea in front of Saturn - excellent quality mulitispectral set. (Jan 17) Also a lot of frames in this set taken when Rhea was no longer in front of Saturn.

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=140388
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=141179

Some, such as this one, appear to be part of an opposition surge study (I am guessing by the shear number of frames taken, coupled with the relatively distant view and low to 0 phase angle). (by now Jan 18)

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=140156

By the end, the terminator is on the other side.

http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS36/N00099978.jpg

There are two multispectral Tethys sets, although they are rather distant. The first example is from Jan 29, the second from Jan 30.

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=141794
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=141910

Sorry if this has already been covered somewhere, but there are also neat multispectral sequences of Saturn and Titan. I know this is the icy moon thread, but since this post is primarily about the icy moons, I figured I would put it here instead of the general forum or Titan forum.

Wide angle, Jan 29

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=141614

Narrow angle, Jan 29

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=141622

Wide angle, Jan 30

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=142121

Narrow angle, Jan 30

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=142135