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Posted by: jasedm Feb 18 2008, 01:25 PM

Information on the current rev has been posted on the Ciclops 'looking ahead' page. This includes the Titan targeted encounter (pretty well- detailed observational timeline here), and a Voyager-class flyby of Janus, with ISS observations at around 160,000km. This won't be the closest remaining pass of Janus (I think the last few weeks of the prime mission have two closer passes) but it should reveal some previously unseen territory towards the south pole (or unseen at a reasonable distance anyhow)

Posted by: Holder of the Two Leashes Feb 18 2008, 11:59 PM

Here is a link -

http://ciclops.org/view.php?id=4788

Posted by: CAP-Team Feb 19 2008, 12:35 PM

Hmm they use Celestia to generate their images. is the Janus model and map somewhere to download?

Posted by: Phil Stooke Feb 19 2008, 03:04 PM

Here!

http://publish.uwo.ca/~pjstooke/plancart.htm

My stuff is all over the place. I'm not sure where they picked it up, but I'm the ultimate source. The shape model might be a new version by Peter Thomas.

Phil

Posted by: volcanopele Feb 19 2008, 04:37 PM

Yeah the images we use for the Looking Ahead page mostly come from Celestia. The Janus model is the default model that comes with Celestia, which I assume is Phil's. Peter hasn't published his shape model for Janus yet.

Posted by: claurel Feb 22 2008, 10:31 PM

If there are any better versions of shape models for Saturnian moons available than the ones currently in Celestia, I'd love to hear about them. I've seen some images indicating that people have make some 3D reconstructions, but I haven't seen any models published that are based on Cassini date.

--Chris

Posted by: peter59 Feb 23 2008, 10:02 AM

I have one question about Janus.

http://www.planetary.org/explore/topics/saturn/janus.html
The closest flyby will be on June 30, 2008 (rev 74) at about 44,636 kilometers (26,782 miles).

http://saturn.jpl.nasa.gov/science/moons/moonDetails.cfm?pageID=8
No targeted flyby. Closest approach: June 1, 2008 -- 14,363 kilometers (8,925 miles)

Where is Truth ?

Posted by: jasedm Feb 23 2008, 12:03 PM

I was wondering this too. There are now some (small) discrepancies in the information concerning moon flyby distances in the final weeks of the prime tour - Cassini's orbital tour has been tweaked quite a bit with trim manoevres since information was first published.
From various sources, these are distances that I have seen quoted for the Janus flyby on June 1st 2008:

14,363 - NASA Cassini-Huygens moons page
32,786
13,691
23,000 - NASA Cassini-Huygens encounters page

And these for the 30th June 2008 pass:

44,731
69,000
66,151 - NASA Cassini-Huygens encounters page
*EDIT*
29,812 - list posted by John S in the extended mission thread on this forum

Obviously, the trajectory after 30th June 2008 was completely unknown before orbit insertion, as it was not certain whether there would be a mission extension.

Posted by: elakdawalla Feb 23 2008, 11:07 PM

Ah, that planetary.org page is outdated -- I'd totally forgotten about those encounter lists when I updated the tour page. I have some serious work to do updating the Saturn icy satellite pages.

My new tour page does not include future encounters with "rocks" because (a) there's a ton of them and ( imaging is not often performed. So for rocks I'm now waiting until images hit the PDS, then I add in whatever encounters there was imaging done after the fact.

Here's the latest information I received from Dave Seal on all Janus encounters during the prime and extended missions. All are nontargeted. June 30 2008 is still the closest one.

00JA (nt) 2004-183T01:51 Jul-01 Inbound 67678 km flyby, speed = 12.8 km/s, phase = 106°
55JA (nt) 2008-003T22:11 Jan-03 Inbound 118244 km flyby, speed = 10.1 km/s, phase = 154°
59JA (nt) 2008-051T19:08 Feb-20 Inbound 110073 km flyby, speed = 17.3 km/s, phase = 111°
63JA (nt) 2008-092T19:09 Apr-01 Inbound 117048 km flyby, speed = 16.6 km/s, phase = 148°
67JA (nt) 2008-131T00:06 May-10 Inbound 120801 km flyby, speed = 16.3 km/s, phase = 156°
69JA (nt) 2008-146T22:50 May-25 Inbound 63900 km flyby, speed = 20.4 km/s, phase = 134°
70JA (nt) 2008-153T22:13 Jun-01 Inbound 32584 km flyby, speed = 22.1 km/s, phase = 109°
74JA (nt) 2008-182T08:57 Jun-30 Inbound 30983 km flyby, speed = 22.6 km/s, phase = 123°
75JA (nt) 2008-189T08:57 Jul-07 Inbound 80944 km flyby, speed = 22.6 km/s, phase = 94°
83JA (nt) 2008-246T23:28 Sep-02 Inbound 86894 km flyby, speed = 19.4 km/s, phase = 156°
88JA (nt) 2008-283T18:56 Oct-09 Inbound 89447 km flyby, speed = 19.4 km/s, phase = 150°
90JA (nt) 2008-298T09:14 Oct-24 Inbound 108161 km flyby, speed = 19.5 km/s, phase = 132°
115JA (nt) 2009-207T17:06 Jul-26 Outbound 94006 km flyby, speed = 9.9 km/s, phase = 59°
126JA (nt) 2010-044T16:22 Feb-13 Inbound 114968 km flyby, speed = 14.4 km/s, phase = 29°
129JA (nt) 2010-097T13:44 Apr-07 Outbound 74669 km flyby, speed = 2.8 km/s, phase = 39°

--Emily

Posted by: edstrick Feb 24 2008, 08:35 AM

I've long thought that a good "figure of merit" for an encounter with a moon or a "rock" is the peak number of illuminated pixels during the encounter. An adjusted figure of merit might be that value with any "imaging excluded" times excluded, for example times with slew-rates too high for imaging.

Posted by: jasedm Feb 24 2008, 10:28 AM

And the 30th June flyby is I believe the only one of the two passes remaining in the prime mission which was/is definitely included in spacecraft sequences for ISS attention (although not necessarily at closest approach) unless this part of the sequence was changed following XM approval.

Posted by: tallbear Feb 25 2008, 06:11 PM

some comments on questions raised and the other info in this thread ....

The "TOUR" has been changed a number of times since SOI ... each change of the Tour alters non-targeted flybys
downstream ..... you need a 'scorecard' to track this info <G>.... meanwhile, info on websites tends to be static
and/or slow to change.

As for the table of Janus flybys from Dave ( an accurate source of current info ) ..... keep in mind that the phase angle
at closes approach is not too meaningful as an indicator of the flyby's 'usefullness' .... 30 min before or after C/A the
phase angle can be substantially different

.... As for the Jun 30 2008 flyby, the phase angle drops to ~ 90 deg about 30 min after C/A ... BUT .... JANUS goes inot
eclipse just minutes after C/A....

T

Posted by: jasedm Feb 26 2008, 09:35 AM

Thanks Tallbear for the information.
There appear to still be gremlins on the Cassini Huygens raw images page, so the Janus images still aren't up yet...(nor anything in the last two weeks - you Titan afficionados must be grinding your teeth by now following the last flyby)

Posted by: ugordan Feb 26 2008, 10:05 AM

Well, there are a few OPNAVs that appeared on the raw page yesterday so... eppur si muove...

Posted by: jasedm Feb 26 2008, 10:14 AM

Said 'sotto voce' no doubt

Posted by: Holder of the Two Leashes Feb 27 2008, 03:39 AM

Janus pictures are finally starting to come in.

Here is http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=144193, picked at random.

And this one appears to be the http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=144149.

Posted by: Phil Stooke Feb 28 2008, 02:45 PM

Beginning. middle and end of the Janus sequence, showing a bit of rotation.

Phil

Posted by: ngunn Feb 28 2008, 03:24 PM

And very nice they look in parallel-eyed stereo!

EDIT: As ordered in Phil's image its actually cross-eyed viewing that's required. I simply printed the whole image in A4 portrait format and they came out the right size for doing this with either adjacent pair.

Posted by: elakdawalla Feb 28 2008, 05:37 PM

Here's my take on the sequence. We're looking down on the rotation. Look at the top and bottom edges of the terminator, and you can see significant motion of the shadows as Janus rotates. Neat! --Emily

Posted by: Phil Stooke Feb 28 2008, 07:20 PM

Isn't it the south pole rather than the north?

Phil

Posted by: ngunn Feb 28 2008, 07:24 PM

Aah, that's very nice. Looks like the pole is close to that comparatively fresh small crater about one third of the way up the terminator. The view can't be exactly pole on because you can see some terrain 'setting' over the limb at lower right as it rotates - just enough to make rough and ready 3D viewing work, albeit imperfectly.

Posted by: elakdawalla Feb 28 2008, 07:36 PM

Dang--you're right. I misinterpreted the Saturn Viewer again. Its preview images show the sunlit portion of the disk of any object with dark black lines and the nightside with light gray lines, and I am forever getting those backward. Thanks.


I don't know if that's the pole -- in fact, I'm pretty sure it's not -- that's just the feature I aligned all the frames on.

--Emily

Posted by: ngunn Feb 28 2008, 07:58 PM

Well I've just looked at the animations here (from Phil's model), also the necessarily incomplete maps:
http://www.solarviews.com/eng/janus.htm

. . but I'm none the wiser. Phil, can you help us locate that pole on the new images?

Posted by: Phil Stooke Feb 28 2008, 09:01 PM

No, not really. Not without accurate pointing information. I'll let Peter Thomas take care of that.

Mama mia! I made that map of Janus in 1993. That was a long time ago... I should say I'm not doing any shape modelling these days, I don't even have the software running any more.

Phil