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Posted by: john_s Feb 4 2007, 03:35 AM

The winner is (drum roll please) PF6h9. Officially adopted on Thursday. I haven't sifted through all the details yet, but from my parochial point of view, I know it includes seven close Enceladus flybys, so that's good. Most of the science groups (Titan, Rings, Magnetosphere, Saturn, and Icy Satellites) were pretty happy with this choice- it packs in an amazing number of science opportunities.

John.

Posted by: volcanopele Feb 4 2007, 05:09 AM

I'm not sure on all the details either. I'm not sure how the Enceladus flybys have changed, but good old PF6 had 2 encounters @ < 50 km, 2 encounters @ > 50 and < 200 km, 2 encounters @ > 200 and < 1000 km, and 1 encounter @ > 1000 and < 3000 km. There appear to be 26 Titan flybys with a good mix of S Polar, N Polar, and trailing hemisphere encounters.

Posted by: ugordan Feb 5 2007, 01:43 PM

Grabbed from the Yahoo Cassini-Huygens group: http://www.spacedaily.com/reports/Tour_de_Saturn_Set_For_Extended_Play_999.html

Excerpt:

Posted by: john_s Feb 5 2007, 03:06 PM

Here's a file listing the geometries of the icy satellite flybys in the chosen extended mission tour. Close encounter geometries may change slightly as the tour is fine-tuned, but by no more than a couple of thousand kilometers, and the dates will not change.

John
 Icysat_Flybys_UTC_NFB.PF_6h9L.txt ( 14.77K ) : 1411

Posted by: djellison Feb 5 2007, 03:35 PM

My word - 17km/sec to an altitiude of 25km...that's FAST. What are the typical exposure times for ISS NA and WA using clear filters?

We're talking a 150 metre footprint for the NA - so 14.6 cm/pixel - but wow - an exposure of, say, 1 second - would blur the image by 116,000 pixels Take a zero off the end for the WA

Doug

Posted by: NMRguy Feb 5 2007, 04:22 PM

Looks like we should get a better look a Mimas on 13 Feb 2010. Phase angle of 99 and distance of about 10,000km. Although it still isn't a "close flyby", it will be about 6.5 times closer than the previous best. And frankly, I wouldn't mind getting a little sharper look at that heavily cratered surface.

Posted by: ugordan Feb 5 2007, 04:29 PM

I see 50-ish ms for NA as typical for Enceladus at phases around 30 degrees. This is in 1x1 binning mode, a 2x2 binning is more than likely to be used due to motion blur so you can get something like 15 ms for NAC. Or 5 ms for 1x1 WAC.

Posted by: john_s Feb 5 2007, 04:33 PM

The super-close flybys will be mostly for fields and particles (or gravity), not remote sensing- in fact we may try to increase the range of some of the flybys to make them more suitable for remote sensing.

Posted by: djellison Feb 5 2007, 04:33 PM

5ms @ 17km/sec - 85 metres.

2 x 2 WAC - 3m/pixel - still HUUGEEEE ammounts of blur - BUT - on the way in and the way out again, NA should be able to get some spectacular images.

Doug

Posted by: volcanopele Feb 5 2007, 04:44 PM

sweet! Thanks, John.

Yeah, don't expect super hi-res images from those very close flybys...

In terms of Enceladus flybys, I am disappointed by the apparent lack of north polar looks during the latter part of the extended mission. Nothing too close would be needed, but it would be nice to fill out the global map at sufficient resolution. There are quite a few close passes over the south pole, though, 2 flybys at around 100 km altitude, and another at 1811 km, though there will likely be a push to see if that one can be lowered, me thinks. All three of those are at decent flyby speeds @ around 7 km/sec. so good data should be obtained from them.

Posted by: john_s Feb 5 2007, 11:22 PM

I just did a blog for the Planetary Society about the extended mission tour selection process- http://www.planetary.org/blog/article/00000850/

John.

Posted by: djellison Feb 5 2007, 11:27 PM

Was just about to post a link to it - excellent piece John - Suprised to see that Dave doesn't actually have a variety of orbits visualized above his head in some sort of orbital mechanics halo But then - if you put your OSX dock on the right side...there's just wierd...

Doug

Posted by: jamescanvin Feb 5 2007, 11:48 PM

That's not weird, just different! I have mine on the right - makes much more sense to have it there on a widescreen display.


Great article John.

James

Posted by: djellison Feb 5 2007, 11:52 PM

Well - when i actually get a Mac (this summer) then I'll speak with confidence...

Actually - it does kind of make sense

Doug

Posted by: Bjorn Jonsson Feb 6 2007, 12:38 AM

Looks like a great extended mission. Big thanks to John for posting the geometries of the icy satellite flybys - very useful. The blog entry was also interesting. Nice to see Mimas getting a close flyby, meaning that over the entire mission each of the icy satellite is getting at least one close flyby. This is far better than expected some years ago. Very close flybys of Phoebe and Tethys weren't expected back then.

Now I hope some SPICE kernels for the extended mission get released soon so I can get a detailed look at the entire 2 year mission extension. In particular I wonder if Saturn's northern hemisphere is going to get globally imaged like the southern hemisphere in September and October 2004 (if so, probably from closer range and over a shorter time though) so I can complement my 25 degrees/pixel cylindrical map of the southern hemisphere with a comparable map of the northern hemisphere .

One interesting tidbit I noticed in the FY2008 budget documents released today: "Cassini was launched in October 1997, arrived at Saturn in July 2004, and will continue to investigate Saturn and its major moon through September 2012."

Posted by: Sunspot Feb 6 2007, 01:03 AM

I'm getting a Mac Mini when Leopard is released. I've been using Windows ME since January 2001.

Posted by: Decepticon Feb 6 2007, 03:32 AM

NT encounters will still happen? I don't mind Some of these far off looks!

Posted by: volcanopele Feb 6 2007, 06:17 AM

Great blog post, John_s!

I noticed something in the image used that I didn't know. The last item listed for each tour is the Delta-V used in each tour. From a Titan perspective, the lower that number the better, as a lower delta-v would allow for a longer, extended-extended mission. The tour selected, PF6h9, has the highest delta-v of the tours in that Excel chart. IIRC, at the end of the nominal tour, there should be around 300 m/s of delta-v left...

Posted by: ugordan Feb 6 2007, 09:06 AM

That certainly puts into perspective what we can expect from an extended-extended mission. These figures might be conservative delta-V costs, though.

Posted by: TritonAntares Feb 6 2007, 07:54 PM

As presumed and the list above displays Iapetus will not be visited closely by CASSINI during this Extended Mission,
but what about far-encounters in a few 100.000 kilometres?
Remember the second closest approach to this strange moon so far on new year 2005 was in roughly 120.000 km!
There will probably be some occasions like this again, but only showing the saturn facing hemisphere with the dark Cassini Regio.
Due to Iapetus 15° inclination such far encounters could give the opportunity to have an additional look at northern or southern polar regions as well.

Bye.

Posted by: EccentricAnomaly Feb 6 2007, 08:58 PM

The DV for the extended mission will probably total around 230 m/s when all of the tweaking is done and maneuvers that fall during good science are moved. The tanks are estimated to have about 340 m/s are the start of the XM, so that leaves only ~100 m/s for the XXM and spacecraft disposal (either crashing or putting into a stable parking orbit). But back when the tour was changed for the Huygens mission we thought we would only have 130 m/s for the XM, so 100 m/s for the XXM isn't that bad when put into perspective.

In many ways the XM is more intense than the prime misson... it will be very exciting.

Posted by: volcanopele Feb 6 2007, 09:17 PM

I'll take a look.

EDIT: Here are the closest I could find:

2009 07 05 05:00:00 - 2,089,800 km (low phase, sub-saturn hemisphere, eastern Cassini regio, Snowman craters)
2009 09 11 19:47:00 - 1,161,000 km (high-phase leading hemisphere, extreme eastern Cassini Regio, western snowman crater)
2009 12 01 15:07:00 - 1,377,900 km (moderate phase (~100 deg.) , southern leading hemisphere, extreme eastern Cassini Regio, western Snowman crater,western Terra Incognita)
2010 02 21 10:00:00 - 1,469,800 km (moderate phase (~50 deg.), southern sub-saturn hemisphere, view of eastern Cassini Regio, Snowman craters, Terra Incognita)
2010 05 08 16:30:00 - 1,234,800 km (high phase (~110 deg.), southern leading hemisphere, crescent view of extreme eastern Cassini Regio and western Terra Incognita)

That appears to be about it. Sorry, TA! Hope the Sept. 2007 encounter is a REALLY good one!

EDIT to the EDIT: terrain coverage descriptions now accurate

Posted by: john_s Feb 6 2007, 10:16 PM

Here's a list of Titan flybys in the PF6h9 tour:
 Titan_Flybys_UTC_NFB.PF_6h9L.txt ( 11.58K ) : 1317


And here's a list of small satellite flybys:
 Rocks_Flybys_UTC_NFB.PF_6h9L.txt ( 30.06K ) : 1160


Titan flyby geometries won't change much in the fine-tuning process, because you can't change Titan flybys without changing the rest of the tour. I'm not sure how stable the "rock" flybys are, though.

John

Posted by: JRehling Feb 6 2007, 10:44 PM

Wow -- 27 flybys. A few of them are a little farther than normal, but that's still a large number -- 60% of the main mission's flybys. I'm eager to see the plans for RADAR coverage and at least one good look at the northern latitudes post-equinox. (Actually, at equinox, it will take a few looks to see all of the north polar region.)

Posted by: elakdawalla Feb 6 2007, 10:54 PM

Just for grins, I took John's spreadsheet of the small moon encounters, plugged in the moons' diameters, calculated the pixel size at closest approach, and figured out how many NAC pixels across the moonlets would theoretically appear if they were, in fact, imaged at closest approach. Poor little 3-kilometer Methone -- nine of these relatively close flybys, and the biggest it'll appear will be 21 pixels across! The story isn't much better for 4-kilometer Pallene. But most of these moonlets will be quite well imaged by the end of the extended tour. I can't wait to put together a family portrait after these flybys are done.

Here's the best of each (and do remember that these are theoretical maxima; the actual number depends on where in the flyby Cassini snaps the pictures; and also keep in mind John's caveat that the flyby altitudes can change a lot with itty bitty tweaks to Titan flyby altitudes):
Atlas: 189 NAC pixels
Calypso: 145
Epimetheus: 856
Helene: 3,512
Janus: 995
Methone: 21
Pallene: 24
Pan: 68
Pandora: 608
Polydeuces: 66
Prometheus: 670
Telesto: 209

--Emily

Posted by: TritonAntares Feb 6 2007, 11:05 PM

BAD NEWS...


Uuuu....
Only incorrect rotation rates or more?

Posted by: volcanopele Feb 6 2007, 11:18 PM

Distances are correct, phase angle is correct, times are correct. However, rotation rate, and thus the terrain visible, is wrong.

EDIT: Terrain descriptions in above post now edited and accurate.

Posted by: volcanopele Feb 7 2007, 08:03 AM

while that highest possible resolution for Helene would be nice, I'm not sure how much we'll get, probably a couple of snapshots, no time for a nice mosaic. The flybys is high-phase incoming, and low-phase outgoing. Helene will become smaller than the ISS NAC field of view at around 5 minutes after C/A.

Posted by: elakdawalla Feb 7 2007, 06:38 PM

Now that http://www.planetary.org/blog/article/00000850/ I thought it'd be a good idea to open a new topic for the discussion. I'm moving some of the posts from the "http://www.unmannedspaceflight.com/index.php?showtopic=1989" poll into this topic.

--Emily

Posted by: EccentricAnomaly Feb 8 2007, 12:06 AM

I think the reason why there were no targeted rock flybys in the prime mission was that no one knew the ephermerides well enough to target these bodys. I don't know how well the rocks are known now, but I'd bet Methone, Pallene, and Polydeuces aren't known very well... being recently discovered and all would mean there would be a lot less data available to calculate their orbits.

Posted by: TritonAntares Feb 8 2007, 12:10 PM

Many thanks, seems like we'll get the Iapetus view we're used to until now.
Maybe some southern polar regions and the Terra Incognita will be added,
if they haven't already been mapped during this september's fly-by.
I'm afraid we won't get a close up view of the Snowman at all...
Then saturnshine images from 2004-12-31 in ~120.000 km distance will still be the best.

Bye.

Posted by: ugordan Feb 8 2007, 12:25 PM

All is not lost, TritonAntares. Remember we might still get an extended-extended mission which will necessarily be less flyby intensive than this one. Who knows what kind of orbits we'll be running then, if they decide to stretch the remaining fuel out it'll probably imply extended orbits. We might get apoapses pretty far out and just maybe get a nice nontargeted flyby of Iapetus. It's up to Iapetus to prove worthy of another look after we see the results of the September flyby.

Personally, though, I wouldn't hold my breath for new mysteries.

Posted by: JRehling Feb 8 2007, 04:15 PM

Of course, it's a given that all saturnshine images will cover the same hemisphere, since Iapetus keeps the same face pointed towards its primary. Unless a close-up in saturnshine comes in the XXM, new saturnshine images are going to add almost nothing to what we've already seen.

In fact, we can be sure that most any nontargeted imagery will show us more of what we've seen, because Iapetus is so far out that it will always be outside of Cassini's apoapsis unless Cassini's really making an effort to get to Iapetus. We will basically see the saturnside view unless a deliberate effort is made to do otherwise.

Posted by: TritonAntares Feb 8 2007, 06:14 PM

I'm aware of this recuring viewing situation, only minor changes are possible due to CASSINI's position to Iapetus on its 15° tilted orbit.
I hoped that - apart from the Sep.10th fly-by - there would have been some opportunities to catch the moon from a few 100.000 kilometres like before under different illumination conditions and/or showing higher latitudes.

Bye.

Posted by: Holder of the Two Leashes Feb 9 2007, 02:37 AM

I'm guessing we're going to have to wait until NASA officially endorses the extension before Solar System Simulator or Saturn Viewer show anything beyond July 2008 for Cassini.

Posted by: Analyst Feb 9 2007, 09:12 AM

Does someone know the deterministic part of the delta v needed? I assume the statistical part (mean of zero) is not a small fraction (2 or 3 sigma) and good navigation can reduce this during the tour and give us more delta v remaining after the extended mission. This is why we now have about 340 m/s (any proof for this number?) after the prime mission and not much less as per plan from 2004.

Btw., has someone a current paper/document about the propellent usage/delta v? I know there is a site at JPL but it is restricted. Kind of comparsion of predicted vs. actual.

Analyst

Posted by: AlexBlackwell Feb 10 2007, 12:32 AM

As you might guess, the Cassini Program doesn't really like to make that type of information generally (i.e., easily) available. Just ask the poster of these http://www.unmannedspaceflight.com/index.php?s=&showtopic=1855&view=findpost&p=31767 http://www.unmannedspaceflight.com/index.php?s=&showtopic=1989&view=findpost&p=47169.

Posted by: tasp Feb 10 2007, 06:38 PM

If I understand the September flyby geometry correctly, we should be getting some nice views of the 'equatorial dots' on Iapetus. (IIRC, these are also just visible in the Voyager 2 images, also)

Is it possible in this time frame to anticipate the detailed appearance of the 'dots'?

Perhaps.

Should a gaseous, thermoreactive material be resonsible for the darkening of Cassini Regio, and further, that the reactive materials being preferentially introduced to the Iapetan environment during passages through the Saturnian magnetotail, then the gradation between the lower, dark Cassini Regio colored areas and the upper (presumably higher altitude) light colored areas should have distinctive characteristics.

For instance, the width of the area between full saturation of the dark coloring, and the uncolored, white areas will be strongly slope dependent. A shallow slope producing a relatively wider transiton between dark and light, and steeper slopes producing a relatively narrower band between dark and light.

Additionally, should the slopes be deeply incised, we will see corresponding incursions of the dark staining into the 'ravines'.


Should the peaks be approximately cone shaped, the banding will be surprisingly regular about the peak, and dramatically uniform in appearance.


If Cassini images of these features show the 'dots' to be stained accordingly, we might be pretty confident in our understanding of the Cassini Regio dark staining, and most probably, the dark bottomed craters of Hyperion, too.

Posted by: Analyst Feb 10 2007, 07:15 PM

These two posts are yours.

Posted by: tasp Feb 10 2007, 09:01 PM

Additionally, craters on the slopes (should there be any) will modify the local slope angles, and the subsequent darkening will be modified accordingly. As in the upper latitiudes of Iapetus, I suspect this trait of the darkening will be more pronounced in the lighter (higher elevation) areas.

We might see a concensus form that the dust from Phoebe idea just doesn't explain Cassini Regio . . .

Posted by: JRehling Feb 11 2007, 12:12 AM

I'll go out on a limb and opine that the dark stuff will not appear at all on the white peaks, and the stratigraphy will reveal that the darkening ended before the creation of the peaks (ergo, a very long time ago).

Posted by: tasp Feb 11 2007, 01:13 AM

Some kind of eruption onto a darkened surface would be very different.

And hopefully we get pictures that are good enough to distinguish between the two.

On going eruptions coupled with on going darkening would be interesting. But I will say the peaks are ancient, and the dark coating is replenished either continuously, or renewed on timescales short compared to the age of the solar system.

Posted by: tasp Feb 11 2007, 01:15 AM

How many different scenarios can we come up with that create white peaks/dark surroundings that might be discernably different to the Cassini lens?

Posted by: Analyst Feb 11 2007, 10:57 AM

I have done a limited analysis of the propellant usage so far.

Sources are:
[1] Cassini Mission Plan
[2] Cassini Significant Event Reports
[3] Propellant Remaining per October 2005 given by AlexBlackwell
[4] Cassini Tour Redesign for the Huygens Mission
[5] Initial Cassini Propulsion System In-Flight Characterization
[6] Cassini Maneuver Experience: Launch and Early Cruise
[7] Cassini Maneuver Experience: Finishing Inner Cruise

The description of the txt file follows:

In head are four blocks, from left to right:

- specific impulse and thrust of the main engine from source [5], the thrust I used is slighly lower than the nominal 445 N; there are several reportings of a small engine underperformance (less than 1%, resulting in slighly longer burn times), 441 N helps to match the numbers, but the errrors using 445 N is very small too
- masses from source [5]
- propellant used until specific dates from sources [3] and [5]; these numbers are a little iffy: in source [5] the numbers are given for EOY 2001, not 01.04.2002; in source [3] for “late October”, these data are used only to guess the monopropellant usage
- monopropellant remaining as per specific dates; the number for 30.06.2004 (SOI) is computed as is the usage per day for cruise (about 6 g/d) and tour (27 g/d)

The 11 columns in the table are:

(1) TCM or OTM number
(2) the maneuver date, can be off be one day because times were given in UTC and PST and I didn’t care to check
(3) maneuver name/event
(4) maneuver duration; for TCM 1 to 17 (including) this has been computed using the rocket equation and the delta v given in column (5), for all other maneuvers these are actual numbers from source [2]
(5) actual delta v using biprop main engine; source [5] for TCM 1 to 17 (including), source [2] for TCM 18 and later
(6) actual delta v using monoprop thrusters; sources like column (5)
(7) and (8) predicted delta v for the tour from source [4]
(9) the computed delta v using the rocket equation, the given maneuver duration (4) and the propellant usage from coloum (13)
(10) the difference between (5) and (9), is of course zero for TCM 1 to 17 (including)
(11) the remaining monoprop using the numbers from above (6 or 27 g/d)
(12) the biprop remaining before the maneuver
(13) the biprop used during the maneuver computed using the duration (4), isp and thrust

I only care about biprop, the monoprop usage is assumed to be linar and monoprop delta v maneuvers are discounted. The monoprop tour delta v has only been 3.4 m/s so far.

The numbers match very good. For instance the computed DSM duration is off by about 20 s (less than half of a percent), the computed bipropellant remaing in late October 2005 is 493 kg vs. 499 kg given by [3] (about one percent error). The delta v difference for SOI is a little large (5 m/s, still less than one percent), I don’t have the exact burn time and used 96 minutes.

The biprop delta v after OTM 92 with 437 kg is 540 m/s, the mean of the remaining prime tour is 202 m/s ([4], old source), coming nicely to the 340 m/s after the prime tour given in this thread.

Any suggestions? I have a .xls file if someone cares.

Analyst

Posted by: Rob Pinnegar Feb 11 2007, 05:17 PM

That would be a wild result if it turned out to be true. It would be very difficult to explain the lack of bright craters in Cassini Regio if the dark material were that old.

Posted by: tasp Feb 12 2007, 06:53 AM

So, we seem to be at the point of saying dark dust deposited on Cassini Regio from Phoebe will look a certain way.

And eruptions of light colored materials onto a dark surface will look a certain way.

And a gaseous, thermoreactive darkening substance, introduced into the Iapetan environment during passage through the Saturnian magnetotail and either totally dissipated or totally used up in much less than the ~80 day period of Iapetus will look in a certain way.


And Cassini orbiter will get us the definitive pictures in September . . . .

Posted by: EccentricAnomaly Feb 14 2007, 05:19 PM

I've seen papers from the Cassini maneuver team at AIAA conference that give great detail of the DV used for maneuvers. You can find them at aiaa.org by searching for the keywords 'Cassini Maneuver' in their paper database.

Posted by: Analyst Feb 15 2007, 07:23 AM

Thank you. I have some of these papers until about 2002. These were (or still are?) available for free. But papers at aiaa.org cost $ 25.00 to 30.00 each. At such prices my monetary interest is tops my scientific one.

Analyst

Posted by: belleraphon1 Feb 15 2007, 01:52 PM

I agree that, moonwise, Titan and Enceladus are the prime targets for extended mission exploration....

But....

For those who say "one more flyby will tell us all we need to know about Iapetus". Reminds me of all those squggly line scientists who once said "Viking gave us all the pictures of Mars we will ever need".

Let's wait for this years Iapetus close flyby and I am sure more mysteries will unfold. Nature is never as nice and neat as our paper calculations........... and those equatorial mountains are saying something very significant about this world's (and the Saturn system) development.

I hope that another Iapetus flyby can be fit into the second extended mission. Otherwise we wait for the next dedicated Saturn orbiter (which will undoubtably focus on Titan or Enceladus) that can spare some time to scan that mountain range....... and at my age I will probably be viewing that from some assisted living facility (yuck..... rather have the ice at Headlands on Lake Erie take me).

Craig

Posted by: ugordan Feb 15 2007, 02:04 PM

Yes, but Mars was/is geologically active. Iapetus looks like it's... well, dead. Probably been for a very long time now. The question is if it even differentiated, it sure as heck has one lumpy shape with all those enormous impact basins.

I like to think about Iapetus the same way as Phoebe. How much more would we learn if we had another close flyby? I'm guessing not that much. Don't get me wrong, Iapetus is one of my favorite Saturnian moons from an imaging point of view and I'd like to see more close-ups just as the next guy. Scientifically, I don't know how interesting that would be.

Posted by: EccentricAnomaly Feb 15 2007, 10:23 PM

yeah it bugs me that AIAA charges so much (even when they don't hold the copyright the expect you to pay them for photocopies). The best I can do is to recommend a nearby university library... often computers in the library can download these papers.... I got one paper this way... and I'd attach it, but it's too big (1.7 MB)

Posted by: belleraphon1 Feb 16 2007, 12:34 AM

Of course I want to concentrate on Titan and Enceladus.....

BUT..................AHHHHHHHHhh... but even the Dead Tell Tales.... (and no, I do not watch CSI). Something very interesting happened(s) at Iapetus that affected the outer reaches of the Saturn system at least inwards to Titan. And the Jupiter system has taught us that "old" surfaces can hide young interiors.... look at the hints of oceans under Caliisto's battered exterior... a moon that is not even completely differentiated. And Ganymede, cratered as he is, has a significant magnetic field and is completey differentiated.

Do not just write off what stories Iapetus has to tell.... I am always reminded of Poul Anderson's ditcum that every body is a " world" with a unique history and it's own personality.

Another reason I want to see us return to the Moon... that "dead" world will teach how to really respect the dead. And live under very harsh conditions.

Craig

Posted by: JRehling Feb 16 2007, 09:24 PM

True. Pretty much destroys my assertion, in fact.

There are small craters with bright rims but dark floors that show us that the dark stuff was emplaced after those craters were formed, and this pretty much tells us that the dark stuff happened in the last fraction of Iapetus's history. I should have reviewed this before posting.

Posted by: JRehling Feb 16 2007, 09:34 PM

I think there's a pretty good chance of that.

They can take a stab wound and determine where the assailant was relative to the victim. Or a bloodstain and determine the geometry of a gory deed.

The interaction between topography and the dark-light pattern is going to tell us a lot we don't know already.

We already know a lot, and it seems to thwart a lot of simple models. Particularly, the Snowman craters give us some trouble. But we've mainly seen the eastern border of Cassini Regio. The September flyby will give us a great look at the western border. That alone will tell us if CR was emplaced from east to west, west to east, or from inside out. Or none of the above, also a real possibillity.

I'm reminded of the pre-Apollo situation with three theories about the origin of the Moon. It turned out that a combination of two of them best explained the data. Maybe Cassini Regio had a single catastrophic event as its origin, but it has had a continuing evolution since then.

Callisto may offer a useful analogue in terms of the interaction of dark surface with brighter, more volatile ice. Iapetus must be a little more complex than that, but that may partly explain things.

Posted by: dvandorn Feb 17 2007, 03:51 AM

That's one interpretation. Another interpretation of the craters with bright rims and dark floors is that the entire crater was once all dark, but mass wasting has exposed brighter materials in the rims.

I tend to agree, though, that the dark stuff probably was emplaced over top of the craters, and happened pretty much after all of the visible craters were formed.

-the other Doug

Posted by: edstrick Feb 17 2007, 10:23 AM

Iapetus is so battered that extra-high resolution will have rather little information to yield on global geology, at least directly, but global coverage is needed at good resolution and sun angles just to see the global geology well.

Where resolution higher than Cassini can provide (except for perhaps one tiny spot) is infrared spectral mapping for composition. Looking at steep crater walls and other topographic features to see the intimate mixing and distribution of ices and the darker materials will give a better understanding of their stratigraphic relations and transport processes and thus the geologic history of the albedo patterns and ice migrations.

Cassini won't be able to do much of that, unfortunately, even on it's fall flyby.

Posted by: TritonAntares Feb 17 2007, 11:53 AM

The basic problem so far has been the lack of encounters in mid-range distances - as far as I remember
one in 120.000 km, 600.000 km and 800.000 km - to poor to allow a satisfiable resolved mapping.
Due to CASSINI's orbit unfortunately only the saturn facing hemisphere could be observed so far.
Not comparable to all other saturnian moons - even the Phoebe encounter showed more...
Septembers close outbound encounter will improve this situation a lot for sure, but still enough regions will only be bad imaged - for instance the northern polar regions (Voyager images being still the best) or the Snowman with its dark terrains.
Hopefully an extension of the extended mission will give us the opportunity to visit Iapetus once more in an outbound passage over this regions not exactly so close as this fall.
If feasible an elongated orbit with its apoapsis outside of Iapetus' course - and eventually a bit tilted - would be favorable.
So Iapetus could be passed several times in say a few 10.000 to 100.000 kilometres showing different longitudes under changing illumination conditions.
But this is certainly at first a propellant question I guess...

Bye.

Posted by: JTN Mar 8 2007, 11:30 PM

Have more details of the extended tour been made public yet?

At the moment, I'm particularly interested in what will happen around the solar ring plane crossing in August 2009. What sort of inclination will Cassini have at this point? Are there any specific opportunities to see the http://hubblesite.org/newscenter/archive/releases/solar-system/saturn/1996/1996/16/? (I realise the latter doesn't necessarily require knowledge of the tour.)

john_s mentioned the RPX in his http://www.planetary.org/blog/article/00000850/, but without much detail of what Cassini will be up to.

I wonder whether there will be interesting deductions to be made from the thermal properties of the ring particles as the sunlit and dark sides of the rings swap places -- we will presumably be able to look at both sides more-or-less simultaneously for the first time.

Posted by: pat Mar 9 2007, 01:12 PM

during the equinox period the inclination profile is something like:

~45 deg up to DOY 205
~35 deg DOY 205 to DOY 221
~21 deg DOY 221 to ~DOY 237
~12 deg from DOY 237

the process for deciding what observations Cassini will make during extended mission has only just begun. At the moment preparations are being made for the division of the extended mission into periods of time and allocating those periods to TWTs (Target Working Teams) and OSTs (Orbiter Science Teams). The process is called "segmentation" and the periods of time "segments". Segmentation will be completed by sometime this summer.

The TWTs and OSTs will then decide what observations will be carried out in their segments in a process called "integration", which can obviously only start after segmentation has been completed.
Integration may take a year or so to complete, I expect the extended mission will be intergrated from the beginning forwards as its possible that the XM might actually begin (July 2008) before integration has been completed.

Right now Cassini science team members will have a good idea of the type of observations they want to make and when they can make them but simply won't know until a segment has been integrated the exact observations and times. Its worth mentioning that there will be far more requests for observation time than there is time in the XM and only a fraction of requests will actually get allocated time and be included in the SOP(Science Operations Plan -- I think) during integration.

The TWTs and OSTs are made up of people from the Cassini science teams, any science team member who is interested in that TWT/OSTs general area of responsibility can participate, supported by Science Planning Engineers from the Cassini Project at JPL. This means that it is the Cassini scientists themselves who decide what science Cassini will perform, of course there are various safety constraints and engineering requirements where the Cassini Project at JPL decides but by and large its the scientists themselves who determine what Cassini does.

Posted by: Gsnorgathon Mar 11 2007, 03:08 AM

I'm less interested in the shadows of the moons upon the rings as I am in the shadows of the rings upon themselves. I expect that will be quite a sight.

Posted by: JRehling Mar 11 2007, 04:19 AM

Good point. Something you can notice on a brick wall when the sun is almost coplanar with it: The first/last shadows become incredibly stretched out as 1/sin(0) goes to infinity and the shadow becomes a kind of infinitely powerful form of magnification of the wall's topography. The right image at the right time could provide what is essentially the highest magnification "image" in the history of space exploration (well, not counting ones taken within 1 km [cm] of the object in question).

Posted by: Rob Pinnegar Mar 18 2007, 06:09 PM

It should at the very least give us a good idea of the thickness and vertical density profile of the F Ring, and perhaps some of the other rings too.

Posted by: Analyst Apr 22 2007, 08:35 AM

I checked my calculated numbers of propellant remaining posted in this thread against some numbers given in http://saturn.jpl.nasa.gov/multimedia/products/pdfs/20060328_CHARM_Webster.pdf document from March 28th 2006 (page 3).

For March 28th 2006 I calculate a spacecraft mass of 2.706 kg, the document gives 2.710 kg. DSM, SOI and PRM used 2.086 kg calculated vs. 2.083 kg given. So I conclude my calculations are pretty much correct.

Based on this we have right now a spacecraft mass of 2.649 kg including 433 kg biprop and 91 kg monoprop. This translates into a biprop delta v capability of about 529 m/s.

Analyst

PS: The propellant remaining number given in the above document (422 kg) seems to be wrong.

Posted by: Greg Hullender Apr 22 2007, 04:38 PM

Impresssive piece of analysis! You chose your handle well. :-)

One thing that confused me at first: in America a mass of "2.649 kg" would just be 2649 grams -- not much at all! Confused me for a bit, until I realized what was happening.

Question (for everyone): Is this business of swapping comma and decimal point a US/Europe thing, or an English/non-English thing? That is, for the speed of light (for example), who writes 299.792,458 km/s vs. 299,792.458 km/sec?

--Greg

Posted by: helvick Apr 22 2007, 05:09 PM

It's country specific. South Africa uses "," for decimal position and "." as a thousands separator. The Irish and British definitely use "." and "," in the same way as the US. The French use a space for thousands separation and the Swiss use an apostrophe. It gets even more different if you move outside of the western hemisphere - you cannot assume that number grouping always happens in threes for example (Japan and China group numbers using a space as a "10 thousands" separator and a "." as a decimal).

Quite mad.

Posted by: dvandorn Apr 22 2007, 06:30 PM

And don't even get me started on what and American and a Briton think constitutes a billion... *sigh*...

-the other Doug

Posted by: edstrick Apr 24 2007, 09:06 AM

How many Carl Sagans does it take to screw in a light bulb?

BILLIONS AND BILLIONS!

<you may shoot me now.>

Posted by: centsworth_II Apr 24 2007, 02:47 PM

Considering the number of minds Sagan has turned
on to the cosmos, maybe it should be:

How many lightbulbs can Carl Sagan screw in?
Billions and billions.

Posted by: CAP-Team Jun 22 2007, 09:51 PM

For those of you who want to "play" with the ephemeris of the extended mission, the official data for the extended tour is now delivered to the NAIF ftp site (for SPICE kernels).

Posted by: volcanopele Jun 22 2007, 10:34 PM

hehe:

Posted by: volcanopele Jun 22 2007, 10:37 PM

if people can play around with these spice kernel files, the file you are looking for is 070620AP_SCPSE_08102_10191.bsp

Posted by: scalbers Jun 22 2007, 11:27 PM

Looks like a double header for Enceladus in 2010 from VP's Celestia images. Should fill in details nicely in leading hemisphere.

Posted by: helvick Jun 23 2007, 06:11 AM

Hey - where did you get that Titan map??

Posted by: volcanopele Jun 23 2007, 09:07 AM

Those graphics are from a few months ago when I was testing out Celestia and spice files. The Titan map I used here is our released Titan map:

http://photojournal.jpl.nasa.gov/catalog/PIA08346

Posted by: jasedm Jul 28 2007, 02:24 PM

Does anybody know if the extended mission has been 'ratified' as yet by NASA?

Also, a thought occurs: If the extended mission does go ahead, might there be any advantage in retargeting some instrument pointing for the last few months of the primary mission??

An example: We now know that Cassini is due to come within 500km of Dione in July 2010. This presumably will yield some very good science, and with that in mind, perhaps some observations of Dione between now and July next year (say in the 50,000 - 100,000km range) could be sacrificed in favour of other targets at that time?? i.e. ignore Dione at that time as we know we're getting closer later, and point the instruments elsewhere.

I don't pick on Dione for any particular reason (it could be mid-range shots of Mimas, or Tethys, or the rings) This principle would be especially apposite for instrument pointing at or around periapsis where there are a lot of tempting targets.

Obviously Cassini's trajectory remains the same, and there might be a tiny bonus in terms of usage of the precious hydrazine.

I understand the constraints on time, forward planning, and uploading of information to the spacecraft, but with around a year to affect any changes perhaps the last couple of revolutions could be made 'more useful' in this way?


Jase

Posted by: tallbear Jul 31 2007, 11:10 PM

This has multiple answers....

First ... All of the time in the PM has already been planned and is "on the shelf" but small observation tweaks and shifts are being made as they move closer to uplink....but all changes get made in the AfterMarket process which goes on nearly 200 days before Uplink.


Next... Various groups are already busy with science planning for the first revs of the XM. ( In fact most of the high priority science for all of the XM has already been laid out long ago ) The schedule for XM Science Planning is very tight and begins at a royally fast pace begining right around Sept 1 2007.


Not only has the XM been approved but the XM Science planning and Timeline Integration is moving along at high speed

Posted by: remcook Aug 1 2007, 09:59 AM

partly related:

http://www.spaceref.com/news/viewpr.html?pid=23130

"Alan Stern, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington, will host a media teleconference at 1 p.m. EDT, Wednesday, Aug. 1. Stern will discuss plans for NASA's Cassini mission to make an unusually close encounter with Saturn's geyser-moon Enceladus and provide project updates for a variety of science flight programs. Planetary and astrophysics program developments also will be discussed"

Posted by: jasedm Aug 7 2007, 05:50 PM

Thanks guys - 200 days in advance is quite some forward-planning.
Hat's off once again to the whole Cassini team for this magnificent achievement.
Roll-on the extended-extended mission......

Posted by: Harkeppler Aug 9 2007, 08:42 AM

Does anyone have precise information on the Titan surface coverage by SAR during the extended mission?

What other mission proposals had been there (PF6h9 sounds complex)?

Is there any useful visualization of the orbits which can be used to tell the people what is going on?

I am giving planetarium lectures in a larger city and would be interested in these details.

Thanks a lot in advance!

Harkeppler

Posted by: pat Aug 9 2007, 11:44 AM

We've moved on from PF6h9 (which was renamed XM0). I think the iterations on this got as far as XM10 before the emergence of the "official delivery of 2-year extended mission trajectory" which is called XM070620. The SPICE kernel of this XM reference trajectory is publically available from the NAIF anonymous FTP site (naif.jpl.nasa.gov:/pub/naif/CASSINI/kernels/spk) and is called 070620AP_SCPSE_08102_10191.bsp for those of you who might be interested in generating your own visualisations.

Posted by: TritonAntares Aug 12 2007, 12:40 PM

Hi,
as Solar System Viewer isn't capable of simulating views of the extented mission so far,
is anybody here able to create some views of Iapetus of the following nontargeted encounters with Celestia or another simulation?

2009 07 05 05:00:00 - 2,089,800 km
(low phase, sub-saturn hemisphere, eastern Cassini regio, Snowman craters)

2009 09 11 19:47:00 - 1,161,000 km
(high-phase leading hemisphere, extreme eastern Cassini Regio, western snowman crater)

2009 12 01 15:07:00 - 1,377,900 km
(moderate phase (~100 deg.) , southern leading hemisphere, extreme eastern Cassini Regio, western Snowman crater,western Terra Incognita)

2010 02 21 10:00:00 - 1,469,800 km
(moderate phase (~50 deg.), southern sub-saturn hemisphere, view of eastern Cassini Regio, Snowman craters, Terra Incognita)

2010 05 08 16:30:00 - 1,234,800 km
(high phase (~110 deg.), southern leading hemisphere, crescent view of extreme eastern Cassini Regio and western Terra Incognita)

THX & Bye.

Posted by: monitorlizard Aug 13 2007, 03:05 AM

I found a nifty little presentation from the May 2007 Cassini Plasma Spectrometer Team Meeeting, about the extended mission, available at:

caps.space.swri.edu/caps/teamMeetings/teamMeetings.shtml (then click on "Meeting #34", then "extended mission")

The presentation is biased towards particles and fields observations, but still lots of interesting bits of info. A
particularly useful part said "an 'extended, extended' mission should be possible", stating that the prime mission will end with 342.3 m/sec delta-V remaining (95% confidence level) and the PF6H9/XM-9 extended mission is predicted to use 216 m/sec delta-V. However, it went on to say that the reaction wheels may ultimately detemine how much longer Cassini will function (one of four wheels is off due to "bearing cage oscillation", and three wheels are needed for normal operations).

Some cool details on Enceladus encounters I hadn't read before, too. Fifteen pages total, well worth downloading.

Posted by: monitorlizard Aug 13 2007, 03:11 AM

Clarification: click on "Minutes from CAPS Team Meeting #34", then "Extended Mission"

Posted by: CAP-Team Aug 13 2007, 06:38 AM

There you go

Posted by: SFJCody Sep 11 2007, 08:21 AM

Cassini's a big spacecraft. Would flying it into the dark material on Iapetus be a good end of mission scenario? Could the impact flash be observed from Earth based telescopes?

Posted by: ugordan Sep 11 2007, 08:35 AM

I'm gonna go with: no.
SMART-1 was barely detected and it was in our backyard, Iapetus is waaaaaaay out there...

Posted by: SFJCody Sep 11 2007, 09:00 AM

Yeah, you're right, the numbers don't look at all good for observability. Maybe it would be worth doing to leave a fresh crater for a future spacecraft to the Saturn system to investigate.

Posted by: tasp Sep 11 2007, 12:59 PM

A 'Deep Impact' style end of the mission has been raised in another forum, and the suggestion is making it's way up through the appropriate hierarchy.

The goal would be a fresh crater of known age for a future mission to observe, and to perhaps establish a rate for the accumulation of the CR 'crud'.

Posted by: Bjorn Jonsson Sep 11 2007, 01:23 PM

A bad idea in my opinion. Iapetus is difficult to reach and the delta-v penalty is significant so if you reach it for a second time you want to observe it, not crash into it. If Cassini has to be destroyed by crashing it into something, crashing it into something easy to reach (and preferably uninteresting) is a better idea I think.

Posted by: Gsnorgathon Sep 11 2007, 03:43 PM

Sure would be nice if they could go for a super close-up look at the rings. IIRC Carolyn Porco mentioned something about that way back when (but more along the lines of "sure would be nice" than a plan).

Posted by: David Sep 11 2007, 08:43 PM

Obviously, if Cassini were to be placed in an orbit that passed through the rings, the most likely outcome is total destruction of the craft. But if the orbit were perpendicular to the rings (so as to give the shortest travel time), and passed through a known low-density area, isn't there some non-insignificant chance that it might actually survive the passage? Aren't the rings ridiculously narrow, so that if you don't happen to hit a boulder the first time, you might actually be through in a matter of seconds -- maybe sandblasted, but still perhaps in one piece?

Posted by: Holder of the Two Leashes Sep 11 2007, 09:44 PM

Going perpendicular, you'd be through the main part of the rings in a fraction of a second. As to whether there are areas between ringlets that are clear enough of material to give a fighting chance of survival, I'm not sure anyone really knows. Perhaps in the Cassini or Encke divisions. I doubt in the B ring.

I'm not sure from your question whether you are worried or hopeful. One pass survived would certainly send back some very unique data. As to any worry that it might continue to live, don't. If it somehow managed to survive one ring passage, it will just keep coming back on subsequent orbits. Eventually... SPLAT.

Posted by: tasp Sep 12 2007, 02:56 AM

I am noting the amazing amount of interest in the current Iapetus encounter, and point out we have not had a Titan or Enceledus encounter generate this kind of interest in a long time.


Therefore:

Be it resolved, the primary goal of the extended, extended mission:

Iapetus

Posted by: David Sep 12 2007, 03:06 AM

I must choose my words more carefully then! It was definitely a hopeful thought. Though I imagine a spacecraft might be better designed than Cassini to maximize the chances of a successful passage.

Posted by: mchan Sep 12 2007, 03:42 AM

Paraphrasing from Silent Running: Cassini ain't built for shooting the rapids!

I've always imagined it would be spectacular to go thru the wake of Atlas or Pan.

Posted by: tasp Sep 12 2007, 12:29 PM

And I would like to point out, Iapetus still has additional wonders for us to explore!

The 'tiger scratches' (around 30 degrees south, and 355 degrees around) are quite fascinating and I strongly suspect they are also a unique feature we have not encountered (on this scale) elswhere.
Conveniently south of the 'tiger scratches' is also a candidate crater for a large grazing impactor. A possible source for the ring materials.

Posted by: rlorenz Sep 12 2007, 12:39 PM

Dynamically that would be a challenge - because Iapetus is so far out there
the orbits are long, so you get far fewer flybys total.

A lot of the interest in Iapetus is simply because it has only this close flyby -
if there are X interesting things about a body (argue amongst yourselves about
how much X is for Titan vs Europa vs Callisto vs Iapetus etc.) and you
discover some fraction f of the remaining mysteries on the Nth flyby
then
first flyby gives you fX, second gives you (1-f)fX, third gives you (1-f)^2fX findings
etc. After 35 flybys, the incremental value of each indeed goes down. If f is very
small, the rate of novel findings declines only slowly

If the observation/operations are well-understood (as I'd argue is mostly the case
for optical/spectral study of Iapetus etc) then f is large - say 0.3 or something
So this first Iapetus flyby has tons of excitement

Enceladus and Titan had more total surprises and exploited more novel
instrumentation like Radar and INMS which took a while to figure out, and figuring
out how to best acquire VIMS and ISS data through the atmosphere also took some
trial and error) maybe f is smaller, 0.05 or less? (Recall many instruments are
recording seasonal or local time variability, radar sees only 1% of the surface at
a time, etc.)

Sooooo, I agree another flyby or two of Iapetus (particularly to get gravity to understand
its internal structure) would be nice, but the question is how many Titans and Enceladi
to you sacrifice to get them? (And as I've argued above, the answer depends how many
Titans you have under your belt already..) I bet after two or 3 more Iapetus flybys, it
would get pretty uninteresting, whereas Titan's mysteries will endure..

then of course these idealistic arguments have to be modulated by what a dynamically
feasible orbital tour can do (delta-V, flyby geometries, making sure the flyby doesnt happen
in eclipse, or during solar conjunction or something..), and then there is ring science, and
Saturn science, and magnetospheric science to fold in....

p.s. don't underestimate Dione

Posted by: ugordan Sep 12 2007, 01:03 PM

Do tell! Does it have anything to do with interesting magnetometer readings?

Posted by: DrShank Sep 12 2007, 07:01 PM

i agree with ralph's assessment, including the comment about Dione. Dione is probably number 3 in terms of geologic and other complexities, behind Titan and Enchaladas. volcanic smooth plains, extensive graben networks and possible outgassing (all these are being worked on....). it is, or was, a dynamic moon indeed!
paul

Posted by: Holder of the Two Leashes Sep 12 2007, 08:07 PM

Enchaladas?

I've always been in favor of ending the mission with a final Titan series ramping up the orbit so much that Cassini gets catapulted out of the Saturian system. This would preserve the spacecraft as a future museum piece. Either the last couple of orbits or the final escape could be aimed for a last swing past Iapetus.

In my daydreams, I see a final inbound of Cassini passing close by the fully lit trailing hemisphere of Iapetus, with the Snowman in all it's glory, on the way to the last ever Titan pass. Then Cassini is hurled sunward, where the last propellant is used to establish a halo orbit at Saturn's L1, where it continues to observe the planet till the day the reaction wheels give out.

Posted by: JRehling Sep 12 2007, 08:22 PM

Light is a pretty good gauge of that. In places where light doesn't make it through the rings, neither would Cassini. More transparent regions of the rings DO allow things to pass through. But since Cassini is a lot bigger than a photon, it would probably only have a chance in the most transparent regions, and very little chance in the "hazy" regions.

Also, I think this outcome would be unsatisfactory even if Cassini were shredded. There would still be a planetary protection issue regarding the fragments, which would now be so numerous that you'd perhaps expect eventual contamination of Enceladus to be maximized. Crashing into a big target gets all of the risk out of the way. Obviously, the most logical choice is Saturn itself -- if Cassini goes in, there'd be none of it coming out.

Posted by: AlexBlackwell Sep 13 2007, 12:10 AM

Forgive me but this scenario, which some also suggested for Galileo, strikes me as too Star Trekkish. Frankly, I'd rather use the propellant and flybys to collect more data closer in and not on the possibility that our descendants, centuries from now, launching a putative space archeology mission to recover a long dormant spacecraft.

Posted by: David Sep 13 2007, 01:11 AM

Well, what would get you a twofer in that respect would be a low-altitude orbit with an apokrone (or whatever the word is) inside the D Ring; from there there's no place to go but down. But I suppose that's dynamically impossible to achieve without crashing into the other rings several times first.

Posted by: mgrodzki Sep 13 2007, 07:21 PM

is contaminating any of these places a real thing… i mean… if we sent it in toward the rings, couldn't it orbit close enough or even… become a ring particle itself?

worst case scenario would be it smashes something and breaks some stuff up. but weren’t they just talking about a part of the rings that seemed to suffer a recent impact? if it happens anyway… whats the diff?

are we so convinced that we are that powerful and influential in the universe? it seems a silly concern compared to the scientific opportunity. you can do a whole lot of exciting things with a disposable spacecraft!

Posted by: Steve G Sep 16 2007, 12:28 AM

They could always add an extension to the extended mission, another six months, where Iapetus (Snowman region) and Hyperion both get a couple targeted and a few non targeted flybys.

A mission ending scenario could have the spacecraft's orbit be adjusted from closest at Titan to Iapetus, then use an optimum trajectory to use Iapetus' feeble gravity to adjust the orbit slightly so that the spacecraft's closest approach to Saturn would be just outside Titan's orbit to just beyond Iapetus. Thus the old lady could hang in there with the reaction wheels as long as possible, still get cloud and ring observations, Titan cloud observations, Iapetus, Hyperion non targeted encounters, and not risk crashing on Titan or Enceladus. She could expire with dignity rather than being crashed into the rings or burn up in Saturn's atmosphere.

Posted by: nprev Sep 16 2007, 12:38 AM

I have to agree with Dr. Lorenz' arguments. (The Dione teaser's got my mind racing, BTW.. )

However, yeah, it would be very nice to get one more close-up of Iapetus, preferably centered on the putative 'tiger stripe' features and the hemisphere that lacks detailed coverage. Perhaps the trajectory wizards around 2014 or so, when Cassini is on bingo fuel, could design a final rev that went back to Iapetus one last time, then flew under (but in close proximity to) the rings before entering Saturn's atmosphere...

Posted by: Rob Pinnegar Sep 16 2007, 01:29 AM

How stable would an orbit like that be, I wonder? Remember that close passes by Titan will change the spacecraft's orbit. So it can't get too close.

I suppose one other advantage of this type of orbit is that it would give Cassini plenty of opportunity to search for any satellites of Saturn orbiting between Hyperion and Iapetus. One would think that there must be at least a few of them there, 'though they must be very small to have avoided detection until now.

Posted by: tasp Sep 16 2007, 01:56 AM

The 'tiger scratches' appear to me to be a new kind of feature, something we have not seen elsewhere in the solar system. (I am of the opinion the 'tiger stripes' of Enceladus, while unique, are unrelated)

Their enormous size, and their 'chasmatic' form are intriguing. I note an apparent radial orientation to 'Joan' and also proximity to 'Joan'.

I am finding it suggestive that the 'scratches' are resultant of compression of deep Iapetan materials in the same direction of the flight path of the impactor that formed 'Joan'. These materials, finding no other release for those compression forces, have bulged upward and fractured the overlying surface materials.

We have noted other clues around Iapetus that it is unusually rigid, and has been rigid for an apparent uniquely long interval.

We might be seeing another indication of that rigidity here.

These scratches, chasms actually, might be the deepest 'cracks' (as a percentage of the radius of the object) in a solar system body we will ever find.

High resolution imagery of the sides and depths of these features can potentially give us a look at materials we might not be able to study for centuries.

Additionally, if UV scans, or radar, or any other instrument on Cassini can be used productively here, they should be.

Illumination angles and space craft viewing angles will be critically important here. I realize an additional flyby of Iapetus is 'iffy' at best, and designing a flyby to optimize study of this feature makes that even more difficult to accomplish, however, the uniqueness of this feature make for a particularly strong case in reviewing the Cassini extended mission for possible encounter opprotunities.

Posted by: Steve G Sep 16 2007, 02:55 AM

I think the only win-win which will give us another Iapetus flyby is to have all of the objectives of the first extended mission accomplished, and focus the second extended mission on Titan, Hyperion and Iapetus.

Posted by: edstrick Sep 16 2007, 05:07 AM

I think the vehicle cannot have an "eternal" mission like the Pioneers or Voyager, unless it can entirely be attitude controlled on hydrazine thrusters alone with a "maximum conservation operations mode" (like Voyagers). If they can do that, and survive the eventual loss of all reaction wheels, the spacecraft should be put into an indefinately stable orbit, IF THAT IS POSSIBLE.

They cannot move the orbit far enough away from Titan that it's not peturbed by random semi-close encounters. They cannot lower the apoapsis well inside Titan's orbit or raise the periapsis well outside Titan's orbit. Maybe they can put it into a resonant orbit that avoids Titan enough not to be kicked out of resonance, but I'd doubt that when they're down to a dribble of hydrazine. Unless somebody covered that in discussion I've forgotten and haven't re-read, I don't know how long they can keep Cassini from hitting Titan or Enceladus.

Maybe they'll decide that's no "biggie" and put it in a long lived orbit that eventually will be peturbed into chaos and eventually clobber something randomly.

Otherwise, I think they should -- if they can -- put it into a ring-gap intersecting orbit at low inclination and try to take maximum resolution ring imagery in hopes it survives the first ring passage, and if it does, repeat till it's out of hydrazine and the orbit "oopses" it into a non-gap part of the rings.

Posted by: tasp Sep 16 2007, 01:19 PM

My 'impression' of how resonant orbits 'work' is that you are not allowed close approaches to the object you are in resonance with.

For utilization of Titan to enter a Titan resonant orbit w/o an engine burn seems precluded, however desireable that might be.

Having said that, if you used Titan to enter an orbit about Saturn with a period that allowed returns to the Titan vicinity with Titan 'alternating' ahead and behind the craft the craft at closest approach, you might be able to set up something quasi-stable that would last conveniently longer than even the most optimistic expectation for the longevity of the spacecraft.


(and I am definitely not an orbital mechanic, if I have messed up all this, please be gentle in your rebukes)

Posted by: tasp Sep 16 2007, 01:33 PM

Regarding another flyby of Iapetus to examine the 'tiger scratches', IIRC, for the sun to be overhead (or as overhead as it can get) the encounter needs to take place very roughly about a week or two after Iapetus passes directly behind Saturn as seen from the sun.

(I realize the chutzpah I must be perceived as having, an additional flyby being such a long shot, and I just don't want another flyby, I am going to be picky about lighting conditions and encounter geometry)

Also in the vicinity of the scratches (pretty much due south) is a potential candidate crater for the ring creating impactor. So a s/c close approach halfway between these 2 sites, with the sun pretty much overhead at that time is what we are looking for.

Seems like such flyby would also give pretty good south polar coverage of Iapetus, a rather neglected area going back to the Voyager flybys.

Posted by: mchan Sep 16 2007, 11:32 PM

The devil is in the numbers in this case. Without actually cranking the numbers, I doubt whether such an orbit can be achieved. Titan flybys are good for rotating the semi-major axis of the orbit around Saturn, adjust eccentricity, and adjust inclination. The flybys cannot raise periapsis from inside Titan's orbit to outside Titan's orbit. A large propulsive delta-V would be required to do this.

Second, even if Cassini could get into such an orbit, the period of the orbit would mean that close approaches to either Titan or Iapetus would be rare. Titan's orbital period is slightly less than 16 days, Iapetus's orbit is slight more than 79 days, almost a 5:1 resonance. Assume Cassini's orbit period is 1/2 that of Iapetus, relatively close encounters to Iapetus would at 158 days and would cover the same view geometry. A non-resonant orbit which would allow different view geometries would mean there will be a much longer wait between encounters.

Posted by: edstrick Sep 17 2007, 07:43 AM

"you might be able to set up something quasi-stable that would last conveniently longer than even the most optimistic expectation "

That's a not unreasonable possibility. A low inclination orbit could be maintained with random, very useful non-targeted flyby's of inner moons, though not with much lighting variation for any given moon, as the orbit would be pretty fixed in inertial space, and only the saturn's system orbiting the sun would shift sun angles. <actually, you might slowly walk the orbit posigrade or retrograde, by biassing the approaches, MAYBE.>

Posted by: JRehling Sep 17 2007, 08:08 AM

Worst case scenario would be:

1) Enceladus now hosts a form of life that evolved separately from life on Earth, and is the only other place in the solar system with life.

2) Cassini is shredded by the rings and one sprocket that harbored a dormant bacterium falls onto Enceladus in an area where there is surface access to its subsurface aquifer.

3) The terrestrial bacterium thrives in the enceladan ocean and completely drives all native life forms to extinction.

4) When our 22nd century Enceladus Ocean Explorer looks at microscope slides of the local water, it finds lots of terran E. Coli. There is no remaining trace of the enceladan life.

Now does anyone think that whole scenario is *likely*? No. But look at the payoff matrix. It would take a heck of a payoff to risk that unnecessarily.

I've pointed out before that by flying a mission there at all you risk that scenario, because a micrometeoroid could cripple Cassini at any time and take its future trajectory out of our control. But guaranteeing prevention of that scenario would mean having no mission at all.

Posted by: edstrick Sep 17 2007, 08:24 AM

Any parts of Cassini that repeatedly intersect the main rings will *BECOME* part of the rings. Debris/dust sprayed from impact will be in orbits/trajectories that include the impact point, and re-intersect the ring the next orbit or half-orbit. Any micro-dust carried elsewhere by electric/magnetic/plasma processes will be UV and MeV electron radiation belt sterilized.

Posted by: tasp Sep 17 2007, 01:49 PM

Cassini's trajectory is not immune to collapsing to the Saturnian Laplacian plane.

Interesting mission concept, btw, for a very heavily armored spacecraft.

Posted by: ugordan Sep 17 2007, 02:00 PM

It's immune enough if you stay outside the rings.

Posted by: edstrick Sep 18 2007, 08:33 AM

The mission we ultimately want is "Saturn's Rings Rendezvous", but that requires a battleship sized nuclear-electric propulsion mission. <like Jupiter Icy Moons Orbiter>

Posted by: mchan Sep 18 2007, 08:42 AM

A mission with periapsis inside the D-ring and apoapsis outside the F-ring but with enough inclination to clear the rings before and after the node crossings would generate some spectacular views from skimming over and under the full breadth of the rings.

Posted by: ugordan Sep 18 2007, 09:17 AM

Yes, but how long would you be able to maintain such an orbit? Inside D ring is basically the outer fringes of Saturn's atmosphere, isn't it? I imagine an orbit like that would decay really fast (short orbital period) in a manner of lowering apoapsis inside the main rings. You'd probably need a lot of station keeping propellant just to keep your orbit from decaying.

Posted by: AscendingNode Sep 18 2007, 02:21 PM

Cassini can definitely do an 'eternal' mission. One option is a large orbit just outside of Phoebe that hangs around for ~50 years and then leaves Saturn and stays in between Saturn and Uranus for over 500 years. Another neat one is using Titan to escape Saturn and then using a Jupiter flyby to escape the solar system. Icing on the cake with this scenario is that you can get flybys of Uranus and Neptune on the way out to do a sort of grand tour. Time is an issue... it takes ten years to get to Jupiter, 20 to get to Uranus, and 30 to get to Neptune. But hey, Voyager has lasted 30 years, so those long times aren't completely crazy

There were several papers presented on these options at the August AAS/AIAA Astrodynamics Conference (Where AAS is the other AAS: the American Astronautics Society) Not sure when the proceedings will be published... but they will be on the AIAA website before too long.

Posted by: JRehling Sep 18 2007, 02:51 PM

None of the derring-do sorts of mission finales are going to happen, even if they were possible. The working lifespan of Cassini is going to be determined by attitude-control propellant, which is consumed with every act that points the spacecraft (ie, pointing the instruments, telemetry). That's the real budget to keep an eye on, and it's going to be used to the hilt predominantly with Enceladus and Titan flybys for as long as that budget lasts. There's no way that anyone would conclude that we've seen enough Titan and it's time to get a look at Jupiter instead. Even if the extended mission(s) had a total emphasis on expanding SAR coverage of Titan, we couldn't map the whole surface with Cassini. But expanding that coverage as much as possible is highly desirable. Cassini will live out its life devoted in large part to that goal, with Enceladus being the primary distraction. I'm sure Saturn and the rings will get some more looks as well, but Titan and Enceladus should drive things until the last drop of propellant has been expended. At the outside, we'll get extended mission(s) that roughly double the Titan coverage of the primary mission and considerably more than double the Enceladus coverage of the primary mission.

Cassini will almost certainly finish the same way Galileo did, plunging into a giant planet. Because Cassini has a high gain antenna, we might get some data from the final plunge as a nice bonus.

Posted by: stevesliva Sep 18 2007, 04:16 PM

As much as I thought that that would be awesome when I read your post, reality just intruded by reminding me that the Voyager cameras were turned off something like 15 years ago.

Posted by: edstrick Sep 19 2007, 08:23 AM

Voyager cameras and eventually all scan platform instruments were turned off because (except for the ultraviolet spectrometer, which no longer has enough data bandwidth available to be useful) they were essentially useless, and keeping them warm enough to avoid thermal contraction damage cost power to run heaters in the scan platform and instruments. Voyagers can no longer spare that power as RTG's plutonium decays and thermoelectric junctions produce less and less electricity per watt of heat flux due to accumulating radiation damage.

Posted by: mchan Sep 19 2007, 12:49 PM

Well, if the apoapsis was being lowered from Titan by aerobraking in the outer fringes of Saturn's atmosphere, there would be a fair number of passes over and under the rings before the spacecraft hits the rings. A definite mission end point.

A variation would be similar to Cassini's Saturn Orbit Insertion trajectory, i.e., periapsis over the D ring but well outside of Saturn's atmosphere with node crossings just outside the F ring. The disadvantage is that the pass over the rings is only on one side, so a choice between lit and unlit sides would be required. Achieving such an orbit would be no easy feat as the periapsis would be above or below the satellite plane so Titan gravity assists can't be used.

Posted by: alan Sep 19 2007, 01:15 PM

My idea for an extended extended mission would be to put Cassini into an orbit that only encounters Titan once ever 4 or 5 months. It wouldn't be an exciting mission but it would allow Cassini to conserve fuel and offer the opportunity to observe any changes in Saturn or possibly Titan as the seasons change.My idea for an extended extended mission would be to put Cassini into an orbit that only encounters Titan once ever 4 or 5 months. It wouldn't be an exciting mission but it would allow Cassini to conserve fuel and offer the opportunity to observe any changes in Saturn or possibly Titan as the seasons change.

Posted by: tedstryk Sep 19 2007, 03:04 PM

I will admit I am opining here, but should fuel allow (otherwise it is, of course, not even a question), I would favor a targeted encounter only if after the encounter data is analyzed, scientists are deadlocked over significant issues (such as endogenic vs. exogenic origin of white/dark material) AND, and this is the real key, there seems a very real chance that Cassini's instrument could resolve the issue with another close flyby. Frankly, I doubt that will happen - Sure, if we had an Iapetus orbiter with Cassini's instruments, that would teach us a lot, but much as I would be ecstatic about another flyby, my reason is that I am an image processing guy and Iapetus pictures are COOL. Now, I know TritonAntares would disagree with me on this, insisting as he always does that the coolest target is Rhea, but Iapetus is a real gem of a target, even if the contrast makes it hard as hell to work with (sorry TritonAntares, I couldn't resist ! ). Still, I think Cassini will likely teach us much more by focusing on Titan and the inner moons. It should be noted, too, that we have a solar ring plane crossing in 2009. It won't be like the last one since Saturn will be near conjunction, hopefully Cassini will be in a good position to observe the rings during this time.

Posted by: AscendingNode Sep 19 2007, 03:13 PM

I think this is the best thing too. Rather than burn the candle at both ends by hard living in an extended extended mission full of lots of encounters, I would rather see Cassini conserve fuel with a low encounter frequency so that we can see more of a season on Saturn, Titan, and Enceladus.

Posted by: ngunn Sep 19 2007, 03:24 PM

I want to register that I like the sound of that a lot as an objective. I'm not joining this discussion proper though because I know too little about what's operationally feasible.

Posted by: Mariner9 Sep 19 2007, 08:46 PM

Concerning the seemingly endless debate on "a second Iapetus close flyby"

One thing that keeps occuring to me is the sheer volumn of data we got from the one close encounter. Compare the dozens of images, many of them at very high resolution, to a typical Enceladus encounter.

Doing a very fast look at the raw images for the March 9, 2005 Enceldus close encouter, there were 75 images taken closer than 50,000 KM
During the Iapetus encounter at simlar distances there were 269 images.

At closer than 5,000 KM it is even more dramtic. Enceladus got 3, Iapetus 77.

Admittedly, the numbers alone don't tell the whole story. But it gives a good general idea.

So I don't think it is fair to say Iapetus got only one flyby compared to so many for other targets. Looks to me like that "one" flyby of Iapetus is equivalent to at least 4 or 5 flybys of an inner moon.

Looks like Iapetus got one hell of a lot of coverage to me.

Posted by: ugordan Sep 19 2007, 09:02 PM

It's true, it did, but your comparison isn't completely fair. You're comparing the flyby of the most distant object Cassini can reach to the closest one to Saturn it is interested in (Enceladus). Flyby speeds at Enceladus are something on the order of 30 km/s while Iapetus was an order of magitude slower. Both are really extreme cases. Titan is the middle ground here (6 km/s typical), but then again its large size permits more distant observations and the haze hinders more of the closest observations on the other hand.

Posted by: Mariner9 Sep 19 2007, 10:23 PM

There was nothing unfair about my comparison.

I simply stated that the Iapetus flyby returned a very large data set compared to flybys of the closer in moons. Reguardless of the reason (and I fully agree that the laws of orbital dynamics are the main one) the fact remains that a single Iapetus flyby returned an ammount of data comparable to multiple targeted flybys of the inner moons.

I brought this up because a lot of the discussion would seem to imply that Iapetus is an interesting body (which I agree with), is deserving of more coverage (which I agree with) and not getting very much (which I do NOT agree with).

So my point is: it's not the number of flybys that matter. It's the ammount of data you get. And we just got a heck of a lot.

Posted by: brellis Sep 19 2007, 10:33 PM

If Cassini were put into a long, slow, energy-conserving orbit, would it be able to serve as comm relay for future missions?

Posted by: tasp Sep 19 2007, 10:46 PM

The possibility the 'tiger scratches' (SE of 'Joan') are a new geological (if I can use that term on Iapetus) form not seen anywhere else is very exciting, and precisely why we sent such a capable probe to Saturn in the first place. I am having trouble imagining why we would not go back to Iapetus to check out something like that.

An encounter, with Cassini at closest approach over the scratches, close to local noon there, could check out the scratches, the possible source crater of the ring system (!!) and one of the Iapetan polar regions.

This is a big piece of 'terra' incognita in the Saturn system. I guess I am thinking we should be looking for what the trade off is.

One or 2 less Titan flybys ?? (Out of how many total ?)

Is there a 'final orbit' for Cassini that gives us this Iapetus flyby and then intersects the Saturnian atmosphere 1/2 an orbit further around for spacecraft disposal ??

Is it possible to have this flyby, and then come back to Iapetus in ~79, ~158, or ~ 237 days and 'splat' in Cassini Regio??

This disposal option is appealing, as we saw with Deep Impact (assuming the upcoming (re)flyby is successful) we get to learn new things. In Iapetus' case, we get to see how fast the Cassini Regio 'crud' regenerates itself (if it does) with the next probe we send out there.

(how 'bout letting Squyers team plan a rover for Iapetus ?? )

Posted by: TritonAntares Sep 21 2007, 07:49 PM

Definitly not Rhea - the primary target is TRITON...
(besides ANTARES, Cassini will never reach due to a lack of fuel... ).

Earnestly, my desired encounter scenario would be an outbound passing above a partly shadowed Snowman on a high inclined orbit giving the possibility to have a closer look on both poles, especially the southern one.
Another possibilty would be two inbound passings, each with the opportunity to observe one pole more closely.
A partly illuminated Snowman should be visible in both runs.

But this is only a dream within a dream...

Posted by: nprev Sep 23 2007, 07:25 PM

, TA!

Anybody know if Chiron could be a stopover on the way to Uranus? Thinking in the remote, remote event that they ever seriously consider sending Cassini out of the Saturnian system that a Chiron flyby/Uranus rendezvous would be a lot of bang for the buck.

(Really blue-skying here; I seriously doubt that Cassini will ever leave Saturn, nor should it unless a really high-value, achievable goal becomes apparent).

Posted by: CAP-Team Sep 25 2007, 09:24 PM

I recreated the simulated views of Iapetus during the extended mission, now using Steve Albers' latest map:

Posted by: Sunspot Sep 25 2007, 10:26 PM

When will a final decision be made regarding the extended mission and any flybys planned?

Posted by: volcanopele Sep 25 2007, 10:41 PM

Which do you mean? The Extended mission or the extended-extended mission. The trajectory has been finalized for the extended mission, so that is more or less set in stone. Not sure where we stand on funding. I'm sure I have an email on that somewhere... For the extended-extended mission, based on the timeline for the extended mission, I expect initial discussion to start in mid-2008 with a final trajectory prepared in mid-2009.

Posted by: TritonAntares Sep 26 2007, 02:56 PM

Neat informative sketch...
Unfortunately the distances are quite large.
Especially the perspective of the Snowman during the 2010-02-21 event would have been excellent from say 100.000 to 500.000 km.

I'm not quite sure - aren't there one or two distant Iapetus encounters during the mission until summer 2008 left?
Would be nice if you could create views for them too!

THX & Bye.

Posted by: monitorlizard Sep 26 2007, 03:38 PM

This is just another wild idea that will never happen, but I'll mention it anyway.

After the extended extended mission, NASA will probably want to burn up Cassini in Saturn's atmosphere ala Galileo, to avoid any possiblility of future contamination of Titan or Enceladus. But how about sending the spacecraft to a very high orbit that could never impact Titan or Enceladus. Specifically, a circular or slightly elliptical orbit that could both repeatly flyby Iapetus and study Saturn's magnetotail (and possibly bow shock as well). At Mars, this would be called a disposal orbit, not optimized for science but for biological safety. Having two things to study would make it an easier sell, and it should take very little fuel to maintain. Iapetus encounters would be few and far between with that kind of an orbit, but a longer lifetime for Cassini would be the upside. Close encounters with outer satellites probably wouldn't be possible with the inclinations involved, but maybe distant observations good enough to determine shapes, rotation rates, etc.

Could a final gravitational assist from Titan be used to significantly raise the perigee, saving fuel?

I just thought the issue of Cassini's future wasn't confusing enough already.

Posted by: dvandorn Sep 26 2007, 03:53 PM

A disposal orbit around Mars is possible because Mars doesn't have any large moons that could deform that orbit over the following decades. But the gas and ice giants have literally swarms of attendant moons, many of them quite large, which create gravitational resonances that aren't completely modeled or understood.

Any large orbit around Saturn carries the risk of a close encounter with Iapetus that could decelerate the orbiter back into the main moon system, with the possibility of impact into Titan or Enceladus. Add to that the gravitational resonances of the other moons, and you have a situation that you cannot guarantee will keep the orbiter from becoming a possible source of contamination.

To guarantee that Cassini will not impact Titan or Enceladus, you really do have to crash it into something. The most obvious and most effective body to use is Saturn itself.

Now, that doesn't mean that you can't skim it a few tens of km over the rings on its way towards its destruction...

-the other Doug

Posted by: tasp Sep 26 2007, 04:53 PM

Or do one last experiment with Cassini instead of just burning it up in the Saturnian atmosphere, and smack it into Cassini Regio on Iapetus, and look at the fresh crater with a subsequent mission to see how fast the 'crud' regenerates.

Posted by: tedstryk Sep 26 2007, 05:09 PM

Even if the weathering process were quick, what would you look at the crater with, having crashed Cassini?

Posted by: tasp Sep 26 2007, 05:27 PM

'subsequent mission' ?? !! ?? !!

Posted by: Bjorn Jonsson Sep 27 2007, 12:39 AM

Crashing Cassini into Iapetus for this purpose is a waste. Getting to Iapetus is expensive in terms of fuel so if you ever get there again you want to investigate it and not crash into it. If you really want to crash something into Iapetus a dedicated DI-style mission makes more sense.

Posted by: ugordan Sep 27 2007, 07:54 AM

Crashing into Iapetus is a total waste. There already are numerous fresh and very fresh impact craters in Cassini Regio, why the wish to produce yet another one (which would be smaller than most of those we saw, anyway)?

Posted by: tasp Sep 27 2007, 01:32 PM

It would be the only crater on Iapetus with an exact formation date known to us.


Subsequent missions can watch and evaluate the rate at which the fresh 'splat' darkens to the same degree as the adjoining Cassini Regio area.

If the dark crud is an ongoing phenomena, studying how fast it 'regenerates' seems rather interesting.

The technique pioneered in the Deep Impact mission can be profitably applied to Iapetus.

Posted by: dvandorn Sep 27 2007, 03:38 PM

Unfortunately, it could be 30 to 50 years until we have another probe out that way (at least, another probe close enough to reliably image such an impact site), and without another camera on the scene at the time of impact, there is a pretty big issue as to whether we'd even be able to locate the crash site accurately enough to find the right crater later, much less 30 or more years later.

It's not the worst idea in the world, impacting a body onto Iapetus and then observing the effects over a period of time... but the observer needs to be there at the time of the impact, to triangulate the impact site and to observe the weathering effects from the beginning. To me, it makes no sense to crash Cassini there, making a crater in a difficult-to-locate position and that cannot be observed until/unless another Saturn orbiter comes along, two or three generations from now.

-the other Doug

Posted by: dilo Sep 27 2007, 08:00 PM

Please stop to talk about crashing Cassini!
I want this stuff to orbit for ever around Saturn because there is my sign in the onboard DVD!!!

Posted by: brellis Sep 27 2007, 11:39 PM

Well, that settles that.

I like the longterm orbit flying by Titan and Enceladus, and watching the seasons change. Keeps options open.

Posted by: tasp Sep 28 2007, 04:16 AM

Hi Dilo.

Sorry to upset you with talk of splattering Cassini.

I find it rather more assuring (being aware of it's eventual demise in any regard) if it is impacted on Iapetus to further one last experiment, rather than to just incinerate it to get rid of it.

If the crash site is someday sniffed out by a descendant of Steve Squyers Martian rovers, imagine how excited the folks who pull that off will be!

Will the dark 'crud' ooze in full strength from the edge inward ??

Will the whole crater just darken gradually in a few hundred years ??

Will it stay white longer than anyone on earth cares ??

Or will it splotch, and splotch, till it all is dark again ??


I hope the crash site has a view of the equatorial ridge, and is near one of the 'off shade' craters. Might as well find the most interesting spot we can.


Regarding accuracy of the impact site, IIRC, Enceladus flybys are planned down to ~20 KM or so. Seems like if we try, in the slower part of the Cassini orbital ellipse we might do rather better. If Goldstone is receiving downlink at the instant of impact, and perhaps if Ariceibo is ranging Iapetus simultaneously (or Usuda if geometry is better) I bet we get the error ellipse down to a km or 2.

Posted by: infocat13 Oct 11 2007, 07:22 PM

My idea for the end of mission would be to pump up cassini's orbit using titan to leave saturn orbit and viset saturn or jupiter trojans........................
find a small one and soft land

Posted by: tasp Oct 12 2007, 03:21 AM

Think I should have said VLA instead of Arecibo up there.

Sorry.

Posted by: ustrax Oct 15 2007, 02:32 PM

http://ciclops.org/index.php?js=1!
Congratulations and a gigantic "Thank you!" to the whole team of such an incredible mission!

Posted by: ugordan Oct 17 2007, 05:13 PM

Maybe I'm nuts, but isn't there something wrong about the rings in this release: http://ciclops.org/view.php?id=3192 ?
Look at the C/D ring at approx 5 o'clock. It' looks as if it's disappearing behind Saturn (it's not if you brighten the image), but shouldn't it remain just as bright in front of Saturn's disc instead of being darkened?

Posted by: tedstryk Oct 17 2007, 05:56 PM

It looks to me like the crescent has been suppressed so that the rings are bright but the bright parts of the disk don't wash out. Part of the inner rings look like they may have been inadvertantly dimmed in the process. I think it is the problem of trying to put a seen on a computer monitor that contains a dynamic range far beyond the capabilities of computer monitors.

Posted by: ugordan Oct 17 2007, 06:16 PM

You might be right there, Ted. I forgot about the dynamic range, the rings would in fact be very dim for a properly exposed crescent, as seen in previous similar mosaics. There actually is a touch of discreteness around Saturn's limb here, probably the cutoff selection. A bit of cheating never hurt anyone.

Posted by: tedstryk Oct 18 2007, 02:16 PM

The dynamic range issue is going to keep getting worse. The rings are noticeably dimmer than they were at arrival, and will continue to dim as we approach the 2009 ring plane crossing. I really hope that Cassini is above or below the ring plane during solar crossing - that could create some fascinating pictures.

Posted by: elakdawalla Jan 4 2008, 07:51 PM

I've been sitting on this for a few months, and have finally gotten around to formatting and posting an updated tour page with information about the extended mission. I've changed the format a bit. Please take a look and send me comments. It does not currently include nontargeted flybys of the moons smaller than Hyperion, because the tour information I was given included a zillion entries on "nontargeted" encounters with those moons, most of which never result in any imaging. I need to go back in and compare to see which of the nontargeted rocks flybys actually produced images, and I'll drop those lines into the table. (Actually, those lines are all in the code, I just have them commented out right now.)

http://planetary.org/explore/topics/cassini_huygens/tour.html

Ted, in answer to the question you asked in October, Cassini is at periapsis and also crosses the ring plane on the day of the equinox (if I have the equinox date right, August 11, 2009). Does anybody know what time equinox happens?

--Emily

Posted by: lyford Jan 4 2008, 09:33 PM

Sounds uncomfortable

WOW! It is quite amazing to see the "ballet" unfold over time on that table.

I am sure this has been posted elsewhere, but is there an animated version of the graphic at:

http://planetary.org/image/cassini_tour_all_1061x533.gif ?

Not real time, of course.

ONE ITTY BITTY TYPO - you have the extended mission ending Mon, Jun 30, 2008 at the very bottom cell of the table.

Posted by: elakdawalla Jan 4 2008, 10:23 PM

I've never seen an animated version of that graphic (referred to as "petal plots"). Those graphics I grabbed from somebody's Powerpoint presentation a long time ago. I'm working on getting updated (and prettier) ones, including for the XM. Here's one showing the whole XM, which I suspect has the fields and particles folks salivating.

--Emily

Posted by: ustrax Jan 4 2008, 10:45 PM

Emily...you are this man's dream come true...

Perfect...just perfect...

Posted by: djellison Jan 4 2008, 10:47 PM

If Dave Seal didn't have a Spirograph as a kid - then someone's gotta buy him one now

Doug

Posted by: elakdawalla Jan 4 2008, 11:59 PM

Fixed--thanks for letting me know. Please tell me if you find anything else!

Oh, and while Dave uses the petal plots, he's not responsible for creating them, someone else is. Those navigators are pretty amazing.

I've now added in the very few nontargeted rocks encounters for which there are images in the PDS -- so those are only up to date as of March 31, 2007.

--Emily

Posted by: belleraphon1 Jan 5 2008, 12:17 AM

Bless you Emily.....

been eagerly awaiting this update with XM included.

Animated petal plot of nominal mission.
http://saturn.jpl.nasa.gov/multimedia/videos/video-details.cfm?videoID=85

Craig

Posted by: alan Jan 5 2008, 12:39 AM

I like this animation at the ESA's site:
http://www.esa.int/SPECIALS/Cassini-Huygens/SEMD6E2VQUD_0.html

Posted by: lyford Jan 5 2008, 12:41 AM

Wow - those orbits make Saturn almost look like a http://en.wikipedia.org/wiki/Lorenz_attractor

Of course, there is a different http://www.lpl.arizona.edu/~rlorenz/ involved in this one

Thanks for finding the link, Craig.

Posted by: belleraphon1 Jan 5 2008, 01:20 AM

Welcome lyford...

have to say those navigators are indeed magnificent....... work of art as well as tech....

off to follow politics.... lyford, (and Emily, and all you West Coast folks) hope you are all weathering the weather in CA ok. In Ohio, braving the snow....

Craig

Posted by: lyford Jan 5 2008, 01:42 AM

That's very cool - but I couldn't resist -

http://www.esa.int/images/WhereIsCassini_up2.swf!


PS - Those of us in San Diego are preparing for - Horrors - actual RAIN!! (Good thing I just got me http://www.subaru.com/shop/model_consideration.jsp?model=FORESTER) - could get treacherous out there - maybe the roads will even get wet!

Posted by: jasedm Jan 6 2008, 11:17 AM

Thanks Emily, have been eagerly awaiting some further details of the XM.
Reading the latest significant events report on the NASA Cassini-Huygens site, I notice that almost 30% of the planned OTM's have been able to be cancelled since SOI (41 out of 141) - this is great news in terms of consumables use - hopefully we'll be reading here of the XXM details in a couple of years time..

Posted by: jasedm Feb 26 2008, 09:54 AM

Does anybody know when (if at all) there are plans to update the JPL Solar System Simulator (SSS) with renderings based on Cassini's extended mission trajectory as now confirmed?
The handful of simulators available on the web are very useful (the new 'CASSIE' tool is especially good for watching the spacecraft's 'petal' plots unfold over time) but I find the SSS very effective for moon encounters when looking at phase angles, and encounter distances.
I know some of you who post here have plugged in the spice kernels and can generate your own simulations, but my computer skills fall hideously short of the requirement to achieve this for myself.
Any thoughts?

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

I can't help you with the SSS but I really should make my Celestia add-on for Cassini publically available since it uses the spice kernels for the extended mission.

Posted by: jasedm Feb 26 2008, 10:21 AM

Yes please

Posted by: ynyralmaen Feb 26 2008, 10:21 PM

I'll second that!

Posted by: canis_minor Feb 27 2008, 01:26 AM

I've heard a rumor that the SSS has been updated with the latest orbits, including the extended mission ones.

http://space.jpl.nasa.gov

CM

Posted by: angel1801 Feb 27 2008, 06:20 AM

I actually tried it and yes, the SSS does now include the XM details!

Posted by: jasedm Feb 29 2008, 09:12 AM

Thanks all, it does indeed now include data for the extended mission - there's a bonanza of stuff to look forward to...

Posted by: CAP-Team Feb 29 2008, 07:23 PM

I used NASA's Horizons system to download the orbit of Cassini from the beginning to the end (1997-10-15 09:28 - 2010-07-10 12:00) in xyz format so you can use it in Celestia.
You can download it http://members.home.nl/astronomievandaag/cassini.zip

Posted by: jasedm Mar 25 2008, 08:10 PM

Thank you CAP-team for sharing that - I haven't integrated the information yet, but I appreciate your generosity.

On a different issue, the following quote was culled from the 'significant events' section on NASA's Cassini-Huygens website dated :

Friday, March 14 (DOY 074):

The final delivery of Cassini Information Management System (CIMS) inputs for orbits 123-134 occurred today. This is the fourth and final delivery of CIMS inputs prior to sequence integration. Orbits 123-134 are contained within the S55 through S61 sequences at the end of the proposed extended mission.

We are now 14 weeks from the end of Cassini's prime mission. Surely the extended mission is no longer 'proposed' !!!!!

My boss needs more notice than that for me to book my holidays....

Posted by: mps Mar 25 2008, 08:56 PM

As far as I know the extended mission is not yet approved by NASA (but no doubt it will be!), so it is de jure still "proposed"
Check the Cassini web site http://saturn.jpl.nasa.gov/operations/index.cfm: "The events listed below are proposed pending official approval of an extended mission."

Posted by: jasedm Mar 26 2008, 09:17 PM

With the changes in NASA management discussed here today, one wonders.
Of course, it would take a gibbering madman to consign Cassini to Saturn's core just yet......

Posted by: tedstryk Mar 26 2008, 10:04 PM

Well, the representatives from Mimas are probably enemies of the mission, given the discrimination they have faced in flyby targeting

Posted by: jasedm Mar 26 2008, 10:14 PM

Luck of the draw............they get their moment a couple of years hence - everyone's dream, an extreme Herschel close-up in the NAC, sub 10,000km.

Posted by: remcook Apr 15 2008, 03:55 PM

It's official now

http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=833

Posted by: mps Apr 16 2008, 06:36 AM

If you look at the Saturn XM tour dates and other space missions timelines, you will see that October will be like a space geek's dream:

Oct. 6 - Mercury flyby (MESSENGER)
Oct. 9 - Enceladus flyby, Cassini flying through the plume again
Oct. 28 - LRO and LCROSS launch (according to Space.com. The official web site says only that they will be launched by end of 2008)
Oct. 31 - another Enceladus flyby

Posted by: ugordan Apr 16 2008, 07:39 AM

... and a potential nightmare for the Deep Space Network.

Posted by: OWW Apr 16 2008, 10:01 AM

Don't forget the Hubble servicing mission....also in October.

Posted by: tedstryk Apr 16 2008, 10:39 AM

The Hubble servicing mission is scheduled for August 28.

Posted by: YesRushGen Apr 16 2008, 03:25 PM

From nasaspaceflight.com,

"Atlantis remains in the midst of processing for the final servicing mission to the Hubble Space Telescope, which is classed as an October 6 NET (No Earlier Than) launch target as a best case scenario "

http://www.nasaspaceflight.com/content/?cid=5403

Posted by: tedstryk Apr 16 2008, 09:43 PM

Interesting. I was basing the date on this - http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/hst_sm4/index.html

Posted by: dmuller Jun 10 2008, 07:48 AM

I'm working on my http://www.dmuller.net/cassini and I have thus far used the encounters listed in the files mentioned earlier in this thread:

Are these dates/times still accurate?

Posted by: jasedm Jun 13 2008, 07:40 PM

Hi daniel,
I like the countdowns you've engineered (My word it's a looooong wait for New Horizons Pluto encounter when you see it like this)
As far as I know the reference trajectory hasn't changed appreciably - a couple of inconsequential trajectory correction manoevres have been cancelled but I think this adds up to negligible changes to the data as published.

Posted by: jasedm Jun 29 2008, 07:05 PM

On the eve of the last day of the Prime Mission, I'd like to extend many many congratulations to the Cassini-Huygens team for a breathtaking mission so far.
Even without the extension, this has been a marvellous ride since Jupiter encounter.
It has been almost flawless in execution, and a delight to be a party to. This applies as much to the openness and accessibility of the data as well as the ingenious trajectory designs and the instrument pointing.
As a Brit who makes no direct financial contribution to the mission, I feel privileged to be able to tap-in to the raw images as they come down, and which have been assiduously posted on a regular basis, for four years (after some initial teething troubles).

The spacecraft seems to be in rude health, and hopefully will continue to be well into the XXM.

Huge congratulations to all those involved.

Jase

Posted by: ynyralmaen Jun 29 2008, 08:47 PM

I can only agree absolutely with your sentiments, but ...

... you may be glad to hear that your tax pounds are supporting UK operations and science on the MAG and CAPS instrument teams, and science on ISS, CDA, and CIRS! (without listing the UK involvement in Huygens!)

Posted by: nprev Jun 30 2008, 12:05 AM

Well, as a US taxpayer, I couldn't be more proud. If given the option, I'd've given NASA the whole sum. Thanks to the Cassini team for all you do!!!

Posted by: jasedm Jul 11 2008, 11:02 AM

The Cassini-Huygens website has posted a recent item whereby the general public can e-mail comments to the webmasters regarding the prime Mission, and the upcoming Equinox (Extended) mission. They are welcoming comments specifically regarding the website, so if anybody here has any comments, now's your chance...

See 'Your opportunity to be heard' http://saturn.jpl.nasa.gov/home/index.cfm

Posted by: jasedm Aug 14 2008, 02:48 PM

Looks like the mission planners have decided on the end-of-mission fate for Cassini:
Execute a sharp, banking turn at half light-speed, and plunge into Saturn's cloud tops
This from the latest Cassie 3d tool...

Posted by: nprev Aug 14 2008, 03:53 PM

Unacceptable! If Cassini has enough fuel to hit 0.5c, then she'd better get X exp N Ms instead!!!

Posted by: peter59 Nov 5 2008, 09:45 PM

We have before us several months devoted almost exclusively to study Titan. Does anybody know how many and which flybys will be dedicated for radar imaging ?

Posted by: remcook Nov 6 2008, 10:49 AM

Almost exclusively to Titan is a huge exaggeration. There's lots of other stuff going on including all these Enceladus flybys you've been seeing and studies of the rings and Saturn's atmosphere for instance. Equinox will be an interesting time for these things.
From a slide I've seen there are 13 flybys in the XM that use RADAR. Not sure what mode it will be in though for each of those, so don't know which ones are SAR.

Posted by: stevesliva Nov 14 2008, 02:57 AM

Brief note about extended extended mission planning:

Posted by: jasedm Nov 19 2008, 12:19 PM

Hmmm interesting Steve...
I wonder what the proposals were to "mitigate the shortfall" of available power?

I know very little about the power requirements for instruments on board, so am guessing here, but what can you not do without?

Thrusters/reaction wheels, computers, communications and heaters

I suppose it must come down to a decision over which science instruments are considered 'most important' and which draw the most power - a very difficult call, which will change on each orbit according to target importance/flyby distance.

I'm guessing that fields and particles experiments don't draw a lot of power, so perhaps mission planners may consider doing without the WAC, MIMI or UVIS for interesting encounters in a putative XXM?

Incidentally, I suppose that XXM planning is now at a fairly advanced stage, as we're a little over a year and a half from the end of the XM

Posted by: jasedm Nov 20 2008, 04:44 PM

As an addition to XXM musings, I notice that it has been at least posited that Cassini could continue actively gathering science at Saturn until the Northern summer solstice in 2017 (see Carolyn Porco's comments in 'Sector 6' on the Ciclops website http://ciclops.org/view.php?id=4728)
She points out that this would be nearly half a Saturnian year since orbit insertion.

Budgetary considerations aside, I was under the impression that propellant usage would allow another year or two at most of science operations after the extended mission finishes in 2010.

Obviously science activities would be severely curtailed with respect to the prime and extended missions, but non-targeted encounters would presumably still come about on occasion, with perhaps a handful of choice very close targeted flybys possible (Rings/Enceladus?) before EOM.

Many many 'if's' and not a few 'but's', but here's hoping.....

Posted by: elakdawalla Nov 20 2008, 04:48 PM

I've been told that the prime mission was a bit propellant hungry because they wanted to cram so many things in to the first four years. The extended mission is a little less propellant hungry, but still has lots of targeted flybys. If they're willing to wait a long time between targeted flybys, emphasize long-term monitoring of atmosphere, rings, and magnetosphere over icy sats -- and it'd help if they could plan for a many year chunk of XXM rather than just two years at a time -- they could be quite conservative with propellant, make it last a long time.

--Emily

Posted by: tedstryk Nov 20 2008, 06:10 PM

That is always a tough one. One side of me wants to be as fuel efficient as possible. However, I would hate to play it ultraconservative and then have it pull an MGS-style vanishing act.

Posted by: elakdawalla Nov 20 2008, 06:32 PM

I imagine the arguments go a lot like the ones about Opportunity's next goal. Opportunity wouldn't be driving to Endeavour -- a goal it may never reach -- unless there was compelling science to be done on the way. The question is whether there's a stronger case to be made for more targeted flybys and a shorter extended mission, or a long "journey" of many orbits without targeted flybys. The latter will win only if the science being done on the journey is compelling enough to compete with the science that could be done with more targeted flybys.

--Emily

Posted by: ngunn Nov 20 2008, 09:47 PM

For me the main target is long term lake and weather monitoring of Titan. That's the place where decade-scale changes can be expected and where the available instruments can study an entire active system from surface to exosphere evolving through the seasons. Many close flybys may not be necessary for this, though a few well-spaced ones would be nice, especially for rotation studies.

Posted by: jasedm Nov 21 2008, 11:15 AM

I suppose most people fall into two camps:

1) Keep a sentinel out at Saturn that is serviceable and able to return data for as long as possible (though at a much less intense pace than the earlier segments of the mission), observing seasonal changes and with occasional Titan flybys to constrain atmospheric properties for future missions, or further Enceladus study.

Cons:
Possible failure of the spacecraft in the longer term before all goals are achieved
Greater cost

Pros:
More numerous non-targeted flybys of other places of interest
Seasonal changes on Saturn and Titan may produce some surprises.
The unknown - What price some images of a Schumacher-Levy type event impacting the rings or atmosphere in the longer timescale?

2) Design a spectacular and daring final two-year segment to the mission

Cons:
Missing out on seasonal changes
When she's gone, she's gone

Pros:
Cheaper

The ability to conduct some seat-of-the-pants investigations with a spacecraft that is already paid-for, and which you won't get the opportunity to do again.
This might include a highly-inclined trajectory with periapsis interior to the D ring (as has been suggested) with very close study of magnetosphere, Saturn's upper atmosphere and rings.
Or remain close to the plane of the rings and skim a few kilometres above them in the final couple of orbits, perhaps with the possibility of fields and particles instruments directly sampling the 'spoke' material and ISS obtaining some very high-resolution images of the ring constituents themselves.

Perhaps we should institute a UMSF poll.....

Posted by: Juramike Nov 21 2008, 12:15 PM

I think that's the key argument right there. (lower risk AND cheaper)

Posted by: ngunn Nov 21 2008, 12:35 PM

Well a Solstice Mission has already been talked about, so some on the team must already be inclining to the long option. It might cost more in the long run, but it might actually cost less per year which I'm sure would be welcomed in the current budget squeeze.

Posted by: sci44 Nov 21 2008, 01:07 PM

I would go with keeping Cassini going as long as possible, with occasional flybys using the lowest energy trajectories possible.
Taking http://www.unmannedspaceflight.com/index.php?showtopic=3883&st=30 post earlier in this thread as a basis, in 2006 Cassini used 40 kg biprop (480kg down to 440kg) and 11 kg mono (104kg down to 93 kg) during a very active tour year. Assuming monoprop to be the limiting factor, if using 27g/day mono for "tour" mode, thats 10 kg year = 9 more years usage (from end 2006). If you are prepared to reduce towards "cruise" mode usage for long periods (6g/day) thats about 2kg/year = 45 more years usage. Of course the limit would then be the RTGs, batteries, gyros and other instrument life - but taking Voyager as an indication of what may be possible, we *could* have 20-30 years more use out of Cassini before its "death plunge", with sufficient biprop left for occasional major maneuvers & targetted flybys. Again, thats all just based assuming those original figures are right.
It would also be really useful to still have Cassini to hand if there is a future mission to Titan, a decade or more hence.

The largish amount of remaining biprop on board is intriguing - I wonder how much would be needed for orbital insertion into Titan, together with an aerobrake procedure? I know this idea was mooted/dismissed a long time back, but it would be interesting to know what the figures are. Would a high orbit around Titan be considered "bio-safe" and stable long term?

Posted by: centsworth_II Nov 21 2008, 05:07 PM

"Lower risk" because you are killing the craft before it has time to die itself.
Cheaper because you are killing the craft relatively quickly and ending ongoing costs.

I think the key argument is which mission will gain the more valuable information. Given the long life of various satellites and probes recently, I think its reasonable to think Cassini can last until the fuel runs out. I do recall some concern about gyros, and maybe that is a legitimate concern for and "untimely" end.

Posted by: Hungry4info Nov 21 2008, 11:51 PM

I haven't done the math, but I would guess that it might be tricky. I would venture to guess that Titan's atmosphere probably fills a decent portion of the volume of Titan's gravitational sphere of influence. Orbit around Titan would have to have an altitude of several hundred km of course, but how high can you get without Saturn's gravity plucking you from orbit?

Posted by: mchan Nov 22 2008, 04:13 AM

Plugging in the numbers into the approximation from the Wikipedia page (caveat emptor), Titan's Hill radius is ~55,000 km.

Ttan's atmosphere is extended. Cassini's flybys had to be raised from the early mission plans to over 1000 km to reduce aerodynamic heating at the flyby speeds. It's a little less dense over the poles, so the polar flybys go in near the original planned 950 km.

The TSSM3 pdf from the November OPAG meeting mentions Titan orbit altitudes. For aerobraking, periapsis is ~600 km (dual purpose of direct atmospheric sampling for the mass spectrometer). Circular orbit is ~1500 km to avoid having to burn propellant to maintain altitude.

Posted by: elakdawalla Nov 22 2008, 05:28 AM

Just a small correction, AFAIK it wasn't aerodynamic heating that was the problem, it's that the atmosphere appeared to be exerting more torque on the spacecraft than their models predicted, which creates a problem for planning the spacecraft's attitude during the flyby.

--Emily

Posted by: Exploitcorporations Nov 22 2008, 10:57 AM

A few asides from the peanut gallery...for the iceball-obsessed crowd, myself included, I think we've gotten a virtually miraculous tour and XM. I'd like to see another reasonably close pass at Hyperion from a different perspective, a couple more close views of Dione's cliffs, preferably in low sun, and as many visits to the various rocks as are possible. Another Iapetus encounter is probably out of the question. Gapfill imaging of the north polar regions of each world would be nice wherever possible as well. In the XM, we have high-resolution coverage of the poorly imaged leading hemisphere of Enceladus, the fractured side of Dione, Rhea again, and Herschel on Mimas to look foreward to already, not to mention the Helene flyby and a few decent nontargeted encounters. A few more SAR swipes at Titan would give us 50% coverage in the long term, and maybe complete IR coverage of the emerging northern hemisphere. I'm inclined to support the long option, with the primary focus on atmosphere and rings, especially in light of the ugly financial picture. It would be cool to see those ring-shadows spread again, and watch the south turn blue.

Posted by: stevesliva Nov 26 2008, 05:41 PM

I never did reply to this because I really don't know, although it is important to remember that without a scan platform good chunks of the instruments aren't necessarily being used at times. Fly-bys now will change pointing several times, but if you're assuming that (for example) the imaging instruments are off for an entire fly-by, you probably get much simpler mission planning as well as lower power consumption. I don't know if you could do it without reaction wheels. Fields and particles, I guess.

Posted by: alan Nov 30 2008, 01:20 AM

Stumbled across this kodak moment using the solar system simulator

Posted by: peter59 Dec 17 2008, 07:49 AM

Completely new design of Cassini-Huygens site.
http://saturn.jpl.nasa.gov/
I liked the old.

Posted by: brellis Dec 17 2008, 08:13 AM

Looks like the ESPN site. Can I get the basketball scores on the Cassini page now?

Seriouserly, I fondly recall the way the Cassini page looked during the long flight to the Saturn system. The status reports gave me comfort, and made me feel very close to the mission itself. IMO there's not much need to go for the "wow" factor with a splashy front page -- there's plenty of "wow" in the images themselves to attract people to the amazing scientific achievements of the Cassini mission.

Posted by: djellison Dec 17 2008, 08:31 AM

I like it. The stuff I regularly look at is still easy to find, and the stuff I didn't know about is now there as well. The old site was a navigational mess.

Posted by: akuo Dec 17 2008, 10:16 AM

I liked the current number of moons counter they used to have on the Cassini site . That was a good way of keeping up with the scores.

Posted by: ngunn Dec 17 2008, 10:30 AM

For me the new site takes ages to start. The raw image thumbnails have a bizarre horizontal stretch. Worst of all searching the raw images is so slow as to be completely impractical. When I eventually got page 2 of 'Titan' 'Newest' to open just now I fiound myself looking at an image from February. I seem to recall we've had more that 10 images of Titan since then.

Call me when it's fixed.

Posted by: djellison Dec 17 2008, 10:31 AM

How about emailing the Cassini web team to report your problems?

Posted by: Bjorn Jonsson Dec 17 2008, 10:34 AM

The new site is horribly slow. All of that Flash stuff on the main page with lots images etc. takes ages to load (several minutes). Hopefully this is just a temporary problem.

However, I like its new look.

Posted by: ngunn Dec 17 2008, 10:43 AM

Yeah. I was half joking. I'm sure they've got people on the case. I thought I'd wait and see how it settles in after a few days, also try logging in from a couple of other terminals, see if others here are having similar trouble etc.. But If I still can't search the raws properly I will certaily contact them direct.

Posted by: djellison Dec 17 2008, 10:47 AM

FWIW - speed wise - it's as good for me now as it was before. Several minutes is certainly not right.

Posted by: Bjorn Jonsson Dec 17 2008, 11:25 AM

Maybe everyone is rushing to check if the site is really that slow, thus making it slow .

Posted by: Juramike Dec 17 2008, 12:23 PM

I can't get any of the selected raw images to open up. When I click on a (distorted) thumbnail, it goes to a generic page, after a multi-second load.

I'm really, really hoping that this all gets sorted out quickly.

[Lucky for me, I'd downloaded the T46 Raws as few days ago, no way do I have the patience to do it now.]

Posted by: djellison Dec 17 2008, 02:40 PM

As I said before, if you're having technical issues - email them in. FWIW - The raw page is as fast as it was before for me. The thumbs are a bit distorted in a slight 4:3 sized window, but that doesn't matter.

Doug

Posted by: MahFL Dec 17 2008, 03:11 PM

Looks ok to me in Firefox 3. It is a little slow but not much.

Then it screwed up on this page......

http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3329

"an
e-mail sent to Cassini.Edu@jpl.nasa.gov.

The "Millenn"

seems some fine tuning is needed.

Posted by: brellis Dec 17 2008, 06:55 PM

I have bad timing when it rolls between 3 lead stories with images, captions and "Read More". Might as well have my eyes closed, hehe.

Posted by: ngunn Dec 17 2008, 08:23 PM

I'm having more luck at home with Firefox than with Internet Explorer at work, but even so the raw images don't seem to come up in correct chronological order all the time.

Posted by: mchan Dec 18 2008, 06:43 AM

The old site had a link on the right hand side that went to a page with what I thought of as CPOD (Cassini Picture Of the Day). IIRC, the link was named "Latest Images" or something to that effect. I did not find the equivalent page on the new site.

Posted by: dmuller Jan 21 2009, 01:20 PM

Just to let you know the Cassini realtime simulation at http://www.dmuller.net/cassini finally includes trajectory data and some fixes to make it load faster.

On that note, if anybody has a standard solution (like an exe file) of converting NAIF SPICE kernel files into (x,y,z,t) coordinates, pleeeease let me know :-)

Posted by: bdunford Jan 21 2009, 08:18 PM

Thanks, Daniel, what a great resource.

Posted by: dmuller Jan 26 2009, 10:51 AM

Thanks to a very kind soul who provided a very easy solution (easy = I can handle it!) I can now load SPICE kernels into the realtime simulations, greatly enhancing the accuracy of the trajectory of some missions. First update applied to http://www.dmuller.net/dawn. Go http://www.shatters.net/celestia/!


You're welcome! Glad that it is of use.

Posted by: jasedm Jun 23 2010, 11:44 AM

With the drawing-to-a-close of the first mission extension, and to express appreciation of Cassini-Huygens so far, I thought I'd put together a brief round-up of the achievements so far of this remarkable mission.

Distance travelled: around 5.5 billion kilometres
Time in flight: ~13 years
Orbits of Saturn: 133
Titan flybys: 71
Enceladus targeted flybys: 11
Images taken: around 200,000

Major discoveries/confirmations:

Standing bodies of liquid methane/ethane on Titan
Active cryovolcanism on Enceladus, and a big hint towards subsurface oceans
6 new moons
Multiple new rings/ring arcs
Rings/ring arcs around Rhea
Organic materials in the Enceladan plumes, hydrocarbons on Hyperion

Images/movies obtained of:

Saturn's north and south poles
Surface of Titan at ground level
Specular reflection from Ontario Lacus on Titan (the first time time has been observed anywhere except earth)
Saturnian lightning and aurorae
Numerous occultations and mutual events between the moons and rings
21 icy moons at better than 100,000km range
Of which 15 at better than 25,000km range
Of which 5 at better than 5,000km range

Other achievements:

Doppler tracking gravity measurements at Enceladus
Multiple radio ring occultations
Radar mapping of around 40% of Titan
Light-curve analysis of many of the tiny outer moons to attempt to discern rotation rates
Infrared analyses of Enceladus' polar vents, a well as the other icy moons

I was trying to think of the most stunning image returned so far, and am torn between three:

Enceladus' plumes rising into the sunlight from beyond the terminator
Close-up of Iapetus' mountains
Saturn from the very high orbital inclination with it's shadow cutting across the rings


The spacecraft is apparently in fine fettle, and we have another 7 years of the solstice mission to look forward to, including more of the same, and those proximal orbits towards mission end - can't wait!

Jase

Posted by: nprev Jun 23 2010, 12:38 PM

Good list.

One question: The rings or ring arcs around Rhea haven't been confirmed yet, have they? AFAIK, we have some inference from magnetometer readings & those odd crater chains on the surface, but that's it.

Posted by: tasp Jun 23 2010, 01:40 PM

Yeah, the Rhea flyby in (IIRC) March hasn't had any F&P data released yet. If there is something wonderful forthcoming that would be great.


I didn't know about the outies light curve studies. Interesting to see if any oddments turn up. BTW, I can't think of any way light curve data would yield orientation of spin axis, but I would be happy to be wrong. I suppose colorimetry data on the outies would be asking too much too . . .

Posted by: jasedm Jun 23 2010, 01:48 PM

Yes, perhaps me being a bit over-eager Nick!

The literature seems a little contradictory in some respects - when reading the reports, you get the impression that a set of rings or arcs is the only explanation for the data, but they can't be definitively confirmed without visual evidence.

Three instruments detected dust directly, and the magnetometer readings point strongly towards something present, as the pattern of fluctuations in the readings was mirrored on either side of Rhea (analogous to the discovery of Uranus' rings when they occulted a background star as seen from Earth). Then there is, as you say, the equatorial band of dark markings on the moon.

Visual observations during the close flyby failed to turn up anything, so if there are rings or arcs, then they're likely larger constituents, and probably with low albedo (that omnipresent dark stuff in the saturn system again)

Perhaps it would be better for now to put this in the "strongly circumstantial, but not confirmed" pot then....

Jase

Posted by: ngunn Jun 23 2010, 02:03 PM

I would include sublimation/albedo/temperature feedback on Iapetus as a major discovery. Also there have been many more big discoveries on Titan besides the lakes, such as convective storms that produce precipitation, river valley networks, complex organic chemistry and the equatorial dune seas.

Posted by: jasedm Oct 28 2010, 08:50 AM

Very detailed update of the Cassini trajectory information over at http://www.planetary.org/explore/topics/cassini_huygens/tour.html Thanks Emily!

Encounter distances for the remainder of the mission change a little, with some minuses and some pluses.

For example, Telesto's encounter distance in May 2012 rises from 2,868km to 10,989km and Helene in June 2011 rises from 1,807km to 6,982km

But Rhea's closest encounter distance in January 2011 drops from 201km to 76km, and Dione's closest approach in December next year drops from 199km to 99km.

As Emily says, lots of geek fun to be had here perusing the detail

Jase

Posted by: cbcnasa Oct 28 2010, 04:02 PM

Awsome Cassini has turned out to be so much bigger than ever expected back in 1997.