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.

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.

Grabbed from the Yahoo Cassini-Huygens group: Tour de Saturn Set For Extended Play

Excerpt:

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
Click to view attachment

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

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.

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.

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.

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

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.

I just did a blog for the Planetary Society about the extended mission tour selection process- here it is

John.

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

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

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

Actually - it does kind of make sense

Doug

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."

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

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

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...

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

Click to view attachment
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.

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.

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

Here's a list of Titan flybys in the PF6h9 tour:
Click to view attachment

And here's a list of small satellite flybys:
Click to view attachment

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

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.)

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

BAD NEWS...


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

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.

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.

Now that an extended mission tour has been selected 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 "Primary Target for Extended Mission" poll into this topic.

--Emily

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.

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.

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.

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.

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.

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.

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

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 two posts.

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.

These two posts are yours.

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 . . .

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).

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.

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

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

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.

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 . . . .

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.

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

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

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.