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Cassini's Extended Mission, July 2008 to June 2010
TritonAntares
post Feb 8 2007, 12:10 PM
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QUOTE (volcanopele @ Feb 7 2007, 12:18 AM) *
EDIT: Terrain descriptions in above post now edited and accurate.
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... sad.gif
Then saturnshine images from 2004-12-31 in ~120.000 km distance will still be the best.

Bye.
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ugordan
post Feb 8 2007, 12:25 PM
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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.


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JRehling
post Feb 8 2007, 04:15 PM
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QUOTE (TritonAntares @ Feb 8 2007, 04:10 AM) *
Then saturnshine images from 2004-12-31 in ~120.000 km distance will still be the best.

Bye.


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.
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TritonAntares
post Feb 8 2007, 06:14 PM
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QUOTE (JRehling @ Feb 8 2007, 05:15 PM) *
...
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.
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Holder of the Tw...
post Feb 9 2007, 02:37 AM
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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.
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Guest_Analyst_*
post Feb 9 2007, 09:12 AM
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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.

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Guest_AlexBlackwell_*
post Feb 10 2007, 12:32 AM
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QUOTE (Analyst @ Feb 8 2007, 11:12 PM) *
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.

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.
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tasp
post Feb 10 2007, 06:38 PM
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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.
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Guest_Analyst_*
post Feb 10 2007, 07:15 PM
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QUOTE (AlexBlackwell @ Feb 10 2007, 01:32 AM) *
Just ask the poster of these two posts.


These two posts are yours. smile.gif
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tasp
post Feb 10 2007, 09:01 PM
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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 . . .
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JRehling
post Feb 11 2007, 12:12 AM
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QUOTE (tasp @ Feb 10 2007, 01:01 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 . . .


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).
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tasp
post Feb 11 2007, 01:13 AM
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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.
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tasp
post Feb 11 2007, 01:15 AM
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How many different scenarios can we come up with that create white peaks/dark surroundings that might be discernably different to the Cassini lens?
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Guest_Analyst_*
post Feb 11 2007, 10:57 AM
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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
Attached File(s)
Attached File  Cassini.txt ( 23.27K ) Number of downloads: 231
 
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Rob Pinnegar
post Feb 11 2007, 05:17 PM
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QUOTE (JRehling @ Feb 10 2007, 05:12 PM) *
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).

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.
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