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Cassini's Extended Mission, July 2008 to June 2010
john_s
post Feb 4 2007, 03:35 AM
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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.
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volcanopele
post Feb 4 2007, 05:09 AM
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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.


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ugordan
post Feb 5 2007, 01:43 PM
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Grabbed from the Yahoo Cassini-Huygens group: Tour de Saturn Set For Extended Play

Excerpt:
QUOTE
+ Cassini will fly by Dione once at 500 km altitude: a moon which is long-dead now, but shows clear signs of violent tectonic stretching during the Solar System's ancient days -- and which also seems to be still releasing a tiny trickle of water vapor, only about 1/300 as much as Enceladus, from someplace on its surface.

+ The spacecraft will fly within 1500 km of Helene, one of Saturn's recently-discovered tiny moons that seem to be loose clumps of icy rubble stuck together only loosely by gravity. Helene, discovered in 1980, is one of two moons that share Dione's orbit at its gravitationally stable "Lagrange points". (Two more tiny Lagrange moons share Tethys' orbit.)

+ In addition, Cassini will skim the surface of Rhea, Saturn's second-biggest moon, at 100 km altitude. Unfortunately, Cassini's lack of a tiltable scan platform seriously limits its ability to cancel out the motion blur that fuzzes up its images during its really close flybys of various moons.


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john_s
post Feb 5 2007, 03:06 PM
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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
Attached File  Icysat_Flybys_UTC_NFB.PF_6h9L.txt ( 14.77K ) Number of downloads: 928
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djellison
post Feb 5 2007, 03:35 PM
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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 smile.gif Take a zero off the end for the WA

Doug
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NMRguy
post Feb 5 2007, 04:22 PM
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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.
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ugordan
post Feb 5 2007, 04:29 PM
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QUOTE (djellison @ Feb 5 2007, 04:35 PM) *
What are the typical exposure times for ISS NA and WA using clear filters?

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.


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john_s
post Feb 5 2007, 04:33 PM
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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.
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djellison
post Feb 5 2007, 04:33 PM
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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
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volcanopele
post Feb 5 2007, 04:44 PM
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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.


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john_s
post Feb 5 2007, 11:22 PM
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I just did a blog for the Planetary Society about the extended mission tour selection process- here it is

John.
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djellison
post Feb 5 2007, 11:27 PM
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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 smile.gif But then - if you put your OSX dock on the right side...there's just wierd...

Doug
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jamescanvin
post Feb 5 2007, 11:48 PM
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QUOTE (djellison @ Feb 6 2007, 10:27 AM) *
But then - if you put your OSX dock on the right side...there's just wierd...


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


Great article John.

James


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djellison
post Feb 5 2007, 11:52 PM
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Well - when i actually get a Mac (this summer) then I'll speak with confidence...

Actually - it does kind of make sense smile.gif

Doug
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Bjorn Jonsson
post Feb 6 2007, 12:38 AM
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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 smile.gif.

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."
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