Rev 16 - Oct 2-21, 2005 - Telesto, Tethys, Dione D1, Dione-Telesto-Enceladus Options

[Decepticon]

Note: Most of the Dione-specific discussion is in a different thread - moderator



Just before closets approach http://space.jpl.nasa.gov/cgi-bin/wspace?t...s=1&brite=1
An hour later.. http://space.jpl.nasa.gov/cgi-bin/wspace?t...s=1&brite=1

And the night side (I really hope we get some night side mapping. Make mapping of the moons much quicker!) http://space.jpl.nasa.gov/cgi-bin/wspace?t...s=1&brite=1



And Enceladus
http://space.jpl.nasa.gov/cgi-bin/wspace?t...s=1&brite=1

[tedstryk]

Well, it will make mapping the Saturn-facing hemispheres quicker. The trailing hemispheres don't have the benefit of Saturn-shine.

[Decepticon]

Doh! Should of known that.

[Guest_BruceMoomaw_*]

Slight slip-up by Ted: it's the "anti-planet" hemisphere of a moon -- not its trailing hemisphere -- that's naturally deprived of planetshine. (Actually, it would be simpler to use the same terminology for other planets' moons that we use for our own: "nearside" and "farside".)

[tedstryk]

Slight slip-up by Ted: it's the "anti-planet" hemisphere of a moon -- not its trailing hemisphere -- that's naturally deprived of planetshine.  (Actually, it would be simpler to use the same terminology for other planets' moons that we use for our own: "nearside" and "farside".)

You are right. Leading/Trailing refers to orbital direction. Thanx for catching that one.

[Bjorn Jonsson]

I'm attaching a 6 image montage showing Dione at various times surrounding closest approach next week. This flyby is similar to the recent Tethys flyby in the sense that the phase angle prior to closest approach is very low.

The distances are relative to Dione's center.

Also I made an animation (6 MB) of the flyby:

http://www.mmedia.is/bjj/misc/css_stuff/re...ione_rev016.avi

This animation starts on October 11, 2005 at 17:33 (distance from the center of Dione: 10453 km) and ends at 18:11 (distance: 10420 km). It has a field of view of 40 degrees.

Attached thumbnail(s)

 

[volcanopele]

That definitely looks like a great opportunity for Saturn-shine

Thanks Bjorn.

[Decepticon]

^2 Flybys 4 the price of 1.

[tedstryk]

Not an ideal ground track (I would have wanted more of the cliffs), but I am still looking forward to this. Darn synchronous rotation!

[Guest_BruceMoomaw_*]

JPL's guide to the Dione flyby is now out ( http://saturn.jpl.nasa.gov/multimedia/prod...description.pdf ). Apparently it will get a good look at the now-famous "cracked wispy" terrain -- and, as with most icy moon flybys (though not, for some reason, at Tethys), the VIMS will be used.

Only 90 minutes after closest approach, Cassini will also make one of its closest nontargeted flybys of any moon -- within 9750 km of Tethys' little Lagrange moon Telesto, which will indeed be imaged. (I wonder if this will be close enough to determine Telesto's mass, allowing us to determine whether the Lagrange moons are rubble piles like the inner moons and Hyperion.)

By the way, http://www.aas.org/publications/baas/v37n3/dps2005/603.htm reports that one odd trait of Dione discovered by Voyager -- the fact that there seems to be a concentration of magnetospheric ions near its orbit -- may be due not to outgassing by Dione itself, but rather to some of the gas generated by Enceladus, which is not greatly ionized by radiation until it drifts into the outer parts of Saturn's magnetosphere. Still no word, however, on whether Cassini discovered any indications of outgassing from Tethys during its close flyby.

[ugordan]

Just before closets approach http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1
An hour later..  http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

And the night side (I really hope we get some night side mapping. Make mapping of the moons much quicker!) http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1
And Enceladus
http://space.jpl.nasa.gov/cgi-bin/wspace?t...porbs=1&brite=1

While Cassini will make a fairly close non-targeted approach to Enceladus, from the recently released Dione flyby description I figure there aren't any Enceladus observations programmed. Instead, the spacecraft will be engaged in a rather lengthy data downlink session at the time of C/A to Enceladus.
Too bad, but you can't have unlimited data storage onboard, can you?

Only 90 minutes after closest approach, Cassini will also make one of its closest nontargeted flybys of any moon -- within 9750 km of Tethys' little Lagrange moon Telesto, which will indeed be imaged.  (I wonder if this will be close enough to determine Telesto's mass, allowing us to determine whether the Lagrange moons are rubble piles like the inner moons and Hyperion.)

That would be great, but I wouldn't hold my breath. The flyby guide says there's a couple of radio science observations, prior to Dione C/A and after BOTH Dione and Telesto C/A. Personally, I think Telesto's mass is far too small compared to Dione and the approach distance of some 10000 km is too much to pick out Telesto's mass from the whole measurement. Perhaps if they included a short radio science observation between Dione and Telesto C/A, but even then, who knows...

[Decepticon]

I've always wondered how many Gigs of data SSR can hold?

[ugordan]

I've always wondered how  many Gigs of data SSR can hold?

Cassini has 2 SSR recorders, each with 4 gigabits of storage. That's about 477 megabytes per SSR (or alternatively 512 megabytes if gigabit means 1024*1024*1024 bits, but I think the figure for bits is 1000*1000*1000).
An uncompressed ISS full-frame 8-bit image is exactly 1 megabyte, the compression that truncates lines on the right guarantees this to be <=512 kilobytes so you can quickly determine how many images you could store in case all memory is available just for images (which it's not )...

For comparison, I seem to have read that Voyagers' tape recorders could also hold something like 512 megabytes, though I could be wrong on this.

[pioneer]

For comparison, I seem to have read that Voyagers' tape recorders could also hold something like 512 megabytes, though I could be wrong on this

I don't think so. The Galileo tape recorder could not hold more than 150 megs, so I doubt the earlier Voyager could hold more.

More like 512 megabits

[ugordan]

I don't think so.  The Galileo tape recorder could not hold more than 150 megs, so I doubt the earlier Voyager could hold more.

Ah, you're right. Just checked, Voyagers' digital tape recorders have a 500 megabit capacity...