Enceladus August 11, 2008 encounter, Close-up observations of plume vents Options

[Floyd]

Just 8 days until the next Enceladus encounter.

CICLOPS Rev 80 Looking Ahead will appear here soon.

Cassini Enceladus 080EN Mission Description is here now.

We get to fly through the south polar jets again.

-Floyd

[edit] Soon = somtime before encounter

[ElkGroveDan]

That's one of your best Stu.

I can almost picture Christmas carolers out for a sleigh ride on the snows of Enceladus.

[belleraphon1]

Hmmmmmmmmmmmmmm...

"fissures that open and close like the bone-dry maws of some fearful buried beasts that feed on vacuum, and scream in pain" I hope they do not scream "Tekeli-li! Tekeli-li!" Just joking... Stu... I get the same feel as you but am not talented enough to express it.

What marvel's will we eventually find there? What wonders lie under those portals to subterranian seas?
A spelunkers dream (or nitemare).

Craig ... a Lovecraft fan

[Bjorn Jonsson]

Yeah, those super-close images weren't originally on my page, because for some reason in Bjorn's database a bunch of the geometric data, including the range to target, was missing for that observation.

In some cases geometric data is missing from the LBL and index files for super-close images for some reason. I've seen it happen for some of the Enceladus flybys, including (if memory serves) the very close nontargeted flyby in February 2005, some of the later targeted flybys and also the very close nontargeted Tethys flyby.

Does anyone know if the ultra-close images to be obtained during the upcoming flyby are BOTSIMs? This is not mentioned in the flyby descriptions I've read (I haven't checked everything yet though).

In any case this seems to me to be the most complicated Cassini flyby so far and one of the most exciting and interesting ones as well - good luck to everyone involved.

[ugordan]

The camera is specced at 5.99 urad/pixel, so at a range of 319 km, wouldn't the resolution be 319000*5.99e-6 = 1.9 m/pixel (assuming a nadir shot)?

Yep, but that image was binned 2x2 so the effective pixel scale is 2*1.9 m/pixel, exactly as advertised.

[volcanopele]

Only the last skeet shot image shown in the attached image from the Looking Ahead article contains a CL1/CL2 BOTSIM. There is a botsim at the start of that trigger, but it is over the nightside.

Attached thumbnail(s)

 

[ugordan]

The reason there aren't more BOTSIMs might lie in what I wrote about earlier - they're twice as data intensive so might limit the speed at which ISS can take images, which in a high speed flyby is most undesirable. This is due to the fact the SSR recorders and their support system (what was it - the CDS?) can handle up to 384 kbps (I think). It doesn't physically prevent snapping a new picture, but the ISS generated packet buffer is emptied slower into the SSR if both cameras are generating much data and new images have to be "queued" until the buffer is emptied.

As a matter of fact, it's not unusual for CCD frames to have a delayed readout (there's a PDS image flag by that name) if the telemetry pickup is slower than the speed the camera reads out lines from the CCD and encodes them. This messes the dark current calculation as the rest of the image just sits on the CCD for a period of time and one can actually see higher dark currents starting at a certain line in some WAC raw images if you really brighten them.

But, I digress...

[jmknapp]

Yep, but that image was binned 2x2 so the effective pixel scale is 2*1.9 m/pixel, exactly as advertised.

Ah, I missed that earlier comment.

Using NAIF data to figure the ground speed of the ISS boresight during this flyby, I get this graph:



The "skeet shoot" is over around 21:11:09, then the 8-tile mosaic starts (not all of the latter shown).

[mchan]

"Tekeli-li! Tekeli-li!"

Well, Bob Shaw, who hasn't posted in over a year, would appreciate that. As do I.

(The images of the myriad of dark circular storm centers in Saturn's southern atmosphere remind me of the eyes of the Shoggoths.)

[dmuller]

Better late than never, I have copied Emily's timeline into the realtime simulation

[Bjorn Jonsson]

The distant (~450,000 km) images from today's 3 hour "early" downlink seem to be do down. At a quick glance I didn't notice any plume material but the automatic contrast stretch messes things up so this may not mean anything.

NAC image with Enceladus nicely centered:

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=165786

Scanning around somewhere near Enceladus:

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=165828

[ugordan]

At a quick glance I didn't notice any plume material but the automatic contrast stretch messes things up so this may not mean anything.

Wouldn't it be kind of weird seeing the south pole plumes while looking down onto the north pole?

[elakdawalla]

I agree with you that it seems weird to be looking for plumes when you're looking down on the north pole, but that observation is described in the mission description as "Inbound Enceladus plume observations (distant)".

--Emily

[Bjorn Jonsson]

Wouldn't it be kind of weird seeing the south pole plumes while looking down onto the north pole?

The plumes are big so they should be there poking above the nightside limb. They may not be conspicuous here due to the viewing/lighting geometry (brightest part behind the limb, phase angle not high enough etc.).

[ugordan]

They probably *are* poking behind, but at that point they're very faint and diluted. I wouldn't expect to see them even in calibrated imagery, a simple sunlit sliver is enough scattered light to drown out anything near.

[jmknapp]

The first image--a WAC image at 21:07:19--will be framed something like this:



From the Verbiscer writeup:

At 21:07:19 UTC, one minute after closest approach, ISS will acquire the first of the skeet-shoot targets, a WAC image centered on a point just over the night side of the terminator at a resolution of 52 meters/pixel.

Looks like some material from that fissure could easily be up in the sunlight but silhouetted against the night side? I think from the NAIF data the angle of the shot is something like 40 degrees from the local vertical.