Enceladus August 11, 2008 encounter, Close-up observations of plume vents |
Enceladus August 11, 2008 encounter, Close-up observations of plume vents |
Aug 3 2008, 06:54 PM
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#1
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Member Group: Members Posts: 934 Joined: 4-September 06 From: Boston Member No.: 1102 |
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 -------------------- |
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Aug 8 2008, 01:37 PM
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#2
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Senior Member Group: Members Posts: 1465 Joined: 9-February 04 From: Columbus OH USA Member No.: 13 |
Sounds like an impressively complicated and exacting maneuver to get Cassini's rotation to just cancel out Enc's apparent motion during the skeet shoot.
From the description, looks like they're taking just one photo at each of the skeet shoot locations--so no closeup "movies" of plumes? What are the odds the plumes would even be visible, looking down on them? Hypothetically, anyone know what the typical shutter times are for the ISS cameras in this kind of lighting, also the minimum cycle time in "burst mode"? -------------------- |
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Aug 8 2008, 02:01 PM
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#3
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
As I understood it, Cassini's rotation won't be able to cancel out Enceladus' motion at all. They'll spin the spacecraft as fast as possible and wait for the moon to overtake the camera FOVs. This will at least lower the motion smear somewhat.
I'm very, very skeptical any plume will be visible at roughly a 90deg phase angle, looking down on sunlit (albeit terminator) area. I don't believe that's even the goal. You can pretty much forget about any "movies" from such a close range. The C/A part of the encounter is practically gone within a minute and the fastest the ISS camera can take frames is IIRC every 20 seconds, and that's using at least 2x2 binning, possibly lossy compression as well and probably the fastest telemetry pickup rate available to the instruments (in other words, it's the only instrument producing significant quantities of data - this probably also excludes "BOTSIM" ISS mode). Shutter times for the WAC can be a few ms only, I think NAC needs at least 20-ish ms (thin air figure) for good S/N ratio at 90deg phase icy terrain illumination. -------------------- |
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Aug 8 2008, 03:00 PM
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#4
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Member Group: Members Posts: 544 Joined: 17-November 05 From: Oklahoma Member No.: 557 |
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Aug 8 2008, 03:05 PM
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#5
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Senior Member Group: Members Posts: 3648 Joined: 1-October 05 From: Croatia Member No.: 523 |
I don't believe a shadow can/will be visible, the plumes are much more subtle than martian dust devils are and the low exposures will likely add a bit of noise to the images as well. The fact the plumes are only visible at high phase angles means they don't intercept much light in the first place. What is intercepted is mainly scattered, otherwise the plumes would appear dark.
Also, keep in mind the solar illumination will be coming in at a low angle so topography will be very pronounced, it would be much harder to spot shadows on that than a smooth martian surface. -------------------- |
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