IPB

Welcome Guest ( Log In | Register )

15 Pages V  « < 2 3 4 5 6 > »   
Reply to this topicStart new topic
2007-09-10 Iapetus (rev 49): Pre-flyby discussion, Closest approach of this odd moon
scalbers
post Jul 28 2007, 10:53 PM
Post #46


Member
***

Group: Members
Posts: 796
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



I'll try attaching a quick Celestia movie if it can fit in the size limit...Attached File  iapetus6.avi ( 481.5K ) Number of downloads: 602


--------------------
Go to the top of the page
 
+Quote Post
scalbers
post Jul 28 2007, 11:03 PM
Post #47


Member
***

Group: Members
Posts: 796
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



Here's a second version of the movie that focuses more on the closest approach...

Attached File  iapetus7.avi ( 475K ) Number of downloads: 583


EDIT:
I've made a longer version of the movie (3MB) as well at the link shown below. Celestia has the closest approach too far away at about 5000km, though at farther ranges the animation should be fairly realistic.

http://laps.noaa.gov/albers/sos/saturn/iapetus/iapetus9.avi


--------------------
Go to the top of the page
 
+Quote Post
MarcF
post Aug 1 2007, 07:50 AM
Post #48


Member
***

Group: Members
Posts: 175
Joined: 16-May 06
From: Geneva, Switzerland
Member No.: 773



Some more informations about the September flyby :

http://www.cosis.net/abstracts/EPSC2007/00...076ebb8f800aea1

A SAR observation will be performed, the only one of an icy satellite.

Will it help to determine the thickness of the dark material (or reveal hidden structures) ?

Marc.
Go to the top of the page
 
+Quote Post
tasp
post Aug 1 2007, 02:04 PM
Post #49


Member
***

Group: Members
Posts: 885
Joined: 30-January 05
Member No.: 162



Wow !!

Perhaps we can characterize the surface roughness for a possible Iapetan rover someday with a SAR observation.

I would love to see a scan of Atlas too, maybe it would reveal new info on the accumulated ring materials.
Go to the top of the page
 
+Quote Post
scalbers
post Aug 4 2007, 06:59 PM
Post #50


Member
***

Group: Members
Posts: 796
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



A fast moving view covering the entire month before encounter, then some time afterwards...
Attached File(s)
Attached File  iapetus12.avi ( 666K ) Number of downloads: 115
 


--------------------
Go to the top of the page
 
+Quote Post
Decepticon
post Aug 5 2007, 01:24 AM
Post #51


Senior Member
****

Group: Members
Posts: 1155
Joined: 25-November 04
Member No.: 114



Are there night side images planned?
Go to the top of the page
 
+Quote Post
nprev
post Aug 5 2007, 01:37 AM
Post #52


Senior Member
****

Group: Moderator
Posts: 6953
Joined: 8-December 05
From: Los Angeles
Member No.: 602



I'm thinking that the radar obs are going to be primarily conducted during C/A for surface mapping, mostly due to the fact that it will be dark there...good use of resources! smile.gif


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post
TritonAntares
post Aug 5 2007, 10:17 AM
Post #53


Member
***

Group: Members
Posts: 267
Joined: 28-September 05
From: Orion arm
Member No.: 516



QUOTE (Decepticon @ Aug 5 2007, 03:24 AM) *
Are there night side images planned?

As far as I'm informed there'll be some attempts to catch the Snowman at the western limb hours after C/A.
Attached Image

5 images along the terminator (blue line) and 2 pics of the 3 craters in saturnshine area.

Before C/A there is no possibility of saturnshine images, because CASSINI is observing the anti-saturn hemisphere, I guess.
A perfect opportunity for radar mapping...
Attached Image


Bye.
Go to the top of the page
 
+Quote Post
Rob Pinnegar
post Aug 5 2007, 12:29 PM
Post #54


Member
***

Group: Members
Posts: 501
Joined: 2-July 05
From: Calgary, Alberta
Member No.: 426



There probably wouldn't be much point in trying to get Saturnshine images of the Snowman. The last set required some pretty long exposures, but since they were taken from 100 000 kilometres out, that didn't cause any problems.

For this encounter, though, Cassini will be so much closer in that any attempt to take Saturnshine images would probably lead to some awful smudging. This would be due to changes in the apparent size and shape of image features during the course of the exposure -- so tracking the camera wouldn't help.

So using the SAR instead seems like a really good idea.
Go to the top of the page
 
+Quote Post
TritonAntares
post Aug 5 2007, 01:55 PM
Post #55


Member
***

Group: Members
Posts: 267
Joined: 28-September 05
From: Orion arm
Member No.: 516



QUOTE (Rob Pinnegar @ Aug 5 2007, 02:29 PM) *
There probably wouldn't be much point in trying to get Saturnshine images of the Snowman. The last set required some pretty long exposures, but since they were taken from 100 000 kilometres out, that didn't cause any problems.
For this encounter, though, Cassini will be so much closer in that any attempt to take Saturnshine images would probably lead to some awful smudging.
This would be due to changes in the apparent size and shape of image features during the course of the exposure -- so tracking the camera wouldn't help.

Attached Image

They'll definitly try to do these two saturnshine shots with a resolution of ~140 m/pxl (NAC).
Maybe somebody can calculate the appendent distance.
We'll see how smeared they actually are. As this is the only opportunity to have a close look at the Snowman, it should better not be missed.
A bad pic is better than none...
Btw., the eastern edge of Snowman C will be in sunlight at the limb. wink.gif

The dark green lined 15-image-mosaic will be taken hours later at ~440 m/pxl (NAC).

Bye.
Go to the top of the page
 
+Quote Post
Rob Pinnegar
post Aug 5 2007, 10:43 PM
Post #56


Member
***

Group: Members
Posts: 501
Joined: 2-July 05
From: Calgary, Alberta
Member No.: 426



I suppose it'll be okay as long as the images are taken long enough before closest approach. I guess that when Cassini is near closest approach, there won't be time for long exposures, anyways.

It'll be interesting over the next 40 days to see Iapetus get closer and closer.
Go to the top of the page
 
+Quote Post
scalbers
post Aug 5 2007, 10:48 PM
Post #57


Member
***

Group: Members
Posts: 796
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



Possibly even daylight images would be challenging right at closest approach. Is it true that the closest imagery planned is for the Voyager mountains? If so what would be the range of Cassini for those images?


--------------------
Go to the top of the page
 
+Quote Post
ugordan
post Aug 5 2007, 10:52 PM
Post #58


Senior Member
****

Group: Members
Posts: 3559
Joined: 1-October 05
From: Croatia
Member No.: 523



140 m/pix translates into roughly 23 000 km range. Alternatively, if they plan on doing a 2x2 binning mode (useful if smear is expected to be >1 pix) that would be halved. A 2x2 bin has an additional advantage in that it increases the s/n ratio 4 times for the same exposure, but at the expense of spatial resolution. Even at 23 000 km the smear would probably less than one pixel for an exposure on the order of a couple of seconds.

Steve, I don't think daylight images will present a problem for Cassini. Remember the flyby speed will be much lower than typically at Titan (6 km/s) and especially Enceladus. Cassini managed to keep pretty stable pointing & tracking for the haze-penetrating CB3 filter even at those speeds and even with thrusters. The CB3 filter requires quite a long exposure to achieve good s/n ratio so this is indicative of the performance we can expect at a more leisurely flyby.


--------------------
Go to the top of the page
 
+Quote Post
scalbers
post Aug 5 2007, 11:04 PM
Post #59


Member
***

Group: Members
Posts: 796
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



Hi Gordan. Good points - I was thinking that the closest approach is around 1200km and that it'd be unlikely images would be right at that distance. There is some background info in post #7 about some close images that are so close the Voyager mountain targeting would be uncertain. Perhaps those are only at 2000km range that would be quite a bit closer than Enceladus.


--------------------
Go to the top of the page
 
+Quote Post
ugordan
post Aug 5 2007, 11:20 PM
Post #60


Senior Member
****

Group: Members
Posts: 3559
Joined: 1-October 05
From: Croatia
Member No.: 523



Ahh, I see post #7 has all the relevant information about saturnshine images as well. My impression from that post is that it's the targetting that's uncertain, not the camera's ability to produce smear-free images. Once targetted, Cassini can inertially track very well. In fact I'd say the limiting factor in the encounter will be the slow camera image rate and the lack of a scan platform for quick mosaicking several overlapping footprints a-la Galileo. Even if the NAC misses the white peaks, we'll still get pretty good context from the WAC I imagine. Remember the Rhea flyby when that 'splat' crater was of interest - even the WAC frame got some seriously high resolution at some 500 km distance.
A WAC frame at 1500 km is still 10x higher resolution than the best NAC coverage we got on New Year's Eve!


--------------------
Go to the top of the page
 
+Quote Post

15 Pages V  « < 2 3 4 5 6 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 1st August 2014 - 05:45 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.