Are there night side images planned?

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!

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

Bye.

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.

Click to view attachment
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.

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

Bye.

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.

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?

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.

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.

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!

Ohhhh, right -- I had forgotten about this when typing my earlier post.

The flyby geometry is really interesting. In early September, the apoapsis of Cassini's orbit will be just a little bit further out than Iapetus' distance from Saturn, but the semimajor axis of Cassini's orbit will of course be much smaller. This means that, when Cassini is furthest from Saturn, it will be a bit farther away from the planet than Iapetus, and will also be moving much more slowly than Iapetus.

This allows Cassini to pass "in front" of Iapetus on the outbound leg, and then watch as Iapetus overtakes it. Then Cassini drops back towards Saturn as Iapetus moves away. This allows quite a variety of observing angles during the whole encounter.

Interesting - this might be worth a Celestia animation or something. Another aspect of the great planning is that while it is of course passing over the daylit side, Cassini is traveling around Iapetus in the same direction that each terminator is moving so we end up seeing more than 180 degrees of longitude that is sunlit over the encounter.

A little bit, yes. In the first few days after C/A, Cassini will recede from Iapetus at almost exactly 200 000 kilometres per day. You can check this easily in the Solar System Simulator.

[Edit, Aug 10th: The point of this is that Cassini will be fairly close to Iapetus for several days, so, as Steve noted above, we'll get a bit more than 180 degrees of coverage. I didn't make that very clear the first time.]

This means that we'll be getting about 14-15 hours' worth of images that will all be better than the ones from the New Year's flyby.

That would be great. Now only if there is sufficient data storage for Cassini to continue taking data instead of having to transmit earlier stored data to free up space.

Be patient, we'll have to wait a while...

This bit about Cassini making observations of Iapetus in the days leading up to the encounter must have to do with Saturnshine observations. So maybe we'll get a better look at Snowman after all.

...and perhaps the Snowman and environs to the SE will get some interesting viewing angles after closest approach. Even though Cassini is moving away there are several days where the terminator is marching so we can watch the sunrise at Snowman.

And here's an initial take on a Celestia animation over the next month looking from above. The sunlight comes from the top with Cassini and Iapetus at the "C" and "I", respectively.
Click to view attachment

Emily's latest blog entry has some info on the upcoming flyby, she apparently talked about it in detail with Tilmann Denk himself.

Ices, oceans, and Fire: Satellites of the Outer Solar System (2007)

Tilmann Denk's abstract about the Iapetus flyby:

http://www.lpi.usra.edu/meetings/icysat2007/pdf/6049.pdf

Eleven ISS mosaics are planned for the time period -55 to +180 min around closest approach.
Spatial resolution down to 10 m/pxl with ISS.
And a lot of scientific highlights with all the other instruments (SAR, UVIS, CIRS VIMS, ...).
Less than one month to wait !!
Marc.

I was also at the Outer Planet Satellite conference - a local one for me in Boulder. I had a chance to talk about Iapetus a bit with Tilmann Denk (and saw Emily there as well). One item relevant to targeting is how close the Voyager mountains are to the equator. The yellow outlined footprints (post #32) are centered just a bit south of the equator. In my map (that could be off a couple of degrees), they are south of the equator in the southern part of the imaging footprint. Tilmann thinks they may actually lie more exactly on the equator that would bring them up into the northern part of the footprint. Either way, hopefully they will indeed show up in that rather high resolution mosaic.

He mentioned they have some ability to tweak the timing of the imaging sequence until very near the encounter based on the latest navigation updates. There was a very nice table of the images on his poster that Emily alludes to in her blog.

Tilmann had on his poster a few RGB filter images. One of these was from the July 2007 encounter showing the Roncevaux Terra basin region near the limb having nice contrast without the JPEG artifacts. We also had a good exchange about the "basin gap" question, though perhaps we'll have to wait until the September imaging to reach a consensus about what is really going on in terms of possible double rims/basins

[EDITED Aug 18 1600 UTC]

Thanks for posting that url. Quoting Denk's abstract:

>the only SAR observation of an icy satellite (RADAR); *** best-ever examination of
>outer-solar system dark material (VIMS);

I haven't been following the icy satellites as closely as many UMSF members, but it seems odd that this is the only time that SAR is being used to observe an icy satellite. If that's correct, what's the reason?

And what is "outer-solar system dark material?" Is that just another way of referring to the dark side of Iapetus?

TTT

P.S. I'll take this opportunity to thank Emily for her indefatigable blogging of the Ices, Oceans & Fire conference in Boulder. Much appreciated. Why can't they schedule one of these conferences for NYC?

I think the dark material is also for instance the stuff found on Phoebe:
http://www.nasa.gov/lb/mission_pages/cassi...a/pia06400.html
but I'm not sure...

"Why can't they schedule one of these conferences for NYC"
next year's DPS is in Ithaca, which is as close as you're going to get it I guess.

Hi,
the following footprint-map (taken from Tilmann Denk's above mentioned abstract) shows a 4x3 and 3x3 NAC-mosaic of 82-131 m/pxl resolution:
Click to view attachment

Any idea of the WAC-resolution of the large field on this map?
This image could be crucial for major findings in this transition region, as the area is over 3 times larger than the one covered by the mosaic.

THX & Bye.

Hello again,
there will be 4 footprints of the Iapetus cresent (map also from Tilmann Denk's abstract) taken hours before C/A at about 490 m/pxl:
Click to view attachment

Here what Solar System Simulator shows for the time window of the 4 images:
Click to view attachmentClick to view attachment
Distance will be between 70000 and 69000 km.

I'm just wondering about the saturnshine hemisphere...
Click to view attachment
If I'm right, Saturn should illuminate the 'backside' of the of Iapetus at inferior conjunction,
thus the hemisphere shown at superior conjunction (270°-90°) - most of Cassini Regio and the Snowman.

There seems to be no try to catch parts of this saturnlit hemisphere before C/A -
I assume the cresent images won't be overexposed - from this distance !?
Otherwise, there do exist numerous pics of Cassini Regio by now.

Bye.

Regarding the "basin gap" question, check out this old abstract by Denk et al:

http://ciclops.org/media/ma/2007/2748_7462_0.pdf

If you look on Page 2, the second figure from the top shows several low-resolution, distant shots of the Roncevaux Terra basin during a multi-day sunrise.

I can't see a double-basin rim, myself.

Fascinating set of Aug 2004 images Rob that I see here for the first time. This will be worth analyzing further. Hopefully (in spite of some travel plans) I'll have the time to do this before mid September! Quite the central peak showing up on the terminator. I could try and add some of the images to my map to help the intepretation. Would anyone happen to have any images (or at least dates), say from the PDS? The Cassini raw images page appears to be overexposed and perhaps is incomplete.

What I've been showing as the eastern member of the pair of basin rims may have too low of a contrast with the higher solar elevation angle (and greater limb foreshortening) to show up at the ~50 km/pix resolution of the August 2004 images. Running this in Celestia is helpful - I think I can identify the "dark triangle" feature as a reference. Below is a possible fit to the second image in the row from Tilmann's abstract. In this scenario the central peak near the terminator in Tilmann's image isn't showing up in the July 2007 imagery as the solar elevation also was higher there.

Click to view attachment

(post edited 1832 UTC Aug 18)

The images you want are OPNAVs so the target is listed as SKY, not Iapetus. There are only 3 images that target Iapetus specifically, with varying exposure - here's one with normal exposure and to its right a sharpened view to remove PSF blur:
Click to view attachment

And here are the 12 opnavs you want taken in August 2004, the bottom row is sharpened:
Click to view attachment

Both composites are 16-bit PNGs, not that it matters much. No resizing done.

And a quick, 4x magnified animation of all 13 frames:

Damn, now I remember reading Tilmann Denk's abstract in 2005 and especially those far distant image series showing the large Roncevaux Terra basin...
Click to view attachment

Doesn't really look like double impact structure any more - but the extent of the central peak is enormous!
Steve, the "dark triangle" is certainly visible in the two pics on the left.

Bye.

Ugordon's 13 frame animation is pretty cool. I think the first frame or two have better lighting conditions and actually display a bit of shadowing that betrays the presence of a second eastern basin rim

I must confess that the animation seems to me to show just the one rim plus the central mound, not a double rim. I still hold out for one rim. But time will tell.

Phil

Yes, the nice thing about this question is that it is likely to be definitively answered in a few weeks. I wonder though what that shading east of the main rim is that shows up in the first frame of the animation? It quickly disappears as the lighting changes, just as the main eastern rim shadow subsequently disappears as its lighting changes.

I would predict that if I project the first frame as an overlay onto my existing map we'd see these two apparent rims match on top of the ones I presently am mapping. Or I could be patient and wait

I don't know, I'm inclined to say one rim only judging by these views alone. Bicubic filtering can play tricks as well, here's an old style enlargement:



The data is too low-res to make a good case, but I would expect a different lighting pattern there in case of 2 rims.

T-22 days and counting...

I guess I found a little bit of time after all. I added a quick remap of the first of ugordon's frames into the blinking GIF I posted in another Iapetus thread. This illustrates how I see a number of interesting features lining up in the various combinations of images:

http://laps.noaa.gov/albers/sos/saturn/iap..._2x_070821a.gif

That's the latest,

Tom Tamlyn asked why the upcoming Iapetus flyby is the only use of the radar instrument on an icy satellite. This is a question I'm interested in as well. This is an educated guess based on what little I know of Cassini. First of all, SAR uses an enormous amount of Cassini's memory to store its data. I think most of the Titan flybys that imaged in SAR had few other instrument observations, partly because of data storage requirements and partly because Cassini has no scan platform so the entire spacecraft has to change its orientation to use different instruments.

The amazing thing is probably that Cassini WILL use its radar at Iapetus in addition to most of its other instruments. I suspect it will be a very small snapshot, not primarily for imaging but to provide data on the physical characteristics of the surface material.

If radar at Iapetus turns up something unexpected, then perhaps we will see it used for other future icy satellite flybys (keeping in mind it can only be used at close range, I think less than 1000 km). It seems to me that it would be interesting to use it on a close flyby of Enceladus's tiger stripes during the extended mission to further characterize the surface at plume eruption sites.

But all this is just bait to bring in someone who really understands the situation to explain it to us.

That wouldn't be me. I could imagine using SAR to better understand the morphology of the equatorial ridge and white mountains, though.

I think these are all clearly factors:

1) RADAR eats up a lot of observing time and even attitude-control propellant. As well as, monitorlizard points out, onboard data storage.
2) RADAR has a much worse spatial resolution than ISS. RADAR returns 300m/pix imagery of Titan at 950km altitude. ISS, in contrast, returned about the same resolution of Iapetus from 55,000 km away. If you don't have the veils of Titan to contend with, the price-performance curve of these two instruments is very lopsided.
3) Nobody's expecting big surprises in the regoliths of the icy satellites. Not at 300m/pix resolution, anyway, if you can get, instead, 10m/pix visible resolution.

While I'm sure that if a full RADAR dataset of the icy satellites existed, they'd want to look at it instead of throw it away, the cost of using RADAR is very slim compared to the expected gain. Even Titan is only going to receive a few dozen RADAR scans -- there's no way they'd want to burn half a dozen more sampling each of the icy satellites, losing the ISS imagery that could have been had.

I might opine that a single RADAR stripe on *one* icy satellite might be a worthwhile peek to see if there are any surprises in the impact-regolith that dominates their surfaces. Again, it's a cost-value decision, I'm sure. Maybe in the extended mission, but I think if they did want to try it, they'd want to examine Enceladus's active features rather than bland impact-cratered highlands.

Final note: radar from Earth can be used on these satellites to determine the gross reflectivity in radar bands. So even that goal would be a waste of Cassini's resources when it can be done at our leisure from a billion miles away. The only use of RADAR would be to map a place much better than from Earth but much worse than ISS.

I seem to remember reading somewhere that Radar can give you information about surface roughness. In other words, average size of the rocks, pebbles, or snowballs, as the case may be.

Since there is a major debate as to what the difference is between the light and dark regolith on Iapetus, perhaps radar can offer one more (and unique) piece of data to help.


Another factor might be the relatively slow encounter speed. When Cassini is close to the lowest (and fastest) part of it's orbit, it can take only a relatively few measurements of the inner moons furing a flyby. But it will be at it's apehelion when encountering Iapetus, so it will have much more time to cycle between the vastly different pointing requirements of the ISS vs. RADAR.

This should be possible to do from Earth. The resolution would be terrible (pretty much one "pixel" for the whole moon), but since the light and dark surfaces are pretty much two different hemispheres, it should be possible to do some investigation from the good ol' Earth.

In fact, Earth-based radar has been used on Iapetus.

Radar Detection of Iapetus
Gregory J. Black, Donald B. Campbell, Lynn M. Carter, and Steven J. Ostro
Science 23 April 2004:
Vol. 304. no. 5670, p. 553

Cassini RADAR has also been used for radiometry (not SAR) on many of the icy satellites.

Cassini RADAR observations of Enceladus, Tethys, Dione, Rhea, Iapetus, Hyperion, and Phoebe
Ostro, et al
Icarus, Volume 183, Issue 2, p. 479-490.

"Iapetus' 2.2-cm radar albedo is dramatically higher on the optically bright trailing side than the optically dark leading side, whereas 13-cm results reported by Black et al. [Black, G.J., Campbell, D.B., Carter, L.M., Ostro, S.J., 2004. Science 304, 553] show hardly any hemispheric asymmetry and give a mean radar reflectivity several times lower than the reflectivity measured at 2.2 cm. These Iapetus results are understandable if ammonia is much less abundant on both sides within the upper one to several decimeters than at greater depths, and if the leading side's optically dark contaminant is present to depths of at least one to several decimeters."

So the gist is: similar at 13cm, much darker (= smoother?) on the dark side at 2.2 cm. This could tell us about the surface roughness at different scales, or about the composition.

Anyway, SAR mode would tell us something different than radiometry, and it's that kind of observation that is so expensive in terms of operations, etc.

Radar can tell you if a surface is rough or smooth at a scale equal to the wavelength of the radar. That would provide general information (but not image resolution) better than the ten meter ISS resolution that Cassini will achieve at Iapetus. I'm a little out of my depth here, but I believe I've stated it correctly.

That's true, but you can do the same thing from the Earth. You would get data that averages over a large footprint on Iapetus, but that would enable a comparison between the two kinds of surface. Indeed, the citation I provided to an article in Science reports on just such a comparison. Using Cassini to do this can be done from farther away, and needn't be done at the precious encounter. SAR must be done up close -- radiometry can be (and already has been) done from farther away.

With no particular evidence at all, I had just figured the radar scan would provide surface roughness estimates across it's swath to perhaps support a future rover mission.

If the 'original' Iapetan surface materials are distinguishable in some regard from the (possible) emplaced ringy material making up the ridge structure, that would be interesting to.

If an oblique impactor lofted materials that formed a ring system, the impactor might have had a differing composition and it's incorporation into the ring materials, and the subsequent emplaced structure, might yet be discernable.

I don't know how Cassini's radar will be used at Iapetus, but here's a thought: if radar imaged a thin strip of the surface that crossed the boundary between the dark and light materials, you could look for changes in surface roughness. You could see if the transition from one region to the other were characterized by a gradational change or sudden change in surface roughness. That could provide evidence to support an endogenic or exogenic origin of the dark material, especially if combined with data from other instruments.

Unfortunately, that sounds like it might use too much data storage, but just maybe the Cassini extended extended mission will look favorably at another close Iapetus flyby.

Hi!

I have just noticed what is the "Wikipedia's picture of the day for Sept 1st.
Iapetus

That's our Ugordan's image!!!

Sweet

I'm not completely satisfied with how it turned out, though, namely a slight hue shift in the clear filter fill bugs me the most. Then again most casual viewers probably won't notice that unless they know what to look for. Touching up that mosaic has been on my to-do list for a while, but I never got around to doing it.

Hi all,
here a link to FU Berlin I got just seconds ago:
049IA – Cassini Iapetus Targeted Flyby (Rev. 049, 10 Sep 2007)

There are a timeline, detailed information about bbservation requests and a table showing the flyby geometry included... Click to view attachment
Here an updated overview of the VIMS requests:
Click to view attachment

But I've just to read for myself...

EDIT: Downlink times
A small fraction of the data will be downlinked to Earth on the late evening of Sept., 10. The majority will follow overnight (US) or during daytimes on Sept., 11 (Europe). Since the Iapetus data have a particularly high priority, all data will either be downlinked twice, or received by two stations simultaneously. The intermediate downlink late on DOY 253 allows to collect about 20% more data during the flyby than would be possible otherwise.

Bye.

Wow, those are really detailed. It's probably as detailed a description as we'll ever get.
Based on satellite PR shot data - there will be a 1x5 WAC sweep of Saturn and moon system, in addition NAC RGB shots of all the major moons will be provided and a NAC ring scan. Here are simulations on the approximate pixel scales we can expect, note NAC has extra 200 pixels in horizontal direction so it has a bigger window:
Mimas
Enceladus
Tethys
Dione
Rhea - could turn out cool with Saturn's limb near, depending on exact time (closer to 02:40 UTC are better) - similar to Europa rising over Jupiter (except in color )
Titan
Hyperion

And a preview of the WAC view around the time. It'll be nice to see the lit side of rings again along with a moderate phase view of the planet.

Yes, everyone, run, don't walk, to check out those web pages that TA posted the link to. I've been trying to digest all the information there for the last four days -- sorry I didn't share, but I told Tilmann I wouldn't post a link or blog until he was pretty much done, and not quite everything is up there yet. At this point, it's set for the weekend; there won't be more updates until Tuesday.

I LOVE the animation and map previews of each observation -- wish we had these for every targeted flyby!!!

Here is a preview of my digested version (no illustrations yet, and probably some typos, send me a PM if you notice any glaring errors)...
http://planetary.org/blog/Cassini_Iapetus.html

--Emily

Good grief, will I have to write a book to write the uber-preview for this flyby

Lol VP, good luck topping this.

There's just so much information to digest here, it's almost like one step away from giving us spice kernels for the encounter.
The closest approach observation is ISS_049IA_ORSHIRES001_VIMS and it has an interesting coverage, 8 clear filter ISS footprints of the ridge. If Cassini ever provides a view akin to a view from an airplane, this will be it. The view flying literally over the ridge should be absolutely s.p.e.c.t.a.c.u.l.a.r. and allow for some great stereo shots as phase angle reduces from 83 to 29 degrees.

Yes - really exciting details from FU Berlin. Thought I'd check whether these closest approach exposure footprints represent simultaneous or near-simultaneous WAC and NAC images? That will be great to see this mosaic at the two different scales.