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Dawn approaches Ceres, From opnav images to first orbit
TheAnt
post Jan 15 2015, 03:53 PM
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QUOTE (DrShank @ Jan 15 2015, 01:13 PM) *
yes, but by then there will be lots more archived to chose from to post on the Pic-o-the-Day site. Each orbit returns dozens of frames. The number will vary depending on altitude and which mapping phase we are in, of course, but I don't have those numbers.


Oh yes you're absolutely right, and I don't believe anyone have the definite numbers of images but its obvious that there should be some who sits and make plans for the imagining campaign at Ceres now already. =)

I checked on the facts and this blog entry mentioned that I had in the back of my head when I posted:
"So over the course of 14 complete circuits around Ceres in 11 days, the spacecraft will turn only six or eight times. Ever the responsible conservationists, the team developed all the details of this plan to acquire as much data as possible with the minimum expenditure of hydrazine." Source
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elakdawalla
post Jan 15 2015, 03:57 PM
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Moved a bunch of pronunciation posts to the Junk Drawer topic. Let's keep the signal-to-noise ratio high, folks.


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DrShank
post Jan 15 2015, 11:57 PM
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QUOTE (TheAnt @ Jan 15 2015, 09:53 AM) *
Oh yes you're absolutely right, and I don't believe anyone have the definite numbers of images but its obvious that there should be some who sits and make plans for the imagining campaign at Ceres now already. =)

I checked on the facts and this blog entry mentioned that I had in the back of my head when I posted:
"So over the course of 14 complete circuits around Ceres in 11 days, the spacecraft will turn only six or eight times. Ever the responsible conservationists, the team developed all the details of this plan to acquire as much data as possible with the minimum expenditure of hydrazine." Source


Yes indeed. the team has done a fantastic job to make the adjustment to the hybrid form of orbital mapping and still meet the main objectives. It was also a very prudent decision to have a significant supply of hydrazine on board. without that it would be a bit more difficult to do the mapping of ceres without the wheels. Ceres has a lot more area to map as well (the ratio can be easily calculated of course from the radii), and also much darker than vesta. this will require longer exposures, but also a longer mapping phase to get the same coverage for stereo mapping. I'm impressed . . .


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TheAnt
post Jan 16 2015, 10:53 PM
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QUOTE (DrShank @ Jan 16 2015, 12:57 AM) *
.... Ceres has a lot more area to map as well (the ratio can be easily calculated of course from the radii), and also much darker than vesta. this will require longer exposures, but also a longer mapping phase to get the same coverage for stereo mapping. I'm impressed . . .


'Prudent' is nearly one understatement, considering the fact that space mission planning usually involves the task of hunting down every unnecessary gramme with even more diligence than a builder of a supercar. =)

And yes, Ceres is quite dark and comes with one albedo of 0,09 compared to the bright Vesta: albedo 0,423. This means there will most likely be a lot of dust that have been captured after various collisions of C type asteroids in the neighbourhood. I guess this asteroid 'pollution' might make it somewhat harder to determine some parts of the history of the asteroid, though I do rather think the idea of seeing Ceres as one surviving planetesimal in the end will be strengthened.
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DrShank
post Jan 16 2015, 11:46 PM
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QUOTE (TheAnt @ Jan 16 2015, 04:53 PM) *
'Prudent' is nearly one understatement, considering the fact that space mission planning usually involves the task of hunting down every unnecessary gramme with even more diligence than a builder of a supercar. =)

And yes, Ceres is quite dark and comes with one albedo of 0,09 compared to the bright Vesta: albedo 0,423. This means there will most likely be a lot of dust that have been captured after various collisions of C type asteroids in the neighbourhood. I guess this asteroid 'pollution' might make it somewhat harder to determine some parts of the history of the asteroid, though I do rather think the idea of seeing Ceres as one surviving planetesimal in the end will be strengthened.


projectile contamination is also a question for ganymede and callisto. we have several members interested in that problem, and ill let them think about that when we get some spectra to work with. my main focus will be impact craters and what we can learn about the interior and icy shell.


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nprev
post Jan 16 2015, 11:53 PM
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Paul, you may know this right off the bat: Where does Ceres rate on the PPP scale? Is it on par with Mars, Europa & Titan, rated somewhat lower, or not even on the radar at this time?

Not directly applicable to Dawn, of course, save that it might be a factor in EOM planning.


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Phil Stooke
post Jan 19 2015, 04:35 PM
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http://www.jpl.nasa.gov/news/news.php?feature=4449


First pics - very nice.

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nprev
post Jan 19 2015, 04:51 PM
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Oh, boy; here we go!!! smile.gif

Looks like the most obvious confirmed feature (since it's also in the Hubble imagery) is that big white spot in the northern hemisphere. Almost certainly a fresh impact crater, of course, but it'll be interesting to see if that high contrast persists at higher resolutions.

I see hints of 'wrinkles' or ridges on the rest of the surface as well as some older big craters. Might just be eroded crater rims from even older & bigger impacts.


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Explorer1
post Jan 19 2015, 04:57 PM
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Yeah, that spot seems like a crater; I can almost make out a dark edge at the top (shadows?).
Very nice!

Also VIRS first light (not in the link provided, strangely enough):

https://twitter.com/NASA_Dawn/status/557214894269800449
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Habukaz
post Jan 19 2015, 05:56 PM
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My layman-self is a bit confused.

This picture has several very obvious crater candidates (including the big one near the middle that makes Ceres look like Mimas looking like the Death Star), but the shiny contrast feature is nowhere to be seen; so how does it fit with the animation?

This picture, on the other hand, has no obvious crater candidates (except from the shiny feature, which is pretty unique), and it also has a big wavy low-albedo feature in the lower hemisphere (looks a bit like to massive craters on a leash).

So, to my untrained eyes, the first picture makes Ceres look a body with a very old surface, while the latter one makes Ceres look a place with a potentially youthful surface (although the image processing looks kind of different between the two images, so maybe that's a clue).


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Hungry4info
post Jan 19 2015, 06:19 PM
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Comparing the new Dawn images to an HST image, I think it's clear that several surface features are visible in both.
Attached thumbnail(s)
Attached Image
 


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Phil Stooke
post Jan 19 2015, 06:20 PM
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replying to Habukaz - At this resolution you can't be making interpretations like that. It is not yet possible to tell the difference between albedo markings and topography, or noise and topography. The next set we get might make those things possible, or maybe the one after that.

Phil


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Habukaz
post Jan 19 2015, 06:44 PM
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QUOTE (Phil Stooke @ Jan 19 2015, 07:20 PM) *
replying to Habukaz - At this resolution you can't be making interpretations like that. It is not yet possible to tell the difference between albedo markings and topography, or noise and topography. The next set we get might make those things possible, or maybe the one after that.

Phil


Well, the lead investigator for the framing camera thinks we might be seing craters:

QUOTE
“Already, the [latest] images hint at first surface structures such as craters," said Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research, Gottingen, Germany.


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Holder of the Tw...
post Jan 19 2015, 06:56 PM
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But I think the operative word there is "hint".
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Habukaz
post Jan 19 2015, 07:09 PM
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QUOTE (Holder of the Two Leashes @ Jan 19 2015, 07:56 PM) *
But I think the operative word there is "hint".


Yes, and that's why I labelled them as candidates. It will be interesting to see what's what as we get closer; I just felt like scribbling down what came to mind when I saw the pictures.

My main point was though that I don't get how the "cratery" picture without the bright spot fits the animation; is it included somewhere within it?


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