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Dawn Survey Orbit Phase, First orbital phase
ElkGroveDan
post Jul 20 2011, 10:56 PM
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QUOTE (machi @ Jul 20 2011, 01:41 PM) *
South pole of Vesta in stereo.


Really nice Daniel.


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machi
post Jul 21 2011, 12:04 AM
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Thank you all!

I prepared one more cross-eye/anaglyph stereo image, using second published hi-res image.
Attached thumbnail(s)
Attached Image
Attached Image
 


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peter59
post Jul 21 2011, 09:07 AM
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Today is Thursday, maybe we'll see images acquired on July 18 ?
http://dawn.jpl.nasa.gov/mission/status.asp
Dawn team usually publishes something on Thursday.


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belleraphon1
post Jul 21 2011, 11:17 AM
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Awesome!

Thanks machi
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Phil Stooke
post Jul 21 2011, 02:17 PM
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Recent images would be of a narrow crescent, but in a few days we will be seeing the northern hemisphere... brand new territory again, and from closer range.

Phil


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Juramike
post Jul 21 2011, 02:25 PM
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With such a lumpy surface, the high-phase images should be pretty dramatic.


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tfisher
post Jul 21 2011, 04:05 PM
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QUOTE (Stefan @ Jul 20 2011, 11:20 AM) *
The distance for that image was (or should have been) 15222 km (center of Vesta). You already know the angular extent of one pixel. You tell me where you are wrong...


I'm curious about the answer as well. I get a diameter of 615km trying to replicate the calculation, and I don't see anything wrong with how Emily is doing it. But that is well outside the biggest dimension of the oblate spheroid model. Is it just that the oblate spheroid is that lousy of a fit for vesta's true shape?
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Phil Stooke
post Jul 21 2011, 04:46 PM
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Hopefully this will be out of date very soon, but here's a composite view of all the closer images we have seen so far. Please let me know if I am missing any.

Phil

Attached Image


(EGD points out - I should have scaled the first to match the long axis dimension, not the polar axis!)


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kap
post Jul 21 2011, 05:35 PM
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QUOTE (Phil Stooke @ Jul 21 2011, 06:17 AM) *
Recent images would be of a narrow crescent, but in a few days we will be seeing the northern hemisphere... brand new territory again, and from closer range.

Phil


It was my understanding that a good portion of the northern hemisphere will be in darkness (winter) for the first months of the mission, am I mistaken in believing that?

-kap
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Phil Stooke
post Jul 21 2011, 05:44 PM
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Only the north polar area itself will be hidden - most of the northern hemisphere will be visible now.

Phil


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elakdawalla
post Jul 21 2011, 05:56 PM
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QUOTE (tfisher @ Jul 21 2011, 08:05 AM) *
I'm curious about the answer as well. I get a diameter of 615km trying to replicate the calculation, and I don't see anything wrong with how Emily is doing it. But that is well outside the biggest dimension of the oblate spheroid model. Is it just that the oblate spheroid is that lousy of a fit for vesta's true shape?

Thanks for checking my math, and now I feel a little more confident in questioning the factor-of-2 enlargement. Here's the DPS abstract on Vesta's dimensions from Hubble data (289, 280, 229 km semi-major axes, or 578, 560, 468 for diameter), which refers to a previous conference abstract with a diameter based on an occultation (561 +/- 3 km). In no way are any of these consistent with any principal axis diameter above 600 kilometers. So either the enlargement factor or the range to the target has not been reported correctly.

I know I'm beating a dead horse here and I think the Dawn team now regards me as kind of a pest and really I am very excited about seeing a new world. But it's hard to do outreach when I know that some of the information that I'm getting must be wrong.


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elakdawalla
post Jul 21 2011, 06:04 PM
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Regarding the enlargement, I like neither the blurriness nor the jaggedness of the limb. Both, I think, do a disservice to the FC which I think is supposed to be a very fine instrument. Now that details can be resolved, it's much better just to post images that are not enlarged. Consider the most recently released image of Vesta. Now consider a Cassini image of Phoebe with the same number of pixels. The Cassini image looks so much crisper, and a comparison between the blurry-looking FC image and really any other deep-space camera image makes FC look like a crappy instrument, when we know it's not. it's not a fair comparison, because the Cassini image started out with 800 pixels, while the Dawn one started out with only 400. But most people don't know that; they just see a blurry, pixelated image.


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Stefan
post Jul 21 2011, 07:54 PM
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QUOTE (elakdawalla @ Jul 21 2011, 07:56 PM) *
I know I'm beating a dead horse here and I think the Dawn team now regards me as kind of a pest and really I am very excited about seeing a new world. But it's hard to do outreach when I know that some of the information that I'm getting must be wrong.


Please realise that at this stage, we face similar uncertainties. There is one thing about which I am 100% sure: the enlargement factor is 2. But then, there are so many possibilities:

1. I calculated the distance wrong, and my colleague made the same mistake
2. The SPICE kernel we used is wrong
3. We used the wrong SPICE kernel
4. The camera FOV has shrunk
5. Your measurement is correct
...

We are using trajectory *predictions*! Would it make a difference if I say that we (the FC team) are going through an extremely busy period, in which our main priority is to ensure the FC is in good health and taking images as planned?
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Stu
post Jul 21 2011, 09:00 PM
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QUOTE (elakdawalla @ Jul 21 2011, 06:56 PM) *
... I think the Dawn team now regards me as kind of a pest ...


I'm sure that's not the case.

...but if any of them do think like that, then I really think they should be grateful that a respected and accomplished science journalist like yourself is so excited by, and passionate about, the mission, wants to ensure its success by writing about it for a public audience, and is trying hard to get the facts straight in order to write accurate reports.


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elakdawalla
post Jul 21 2011, 09:06 PM
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I apologize for being such a pest. I think I don't properly appreciate or understand the differences in navigational certainty between an ion-powered mission -- and one that's approaching a small body with relatively poorly constrained mass -- and the kind of orbital or flyby missions I'm accustomed to writing about. I'm glad to have a definitive answer about the enlargement factor, and now at least I think I understand which bits of information are the sources of the uncertainty. I had assumed wrongly that the range to the target was one of the more precisely known bits of information. So, sorry! I hope you'll take my pestiferousness as a sign of my real interest in and excitement about the mission!


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