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Phoenix - spring images, HiRISE views of Phoenix after the long, long winter
centsworth_II
post Apr 15 2010, 12:48 PM
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QUOTE (akuo @ Apr 15 2010, 06:19 AM) *
As far as I can see from the animation, the lander's shadow hasn't moved very much at all....
I've placed an outline of the lander from the first image on the second, matching a couple of points as best I could.
The most obvious question is, what happens to the shadow from the right solar panel?
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nprev
post Apr 15 2010, 12:55 PM
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I see what you mean. Would be nice to get a pic with a lower Sun angle, but IIRC MRO's in a Sun-sync orbit, right?

The difficulty thus far finding MPL is becoming less & less mysterious, it seems.


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centsworth_II
post Apr 15 2010, 01:02 PM
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QUOTE (nprev @ Apr 15 2010, 08:55 AM) *
...Would be nice to get a pic with a lower Sun angle...
I thought the sun was low in these spring images. We had to wait until it rose above the horizon at all before the image campaign began.
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vikingmars
post Apr 15 2010, 01:46 PM
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Thanks to you nice image processings, Hungry4info and centsworth_II , there are now several options that can be discussed to better understand the current state of the Phoenix s/c :

1. the dark color of the s/c itself : even though there is a low sunlight, it is no longer coloured white or gray (body) and blue or dark blue (solar panels) :
(i) Is it covered now by dirt left by a mix of ice and dust and... what else ?
(ii) Has the s/c completely collapsed under the heavy ice load (2.6 tons...) and was almost flattened to the ground ? (meaning a quasi "flat" shadow) ;
(iii) is the body intact with only bent or collapsed parts : leg(s), solar panels... ? Then, there is a difficulty to differentiate between the colors created by the shadows and the colors showing real parts of the s/c itself...

2. the shift (move) of the center of the s/c :
(i) has it moved when the ice buit up or sublimated (s/c pushed aside) or just "slided" on it ?
(ii) has it tipped over ?
(iii) is it tilted on one side ?

=> I'm now really waiting to see the next HiRise images with an higher Sun... huh.gif
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elakdawalla
post Apr 15 2010, 01:51 PM
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QUOTE (James Sorenson @ Apr 14 2010, 08:49 PM) *
I'm just curious as to know if the Phoenix flight DVD or a model was load tested before launch? Considering how much C02 ice was probably on the deck, as well as the DVD it self, plus if Phoenix actually did tip over, that little disc sure has been through allot of torcher.

It wasn't load tested. The major tests it has undergone include thermal vacuum testing (where it's placed in a vacuum chamber and then run through temperature extremes, mostly to ensure it wouldn't either break due to thermal stress or outgas anything that would impact any of the science) and shock/vibration testing (simulating the rigors of launch and landing). The Phoenix DVD is a much simpler animal than the MER DVD; it has no fancy assembly attaching it to the lander. It is merely a silica glass DVD that is attached to the deck with adhesive and Velcro. My instinct tells me it should be fine under a load, but I don't know. Tipping over Phoenix (if that has happened) should have had no effect at all on it.


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vikingmars
post Apr 15 2010, 02:13 PM
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QUOTE (elakdawalla @ Apr 15 2010, 03:51 PM) *
Tipping over Phoenix (if that has happened) should have had no effect at all on it.

Ouf ! Dear "Bloguette par excellence" (it's a great name in French) : I think my name as PSoc member was on it... I might have survived (like other PSoc members) the harsh of the Martian winter after all ! laugh.gif
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ElkGroveDan
post Apr 15 2010, 02:16 PM
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QUOTE (vikingmars @ Apr 15 2010, 06:46 AM) *
(i) has it moved when the ice buit up or sublimated (s/c pushed aside) or just "slided" on it ?


I've been pondering this possibility as well. From my perspective I don't see any "missing" shapes in Centsworth's comparison above (thank you for that).

Another thing about the "weight" of the CO(2) on the panels. That would only be a problem if the ice falls like snow from above. If the CO(2) forms directly from the air like frost, then we'd have an even deposition of ice forming both on top of and under the panels. In that case the panels wouldn't be subjected to "weight" any more than a metal table dropped to the bottom of the ocean would collapse from the weight of the water above.


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ugordan
post Apr 15 2010, 02:27 PM
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QUOTE (vikingmars @ Apr 15 2010, 04:13 PM) *
I think my name as PSoc member was on it... I might have survived (like other PSoc members) the harsh of the Martian winter after all ! laugh.gif

While the DVD itself might look physically intact, I wouldn't really expect it to be readable after the low temperature extremes it went through. So I wouldn't bet any of "us" survived either. ph34r.gif


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djellison
post Apr 15 2010, 02:39 PM
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Unlike normal DVD's, this one was actually a glass disc that is more analogous to being a master from which normal DVD's get stamped than a typical DVD-R or off the shelf movie DVD. It's a fairly robust thing.
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Hungry4info
post Apr 15 2010, 02:44 PM
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I can't imagine any sort of "micro-glacial" action (making up terms here) would cause the observed change in position of the lander without destroying that disturbed patch of ground that was created when Phoenix landed. The ground seems fairly unaltered.

So...

Ice accumulates everywhere on the lander, sun comes up and is low and only in one part of the sky, so only the ice on one side of the lander evaporates, the centre of gravity shifts over, and Phoenix topples over? Maybe throw in a bit of wind that must have occurred to alter the observed shape of the parachute.


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marsophile
post Apr 15 2010, 03:28 PM
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For the lander to topple over, either the center of gravity of the load would need to be beyond the area of the legs, or one or more of the legs would have had to fail. How strong were the legs?

The center of gravity of the load might be beyond the area of the legs if a wind-driven sublimation process left an overhang. I think the solar panels extended beyond the legs, so a load there might tip the craft if the panels did not snap off first, but it does not look like it tipped in that direction.
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nprev
post Apr 15 2010, 03:32 PM
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To me, Centsworth's image doesn't suggest that Phoenix tipped, but it does look like the right solar array isn't where it used to be. Could it have drooped due to frost accumulation and/or cryothermal effects?


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Hungry4info
post Apr 15 2010, 05:13 PM
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For the dropping scenario, assuming the lander is upright and the solar array attached, I would assume that the solar array would protrude from the lander less than it does in the post-landing MRO image. We observe the array as being farther from the lander in the post-winter image than it was in the post-landing image, but still in roughly the same relative orientation. Maybe it got dragged along, even if it is on the ground.

Another thing that just hit me is that we can clearly see the shadow of Phoenix in the latest post-winter image. There is no solar array in the way to block our view of that shadow as there is in the post-landing image. I interpret this as the array resting on the surface.

· Lack of observed shadows from the solar arrays (for any illumination angle with which we can see the lander's shadow, the arrays shadow should be visible)
· An apparent increase in the array-lander separation between the post-landing and post-winter images.
· A well observed lander shadow, without the array blocking a portion of it that we would expect to see if the arrays were still at the same altitude as the deck.

If anyone can think of a way that the arrays can be attached despite these lines of evidence, I am all ears.


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Deimos
post Apr 15 2010, 07:00 PM
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Hmm, hot topic. I looked at this a bit ago and agree with much above (except tip/shift of the lander), but maybe can add a bit. I think I placed the lander model just slightly sunward compared to the image above. Zoomed out enough, it looks like you can make out some edges, but the lander is dust colored now. FWIW, a better image is needed before even I would believe my conclusions.

I used a model with model shadows for the timing. From that I'd say the one negative is the apparent shadow and the model still seem to overlap some. I'd want a better image to really conclude a negative from that (same with the positives). The most perplexing thing is that the shadow really doesn't look like the lander body shadow; it matches with the body shadow plus the east SA shadow. The west SA shadow is missing, but the model says only a sliver of it should be visible.

An earlier image had me 50% convinced the west SA had collapsed, but I haven't seen anything to confirm or deny that.

If the east array shadow is present, we got some 'splainin' to do. The collapse prediction does not rely on any assumption that CO2 deposition is like snowfall. Frost would form on the coldest surfaces. Surfaces are primarily cooled radiatively, with some reservoir of heat depending on the volume being cooled (among other things). The top of the SA radiates to space or at least the upper atmosphere. The soil under the array radiates to the array. The array has little heat reservoir, the soil has more. The array is the cold finger. Frost accumulates on its top. Maybe on the bottom. But not on the surface underneath, until the array is encased in frost. If the SA survived, it is not due to frost building up to its level from the surface. Some mechanism (wind-related? seems unlikely) kept it defrosted. My impression is that if you built up the frost 1 monolayer of molecules at a time, uniformly, the arrays could hold a lot--but not the back-of-envelope expected amounts. The tolerance for non-uniformity is low. Use one as a table to hold a glass of wine and you have a mess (hmm, does that give away too much about the location where conversations like this take place?). And while one can imagine uniform deposition, one certainly doesn't get that impression from the images.
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ElkGroveDan
post Apr 15 2010, 10:04 PM
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Thanks Mark for the informed input on both topics.


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