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Spirit cleaner?
fredk
post Jun 22 2007, 05:15 PM
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QUOTE (RobertEB @ Jun 22 2007, 03:00 PM) *
When humans walk up to her one day in the future, I want them to see her sitting on Home Plate like she was as an explorer.
Home plate? I want them to see her in the Promised Land!
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dilo
post Jun 23 2007, 01:34 PM
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Well, seriously, I think that now that power is up, they should try move fast the rover in order to maximize exploration in the incoming months! This because frankly I doubt Spirit will survive another winter... moreover, last mission extension is approaching to the end (around Sol 1350, if I recall) and, while another year extention is possible (and auspicable), with actual budget issue there is the risk of a commandend shutdown within 5 months from now! sad.gif


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djellison
post Jun 23 2007, 04:16 PM
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While they have one mobile rover, it's unlikely the program will be shut down.


Spirit probably wont survive another winter - all the more reason to do the good science infront of us smile.gif

Doug
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alan
post Jun 24 2007, 05:42 AM
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Must be getting windy, a few more clean patches are visible between sol 1231 and 1234

Attached Image
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jaredGalen
post Jun 27 2007, 07:00 PM
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All this cleaning might be timely but hopefully not fruitless, big storm a comin'....maybe.

http://www.space.com/news/070627_mars_storm.html


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dvandorn
post Jun 27 2007, 07:19 PM
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Well, isn't it almost a truism that semi-global and global dust storms on Mars tend to occur as the planet approaches and works through its equinoces? Those are the times when the most extensive atmospheric transfer between the poles occurs (as CO2 sublimates off the cap approaching summer and condenses onto the cap approaching winter), and so generates the greatest global winds.

We've survived regional storms since the MERs landed, we can only hope that this storm (and any others that may pop up over the next couple of months) will remain regional and not go semi-global or global. We could still see both rovers die within days of each other if a global dust storm of the extent, say, of the 1971 storm were to develop.

Do note, though, that the rovers might well become cleaned by the more energetic winds to an extent that they *could* survive even a major dust storm. The HiRISE color image of the Viking 1 lander, for example, demonstrates that it is still primarily non-dust-covered, and we know it has endured several global dust storms. Depending on the rate of deposition vs. the rate of cleaning during such a storm, we might be able to get the rovers to advantageous slopes and weather a storm, as we have weathered Martian winters.

-the other Doug


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BrianL
post Jun 27 2007, 07:34 PM
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QUOTE (dvandorn @ Jun 27 2007, 01:19 PM) *
Depending on the rate of deposition vs. the rate of cleaning during such a storm


Well, just in case this turns into a poll, I'm going to join the deposition camp now. Clean-sweeping burned me last time and I still haven't forgiven it. Don't even get me started on my feelings about the far side of the crater. laugh.gif

Brian
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David
post Jun 27 2007, 09:09 PM
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QUOTE (dvandorn @ Jun 27 2007, 07:19 PM) *
Do note, though, that the rovers might well become cleaned by the more energetic winds to an extent that they *could* survive even a major dust storm.


Let's say we have the most optimistic scenario -- the dust in the wind gets blown by, and whatever dust is on the rover gets blown off -- how much would power drop, not from the dust on the rover, but the dust in the atmosphere? How long would the storm have to last before the rovers would become irrecoverable?
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helvick
post Jun 27 2007, 09:57 PM
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Assume for a moment that the dust on the panels has reduced efficiency to 75%. The numbers for in and around now for Spirit would be:

CODE
Tau       Whr/Sol      Beam
0.9        730         38.0%
1.5        609         19.2%
2          529         12.5%
4          314          1.8%
6          198          0.3%


So things would have to get very bad for this to be lethal right now. The highest Tau values we've seen so far are 1.84 for Opportunity (Sol 489) and 1.53 for Spirit (Sol 511) .

On the plus side the drop in Tau reduces the power loss as a result of shade within Victoria.
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fredk
post Jun 27 2007, 10:15 PM
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Those numbers are interesting. When the tau increases from 0.9 to 1.5, the direct sunlight ("beam") drops by almost half, while the total available power drops less than 20%. Unless I've missed a square root, that means that a lot of the attenuated direct sunlight eventually makes it to us as scattered light, ie the sky gets a lot brighter.
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djellison
post Jun 27 2007, 10:26 PM
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No - thats what happens, the direct drops, the indirect increases. For 'close ops' to a cliff, you'd want a clean rover, but a filthy sky smile.gif

Doug
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helvick
post Jun 27 2007, 10:40 PM
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As Doug says that is what happens - as the dust levels rise the direct beam insolation falls off pretty rapidly in an exponential decay curve (~exp(-tau) ) but the diffuse light actually rises initially and only starts to drop after around Tau ~ 1.8. The exact detail is I used for the above is from the formulas from this paper by Applebaum and Landis http://ntrs.nasa.gov/archive/nasa/casi.ntr..._1994010257.pdf
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Tom Tamlyn
post Jun 28 2007, 03:33 AM
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Fascinating to read in the Applebaum & Landis paper the discussion of dust accumulation ("There may be removal of dust by wind as well as deposition"), and the possibility of designing solar arrays that could "flap" to remove dust. See pp. 12-13.

How high are the values of Tau for the biggest Martian dust storms, like the one encountered by Mariner 9 in the first months of its orbital mission?

TTT
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dvandorn
post Jun 28 2007, 04:07 AM
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Or, more specifically, what was the greatest tau value recorded by the Viking landers when they endured major global dust storms? Each went through at least two major dust storms, and I know that *some* estimate of tau during those periods has been made.

Also, I know I've seen sequences of Viking lander images showing dust buildup after dust storms. I'd be interested in seeing those again, to get a feel for the kind of short-term buildup we may be looking at for our rovers.

-the other Doug


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fredk
post Jun 28 2007, 04:09 AM
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Spirit's Solar Power Levels Continue to Rise
Another cleaning has occured. Power has risen to 738 watt-hours!! biggrin.gif biggrin.gif
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