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The Storm, Dust storm of 2007
vikingmars
post Jul 22 2007, 08:59 AM
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[quote name='MichaelT' date='Jul 22 2007, 10:06 AM' post='95554']
I had a search for some Viking data of the great dust storm in 1977 to find out what happened to temperatures then. .../... I do not know how representative such a temperature record is for a Martian dust storm, but, it shows that the daily average temperature does not increase. Rather, the diurnal temperature range is greatly reduced. he nightly minimum is higher, but, the daily maximum also much lower. That nights are warmer is certainly a good thing. What about the much lower daily maximum, though? Any ideas?
Michael

smile.gif I confirm, Michael :
Here are your figures of temperatures (Celcius) during dust storms measured by VL1 and VL2 :
5:00 AM 2:00 PM
VL1 -83 -69
VL2 -81 -71

Yes : the rovers will suffer a lot ! sad.gif
Enjoy (if I may say..) wink.gif
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Astro0
post Jul 22 2007, 12:05 PM
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Stu... perfect words as always.
I've been working on a illustration for 'The Storm' and now you've created the words to accompany it.
Brilliant prose. I hope that other UMSF'ers appreciate it as well.

Cheers
Astro0
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tedstryk
post Jul 22 2007, 02:22 PM
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Don Parker's new shots really show how bad it has gotten.



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diane
post Jul 22 2007, 04:33 PM
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Playing what-if: What if the batteries go to zero, but the temperature doesn't go low enough to damage the electronics. Would it be possible to restart the rovers when power is available? If power goes to zero one or more times, would that in itself be damaging to the batteries?
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djellison
post Jul 22 2007, 04:36 PM
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I don't think that's a damaging scenario - Li-Ion's don't have memory issues like some older technologies - but I think the tie in is that a little bit of battery activity is possibly required to keep them warm enough to avoid damage.

Doug
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Guest_Sunspot_*
post Jul 22 2007, 04:40 PM
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Guests






Is the next planned communications session sometime today?
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djellison
post Jul 22 2007, 05:41 PM
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http://trs-new.jpl.nasa.gov/dspace/handle/2014/39793

Very interesting stuff - well worth reading.

Doug
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Mark Adler
post Jul 22 2007, 08:29 PM
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QUOTE (diane @ Jul 22 2007, 09:33 AM) *
Playing what-if: What if the batteries go to zero, but the temperature doesn't go low enough to damage the electronics. Would it be possible to restart the rovers when power is available?

Maybe.

The big problem there would be the loss of the mission clock, which of course runs off the batteries. (It's connected directly to the batteries, with no intervening switches.) Upon complete discharge and a subsequent recharging and reboot, the clock would be reset to a known value, but with no relation to the current time. All planned wakeups and communication windows which are specified by the value of that clock would then be lost. You would have to rely on solar array wakeup and and fault mode communication windows to get commands in to the X-band radio to try to set the clock and reboot.

It's never been done, but in theory it should work. It might take several sols, since you don't know when it will wake up, you don't know how graceful the last shutdown was (probably not very), and you don't know what fault mode(s) it might be in. The system wasn't really designed for this -- during development, the loss of the mission clock from a complete battery discharge was an accepted loss of mission failure mode. The probability of such a failure in the first 90 sols was considered very small. Still, there's isn't anything that I'm aware of that would prevent such a recovery.

The Spirit sol 18 reboot cycle was also an accepted loss of mission failure mode, but we had enough back doors to recover from that one anyway.

By the way, it's so dark currently at Meridiani, Opportunity isn't getting enough current from the solar panels at any time during the day to trigger a solar array wakeup. While the batteries can recharge at a low light level, it requires more light than that to wake up the rover sans alarm clock.

QUOTE
If power goes to zero one or more times, would that in itself be damaging to the batteries?

It would degrade the batteries slightly, decreasing their lifetime. You try to keep them above a 40% state of charge to maximize lifetime. (Full discharging doesn't help Li-ion batteries like it does for some other battery chemistries.) However these batteries have been doing so well, I suspect there would be little impact from a few 100% discharges.
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djellison
post Jul 22 2007, 09:27 PM
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Thanks for the update Mark.

If the circuitry is such that it can charge even without an array wake up - will each sol be, technically, power positive?

Doug
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diane
post Jul 23 2007, 12:00 AM
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Mark, thanks for a very informative answer!
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Mark Adler
post Jul 23 2007, 03:28 PM
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QUOTE (djellison @ Jul 22 2007, 02:27 PM) *
If the circuitry is such that it can charge even without an array wake up - will each sol be, technically, power positive?

Yes, if there's enough energy to run the clock, the battery controller board, and whatever heaters want to come on (at the time they want to come on), then that sol will be power positive. Any excess energy will begin to bring the batteries up to charge.

If the mission clock is reset, then we will have to wait until somesol when the solar array current gets to two amps for at least 10 to 15 minutes, at which time there will be a solar array wake-up of the computer. The last peak array currents on Opportunity were around an amp.

One thing I don't know is how gracefully the battery controller board will turn on given a slow rise in bus voltage from the solar panels.
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djellison
post Jul 23 2007, 04:21 PM
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Ahh - so actually - things are better than I thought they might be. Still a bit crap - but not quite as doom and gloom as I thought.

I'm going to plough through the JPL TRS search again and see if I can't understand and interpret this at a system level a little better - BUT - I think this may be the sort of flow of things as I understand them. I'm still not sure whever the cut-off of deep sleep is though.

Obviously ITAR has both hands firmly around the neck of any detailed info on this stuff - BUT - from here :
http://hobbiton.thisside.net/rovermanual/
specifically here
http://newport.eecs.uci.edu/impacct/d_rese...-PACC092600.ppt - very very out of date but I'm sure the figures are still roughly accurate
Suggests the 'battery charger board' ( I assume the battery controller board which you refer to) pulls 200mW - <5Whrs / sol.

Rovers are complicated. smile.gif

Doug
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ElkGroveDan
post Jul 23 2007, 04:51 PM
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QUOTE (Mark Adler @ Jul 23 2007, 07:28 AM) *
One thing I don't know is how gracefully the battery controller board will turn on given a slow rise in bus voltage from the solar panels.


Mark, are these things you can test with the spare vehicles and equipment you have at JPL, so you'll know what to anticipate? Do you have a cold facility?


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Tom Tamlyn
post Jul 23 2007, 06:07 PM
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Cautious optimism as reported in space.com (italics added)

Mars Rovers Weather Worst of Dust Storms


>Steve Squyres of Cornell University, the lead scientist for the Mars Exploration
>Rovers (MER) project, said that both Spirit and Opportunity are in
>"excellent shape" based on a radio transmission received this morning.
>
>"Both came through the weekend beautifully," Squyres said in a telephone interview.
>"They were both power positive over the weekend, meaning they were generating
>more power than they were consuming."
>
>The amount of sunlight penetrating the dust-choked martian atmosphere has
>increased slightly in recent days, and the batteries of both rovers are fully charged,
>said Michael Meyer, lead scientist for the Mars Explorations Program at NASA
>Headquarters in Washington, D.C.

***

>"At its worst, tau was a little over five [for Opportunity]," Meyers told SPACE.com. "
>It now has dropped down to a little less than four."
>
>The tau value for Spirit, hunkered down half a world away from its twin,
>has dropped slightly and is currently just less than four, Meyers added.

Of course the storm could get worse again, as the article mentions.

TTT
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jaredGalen
post Jul 23 2007, 06:20 PM
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With a Tau of 5 and <1% of sunlight getting to the surface, how much worse could it get? What would it take to really knock down diffuse lighting worse then it has been and to a truly catastrophic level?

For solar reliant machines, these rovers really are marvels of modern engineering, coming out power positive after what was the worst of the storm to date. A credit to the people watching out for them.


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