This may be viewing Mars through rose-colored glasses, but Our Intrepid Explorers have been though several tight situations and they've managed to survive. I'm sure they'll weather this dust event. And if not, it's ben a good ride...

--Bill

Anyone unfamiliar with Vikingmars's work - or wondering "how he does it" should check out his stunning book "Visions of Mars", which is truly a thing of beauty. If "Roving Mars" is The Book for engineering types, then Olivier's book is The Book for all us romantics and frustrated artists out here.

Been working on this for a while, hope some of you like it...

THE STORM

The Sun has almost gone now,
fading from my sight behind
a molasses-murky sky, and Earth’s
post-sunset sapphire spark
is just a distant memory.
I cannot move, and drooling over new Victorian vistas
must await until Sol’s golden glow
warms my frozen heart again for I am cold,
so cold, and feel ten thousand sols old
as I stand here, fearful that the dust I see
fouling the sky above me will fall suddenly,
smothering me, Mars murdering me
with her deadly pillow of particles
pushed down against my face –

But I am not dead yet, and although
I itch insanely, and would scratch myself
to wreckage if I had been built with hands
I shall stand here, sentinel-still, until
the sky begins to clear… or I hear
my stubborn heartbeat start to slow,
and then I’ll know my stay
on Meridiani’s rolling plains is at an end
and you, my faithful friends Out There,
must promise not to mourn for me,
but celebrate my life and all the wondrous sights
we saw together. Never think
of me with sadness, but be glad
we walked this world hand in hand,
cresting wind-carved dunes, swooning
at the sight of sunlight painting
Endurance’s epic walls,
falling to our knees in awe as
Victoria’s rippled floor opened up before us..!

But trust me, while a single warming spark
sputters on inside my shivering heart
I will prevail, and as the dust clouds sail
across my sky I shall just close my eyes
against the wind and bide my time,
for Barsoom gloomiest, darkest day
is still a thing of beauty… And if I am to die
here I will still have lived a life
far longer than was planned in this land
of rock and stone. Meridiani is my home,
and if Victoria is to be my lonely
tomb then there is no view I would rather see,
as I drift into my final, well-earned sleep.

© Stuart Atkinson 2007

I had a search for some Viking data of the great dust storm in 1977 to find out what happened to temperatures then. I found this interesting page by J.E. Tillman, which contains some interesting figures and links to viking data: http://www-k12.atmos.washington.edu/k12/re...e_overview.html

It also contains a figure with the temperature at the VL 1 site from the beginning of the dust storm:

(courtesy of NASA/JPL)

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

ps: Nice poem, Stu!

As long as the rover is internally warm enough, then there shouldn't be any component failures - it doesn't really matter how hot it gets - as long as it's not too hot.

The challenge is this. Is combination of whatever energy they are using inside the WEB plus the 8w of RHU's (two on the rem, 6 on the bettery) enough to put enough heat into the WEB to keep the night min.temp. above whatever temperature would cause a failures?

Given that the use of deep sleep has been a regular thing - and that survival heaters were used only during the very coldest nights with Spirit - and that graph suggests 15-20 degrees warmer minimums - then I don't see it as a problem.

[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

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 !
Enjoy (if I may say..)

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

Don Parker's new shots really show how bad it has gotten.

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?

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

Is the next planned communications session sometime today?

http://trs-new.jpl.nasa.gov/dspace/handle/2014/39793

Very interesting stuff - well worth reading.

Doug

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.


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.

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

Mark, thanks for a very informative answer!

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.

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.

Doug

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?

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

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.

Suppose that the storm ends and the high air-born dust just falls with the wind dying down at the same time. How thick would the layer of dust be on the Rover's solar panels?

That's the most promising piece of information IMO :-). If they can keep batteries at full charge after these sort of conditions, it must take weeks of tau 5.5+ to really danger the rovers.

Extraordinary. People have been asking me 'how long can they hibernate' - and under these sorts of conditions, it would seem the answer is basically however long they need to. The systems design - although never designed to - can handle this beautifully.

Doug

Superb.

MarK, thank you for the fantastic info and insights.

its great to hear that the "line of death" is much lower and a indeed much more complicated than thought just a week ago!

and the rover teams accomplishments even more impressive !

Well, here is a NASA update from today July 23 with a few more details. next com session set for Thursday July 26

NASA Mars Rovers Braving Severe Dust Storms
July 20, 2007

Updated July 23, 2007

NASA's Mars Exploration Rover Opportunity sent signals Monday morning, July 23, indicating its power situation improved slightly during the days when it obeyed commands to refrain from communicating with Earth in order to conserve power.

Dust storms on Mars in recent weeks have darkened skies over both Opportunity and its twin, Spirit. The rovers rely on electricity that their solar panels generate from sunlight. By last week, output from Opportunity's solar panels had dropped by about 80 percent from a month earlier.

Rover controllers at NASA's Jet Propulsion Laboratory, Pasadena, Calif., commanded Opportunity last week to go into a very low-power state and to communicate only once every three days. The rover transmitted a small amount of information today. Next scheduled transmission will be Thursday, July 26, though controllers may command Opportunity to send information on Tuesday, July 24.

Meanwhile, communications from Spirit over the weekend indicated that the sky had cleared slightly at Spirit's location on the other side of Mars from Opportunity.

"The outlook for both Opportunity and Spirit depends on the weather, which makes it unpredictable," said JPL's John Callas, project manager for both rovers. "If the weather holds where it is now or gets better, the rovers will be OK. If it gets worse, the situation becomes more complex.

The MERs continue to shine as examples of truly superior systems engineering, all right. If I wasn't so far along on my topic already, I'd change my thesis subject to them. Maybe one of my classmates who are still looking for an idea might be interested.

Absolutely incredible machines, these little rovers. Blessed with a special genius.
I am in awe..... they are our Martian Voyagers... always striving to phone home........

Thanks Stu for the prose. Thanks Mark for the insight and updates.

Craig

It would be really cool if Spirit (since its situation is a bit better) could take a 3 color panorama right now. It could be heavily binned, since the purpose would be to show the overall scene in the dust storm, not resolve fine details. But whether it was a partial or a 360 degree pan, it would be a really nice addition to the MER collection.

I'm tempted to give in to a small sigh of relief, but the last time I did, the storm regained strength. If we do see yet another peak on the graph, I won't be nearly as worried as the last time. It's absolutely amazing that Opportunity was power positive through this last peak.

I don't remember anyone posting a link to Mars Oddyssey's Themis monitoring of the dust storm. I discovered it today while looking for news on the storm.

Mark's updated the figures a little

We're now at the point in the decay where during the last decay - we had another outburst.

Doug

Best news for a long time!

Anyone else noticed this "stain" in the centre of Oppy's tracks as seen on the new pancam shots..?

Click to view attachment

I know she's getting on a bit now, but I hope Oppy hasn't developed any incontinence problems...

At least the sky looks a bit lighter tho...

Click to view attachment

Looks like the removal of a lighter coloured crust rather than any sort of staining to me. Some MI's would help.

The last horizon survey image ( which I think is the one you've posted there ) was actually from 1235, 8 sols ago - and is infact - when calibrated - the darkest slice of this cake
http://marsrovers.jpl.nasa.gov/gallery/pre..._horizon_br.jpg


Doug

Was using the word "stain" v v loosely. Wasn't actually suggesting that Oppy had.. well, you know...

The last horizon survey image ( which I think is the one you've posted there ) was actually from 1235, 8 sols ago - and is infact - when calibrated - the darkest slice of this cake

Really? Took it off the latest set of pancams released. Oh. B****r. I'll get me coat.

Well - I think it is - what's the actual file name of any one of the three files involved? Somewhere out there ( and I can't find it now..grrr) is a website where you drop the file name in and it converts it to the information for you. That - or using MMB - will tell you when the image was taken.

Doug

My bottle's half full, Doug.

The Mariner 9 dust storm took several weeks to clear - given that this storm isn't as intense, I wonder how long we'll have to wait until the high Tau conditions tail off. Any thoughts?

Andy

http://www.tnni.net/~dustymars/Observing_Mars_6

Since 1971, the year of the "Great Dust Storm of Mars," the ALPO Mars Recorders have suspected that these disturbances came in pairs. We have seen that in 1971 a major dust storm occurred on 213° Ls, followed by a "planet encircling" dust storm on 259° Ls. Again, in 1973 a major storm began on 244° Ls and was followed by a "planet encircling" storm on 300° Ls and [Martin, 1974]. The Viking Lander recorded two "planet encircling" storms on 204° and 268° [Tillman, 1988]

This is only the first big storm this season. At present, it's 282° Ls. And the big 1971 storm began to dissipate by 314° Ls. Still a long way to go...

Almost entirely off-topic: Still A Long Way To Go - an uncannily appropriate lyric.

It's truly extraordinary that both rovers are fully charged after the last couple of weeks. Unless the dustfall at the end of the storm covers the solar panels, it looks like MERs are virtually immortal - if they can survive this, even a prolonged, full-on global storm might be survivable.

Thanks for the info, OWW...

So now the question would be, once this storm's abated, do the Opportunity planners take a dip into Victoria, with the risk of getting caught somewhere less pleasant towards the end of a potential 50-60 day window, or sit still for two months with at least the potential for no more bad weather (is storm #2 chance or certainty?) and the risks that accompany an aging rover?

Andy, glad to not be decision-making.

I'm not a MER mission planner, nor do I play one on TV, but I would not hesitate to get in there and get valuable science done as soon as conditions permit. A follow-up storm might or might not happen. I don't see them being that far in that they couldn't quickly retrace their steps and get back out unless a massive storm suddenly took hold right in this area. I haven't seen that kind of bad luck yet on this mission (touch wood).

Brian

Why would being in the crater be worse than being outside?

Because being flat on the plain you get the maximum indirect illumination of the arrays by the dust. On a slope - that will drop off (which every direction the slope is)

With clear skies and 800 Whrs, it doesn't really matter given that the slope runs down to the East (better power in the morning, but lower power in the evening) but with almost all the power currently coming from the difuse route - you want to be flat as you can.

Doug

Reading over the original mission description, I found this chestnut:


How things have changed from then!
The bestest words I have heard this last week are not "Deathly Hallows" - They are "Power Positive!" *




*Though it does sound like some cheesy self help course or weightlifter diet additive when you say it by itself.

I expect it wouldn't have amounted to a great loss of power if Oppy had been on the planned ingress route to the white layer. Being inside the crater would mean that the apparent horizon as viewed from the rover would be higher than the true horizon, so less sky would be visible. But the white layer is only 4 metres or so vertically inside the crater. The nearest cliffs to the expected ingress route are on Cabo Verde, about 30 m away (recall that they don't plan to drive near any cliffs!). That means (allowing for the height of the solar panel deck above the ground) that only 6 or 7 degrees of the horizon towards Verde would be obscured. Similarly, because of the tilt of the crater slope, a "sliver" of sky very roughly 15 degrees maximum width at the near rim and tapering to zero width at the far rim would be obscured.

You could imagine working out this way what percentage of sky, or how many steradians, would be obscured at the expected white layer study sites. No doubt an accurate elevation model would help here. I very crudely estimate a fraction 0.13 of the sky would be obscured at the white layer.

But there are more factors than just solid angle obscured. The solar arrays are much less sensitive to sky illumination from near the horizon than from overhead, just because light from near the horizon strikes the arrays at a glancing angle. Thus to estimate the power loss you must multiply that 0.13 fraction by a small geometrical factor, which is going to be something like the sine of the typical altitudes of obscured sky - that works out to another factor or order 1/10. Also, from the latest pancam images the sky appears to grow darker near the horizon. Therefore you get down to the 1% order of magnitude for total loss of power at the white layer.

Of course, if levels are truly critical, then even a couple percent reduction (like from 100 Whrs to 98 Whrs) could conceivably be fatal. Still, this likely wouldn't have been very important. I could see us entering Victoria soon after power levels allow mobility.

But, when the storm(s) end, wouldn’t more dust settle on Oppie inside the sheltered crater than on the rim? And wouldn’t there be less wind down there to remove said dust?

This is interesting fredk. On a much lighter tone but using your idea, in the absolute, we can also demonstrate that having put solar cells under the solar panels could have brought some energy too! ...and even basicaly having put them anywhere on the rovers.

Does anyone have quantifiable differences?

To the best of my understanding, the difference in power would amount to about 3.5% if it were all diffuse.

Updated: I didn't read Fredk's post prior to this response. It seems consistant with my estimations.

Months, not weeks...
The storm started in Aug or Sept 71. When Mariner arrived in November, most of the surface was hidden except for south polar cap and the top of the Tharsis volcanos and Olympus. Craters were visible as bright circular spots due to increased scatter from the deeper dustier atmosphere compared with adjacent higher terrain, as was Valles Marineris. After proving that their pre-planned mappign and observation sequences were near worthless, they replanned repetitive storm observation sequences and mapping tests to see how things were clearing. They finally started systematic mapping of the planet in January 72, starting with the least dusty high southern latitudes and progressively moving northwards.

Are they calling this a global event yet?

I haven't heard that term used in public yet, Ed. This storm seems not to have engulfed the entire planet so far. It has, however, encircled the planet.

The Odyssey Themis dust storm monitoring page has been updated with an atmospheric opacity map for July 22-24. Per the latest map, it appears that opacity has improved somewhat for both rovers. But it's not obvious yet that the storm is dying as of Opportunity sols 1243-1244.

Big storms used to be called global, but Viking and later data showed that that was not strictly true as polar region dust levels are low enough the surface remains visible. Some papers <late 80's?> called the 1971 greatest-ever storm as truely global, while calling other storms as "globe encirclig"

Most pre-1971 storms were not observed well enough to make a clear distinction, and it's likely storms occured during perehelic solar conjunctions and the long periods when Mars is on the far side of the sun and until CCD imaging and advanced amateurs, was essentially not being observed at all.

The basic fact is that the historical record of storm statistics stinks.