I've been keeping an eye on the sundial images looking for signs of a cleaning event. I've noticed some changes in the latest to be downloaded although they may be due to changes in the lighting.

Click to view attachment
A : clean patch at top of circle streak at bottom
B : increased contrast from dust left behind next to mirror
C : clean patch next to wire

Also note the missing clumps of dust on the deck
Click to view attachment

A broader view show a contrast between sol 1221 and 1227
http://207.7.139.5/mars/spirit/navcam/2007...I4P0165L0M1.JPG
http://207.7.139.5/mars/spirit/navcam/2007...00P1914L0M1.JPG

Has anyone heard if there has been a change in the power levels?

The lighting would appear to be almost exactly the same, as the shadow positions are almost exact.

I think you are correct about the changes you point out. I imagine the overall cleaning effect would be small, though.

Just saw the latest images and rushed here to find out what more knowledgeable people were saying about it. But my impression was also that she's had a cleaning event.

The definitive answer would come in the form of a boost in power.... waiting... hoping...

Yes! We're above 600 Whr!!

http://marsrovers.jpl.nasa.gov/mission/sta...ll.html#sol1219

When you look at the rocks in specific and the surface in general, it sort of makes sense that an object like a MER would get wind-cleaned several times over the course of a Martian year.

If there was nothing happening on this surface except steady dust accumulation, the local surface would be buried in millions of years' worth of dustfall. The winds have to be capable of moving the dust along, or else the rocks would have dust caps and be buried in airfall dust. The fact that the rocks are not generally dust-covered (and are in fact aeolian-sculpted) and the soil is not completely covered with airfall dust argues for enough wind to blow the dust off the rocks at a greater rate than the dust falls out of the air.

Of course, no one could have known if the periodicity of deposition/deflation events would be timed well enough to keep a solar powered rover working over a long haul. And extreme dustfall events, like global dust storms, would still probably doom a MER. But, on average, what we observe on the scene suggests an environment where solar panels will be cleaned just slightly more than they will be dirtied.

If you want more proof of this general charateristic of Mars, look at the HiRISE images of the Vikings. They retain some of their blue-white coloration to this day, which means they have been cleaned more than they have been dirtied. It's only a gross confirmation, but it suggests that objects on Mars won't become (or remain) completely dust-covered on the scale of decades to centuries.

-the other Doug

The news we've all been waiting for!

Oh, yes, and I forgot to add: Above 600 Whr!!!! Hallelujah!!!!!!

-the other Doug

This is great news! That great a percentage increase is impressive, considering just how dusty Spirit was.

Here's a pancam comparison between sol 1213 and 1223, showing one spot (also visible in alan's images above) partially cleaned by the wind:

Alan: You're the man with the first good news in a long time. Congratulations.

I recently noticed some DDs apparently moving toward Spirit, which seems to be an unusual direction for them.

Very good points, O'Doug.

Most excellent news.

OK where's Helvick? We want to see that chart now!

Looks like a self portrait was put in work yesterday after the cleaning. I'm REALLY out of stitching practice

The solar cells looks patchy, like the wind cleaned some parts and left clumps of dust behind. This is in contrast to the overall hazy appearance of Spirit's deck previously.

Great news about the power levels!

We're well past the edge of my charts now and my extrapolations would appear to have been too conservative. I had thought she was at slightly below 400whr prior to this cleaning event but it appears that she was actually about 100whr higher. This is probably due to errors in the insolation\atmosphere model that I used (which is based on pre pathfinder data IIRC) and an over aggressive estimation of dust deposition.

I'll rebuild the chart and try to adjust for the errors to see what that produces. It will take a day or two though to dust them off, so to speak.

Great news though - this gives her another respectable extension on her life expectancy.

Well, it's got to be asked : Was it a DD or a wind gust that cleaned Spirit?
Do we know if this one happened at night, or during the day?

I was actually wondering about that. How finely can they pinpoint when the cleaning event happened? With what time frequency are the solar panel outputs measured during the day? Obviously it isn't measured at night, so if it happened at night, I'm guessing all they can say is that it happened at night. When were the pancam images taken that bracket the event?

--Emily

This is the best I could get out of Autostitch

Click to view attachment

Yeah -- you can see she's cleaner than she was, but it wasn't a full cleaning event. The panels near the ends of the wings are still pretty dirty.

Still, any cleaning whatsoever at this point is a gift, and I accept it gladly...

-the other Doug

As I recall these events aren't isolated ones. I bet we'll hear about another one in a few weeks bringing it up to 825 whrs. Didn't we reach a point the last time where they were keeping her up all night to shed excess heat from the return to 900 whr?

I hope your prediction is correct, but wasn't Spirit at a higher, more windy elevation when the previous series of cleaning events took place?

TTT

Yep, she was right in a pass when she get the "big" cleaning event which, to me, think logical. By any mean, yes, she was much higher.

"I doubt they get engineering data at a high rate all the time the puter is powered up. Maybe not much or any when it's more or less on standby. Generally, I think events will probably happen between blocks of data.

Anything after sunset and before sunrise can't be detected by solar power changes regardless of whether the rover is taking data or not!

I've asked about the engineering data before (and I was specifically looking for the periodic Solar Panel output currents) but was told that that's not going to get published. As I understand it engineering data would have to be stringently reviewed to make sure it didn't breach ITAR and that would be too much paperwork for not enough end user benefit and to be fair that was a perfectly reasonable answer.

I haven't been able to find any data on the sampling period for this either so I can't say if it is taken more frequently than once per day. Prior cleaning events have generally been vague about the precise timing - generally indicating that power levels have increased between sols so it is possible that only one sample measurement is recorded per sol.

That doesn't make sense to me. I would have thought that engineering data consumes a relatively small amount of bandwidth compared to images and spectrometers. I think I appreciate that there are many sensor feeds, but surely they monitor panel output more often than once/sol! Where am I going wrong?

I was looking at the picture above and I noticed the hinges when a thought hit me. Would closing the solar panels and opening them back up help knock the dust off. Maybe they could even shake them a little.

The only problems I see are, one- dumping the dust elsewhere on the rover. Two- the possibility of not being able to open them again.

Pete Theisinger was asked about closing the solar panels in an effort to get rid of dust on a webcast that I've seen. (I believe that it was during the Q&A after a von Kármán Lecture given before the rovers landed.)

In light of the risk that the panels would not reopen, he said (to paraphrase) that he could not conceive of a circumstance that would justify taking such a risk. And of course the dust is "sticky," so the potential benefit might be very little.

TTT

I'd find it hard to believe that there is even a way to do this.
I would assume they were designed to lock in the open position.
I'm sure it would take a whole different design, with different latches,
and motors to accomplish this. The intent was to open the panels
and leave them open. The design would have been the minimum
required to do this reliably and nowhere near as complex as that
needed to reclose and reopen them.

I don't know if they lock in place or not. I would probably design them to do so if I was in charge.

If they don't perhaps they could try shaking the dust off as a last ditch effort.

However, when Spirit does finally die, I would hate to see her die with her panels stuck up. Doesn't seem fitting for a rover that has done so much.

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.

ITAR again. Well, it could be helpful to build solar powered nuclear bombs roving around. I am sure this could be helpful information for the ExoMars designers.
In the long term, ITAR will reduce the capabilities of the US aerospace industry to be competitive. Sorry, I had to say this.

Analyst

Home plate? I want them to see her in the Promised Land!

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!

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

Doug

Must be getting windy, a few more clean patches are visible between sol 1231 and 1234

Click to view attachment

All this cleaning might be timely but hopefully not fruitless, big storm a comin'....maybe.

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

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

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.

Brian

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?

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:



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.

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.

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

Doug

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

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

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

Spirit's Solar Power Levels Continue to Rise
Another cleaning has occured. Power has risen to 738 watt-hours!!

Most excellent indeed.


The new Mars forum question:

"How many MERs will be working when MSL lands?
0, 1, or 2

Tau values were made by Viking Landers based on pre-programmed solar brightness observations. When the sun wasn't visible at exposure settings used, the values are lower limits. I *think* values of optical tau over 6 were indicated. Scene brightness levels dropped DRAMATICALLY, with darker horizons than higher skys and with more or less no shadows. Many/most of those images were badly underexposed Of course, once new exposures were selected and upllinked, the opacity dropped a lot, and the images were badly whited-out.

Thermal infrared tau values were measured from orbit with the infrared thermal mapper, a multi-channel radiometer and are about 1/10th (as I recall) the optical values.

Pre-Viking data are poor. Mariner 9 data was re-analyzed but I don't recall results and the worst of the storm was 2 1/2 OR 3 MONTHS before Mariner arrived.

I don't have precise data but again there are approximation formulae in "Solar Radiation on Mars - Update 1991" J. Applebaum, G.A. Landis. (NASA Technical Memorandum #105216) for both of the 1977 global storms that yield optical depths by latitude and LS. Both of these peak at around 5.

That should equate to around a 70% loss in insolation which in turn should equate to about 1.5-2 f/stops from an exposure POV. That would be noticable shouldn't have caused dramatic under/over exposure of images so I wonder if the model underestimates the values? Any ideas?

This should be enough for the next winter (on a slope), shouldn't it?

Analyst

738 Whr means she is still losing about 25% due to dust. Last summer at peak when she was generating 956 Whr the dust loss factor was around 5%. So she's getting cleaner but I don't think that surviving the winter is guaranteed yet. She bottomed out at 280Whr in mid winter at Low Ridge so right now we'd be looking at around 220Whr for the minimum next winter assuming nothing else changes (and dust deposition follows last years pattern).