Interesting mix up of terms there - Tau and Dust Factor are not the same thing, looks like someone left out part of the sentence.

Remember, too, that we're not just talking about a pretty straight-line graph in which the amount of dust entrained in the atmosphere relates directly to the amount of dust deposited on any given surface. There are a lot of microclimatological effects right along the surface that greatly impact dust deposition rates. If we were to park Spirit on top of El Dorado for a winter, for example (and I know, it would never happen, it faces the wrong way, etc.), you'd likely never survive because the hills force a turbulence that drops dust out of the air selectively onto the El Dorado formation.

IMHO, Spirit spent last winter in a place that tends to collect a little more dust than other places within reach. If she can claw her way up the side of a hill that faces into the prevailing winter winds, as opposed to sitting in a "deposition sink," she might have a better shot at surviving her next winter. But if she stays exclusively in the Home Plate area and doesn't get very far from it, the deposition rate may be just high enough to kill her without an extraordinarily vigorous cleaning event just before the onset of winter.

-the other Doug

If Spirit makes it to next winter, I think they'll take
a lot more care getting her into the best position
possible, as opposed to the rushed job last winter.
I wonder how far the positioning last winter was
from "perfect", how much better could they do
strictly from an angle-to-the-sun standpoint.

They didnt want to do a rush job last time - remember they were trying to get to McCool hill which would have been amazing - but the stuck wheel, and then the Tyrone sand trap...things went against the rover so they had to get somewhere, fast.

Doug

I didn't mean to imply that they planned it that way. I'm presuming
that the result was a less than optimal, but still adequate, positioning
for wintering. My question is, how much better could they do next
winter in terms of positioning for solar energy gathering? Is there a
lot of room for improvement, or did they get pretty close to optimal
positioning in spite of the difficulties last winter?

Well - with a stuck wheel they can't really climb onto the sorts of slopes that would be much better than Low Ridge haven. 20-25 degrees would have been better I would have thought - but the rover just can't get to that sort of terrain any more.

Doug

Even if the slope is rock with no significant sand to drag through?

Brian

I'd say so, yeah. You drop not only 18% of your traction, but add a whole lot of drag even on rock. Slightly moot point given that there isn't a lot of exposed rock without sand involved near Spirit.

On the other side of the planet they've said that if they go into Victoria, then have a wheel fail while inside, it would be very hard to get out again.

But fortunately getting to a steeper slope may not mean having to drive uphill. If we find ourselves still on Homeplate by late fall, it should be easy to drive from the top of HP partly down the north edge, which would face the right way. I don't recall any figures for those edge slopes, but I suspect they're better than what we had at Low Ridge haven - was that only 10 degrees?

Strategy for getting Spirit on 25 degree slope:
Climb a rise up a less steep slope, then
descend on the steep side and stop.

Looks like good slopes in yellow circle.
Spirit should be there in time to winter.

Click to view attachment

Right!

The best they could do for the day that insolation is lowest ( around Ls 95 ) is to tilt to ~34.6deg facing due north , that would result in about 31% more power than a horizontal panel on the same sol.

The initial tilt angle at Low Ridge was 10.8deg which gave them about 15.7% more power than a horizontal panel on that day.

34 degrees is probably way to dangerous but a 20deg slope should be possible and that would yield a 25% increase in power.

The exact improvement varies over time as the suns declination changes - the above numbers are really only good for the weeks around mid winter.

That's a good time to have the maximum improvement!

The subject of tilt begs the question, why don't the panels pivot to track the sun? I'd never thought about that. In the design process, if there's already a motor to unfurl the panels upon landing, couldn't that same motor rotate the panels and shake off dust in the process? I'm sure they thought about it, but I'm curious about the pros and cons.

Apologies if this question was addressed in an earlier thread. I'm a newbie, so I'm just learning how to read

The dust probably wouldn't come off if you tilted the panels - it's fairly clingy. The motors only work one way ( I think) - I think they lock in place on deployment. And of course, what do you do if you end up with an array stuck up at an angle.

Doug

Further to the same point, the deployment motors were only expected to work once. Designing and building them so that they would have continued to operate reliably in the Martian environment throughout the mission would have been something else.

TTT

Ahh, that's the part I wasn't thinking about -- that, and using the motor continuously probably drains more power than you'd gain from tracking the sun. Then, at some unknown point the motor dies, and what if it freezes at a sunrise or sunset position. Well, I'm just glad I wasn't making that particular decision during the design process

Cleaned Again: Spirit Self Portrait

http://marswatch.astro.cornell.edu/pancam_...ent/adeck3.html

woaw.. she looks good!

Nico

But she could look better! Come on you devils/angels! You missed a few spots.

I never appreciated how variable the dust covering could be from panel to panel until I saw that pan, alan....

Looks like the cleaning has been more efficient in the center panels (or maybe they were cleaner to begin with?). If it is turbulence that helps clean the panels, maybe it would be a good idea to have "turbulence provokers" on the sun panels of future rovers? Maybe wispy stalks standing up from the rover deck, thin enough to not cast shadows but still churning up the air. Just brainstorming here...

Being from sol 1229, I think that self portrait was after the first cleaning of this season. The second cleaning, which boosted Spirit's output to 50 W-hrs greater than Opportunity, was on sol 1233. We have gotten only a few navcam images of parts of the deck since then, so it is difficult to see what may have changed.

From the latest Planetary Society report, this description of the sol 1224 cleaning event:

Yes, only a devil would tidy up so haphazardly.

Looks like some guys will finally get actual data to verify their simulations

Dust from the storm in Meridini appears to have been transferred to Spirit's side of the planet.

The shadows are getting weaker

Click to view attachment

Scattered sunlight is visible in the navcams taken recently

Click to view attachment

sol 1204 - 1244 L2 comparison of Husband Hill:

Horton, that is dramatic. A layer of dust almost completely hides the dark sands. And in just a few days. Wow

Bloody hell! The way the whole area beyond the middle-ground horizon is softened makes me think we're seing one of the DD's that deteriorates into just a swirling body of dust heading across the foot of El Dorado. Well spotted.

Doug

Ah, that explains why the color images of the left and right sides of El Dorado are so different.

Ah, indeed:



The right frame is 98 seconds after the left -- which seems to be clearer -- but still dusty.

SO, a dust devil was moving right to left?

I'd say left to right. The gust could easily have passed before the right side was imaged.

Interestingly, I'm pretty confident you can see another gust (maybe the same one?) just below the foreground "horizon" in this L7 frame. That foreground horizon is about the same distance in this frame, but it looks much darker than in the previous frame I posted.

All this really makes me wonder what it would be like standing there with the rover. We know the rover must only image a small fraction of all dds/gusts that pass by. How dynamic or "alive" would the air be at 1pm on a summer afternoon? Would something be happening somewhere around you at all times?

Well noted indeed, and what a catch.

I was just going to note that the 1244 view that Hort posted looked less to me like deposited dust and more like dust being raised and actively blown along on the wind at the time of the picture. I'll say -- miss one day for lack of broadband and you miss out on worlds of adventure!

Cheers,


-- Pertinax

Hi All,

Is there a website of returned engineering MER data (similar to returned image data) ??

It would be nice to see the per sol: Wh, temps, amps, -etc

tnx

Sorry All, I was away and missed the whole thing, DD & big storm. May be you've talked about it but as I'll need 2 days before been updated on the whole UMSF , I'd better ask this question now : can the event that have cleaned Spirit as described by SS be a premice of the Big Storm instead of a "normal" dust cleaning event ?

Yes - cleaning is usually thought to be due to high winds

Dust storms are thought to cause high winds

Thus - major cleaning and dust storms tend to be closely related.

Maybe it's something to do with the change in illumination - BUT - Opportunity looks utterly A1 clean right now.

Doug

I don't know how it works, a meteorologist can help on this, but I was thinking of a kind of depression created by the storm that would have led it by a few hours. Does it make sense?

Giving another talk later this week and would appreciate advice on this pic I've made for it...

Click to view attachment

With all the extra atmospheric dust is the sky too blue? Not blue enough? Not going for 1000% scientific accuracy this time, just wanting to try and put across the beauty of Mars...

Just checked out my window here on Mars, and yes, it looks about right.

Stu, I would make the sky bluer around the sun. It is, after all, a Martian sunset.

I noticed that the sundial shadows are most distinct in the L6 image when the base image was taken - which means the direct light was bluer than the indirect light.

Thanks hort, bluer it shall be I was just unsure about the optical effect of all the "storm dust" in the atmosphere, you know?

Wish I could see that for real... how cool would it be to see that Sun sinking behind those hills and then see Earth shining in the twilight...

Hey, just noticed this is my 1000th post!

New pics on the exploratorium for Spirit

Look at the panel :
http://qt.exploratorium.edu/mars/spirit/na...CMP1665L0M1.JPG
It seem to be cleaned, isn't it?

Yep, another cleaning event for Spirit's solar panels.

Spirit's forward hazcams weren't so lucky

http://qt.exploratorium.edu/mars/spirit/fo...CMP1214R0M1.JPG

Yikes! Thats a spectacular and unique amount of dust accumulation. I wonder what percentage of total erosion and deposition occurs during these periods of near global dust storms?

Brian

Looks like the winds picked up sometime between 1247 and 1248, which might have also been the event that dusted up both front hazcams.

Here's the capture magnet, in L4:

good eyes slinted

A comparison between 1238 and 1250

Click to view attachment

By examining the circled areas you can tell that the latest cleaning event the wind blew the dust in the opposite direction as before.

The Silica Valley tracks have been virtually wiped out in the last couple of weeks. Amazing stuff.

Doug

That raises the question of whether there would be any useful advantage in having dust covers (or some equivalent) for cameras in future (long-lived) Mars landers like MSL. Or would such things be more trouble than they were worth? (Eg one more thing to break down on an aging lander.)

======
Stephen

1200 sols without significant dust deposition on lenses - and workarounds for when there are anyway (new flatfields onboard etc). For a 600ish sol Primary mission for MSL - such a thing isn't going to be necessary or required. Yes - I know it will likely last MUCH longer, but the primary mission is what you design for.

Doug