This is not an old proverb. This is a direct quote of one of the USA's finast philosphers and ball players, Yogi Berra. Check out http://www.yogiberra.com/yogi-isms.html Your invocation of one of his more memorable yogi-isms reminds me of another of his sayings of which I would judge this site has litle risk of fullfilling, and I paraphrase ....'This place is so popular, nobody goes there anymore.'

Thanks to all for such a pleasant daily experience.

Recent images with exposed rock below the dunes reveal a surface that appears very fractured (and weathered?). Does this have to do with the adjacent crater impacts, a result of water, or other causes? In addition, there appears to be no debris from the meteor impacts, why is that?

Today's launch of NASA's Mars Reconnaissance Orbiter has been postponed due to a software issue involving the Atlas V's Centaur upper stage. The next launch window is Friday, Aug. 12. More details to follow. (Aug. 11, 6 a.m.)

Recent micro - images show a mixture of berries and fines. I assume that berries are too large to be wind transported and this would suggest that the dunes are not as recent, having resulted from some other action besides winds alone.

On the other hand, this mixture of sizes creates a very strong matrix (highway bases are made of mixtures in size similar to this, to create a very strong base for pavement). I would think that such a mix should support the rover well. The fact that it pentrated the dune surface and dug in suggests a much weaker matrix such as one that assembled by wind blown fines. These dunes would continue to reshape continuously as winds shifted material.

On the other, other hand, I believe round shaped gravel, although it initially compacts better than irregular shapes, also behaves more like a fluidl than irregular shapes when disturbed laterally such as by wheels rotating.

On the other, other, other hand . . .

Looking at post 28 photo by Tesheiner, I get more of an impression that the dunes are shifting over a flat surface below that is exposed only in the valleys between dunes. When Opportunity backed up over the crest of the dune preceeding Purgatory it appears that the wheels set deeper into the drift at the crest than in the valley. If this is the case for all dune ridges in this area, then sticking to valleys might offer better driving conditions. How far ahead can they determine the layout of the dunes to choose a best path and maximize coverable distances? When it is necessary to cross a dune are they better off crossing perpendicular than at the shallow angle that occured at Purgatory?

I like the idea of multiple vehicles. They would make the entourage more adaptable to changing conditions. Specialized vehichles could scout ahead and take greater risk. Slower, safer science packages could follow where it is safe. All could serve as components for rescue. The entourage could accomplish more than a single vehicle and the group would be more adaptable. Sort of a "Wagon Train" to Mars. More "experienced" readers may recognize this reference from way back in the last millenium.

I remember reading that they were exiting on an arc. Wouldn't we be seeing the wheels biting into the side of the trench a bit and perhaps trying to ride up the side a bit? Or are they keeping the angle at a minimum to increase friction at the side without trying to push into the side. I would think that any displaced material from the side wall would fall into the oncoming track and help raise the wheels up as the rover backs out.

Extracting Opportunity from its current situation is not terribly difficult. Design modifications in a future craft could easily provide a solution. For instance, if the instrument arm were strong enough to support the load without damaging itself the rover could lift itself out of this situation in the same way a construction backhoe can lift itself and shift position without using its wheels. In future expeditions we will encounter more difficult situations as we take on more challenging terrain. How robust is the instrument arm on the MSL? A robotic arm capable of drilling, lifting rocks etc could certainly serve as a backhoe to extract, lift or even turn a tilted rover upright again.

Another thought….We will always be limited in our exploration by our willingness to take any risk with the craft. The rovers are very valuable and easily damaged. One alternative might be to separate the instrumentation from the mobile unit using a rugged faster vehicle to travel and bring samples back to a stationary instrument platform.

My first impression here was that I was looking at mud. The surface appears smoother, more reflective, perhaps finer grains collecting in a sheltered location?

The amount of fill in the left wheel trench is greater than that in the right without any spill to the sides. Does this reflect :

different volumes of material due to different densities before they were disturbed,

deeper pentration by the right wheel below the surface,

better traction on the left wheel moving more material forward as it backs out.

or is there a larger pile of loose material in the way of the right wheel as it continues to back out?

Can anyone comment on how the surface materials in these drifts are bonded into plates?

THANK YOU for this explanation! Most helpful for a non-geologist.

Could repeated forward and backwards movements also further compress the current wheel pit, setting the rover deeper into the soil?

Should we look for another software upload and reboot in the near future?

This picture taken before getting stuck shows the rover riding on bottom and windward side of the dune. I am assuming that prevailing winds come from the right and the lighter colored deposits on the left side of the dunes is dust settlement on the leeward edge of the crests. Since the angle of approach is very shallow, and the majority of the rover’s weight is on wheels in the trough, there would have been very little pressure on the lead wheel as it crosses the next crest. IF the angle of approach to a new crest is perpendicular, there could be additional load on the lead wheels resulting from the downhill orientation of the rover. The additional pressure could force the wheel through the surface crust, causing the wheels to dig in. The other wheels would then dig in if they continue to turn.



Looking back at photos before entering the etched terrain I see plenty of blueberries suggesting a change in the soil composition. In addition, I see regular wave crests that suggest to me a continuous regular wind from a prevailing direction. I would expect that the windward side of the dunes would be lighter material that is dropped on the leeward side. This could result in a less dense, more recent surface cover at the edge before the crest. (Assuming I have the wind direction interpretted correctly).

I am interested in how the wheels operate. Is there anywhere I can obtain specific information on the rover design diagramming the suspension design, dimensions, load distribution and/or other capabilities and limitations?

Any changes in the strategy for driving the rover will depend upon what has caused its current problem. Several questions come to mind:

What exactly caused the wheels to dig in? Did the front wheels dig in because the density of the surface material was so much less? Was the angle of attack and specific load on the wheel different in this approach than with other dunes that have been crossed? To what extent have conditions changed or was this the result of a bad combination of previous condition? Is this situation the result of unique conditions that can be avoided?

If soil deposits are building up on the rover’s approach side of the dunes only we may be able to adjust the angle of approach to float lead wheels over the softer areas with less load on the approach wheel by varying the approach angle. Assuming that the windward side of the dunes have less low density topping, it may be possible to move parallel with the waves with greater confidence. Crossing over dunes would require more guidance from home.

Do we have adequate mapping of the etched terrain to find a track through the maze that leads to the crater?