I'm thrilled that Oppy's out of the dune, and I'll admit that I have not scoured and computer processed the raw pictures like good forum members should, but I think I still raise a good question: Do any of you have any ideas as to how on Earth (or Mars, rather) Oppy will be able to get to Erebus or Victoria given that it looks like the terrain leading up to these astrogeological treasure troves is the same as what got Oppy stuck in the first place? Does it sound viable to drive around the culprit dune staying in the valleys inbetween to get there? It seems this would be a majorly long and inefficeint switch-back driving method, but honestly, is there any other foreseeable way?

Cruising in valleys between the dunes is my recipe till Oppy get to safer ground. And I think that from Erebus forward to south the white areas are exposed bedrock where it is safe to drive even using blind drive.

As I understand it, the rovers can be programmed to do auto-nav sequences in which the height of obstacles to be avoided is a variable. In other words, until we get out of potentially dangerous drift territory, Oppy's autonav could (conceivably) be set to avoid any object higher than, say, 20cm above its current position. That would naturally lead it to follow interdunal areas.

It would be slow, but steady (10 to 20 m per day, maybe) but it would get us out of this landform, where we can drive faster again...

-the other Doug

I expect to see some very slow and cautious manuevering.

Quoting the MSNBC story :
The "highway" could be a stretch of exposed bedrock, leading toward Erebus Crater — which would be a very good thing for Squyres and his colleagues. Or it could be a huge pile of Martian dust.

MRO imagery cant arrive fast enough eh? The problem is that whilst MGS MOC imagery is good, amazing even with CPROTO, it's still not quite good enough to navigate with on the scale of MER.

Doug

Plus even at great resolution you can't know for sure what things look like till you get there. Top down view is deceptive.

scott

One of the things used to "aize" the resolution and camera size on Recon Orbiter is the ability to see details at a rover's size well enough to use them for navigation and site geological investigation. Even the best CPROTO stuff from Global Surveyor just poo's out as we approach the level of detail we need.

According to the picture which shows the right line from Oppy present position to Erebus, has intricates formations of dunes. It is like a maze of lines. (1)

1) http://www.unmannedspaceflight.com/index.p...ype=post&id=635

The wind pattern is from East to West. The east side, has firmer sand (less loose sand) and the west side is where sand falls from the windblown. Hence, it is safer to climb from East to West than from West to East.

2) http://www.unmannedspaceflight.com/index.p...ype=post&id=639

The best way is to navigate between valleys and not on crest. If the Oppy has to cross a crest and the pending slope must be low (10 degree or depends on the compact of land "evaporite with blueberries" or "loose sand").

According to the picture, the best way is to avoid to cross a "sea of dunes" since it is very complicated to drive by remote control. The zone which has flatter lane is on the western side of the picture 2). So Oppy must travel a little toward western lands until get a flatter land before heading to south where is Ebrerus' outcrops.

Rodolfo

Yep - Follow the Blueberry Road. Well,the greyish road that might be blue in the right light. Oh alright, flat looking bit that I've decided might be a road.

OK flatish.

Aw heck - any Rover drivers lurking who can put me out of my misery?

Follow the "Blueberry Road" (SW) or "Erebus Highway" (SSE)...
It is difficult to make a decision just based on an image taken by MGS.

I remember someone posted a 360º panorama in which Voyager crater was still visible (and it was a navcam pano). In such a case, it would be possible to resolve - if not on this same pano, on a similar one made with pancam images - the features that makes "Erebus Highway" and also guess about how the dunes develop on the way ahead (getting bigger or smaller) either SW or SSE.

I've tried to find such pancam 360º-panorama but no luck.

Tesheiner

Thing is - Erebus and Erebus highway are probably a little bit lower than where we are now

Doug

In such a case, we should be near the "Hell of a view" point, right?

See: http://www.unmannedspaceflight.com/index.p...findpost&p=7727

This is the 360 pan:

http://www.unmannedspaceflight.com/index.p...ype=post&id=529

but more useful is this previous post:

http://www.unmannedspaceflight.com/index.p...ype=post&id=470

The second is a sol 437 pancam image of the southern horizon, and the lower version shows it with 10 times vertical exaggeration. Erebus is a group of light and dark spots. The 'highway' just shows up as a group of white spots at left. From this distance there is no useful detail to help plan a drive.

Phil

Thanks Phil.

Looking to those images it is still not possible to determine if "Erebus Highway" is basically sand or bright rock.

Besides this point, I have to correct myself when previously said that "we should be near the 'hell of a view' point".

This is a bit OT, but I just combined the vertical profile posted here with one of the MGS images included in the original report (link), and this is the result.

Click to view attachment

That point is located more or less mid-way between Erebus and Victoria.

Tesheiner

So at present we appear to be near the contact between units C and D on the Vertical Profile map?

--Bill

Actually on D.

This picture below is the one from my previous post but now with the Route Map (posted by Pando) on top of it. The resulting image is not so clear, but could be enough as a context map.

Click to view attachment

Tesheiner

It looks like there is some ways to go before Oppy sits on the rim of Victoria - 200 sols perhaps? (lots of distractions and hazards along the way)

Or do you think controllers will push for Vic without delay.

I think they'll try and get to a progress comprimise, one that balances progress versus the risk of getting stuck again.

If they make progress at half the speed as before, but dont get stuck, it's a better deal that getting stuck for a month every couple of weeks

Doug

Hope that Opportunity's travel would be like a dramatic movie trying to avoid in getting stuck again.

Stand up Oppy and be smart. It would be a lot of fun time in getting to Erberus highway and also to Victoria's cracter.

The result of a weeks planning... ½ meter forward

http://qt.exploratorium.edu/mars/opportuni...TQP1214R0M1.JPG

Let's hope we'll see some more during the weekend.

Hopefully she don`t get a ticket for speeding...

Are we there yet? Are we there yet? Are we there yet?

That's a lot better than 2 cm's

And why drive further if the plan is to investigate the dune with the IDD? I bet they will do a 180 degree turn on monday and spend the rest of the week disecting that dune with the arm. If not for science, then for revenge.

Any update yet on the stuck front left wheel? I don't recall anything definitive on the cause of that. Something like that is bound to cause a slight bit of a grinding action in the dirt, and if there's a thin, semi-fragile crust, that grinding might put the wheel right through the crust.

They can't really do an in-place 180 with the stuck steering on one wheel. They drove further so they have some room to maneuver.

The steering on that wheel is still stuck, and is disabled on the rover. I think they may do some tests again before they get going longer distances... But there is a danger that if it moves and gets stuck again, it may get stuck at a steeper angle, and then it's a much bigger problem than it is now.

Just test it by trying to straighten it out from the few degrees toe-in it has...

IF a wheel get stuck in a bad position, don't they have the ability to blow a fuse and thereby make the wheel dangle freely?

Seems to remember it from when Spirit had its own steering problems.

If it dangles freely though, it might not make for a good driving wheel at all. At least now, it does have the ability to help push or pull the rover, albiet with slightly higher friction than the other wheels. But it still can do something. Who knows, maybe with trying to turn in place, all the grinding on the ground might jar it loose. I was hoping that the time in the trench might have somehow helped that, but it'd probably need something more solid than fluffy sand to have any effect.

As I recall from Spirit's wheel problems, though (which had nothing to do with the steering actuator), the wheels cannot be left to just turn freely. When Spirit was trying not to use its one bad wheel, that wheel was simply turned off and Spirit dragged it along. That's why Spirit had to drive backwards -- it could maintain good speed and controllability dragging a "back" wheel, but not a front wheel.

In Oppy's case, the wheel turns fine, it just can't be straightened out. As I understand it, it can move from its seven degree toe-in position all the way hard over in the same direction, and back, but no further the other direction.

When Oppy got stuck, it was using its bad wheel but it was driving backwards to lessen the impact of that wheel's toe-in position. The controllers had run into some issues making Oppy drive straight in this configuration, and had made some changes that helped, just before we got stuck. That *may* be one reason we got stuck -- Oppy has to make smal "turns" as it drives backwards just to keep moving straight; it may have made one of those small turns with its "front" wheels just at a point where such a slight turning of the wheels caused them to dig in to the drift it was traversing. I'm sure that's one of the things the MER Team will be examining when it takes a very close look at Purgatory Dune.

-the other Doug

Click to view attachment

Here's a sketch of the Opportunity route in the few sols leading up to getting stuck. It is NOT to scale... the areas with details are further apart than this suggests. (I have been sketching the routes like this since the landing for both rovers).

It is based on all images from about this time, hazcam and others. You can see two places where three point turns were made to reverse direction. The top one followed what looks to me like an attempt to turn 180 degrees in place, but which proved difficult and inadvertently dug a trench.

So we should see another of these shortly!

Phil

I'm not talking about the bad right front wheel on Spirit.

Spirit had its own steering issue back in october were one of the solutions could've been to blow the steering motor and let the wheel turn freely in whatever direction it wanted.

http://www.spacedaily.com/news/mars-mers-04zzzzzzzs.html

Spirit's problem was different. The steering actuators can be put in an electrical state where the motor's windings are shorted. This causes the motor to resist changes in steering direction (dynamic braking). Spirit's problem was that the actuator failed to switch out of this state properly (which is necessary to actively turn the motor). They indeed have a fuse that can disable the dynamic braking function.

Opportunity does not have this problem. Rather, the motor fails to turn the joint at all.

Really? Have they tried exercising the wheel? Rotate it to one side, give it a spin one way, two the other way, and then rotate it a little straighter, spin it again, and keep trying somewhat in that fashion?

Yes -- as I understand it, they moved the wheel from its seven-degree toe-in position to what looked in the pics I saw about 90 degrees to straight forward (continuing in the toe-in direction), then moved it back as far as it would go, which was back to the seven-degree toe-in. It won't move any farther towards a toe-out position.

They don't want to exercise it a lot further, since it's now only a partial actuatior failure. I guess the theory is that it could become a full failure at any time, and that, of the positions they can get that wheel into right now, the seven-degree toe-in is the "least bad." Moving it *at all* runs the risk of it getting stuck in a worse position.

-the other Doug

Oppy finally starting to turn around

http://qt.exploratorium.edu/mars/opportuni...V4P1213R0M1.JPG

Look at that sand mountain

http://qt.exploratorium.edu/mars/opportuni...V4P1311R0M1.JPG

And a nice view of Purgatory

http://qt.exploratorium.edu/mars/opportuni...V4P1914L0M1.JPG

http://qt.exploratorium.edu/mars/opportuni...V4P1914L0M1.JPG

What do we reckon is with the funny darker patch at bottom right, on the dune nearest the rover? Is it just a shading effect, or some different material, like that darker soil that was noticed in the edge of the tracks?

http://www.unmannedspaceflight.com/index.php?showtopic=1073

[edited to ask the question better]

I already noticed it during stitch of Sol488 NavCam images, and I found it also in Sol448 images, so is stable and cannot be a shading effect...!
Your suggestion about bossible correlation is interesting; I cannot avoid to think that perfectly circular could be someway related to "tiny craters" previously encountered...
Meanwhile, here the funny animated sequence of the last 2 days maneuvers:
http://img83.echo.cx/img83/5444/manovra4914os.gif

Yes, and Oppy does seem to be kicking up a lot of light colored dust on this turn.

--Bill

And here we have a navcam pano taken yesterday (Sol 494?).



We can see "Purgatory Dune", the rover tracks and the first and second of this three-leg manouver to turn Oppy 180 deg.

And about these circular patches, we can see the one refered by Astrophil and another to the right of purgatory.

Tesheiner

And there are two to the left of Purgatory as well... These patches are pretty weird, I hope they look at these closer with IDD.

From this angle, it seems like Oppy got stuck when it began straddling the ridge line of the dune, riding along with Oppy's centerline right over the ridge line. It may be a trick of perspective, but from this angle it looks like the leading right wheel began going downhill, but the trailing right wheel was still going uphill, just before Oppy got stuck.

... and another dark patch to the right of purgatory, and maybe another on the dune behind purgatory (but it is too far to be sure).

Maybe these patches are not something like those "hey, look to this strange rock with square edges!" things; who knows...
And yes, closer images (even pancam with additional filters) would be nice.

Tesheiner

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?