I like it when people are optimistic. I am terribly concerned this time though. Normally, i have a lot of faith, but to me this seems by far the most serious situation oppy faced considering mobility. I don't want to be pessimistic, but anyone that has seen the wheels of his car (even a 4x4) in loose material (sand, snow, mud, whatever) this deep, knows what i am talking about.
I hope they get out, back up and think before entering this stuff again. For this reason they decided not to enter the dune-field in Endurance, remember ?

Yes, it looks like it was driving just fine until it reached this dune/ripple. I guess we'll have a better idea of what they plan on doing when the next batch of images come down.

Attempting to reach Burn's Cliff (Sol 270):

http://marsrovers.jpl.nasa.gov/gallery/all...LP1214L0M1.HTML

http://marsrovers.jpl.nasa.gov/gallery/all...5P1210R0M1.HTML


And Spirit a few sols back (Sol 453)

http://marsrovers.jpl.nasa.gov/gallery/all...GP1213L0M1.HTML

http://marsrovers.jpl.nasa.gov/gallery/all...BGP1313R0M1.JPG

At least the rear right wheel (or seeing as they were driving backwards I think - the front left wheel), it doesn't seem to be buried as much as it's opposite number.
Which is nice



And one more observation, in the images posted by dot.dk on the last page the
wheels are turned suggesting it maybe tried to do an "end of drive" turn, or something?

Not if it was a blind drive I'd say. A blind drive is just a command "go at this speed for this amount of time" isn't it ? In that case, the wheels just keep turning until the sequence is completed.

Even blind drives still have built in high water mark limits for slope, slippage and motor current etc. I'm suprised that it ploughed on as far as it did - but They'll just back out of it I'm sure - however the challenge is..

why is THIS dune so soft?

is this going to be the behaviour on dunes in the future?

what driving strategies can minimise this?

what are the best slippage, slope and currrent limits to continue driving over this stuff?

I'm sure eng. meetings are taking place almost as we speak to try and sort this out.

Doug

How many dunes, must Oppy sail / Before it sleeps in the sand?

I hear Thomas Gold's ghost cackling

In THAT case the explanation why she entered the powdery stuff this far, is because it might be of low density compared to the previous soil. I must say the texture and reflectivity does appear different to me in the last meters of the drive.

Maybe it is so loosely packed (high porosity), that oppy did not experience any change: as if the layer wasn't there. Maybe it drives ON a more firmly packed soil, 3 inches underneath, topped with powdery, fluffy material with low density/high porosity that is pushed aside very easy? Maybe the slipage like profile we see in the last meter wasn't slipping, but just a manifestation of another, new material under our feet that is easily disturbed and deformed in another way than the soil before.

I just wanted to have a crack at this....

ARB/ACM faults clear, PMA az/cam el/mtes nom, S/C att coarse, DP in Flash (D-3305) 4096, Pre ODY PCAM cal target P1424123 04, MTES_NAIF_SCLK: MTES SCLK = 1/05243365663.091.


ARB/ACM..not sure, PMA az/cam (pancam mast azimuth? camera) el/mtes nom, (electrical minites nominal? (S/C att coarse, DP in Flash (D-3305) 4096, Not sure)

Pre ODY PCAM cal target P1424123 04,(Pre Odyseey pass Pancam calibration target number...) MTES_NAIF_SCLK: MTES SCLK = 1/05243365663.091. (Minites Clk time?....... )

Just wanted to try.... prolly wrong....


hope oppy gets out soon.

John

An overview around the bad place (Navcam):

(400KB) http://www.greuti.ch/oppy/oppy-sol446-navcam-k.jpg

(950KB) http://www.greuti.ch/oppy/oppy-sol446-navcam.jpg

So where are those tire chains when we need them? Anyway, I think this is pretty serious, having some experience getting stuck in the snow belt in Ohio. The best option is back out, slowly as possible to minimize torque so thay do not bury the wheels any further.

Just a real crazy thought but if they were severely stuck, maybe they could extend the arm, plop it down deep into the soil and then PUSH their way out while driving the wheels at the same time. I know, a crazy measure, but if they are not moving anywhere for a real long time they would have nothing to loose.

Good thinking !!

You can see in this Navcam pic that as soon as Oppy hit the lighter colored soil it began to trench much deeper. Here's a theory: the darker soil supports Oppy much better because the blueberries tend to compress only just a little bit (being more like pebbles than sand). However, this lighter colored soil has fewer (or none) blueberries and is much more like very very fine sand that the wheels literally sink into.

http://qt.exploratorium.edu/mars/opportuni...DIP1999L0M1.JPG

Might be. There is a distinct difference in reflectivity (or colour) between the last 2 meters and the terrain before. BB might devide the load of the wheels more spread out through the profile of the toplayer. Maybe even somewhat sideways, while just the fine grains are pushed only downwards because there's less cohesion between the particles. Also, i think that the BB is associated to some other kind of feature: a crusty like toplayer. The last meter or so doesn't seem to have this property at all.

Considering the load on one wheel (about 10 kg's), this stuff must be as soft as freshly fallen snow !!

another crazy thought in case the material is too soft for the push-trick to work, assuming that the arm could reach the soil near one or two of the wheels (???)
Try to push/scratch "shovel" some of the sand away from in front of the wheels
This would possibly require sophisticated software and
maybe many days/weeks of high-precision arm-movement:
.... but if there is no other choice.

@tman: I really hope that this wa not your last Navcam-Panorama from Oppy

That's an interesting idea......do you think it would really be possible? I suppose it could be tried as a last resort.

The arm was built to carry the instruments, and the instruments only. It doesnt have the power in the motors, or the strength in its structure to lift the rover.

It's not like we're trying to climb up a 40 degree slope here - backing out is a very valid option I'd have thought.

Doug

Then what? Try to maneuver into a trough rather than over the crest of a dune?

I'd suggest running between dunes as much as posible.

Doug

I'd suggest a wedge with a slight divot shot.

It does appear that Oppy has stumbled upon some fundamentally different stuff - I don't recall ever seeing the treads on the wheels filled in so perfectly. Must be very fine powder like material... Odd, since we seem to have crested quite a few larger dunes before with minor sinking.

(Boy, I go on a road trip for 2 weeks and look what I miss: Spirit's Big Find and Opportunity's Big Trap!)

We had the deus ex machina dust devil cleaning events that brought new life to Oppy and Spirit. Maybe we should plan on a sustained horizontal wind that will enable Oppy to lift off the ground, glide over the dunes, and be magically placed on the rim of Victoria.

Here's hoping...

I've seen that in the wheels of boths rovers when they've got stuck in the soil....

Opportunity inside Enduance Crater: http://marsrovers.jpl.nasa.gov/gallery/all...LP1214L0M1.HTML

In that picture, the left wheel is in even deeper than it is now, but the other wheels remained relatively clear.

If we ever did get stuck (and I don't think we are), I would think the best hypothetical use of the arm would be in the direction of motion, not in the lifting direction.

The arm can generate up to 80 Newtons of force, but probably the number is lower when pushing at the ground in the driving direction. The real problem however is that you would probably end up burying the instruments in this soft sand before you developed any appreciable force.

This is Tman's pan in a polar projection. Viking and Voyager are just visible at the top and the dark strip which is presumably part of Erebus is near the bottom.

Phil

Click to view attachment

Maneuvering accurately between so many ripples is going to be very time consuming, especially with one wheel behaving unpredictably.
This sand they're seeing seems like it's got the consistency of fluffed flour. That would explain why the rovers sink into it so easily, and why it sticks to the wheels.

So what happens if they just keep spinning the wheels? Does the rover very slowly move forward, or does it just wind up digging itself into the ground until the wheel support arms are all that's holding the rover up?

If oppy can't back up and take a different route this looks like a job for skycrane.

Worried but hoping
Reckless

Time for a tire change.

http://www.rccrazy.com/images/news/Mini-Paddles.jpg

Thanks - I missed that - though you can still see the tread a bit in that pic. It's also hard to tell (at least to my eyes) whether we are facing up hill or down from the hazcam shots. Judging from the ripple lines, it looks to me that we are straddled over a crest, and may actually be tilted down slope a bit, in the "wrong" direction to back out. I hope I am mistaken about this as well.

Let me rephrase - I don't recall seeing all the wheels dug in so far before. But perhaps we are all panicking over nothing - could this be a new 6 wheel trenching routine?

Hahaha, yeah, and the skycrane thrusters would clean up Oppy's solar panels too!

This is of course what I meant, i.e. using the arm to push OUT to add more horizontal force to the drive, not UP to lift the rover wheelsout of their tracks.

quote=gregp1962,Apr 27 2005, 02:55 PM]Time for a tire change.

http://www.rccrazy.com/images/news/Mini-Paddles.jpg

[/quote]


Heh or how about a pair of these?

Click to view attachment

Tank Tracks would be a nightmare - stuck on rocks, bogging down with dust, nowhere near as much mobility as the rockerbogie

Doug

NASA went with the 6-wheel Rocker-Bogie design for Sojourner (and then for the MERs) only after almost a decade of both computer simulations and actual ground tests had shown it to be the best possible design for ground-crawling rovers. It has tremendous ability to crawl over very large rocks, and it distributes the vehicle's weight evenly across all the wheels at all times. It is likely to be the official design for wheeled rovers everywhere in the Solar System for a long time to come.

Make that "the official design for GROUND-CRAWLING rovers everywhere in the Solar System for a long time to come."

It seems strange to me that rear wheels are turned in opposite directions. It isn't proper position not for straight moving nor for rover's turn. Moreover, the tracks seem to be corrupted between ridges, where sand wasn't deep. Could it be a software glitch which caused inconsistent turn of wheels and subsequent dig into the soil?

The wheels will be pointing in funny directions because at the end of a drive they turn the rover in place to put it in the best position for the UHF passes that afternoon and the following morning

Doug

http://athena1.cornell.edu/news/mubss/

Steve doesn't seem too worried. And I'm not either. They will get out of this. The interesting thing is the soil. I'm betting it's the global dust that is collecting here for some reason. It might be tough going from here on out. It could be that the stuck wheel might have something to do with digging in. In this image...

http://marsrovers.jpl.nasa.gov/gallery/all...GP1223L0M1.HTML

... the left wheel (with respect to the front of the rover) is not positioned for a turn in place. It looks more like left turn (with respect to the drive direction). Soft soil combined with that type of turn would be a real drag (and I mean that litterally).

ed

The strange thing about this is that when Opportunity drove out of Eagle Crater onto that vast flat plain, I never thought for second we would have a problem like this.

if we ever get out of this ...
I hope that the plan to go for Victoria is not abandoned altogether.
Sure we will find a possibility to get there despite the sand-difficulties !

... and I'm also still looking forward for Spirit to reach that Summit

Given that the rovers mass 180kg, on Mars that's about 600N of force at the centre of gravity of the rover. Assuming that this CG is at the midpoint of the wheels, for an arm with a pushing force of 80N, it'd need to be able to reach a point 5-and-a-half times further away from the front of the rover than the half-wheelbase of the rover, in order to lift its front wheels up, the fulcrum being the back wheels. That's not possible, surely? The stretch required is just way too long?

That said, with a shorter reach, you could at least lighten the load on the front wheels, which might make a difference in this sort of situation. Though that doesn't remove the risk of damage to the instrument package, of course.

Andy

What about RATting the soil just in front of the front wheels (in fact rear in the moment - oppy is driving backwards, right?), is it possible for th IDD to reach these locations?

The left track of Oppy at the beginning of digging. It's a raw L257 filters miscoloured image.

(550KB) http://www.greuti.ch/oppy/oppy_sol447k_L257.jpg

It seems this digging come only from the left forward wheel (Oppy moved backward).

IDD couldnt can only reach the area between the two front wheels - and the rover was driving backwards (and will do most of the time since the steering actuator issue) - and I say again - you try and use it to get out of a situation like this, and it WILL break - no question about it.

They drove into this situation - it's very likely they can drive straight out again.

Ratting is no use - you'll just stir a small circle of dirt.

Talk of using the IDD to aid mobility in anyway is madness

Doug

I have been trying to find imagery indicating the full range of the work volume obtainable by the arm. I know it exists, i'm just not having much luck. Given the power of the motors and length of the arm it must be possible to do an analysis of the force that can be applied at different parts of the work volume including where the IDD intersects the ground.

I must say that i disagree with the notion that talk of using the IDD to aid mobility is madness, certainly the chance of it ever being used for this purpose is for all intents and purposes nil. However, if you are a few newtons short, using the IDD certainly becomes an option. We know that the rovers are far more durable than the engineers let on.

I have posted the following movie elswhere in the forum before, it is an animated giff of sojourner deploying its APXS, forgive me if i'm wrong but that dip of the rover in the last frame looks like a form of mobility to me.

Making a 10kg rover tilt ever so slighlty when pressing a simple mechanism onto soil is fairly understandale.

Taking a 175kg rover and trying to move it with a 5dof arm...isnt

Doug

hi doug,

Sure it's understandable why sojourner wobbled. I bet the MERs wobble slightly when the IDD is being used too. To be clear as I said in my post I think the chances of the IDD on the MER being used for mobility are essentially nil.

However, the possibility of using the IDD for a purpose other than what it was expressly designed for is something that interests me, for no other reason than it gives another avenue to fully explore and understand the technical capabilities of the rovers and the options of the team operating them, it may be madness to think about using the IDD for mobility but it is not madness to talk about its capabilities.

I spent a while unsuccessfully trying to find a diagram of the IDD work space, frustrating as I know such diagrams exist. In fact I would bet a mars bar that force maps of the IDD work volume (even if it has only been calculated for a couple of positions) have been generated by the rover engineers, as part of either the design or operation phase.

Having eyes on another world is one thing but being able to interact physically with that environment is why the arm is there, knowing the capabilities of the IDD is just one more factoid that makes the mars in the images from the rovers seem more real.

The relevance of discussing non-standard uses of the IDD also affects other aspects of the mission. I have been mildly surprised that no rocks have been tipped over using the IDD. Even if they are small ~10cm in diameter, surely bucket-loads of interesting science can be done by examining soil that has been protected by the rocks. Of course breaking the arm on mars would be a tragedy, especially when there is still plenty of good science to be done. But hey, that’s what engineering models are for.

So using the IDD for mobility no, but rock tipping? Well perhaps yes.

If I wanted to listen to madness about the rovers I'd be in a different mars forum.

I'm not sure what diagrams you're talking about, but the CAD drawings that were released a couple of months ago, showed the arcs that all the different parts can make. Some searching on gear ratio's and some good old trigonometry and statics will give you the forces exertable at different arm positions.

But something else: It's not so much about forces that can be generated dynamically (how do you push a 180 kg rover out of 4 inch holes in the soil), it is about maximum static load exertable on the arm in fixed position (how do you prevent a rover from sliding back in these holes during slowly creeping out). Here's what i mean: push the RAT side (prevent the rest of the arm instruments get dirty) in the soil. While commanding to drive an inch or so, move the arm in such a manner, that it stays on the same spot in the soil and freeze it's position at the same moment the wheels stop moving.

It would be madness to do it now, but when oppy is stuck and it might be the only possibility to help her out of there, i'd prefer a broken arm (or just dirty instuments) above an immobile rover.

Let us wait and pray that nothings wrong after all....

Oh my ...

http://qt.exploratorium.edu/mars/opportuni...DIP1314R0M1.JPG

The whole wheel (28 cm) is in this stuff.....how could this have happened ?

The next rover definately needs a device that detects this sinking in...

This is very dangerous situation. You can see that rover (probably) tried to turn in place automaticly as it faced difficulties. All but the broken wheel has been alinged turn-in-place, this must be uncommanded as i cant think of any reason trying such manouver. Good thing is, that the pit between the front and rear tires seem to be trampled somewhat, so middle/rear wheels give probably good traction if there is harder soil underneath this powder cover.

Being unable to turn one of the tires disables completely the ability to turn in place when the soil is soft. Seems like there will be even more looser soil further down we go, so i'm fearing that it will lead to "mobility kill" eventually. I think they will probably suspend all automated drives from now on.

The rover is positioned on the top of dune and alongside of the ridge, so we are very close being bellyed on the sand. Front wheels have to overcome almost all of the rover weight when climbing (and currently, when descending), due to the design of the rocker-bogie system. With rear wheels this would not be the case as they are linked with middle wheels.

Don't think so. As Doug said allready, the turning is standard procedure in order to place the rover in an optimal position for data transfer, not because of some kind of hazard. And i think that the best way for a rover to respond to unexpected or dangerous situations....is simply stop moving and await further orders. And that's exactly why i DON'T understand why the wheels are in this position. Maybe the command sequence to drive and turn afterwards were send up in one package (without imageing in between) because they simply did not expect this to happen after 5 km's of driving without problems. Which is completely understandable.

My hands are sweating and for the first time since Spirit's software glitch in feb. 2004 i'm feeling we are going to loose a mobile rover.

Can someone reasure me that i am wrong ? I don't feel so well.

I don't think they were trying to turn in place. They aren't able to do that with the stuck steering actuator. The last turn-in-place created a nice trench. You can also see that they have been doing "Y" turns to change from forward to reverse driving. (At least that's my interpretation of the images.)

But if I'm not mistaken, it is standard practice at the end of a drive to turn the wheels (without driving), to get a bit more stability. If that's the reason the wheels are turned now, I don't think much harm was done.