[MOD NOTE: This thread follows on http://www.unmannedspaceflight.com/index.php?showtopic=7659&view=findpost&p=200171.]
Ed: zooming in on that marvellous underbelly MAHLI montage, there appears to be further (and previously noted) deformation of the wheel surfaces.
Damage is most evident in the view of the front-left wheel inner surface.
Such wear has previously been discussed and concerns allayed.
Nevertheless, the front left wheel surface *appears* to have been punctured.
No, I wouldn't be concerned.
Yes there is a bit of damage, yes there will be 10x as much when we get to Mt Sharp, but the wheels will still be fine to drive on, this was expected.
Your going to have to regularly reassure us.....it looks bad to the layman. Of course at least the wheels can be regularly photographed as MSL roves accross this amazing landscape .
Isn't the "puncture" merely a glint of light? Could there be anything on Mars hard enough to make a narrow puncture through that much metal?
Being in shadow means they couldn't reflect the Sun, but they still could see some part of the sky and reflect it. The sky is a big thing so it's hard to block all of it!
I am sure this wheel debate will roll on for some time (pun not really intended). I have not found the specification for the material for the rover wheels, but judging from the number of dings in the rims we know the material is very ductile, but it appears to be a high performance aluminium alloy. Reassuringly aluminium remains ductile even at extremely low temperatures, but good to see that drives have occurred at mid day when the temperature ranges reduce any fatigue issues created by very low temperatures.
I would not be concerned with small punctures in the rims, after all we already have the 'Morse Code' cut outs, nor would I be concerned with a plethora of additional dings that we can expect during the remainder of its mission, but am concerned about possible 'work hardening' of the material which over time could reduce the ductility of the material that could lead to undesirably issues.
I am sure the engineering team and drive planners will remind the science team from time to time that the rover wheels are not designed as rock crushers and that we would like them to last as long as the power supply
See slide 32 in http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/42424/1/12-0690.pdf
Okay Doug, thanks for this very clear explanation
Wonder who took those.
And the wheels got a lot worse than that before they were replaced. A LOT worse.
Worst one at that point looks to be the middle right - rips and tears all over it
Good thing Mars surface gravity is only 0.38g.
Given the level of damage observed so far on the rover wheels and the small distance traveled, if you linearly extrapolate future damage vs distance traveled, how far can the rover drive before a wheel fails? I know no one can answer that but I would assume modeling is being done to try to answer that question??
I would also assume the rover drives will be planned to avoid sharp rocks whenever possible?
Good thing there's no shortage of soft surfaces on the way to Mt. Sharp. The dune fields are looking inviting, ironically (obviously we haven't seen them from the surface yet so pure speculation on what they're like).
Doug has seen the damaged VSTB wheels in person and I haven't, so he's in a better position than me to know if the anodizing is actually broken off or not.
The likely failure point will not be on the wheel tread surface itself, but at the annulus on the inner surface where the wheel spokes attach to the wheel.
--Bill
Cool design. Wheels are NOT a likely failure mode. How many ways need this be said before the subject is dropped?
OK, that was pretty funny.
Yup - hats off to that one
The MER and MSL builders got a lot of things right when they put them together. I'll assume they know what they're doing with the wheels.
Correct me if I'm wrong:
I understand the punctured aluminum is little more than soda can thickness and provides little or no structure strength.
I understand the cleats are considerably thicker and beefier and it is these that provide shape and strength.
I understand that the wheel motors are insanely high torque and could rotate the wheels if they were triangular shape.
I also assume that the wheels (initially with full undamaged surface area) would tend to float on dust and other lightly packed terrain. This I assume will change over time as the thin aluminum gets punched out and ripped up. Now you have less surface area, and the cleats will tend to sink more easily in sand. And at the same time, this digging-in would provide excellent traction. And perhaps even better traction when challenged against more rocky material.
Make no mistake, I was horrified to read about this! But if what I said is true, and I'm right, and the builders did their job, then there's nothing to worry over.
One question related to this topic, ... I hope.
As far as we know MER wheels are made of Aluminium 7075-T7351.
Could anybody confirm MSL wheels are the same alloy?
Thx.
Another hole
http://www.midnightplanets.com/web/MSL/image/00424/NLB_435147127EDR_F0191066NCAM00354M_.html
Go to any aerospace grade machine shop.
Or visit directly Next Intent where they produced all MSL and MER wheels http://www.nextintent.com/portfolio-2.
Sol 463 MAHLI x-eyed stereo of the left central wheel:
Wow.
http://astrogeology.usgs.gov/news/astrogeology/sol-469471-update-on-curiosity-from-usgs-scientist-ken-herkenhoff-tearing-on-wheels
Well there you go, if the team were concerned about the wheels, then all of our concerns were validated.
Happy Thanksgiving by the way, to those that are celebrating it.
Are there any papers on MSL wheel design trade-offs?
One way to look at this is that the cleats really do most of the work, and they are a lot more robust.
Phil
So one can posit a scenario where rather than picking up a rock in the wheel as did Spirit, as the skin of the wheel deteriorates Curiosity could pick up a rock jammed between cleats. Wouldn't stop operation but would make for amusing comments.
Who says MSL has no sample cache...
It would be interesting to know what other wheel options and materials they considered. What role has the function as the landing gear pads played in the wheel design?
http://astrogeology.usgs.gov/news/astrogeology/sol-472473-update-on-curiosity-from-usgs-scientist-ken-herkenhoff-watching-the-wheels:
Yes it can and just such an experiement was done using the Sojourner Rover. It was called the http://www.grc.nasa.gov/WWW/RT/RT1997/5000/5410ferguson.htm (WAE). Thin films of different metals were emplaced on the http://commons.wikimedia.org/wiki/File:Mars_Pathfinder_Wheel_Abrasion_Experiment_.gif. A photovoltaic cell was used to periodically measure the reflectivity and record the level of abrasion thus characterizing the surface properties.
Thanks a lot! So there is a good chance, that we get additional science benefit from the wheel monitoring.
A small question: could the recent wheel status worsening be related to the long, high average speed drive on http://www.unmannedspaceflight.com/index.php?s=&showtopic=7457&view=findpost&p=205060?
No - 472 was the last drive, so we have not seen any MAHLI images since then. The 472 images are from before the drive.
Phil
I doubt there is a huge amount of straight scientific data about the surface to be gleaned from examining the wheels. However, there is good engineering data about the interaction of this particular wheel design with a fairly representative Martian surface to be acquired.
There has always been a dissonance between "pure" scientific data gathering during space flights, and the acquisition of engineering data that can be useful in the design phase of the next vehicle to come along. Both are "scientific" goals, but the engineering data is used to both improve future spacecraft and to better understand and improve our engineering models (which usually led to the designs and materials being used and evaluated).
Or, to put it another way, the "pure" scientific data is usually all about studying the environment we've come all this way to look at, while the engineering data is to look at the systems that got us there and keep us running so we can pursue the pure science goals.
-the other Doug
Well said Doug, and both areas of analysis are of equal importance on a mission.
What surprises me about the wheel damage isn't the dents. That would be expected in thin aluminum. But the gaping holes are surprising to me. It's like the alloy is very brittle.
Given the fact that much larger holes were manufactured into the wheels for the JPL Morse tracks, my concern level is zero.
So why not put this thread to bed.
Group therapy for the morbidly pessimistic.
Pictures of the wheels are great, particularly when a wheel is perched on a rock. That tells us that a particular rock is mechanically strong, unlike some of the poorly consolidated sediments around. There should be a place for posts like that. But I agree: time should be called on endless unfounded worries about the wheels.
We get that, but the other holes show that the ones you asked about don't matter. They can't spread far because of the big cleats. It's interesting to see this but it doesn't matter.
Now let's get back to looking at the stuff you can see through the holes: Mars.
Phil
Why not use tires made of a titanium alloy?
I think that it's safe to say that the admin/mod team has decided to keep this thread open since over time more holes will appear, and hopefully it will function as a place for people to find answers (esp. those new to UMSF), which have been graciously provided by members such as mcaplinger.
However, alarmism will not be viewed favorably, nor will criticism of the project team or designers.
Engineering is all about compromise. We could have had massive wheels impervious in all respects to anything, but probably would have had to lose one or more instruments, and/or change something in the EDL methodology, and/or, and/or...it tends to snowball.
The wheel design is highly robust & survivable, and it's the best compromise that could be derived based on overall system performance requirements.
Enough said.
I am only asking questions to learn about the engineering design process and considered wheel options – unfortunately so far with little success.
Nobody's preventing you from doing so; again, that's what this thread is for.
My comments were not directed at anyone in particular; just wanted to define some boundaries.
These stereo views seemed to go better in this thread than anywhere else. The slight axial tilt of the camera during the MAHLI surveys allows for a reasonably robust stereo image of the center wheels on either side. Here are a few recent views (with brightness levels bumped in a few to bring out some detail in the shadows) ...
...from Sol 476:
http://www.edtruthan.com/mars/Sol476-Mahli-Wheels-1-Anaglyph.jpg
http://www.edtruthan.com/mars/Sol476-Mahli-Wheels-2-Anaglyph.jpg
...and from Sol 472:
http://www.edtruthan.com/mars/Sol472-Mahli-Wheels-1-Anaglyph.jpg
http://www.edtruthan.com/mars/Sol472-Mahli-Wheels-2-Anaglyph.jpg
(..and not to beat a dead topic, I personally think the wheels will be just fine even with a great number of holes - they have huge built in "JPL" holes - so it's hard to imagine enough damage to seriously impact the rover's mobility...)
A quick google search unearthed the following: 80+ pages of informed insight into the next generation (in which MSL is referenced) of rover wheels, and the engineering challenges/trade-offs faced by the terrain they would be exposed to. Admittedly the article references largely re-configurable wheels, but some of the challenges faced and the outcomes settled upon are instructive.
http://strategic.mit.edu/docs/SM-48-Baker-B-2012.pdf
I'd like to see more emphasis on the wheels as a science instrument. Streaks, scratches, dents, holes, tears can be seen as measurements.
Here just some simplified ideas:
Probably almost everyone working in mineralogy is best-familiar with determining http://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness or using http://en.wikipedia.org/wiki/Streak_(mineralogy).
The frequency of scratches tells something about the abundancy of mineral grains harder than the aluminium alloy; streaks tell about cementation or about minerals softer than the alloy.
The very surface will be oxidized.
I've mainly been referring to the metal below the oxidized layer, which http://www.unmannedspaceflight.com/index.php?s=&showtopic=7658&view=findpost&p=205200 suspected to be http://en.wikipedia.org/wiki/7075_aluminium_alloy, consisting of aluminium, zinc, magnesium, and copper. Pure aluminium is rarely used.
Remains the question about the scratch resistance of the oxide layer.
Well you are certainly thinking well outside the box there Gerald and full marks for that although I honestly cannot see any real utility in your suggestion. I guess that the hardness of the anodized layer will have been assessed although you would be pretty safe thinking it to be 7 < <9 (MOHS). Basalt has a MOHS of around 7 but the punctures in the wheel would be caused by small cross sectional contact where the effect on the basalt would be compression. There is no real time visual monitoring so no information available on when or where an incident (scratch, rear, puncture or crazing) occurred, or the dynamics. The anodized coating will have a different coefficient of thermal expansion than the underlying aluminium so there could be a degree of crazing caused by the Martian temperature variations which at the image resolution available would muddy the waters.
http://mars.jpl.nasa.gov/msl/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1573
little punched-out shred http://www.midnightplanets.com/web/MSL/image/00488/0488MH0262000000E1_DXXX.html and the http://www.midnightplanets.com/web/MSL/image/00488/0488MH0263000000E1_DXXX.htmlas well, seems to have been pushed in quite far. soon as it falls off were doomed!!
the inside surface is rendering with some pretty convincing displacement mapping now.
Seems a bit of the wear worry is striking a chord with the team as well. While none of the dents and dings are serious, it apparently is more than they were expecting this far in. From the link above:
Yeah, and any pause to inspect the wheels is clearly at least briefly harmful to the goal of getting to Mt. Sharp as soon as possible, but hopefully in the grand scheme of things it is a miniscule one, so I'm not going to change my subtitle for this thread....yet.
I was thinking about how to harness the powers of this forum for good when it comes to the wheels. One question I often have when I see wheel photos is: are those new holes? Or are they old holes? If they are old, are they bigger than they used to be? I made myself a map of the wheels and was thinking about trying to note precisely where and when specific tears and holes were first noticed, hoping to use it to check subsequent wheel images to see if holes are new ones or old ones but it's a bigger job than I have time for. Maybe the attached PDF/PNG map of the wheels would be of some use to people...?
http://planetary.s3.amazonaws.com/assets/images/z-misc/2013/20131221_wheel-tread-map-01.png
wheel_tread_map.pdf ( 1.53MB )
: 1060
If they are concerned enough to be thinking about route changes, as Erickson is implying, what would that mean? Sticking closer to sandy, rock-free ground? The obvious place to go in that case is the dune field itself, but then there's concerns about getting stuck, and of course missing waypoint 4. Trade-offs, trade-offs, and more trade-offs...
I think, it has been Zelenyikot, not quite sure.
In the short run, I just can provide as an example, that the idea works with the APXS inscription:
Here is an animated gif of the MAHLI images. It's not perfect, I tried to align everything to the wheels, so the horizon is going to flop up an down.
small
http://www.flickr.com/photos/43581439@N08/11490943014/sizes/o/in/photostream/
Large
http://www.flickr.com/photos/43581439@N08/11490853885/sizes/o/in/photostream/
I was concerned when they went with the flashy (tall/ low-profile) aftermarket rims instead of the stock steel wheels. Yes, hubcaps look tacky on a 2.5 billion dollar super-rover, but in this case style over substance may cost us longevity.
Stock steel wheels? Aftermarket rims?
Steel wheels would have been far to heavy and costly. There is nothing wrong with the design of MSL's current wheels. Damage was expected and like it has been said over and over, will NOT impair mobility.
It will be interesting to see if there are any design changes to the twenty-twenty rover wheels based on these observations.
Four Sol 490 MAHLI images provide better coverage, here for one of the wheels:
http://makeagif.com/BrxS0e
Almost sure to be some design changes. The space and weight trade-off considerations must cause some angst in mission design between the science and engineering design teams. The MER wheel and rocker bogey design was brilliant, with Opportunity still hobbling along having covered a distance of 65 times the mission success criteria, albeit primarily on soft sandstone. Curiosity's mass is 5 times that of a MER which required a modified design. But wheel design has to be based on a guestimate of what the ground environment will be like and while Curiosity is traversing sedimentary rock, she (is that gender correct?) has encountered a lot of sharp angular clasts which have done some cosmetic damage, although the structural integrity of the wheels is unaffected. Still, one thing we can be certain of is that the next rover will generate the same tired old blogging arguments on tracks versus wheels etc.
The gender is correct.
My humble try towards a "tread map" of the left front wheel, Sol 490, based on the same MAHLI images (0490MH026200000?E1_DXXX.jpg) used for the above animation:
Cool!
All of the MAHLI images of right side of Curiosity from Sol 488-490. I'm working on the left side now.
Today I read in a French space magazine that NASA is thinking about changing the MSL route to Mt Sharp. The accumulated denting of the wheels is higher than originally anticipated, so a more benign route with lower wheel-damaging potential is being considered.
Assuming there are energy expense issues related to driving (with dented wheels) vs. science objectives over the projected lifetime of the power source, do alternate smoother terrain routes already compromise some of the science? Is the base of Mt. Sharp such a prize target for examination that we need to "head for the highway"?
edit: I really want to see the view from the peak!
We all do; but the main science is the 'badlands' type terrain on the lower portions. The upper reaches are mostly windblown dust. I imagine the REMS team would like going to higher altitude to measure differences in temperature, pressure and winds compared with the base, but they're just one instrument. It's all about trade-offs...
Does driving in general expend more energy than stationary science instruments? I assume so, but can't find that info on the Google Skimmer.
chem-cam examination of http://www.midnightplanets.com/web/MSL/image/00493/CR0_441262493EDR_F0240408CCAM10492M_.html? first i'm aware of.. a al http://www.unmannedspaceflight.com/index.php?s=&showtopic=7658&view=findpost&p=205241 prescient comment.
If there will be some plan to alter course to avoid wheel wear+tear, even though all this not too outside expected parameters and poses no problem at current rates, it raises the question exactly what goal re-routing for smooth sailing would be expected to accomplish? a smoother path probably means it will be covered more with sand and dust and fewer scientifically interesting outcrops to investigate. on the other hand, fewer science-stops could translate to arriving at the entry point or badlands sooner, if that's the point, but perhaps less to tell of the journey there...
one wonders what sort of performance the rover will have in soft sands, years from now after most of the soda-can films between the lattices have finally worn and flaked off. I suspect skeletonized wheels could actually be beneficial in a 'purgatory' situation..?
Though they're correct in that this is not a dramatic 'mission killer' like many implied at the start.
It's more on the line of stuck heaters or right front wheels on the MERs.
Minor deviations from the planned track to 'swerve' around potentially damaging terrain seems like good applied common sense to me.
Thank you Gerald, my interpretation of what was said were off then, it had me think of the largest scale.
So just as what Serpens said, then this is something that make sense.
Happy new year!
There are some really awesome http://www.midnightplanets.com/web/MSL/sol/00502.html, plus a http://www.midnightplanets.com/web/MSL/image/00502/NLB_442059532EDR_F0250000NCAM00526M_.html.
Here's a mosaic of those chemcam images.
...Great mosaic, surely a fix-it ticket 'till the buttes
To me the holes and tears tell the story, that several of the rocks are as sharp as knifes, some with almost the hooklike properties of a http://en.wikipedia.org/wiki/Can_opener.
That's certainly important to know for future missions, in cases where exposed vessels may need to be kept under pressure.
Edit (Jan 5 2014): A Sol 502 illustration:
Precisely, serpens, and well said!
Also, a nod to Gerald: Yes, any knowledge gained from not only the science but also the engineering performance of not just the wheels but ALL MSL mission systems under real-world conditions (that world being Mars in this case) will undoubtedly be used to refine future designs in all respects.
That's why it's called exploration, folks. We're right in the face of the unknown, in every way, and during every sol. It's not for the faint of heart.
ADMIN: Previous four posts removed. Please read the Forum News>Important Announcements>http://www.unmannedspaceflight.com/index.php?showtopic=7773.
thank you for this discussion and for the images posted, and in particular that posted by Astro0 9 posts back.
When I was looking at this, I was concerned that, at the end of what appears to be a crack or break in the wheel surface material (unless I have completely misunderstood the image - in which case, please forgive me - this is my first post here), there looked to be a distortion of the wheel surface continuing in the direction of the break, suggesting that a crack continues in that direction. I downloaded the image and fiddled with the contrast (attached) and believe that my initial observation is correct. In terms of monitoring the progress of the damage to the wheel, it will be interesting to see whether the cracking continues in that direction.
modified to make image clearer
These two MH wheel views happen to show almost identical faces of the LF wheel - load them up in different windows and flip between them to see the changes between sols 488 and 506 (three shortish drives between them):
http://mars.jpl.nasa.gov/msl-raw-images/msss/00488/mhli/0488MH0262000001E1_DXXX.jpg
http://mars.jpl.nasa.gov/msl-raw-images/msss/00506/mhli/0506MH0262000000E1_DXXX.jpg
Apart from some new small scratches, there seems to be a new hole near the bottom of the wheel.
(Mods - sorry, I meant to post this in the wheel thread.)
Mod: Done.
To me it looks like the hole was there before, but with shaded ground behind it instead of illuminated ground.
Phil
Phil, I think fredk is referring to the red-arrow highlighted feature:
You may be right, Dilo - at first I thought that couldn't be sunlight shining through a hole because the inner wheel surface is quite dark grey, as you can see from the other light spot. But if there are patches of soil sitting on the bottom of the wheel, they would look bright orange when sunlit of course. Once we get a rotated view of the wheel we'll know for sure.
Yeah, I stared at that for a while this morning and couldn't decide either whether it was a new hole or a sunlight patch. I was leaning toward sunlight patch but don't see strong enough evidence to overturn anybody's call either way.
Looks like the ~1-meter drive on sol 513 was equal to a half-turn of the wheels, with MAHLI imaging of all wheels at 4 positions - I suppose the repeatability test for arm position the other day was with this in mind, though I don't know if we could tell other than from SPICE files if the arm was stowed for each step, or if they found a spot smooth enough to leave it deployed for these small steps. Wonder if they will do the other half-turn next sol, or if those positions are covered by other recent imaging? They downlinked and posted the images quickly, too - about 6 hours after taking them.
The good news is that there's not much discernable difference between sol 490 (right image) and sol 513 (left) on the worst spot on the front left wheel.
Should have read the news first. From Ken Herkenhoff (full text http://astrogeology.usgs.gov/news/astrogeology/sol-513-update-on-curiosity-from-usgs-scientist-ken-herkenhoff-early-planning):
Are all the wheels "in sync" ??? i.e. do they all show the same exact number of rotation on a given drive?
Olivier
They would if you were driving in a perfectly straight line on a smooth surface. But on a rugged surface, and with turns, you obviously have different numbers of rotations. For example, during a turn, the outer wheels make more rotations than the inner wheels.
Plus there will always be some wheel slippage, which will be different for each wheel.
I believe that each wheel is independently controlled as well if they emulated the MER design philosophy. Therefore any rotational synchronization in term of identical RPMs (often over several Ms, frankly) would indeed have to be straight-line and frankly coincidental given external factors like slippage.
With all this recent wheel imaging, it really seems like it should be possible to produce a systematic survey of the current condition of the entire circumference of all the wheels. Just throwing that out there in case someone has the time to organize images into such a survey....
I've ideas for a 0th and 1st approximation of an "undistortion" algorithm for the wheel images. For the 0th approximation three points should be sufficent to retrieve the mantle of an assumed cylindric wheel. A fourth point as parameter may already be sufficient to take account of the perpendicular curvature.
This shouldn't be too difficult to program. May be I'll dare a try on Sunday.
Yes please Gerald.....'Dare Mighty Things'!
I'm trying to get a handle on wheel geography in order to interpret the survey images and look for changes. These are all from the sol 513 MAHLI imaging. I count 20 inter-tread areas (where the punctures are forming) between treads. Because the Morse code makes such a good landmark, I am counting upward and downward from those spots to name the inter-tread areas, 10 up and 10 down. I'm noting locations of tears and punctures as they are closer to the rover (medial) or farther from the rover (lateral) or in between (central). So far I've just looked at the right-side wheels. Here's what I've found in this one set, keeping in mind that the RF wheel was incompletely surveyed. There were some spots I wasn't sure about. Now I need to complete the survey on the left side, and then compare back in time to try to note any others that I missed on this survey, and to try to put some constraints on when the tears initialized and worsened.
RF
6 down - big puncture, center
Right-hand image, second one down: Number 8 has a T-shaped mark just to the left of the number.
Next image down: that same T-shaped mark is on the space numbered 9.
I don't see any other numbering errors.
Phil
Thanks, I fixed that.
Here's the rest. I wonder why the left middle and left front wheels have suffered so much more than the others, and why the two rear wheels appear to have escaped injury so far.
LR
Nothing major
As has been pointed out, the MSL mobility testbed unit displays similar rips and tears in the wheels. It might be instructive to see the current status of the testbed wheels, along with a rough history of the number of meters it was driven and over what surfaces. I recall seeing video of the testbed recorded well before Curiosity landed that shows significant ripping and tearing in its wheels, so it must not take a huge amount of driving for these things to appear.
For the testbed experience to be truly applicable to the asset on Mars, I imagine the weight of the testbed would have to be roughly one-third of the actual MSL. I recall that the MER mobility testbed was weighted in this manner, I'm assuming MSL's was, too.
-the other Doug
The soil in the testbed area doesn't bear a lot of similarity to the exposed, angular rock of the Gale landing site.
Okay. Well, hey, it was a thought. Might still be interesting to compare the testbed wheels to Curiosity's, if just see if the wear and tear on this wheel design is inherent in the design and will occur pretty much irrespective of the surface conditions, or whether a surface with a larger admixture of sharp-edged stones will (as common sense would suggest) cause more rips and tears.
Again, I have no doubt that the wheels will work fine even if large sections of the thin aluminum end up getting ripped and torn. As with many of us, I'm sure, I just find this an interesting engineering exercise. (The absolute worst image I have is of Curiosity sort of humping up and down if a large piece of metal ends up sticking out of one of the wheels, a dynamic I find unlikely considering that even if a piece were to catch on a rock and rip radially outwards, the wheel motion would then tend to push it harmlessly back in towards the wheel hub.)
-the other Doug
Yeah, I could believe that the rear wheels are somewhat protected, in that some sharp protruding rocks are pushed or rotated down by the front and middle wheels. Conceivably there could also be some difference due to the asymmetric rocker/bogey design.
It's big heavy arm and a lot of torque there if it's stuck out....but....if the rover moved enough for a wheel to get punctures during that process... we would see it in imagery of pre/post arm deployment. We've seen some motion...but only a tiny bit.
After thinking about it for a while, I've changed my numbering system because I decided the up/down nomenclature would get confusing. Here's the summary again of the status on sol 513, with a map of the places I spotted holes. The map should be regarded as "notional" -- it's very sketchy.
http://planetary.s3.amazonaws.com/assets/images/4-mars/2014/20140120_wheel_survey_sol513_all.jpg
I'm persuing your approach of the pdf template.
Here a 720 degrees version of http://mars.jpl.nasa.gov/msl-raw-images/msss/00513/mhli/0513MH0264000001E1_DXXX.jpg:
http://imgur.com/jgK24ql
Not yet quite perfect. But composing/stitching four appropriate fragments of this kind of images could return a geometrically almost normalized view of a wheel mantle, hence allowing a better comparison of changes, or even providing the basis for a texture applicable to a 3d-model.
Pretty cool! That twist in the middle was quite a puzzle, until I realized you're projecting the inside surface of the wheel in the part of the view where that's what's visible, and the outside surface where we see that, and the brain-bending twist is where the viewer's sightline is tangential to the wheel's surface. Nice. It looks really excellent in the positions where it's at a moderately high angle to the camera.
Thanks for explaining the image! I could't have done it better, at least late in the night after a long day.
The underlying idea of the projection is, to wrap a rectangle around a cylinder, bend and translate this cylinder a bit, until it matches with a wheel in 3d relative to the camera, then simulate the mapping of the wheel by the camera. To put the color of a pixel within the rectangle, get the color of the raw image at the described transformed position.
My simulation of the wheel and the mapping by the camera needs some more refinement to get a well-standardized geometry.
I'll work on this in small steps, and let you know, when it's more or less satisfying to my eyes.
Emily, this "map" of the weels is so good! Can I use it in a space exploration french forum to illustrate theses weels anomalies? Citing that this is your work, obsviously!
Next step of Sol 513 MAHLI left center wheel image processing:
By wrapping the wheel into a cylinder-like surface (radius varying according to an appropriate parabola), and projecting it into the raw MAHLI images
http://imgur.com/CXSuZiX
the surface of the wheels gets geometrically standardized to a near-rectangle
http://imgur.com/5hSfJ0z
Cropping and stitiching results in a transformation to a standardized geometry (similar, but not quite identical to the cylindrical map projection):
http://imgur.com/yaVNWNa
Seriously cool - and exactly what I envisioned a wizard could do!
Now the next step is obvious - repeat for later sols and animate to see the changes. Hopefully you can turn at least most of the steps into an automatic pipeline so it's not a tremendous amount of work for each set of images...
Thanks!
The manually difficult unwrapping is mostly automized, reduced to a couple of parameters which I need to adjust between images. So I'm optimistic, that the steps you're suggesting become feasible.
I didn't yet test the other five wheels. It's probably one or two further parameters to be adjusted, mainly the distance to match size and perspective.
I'm dreaming of a fully automated feature recognition subroutine to eliminate any manual adjustment, but that's certainly more than a few hours of work at a week-end.
i c u r doing this job since quite while.
Actually point 3 has been already discussed on the MER forum.
The problem with "tank tread" designs are the mass penalty and, more importantly, treads can get thrown or break.
When that happens then your rover becomes crippled. With the current design, even if one wheel fails you can still move.
Spirit was able to do this for years
Thanks for that link.
The video indicates that the rover can do about a 20 degree slope in soft sand if I am understanding properly. Was there a hard spec on the maximum angle that the rover could traverse in soft sand?
I watch this site every day and get a feel for the anxiety that everyone has felt about trying to drive over a ~ 3ft dune. Now that Curiosity has done that I assume the anxiety will lessen for the same size dune in the future?
Since it is pretty much impossible to perfectly simulate Mars on Earth I guess we will never know for sure what the limits are on dunes until we measure the result for the first time with the rover on Mars.
I also understand the reluctance to find those limits.
Pretty much anywhere we go on Mars is going to have sharp rocks and dunes.
On the next rover mission we should be able to place a larger payload on Mars using the same rocket due to the more favorable launch window, (pretty much the best perihelic opposition for the next 13 - 15 years).
I hope that the wheels can be beefed up or replaced with something better. Folks have been saying that the next mission will not be a carbon copy of this one or even close.
Depends on the landing site surface, which is far from decided. It could be like Meridiani for all we know.
Another nice set of MAHLI wheel images has been down-linked from sol 0537. One advantage with this set is the light dusting of sand on the inside of the wheels, that has helped to differentiate between small punctures and reflected light off the dimples which has sometimes been interpreted as punctures.
A few quick seconds in this update show the rock tests in the Mars yard:
http://www.youtube.com/watch?v=PiBbFC4Isr0
no luck trying to find MAHLI pairs to create a stero view, but rolling along, heres a gif from SOL 546..
Sol 549 MAHLI took 5 images for each wheel. So I think, there is a chance to get a complete coverage of the wheel surfaces with this series.
I posted this in my blog yesterday, just looking at 2 of the wheels, the left middle and left front. I paired sol 513 and 546 images in similar positions to compare them. While I hate to suggest that any more pixels be devoted to wheels than already are, it does seem that a 5-position series would do better at completely characterizing them. Or maybe just a bit more rotation between adjacent pairs -- but then it would be harder to compare one sol to another.
http://planetary.s3.amazonaws.com/assets/images/spacecraft/2014/20140220_wheel-survey_comparison_sols513-546_lf-lm.jpg
That's nice! Some of the pairs can almost be used as x-eyeds for comparison.
The exact same (relative) wheel and camera positions for corresponding images would be ideal for monitoring. But I doubt, that this is technically possible with reasonable effort.
For a longer-term sol-by-sol investigation I'm still hoping to be able to solve the automization. This could then be used for consecutive image processing, e.g. for marks, where changes occurred. It would also be easier to compare MAHLI with Mastcam images.
There's a new hole in the right middle wheel, at position 8 near the center, between sols 546 and 554. It's easiest to see the before-and-after comparison in the bottom pair of images, where the holes are backlit.
http://planetary.s3.amazonaws.com/assets/images/spacecraft/2014/20140226_wheel_survey_rm_554.jpg
Could the drive along the edge of that giant bank of dark sand dunes?
finally some sloppy wheel crosseyes from SOL http://www.midnightplanets.com/web/MSL/image/00559/0559MH0263000000E1_DXXX.html & http://www.midnightplanets.com/web/MSL/image/00560/0560MH0261001000E1_DXXX.html MAHLIs
Here's a worrying photo from S564.
I'm sure the team are keeping a close eye on the http://www.midnightplanets.com/web/MSL/image/00562/0562MH0262000003E1_DXXX.html ...
These are not the 'droids you are looking for, move along...
Curiosity posing in front of Mount Sharp on sol 564:
https://www.flickr.com/photos/105035663@N07/13085290784/
http://www.midnightplanets.com/web/MSL/image/00631/0631MH0002590000203729E01_DXXX.html (http://www.midnightplanets.com/web/MSL/image/00631/0631ML0026110000302549E01_DXXX.html).. didnt see any mention of this elsewhere or i wasnt paying attention..., perhaps it has dropped off by now ...unless its lodged in there whreel well!
EDIT: fell out sometime before http://www.midnightplanets.com/web/MSL/image/00635/0635MH0002590000203765E01_DXXX.html
Hole opened in the left middle wheel between Sol 660 and Sol 667:
Ouch. I noticed the last time I mapped wheel wear that the middle wheels appeared to be accumulating new tears more rapidly than the front ones.
That has been a drive of about 500 meters; thus roughly extrapolated, we should be prepared to about 5 to 10 additional similar tears or holes till Murray Buttes - although we've always to look with precaution on extrapolations.
Not really frightening under normal circumstances; we'll have to get accustomed to it ... and keep the eyes open.
In this case we can see that the place was already damaged so, I guess, it was "easily" removed. Actually, we can't see yet whether the missing part is torn inside the weel or has been lost. Do you think there is any change of loosing a torn part of a weel? If yes, we'll have to look closely in the rear direction to see if we can see it.
The upper left fragment (in the image) is evidently torn inside. I didn't find immediate evidence yet, that this does hold for the lower right fragment, too. But the aluminium alloy should be sufficiently ductile to make it more likely, that no large fragment is lost.
A potentially lost fragment should behave similar to a pebble, cause some minor loss of weight of the rover, but without obvious implications to functionality.
I don't have access to that journal, unfortunately. That's a cool graph. Are the "front" wheels in this journal article on the bogie, or the rocker? I know that the rocker-bogie suspension system performs better bogie-first -- the JPL rovers are all built "backwards" so that if they get into trouble they're better-positioned to extricate themselves. But the graph is labeled "MER" so maybe it is rocker-first.
That paper states
Weird drive on sol 667--only 1.2m spread out over almost 2 hours. The http://curiosityrover.com/tracking/speedplot.php?drivenum=200 shows it was in four equally-spaced bumps, and http://mars.jpl.nasa.gov/msl/multimedia/raw/?s=667&camera=MAST_ and http://mars.jpl.nasa.gov/msl/multimedia/raw/?s=667&camera=MAHLI took images of the wheels along the way. Worrying about the wheels has been officially deregulated.
It'd be interesting to see 4 images of a particular wheel combined to "unroll" it into a continuous ribbon showing the wear pattern.
That's not weird, that's a standard wheel-imaging drive -- they do those every few hundred meters in order to monitor damage. They seem to be performing them on weekends for the most part. They recently made a tweak to their wheel-imaging routine: It used to be they took MAHLI images centered on each wheel (6 images), in 4 different positions. Now they are taking images of middle and rear wheels together (so only 4 images total), in 5 different positions, which gives them a more complete survey. They've also added Mastcam and MARDI documentation.
Also, note this talk planned for the 8th Mars conference in Pasadena:
Ah, I should have looked back in this thread at some of your wheel maps. Looks like they've been doing this since about January?
As for what they did about it, does it refer to this item from February?: http://www.jpl.nasa.gov/news/news.php?release=2014-055
Yes, I expect the public event to just be the story behind how they determined they should drive backwards, and drive in valleys instead of on high ground -- a nice story about how you solve an unexpected problem on a distant planet! This story is neat in that it's an engineering problem but understanding how to solve it required very close cooperation with the science team, which is kind of unusual for solving problems with spacecraft.
Any prospect of a video replay (official or bootleg) of the July 16 talk by Grotzinger and Heverley? It looks as though it might be particularly interesting to our crowd.
On June 9, the Washington Post featured an http://www.washingtonpost.com/national/health-science/too-bad-theres-no-aaa-on-mars-as-the-curiosity-rover-faces-equipment-trouble/2014/06/09/c055fe54-eb25-11e3-93d2-edd4be1f5d9e_story.html on the MSL wheel issue.
"Critically ill"? Nothing to see here but an "epic-scale problem." Glad they were able to pivot, literally.
Everything you want to know about Martian wheels but are too afraid to ask...
https://archive.org/details/nasa_techdoc_19930008925
A JPL/University of Texas study done in 1991... Enjoy !
[Disclaimer: The images of this post are not actual images from Mars.]
This provides an idea of how far you can go until a wheel fails:
I'd also assume, that the principle of redundance on each subsystem level is applicable to the wheels, meaning one or two wheels should be redundant to some degree. But I've no link to a paper I could reference to, to underpin this assumption, just some extrapolation from the MER rovers.
... Here a Sol 679 image of a passenger on the right middle wheel:
Has there been any attempt made to determine the composition of the rocks that are doing the damage? All I've seen is a reference to an unexpected number of 'small, pointy' rocks in the soil, so I've been assuming that these are shards of basaltic rock that seem to be ubiquitous at every landing site to date save Meridiani.
They could only do that statistically, since I doubt anyone has identified a particular rock punching a hole in a wheel.
Also it sounded like part of the problem was an underlying surface that didn't "give" when driving over a rock. Perhaps under those circumstances there are enough sufficiently sharp garden-variety pieces of basalt to do the damage.
Ah, thanks, missed the part about the substrate. Wonder if perhaps the entire area has underlying hard-tack evaporites.
That was really clingy soil on Sol 673. Right centre wheel.
Temporary patching on a few cracks
They intended to write a nice "JPL" at regular space on the soil. Well, the message will be a bit confused now...
The wheels have met a few rocks between Sol 34 and now...
Looking at that picture with the “ouch”, I realize all of a sudden that mentally I’ve moved on from any wheel concerns.
The cleats look fine even though a bit of tincan aluminium came off, so what. My frame of mind is “it looks sturdy, good to go for many, many more miles - all as predicted by the UMSF experts (who told me so in no uncertain terms!!) – see the thread.
After all these sols the mission is now getting tantalizingly close to the primary science objectives and that’s what I’m thinking about mostly for MSL.
We had been a lot on softer terrain, but the stretch from about sol 690-703 went over some nasty sharp rocks in hard surfaces. Not surprised we did some damage over that time frame.
I find myself confused over why MSL's wheels have suffered damage but I never heard any reports of Spirit/Opportunity wheel damage. Is it because MSL is so much heavier than the MER rovers or is it because of different wheel designs? Obviously, Opportunity was a much more benign (less rocky) environment for much of its mission, but I don't think you can say that about Spirit. It all makes me wonder if NASA should go back to the MER wheel design, appropriately scaled up for MSL weight, for the 2020 rover.
The different wheel design is only part of the story. It's mostly because of the terrain. I've heard the caprock at the Curiosity site described as being "like sharks' teeth embedded in concrete." It's not only that the rocks are pointy, but that they don't shift at all when the rover drives over them. Loose rocks sitting on sand get pushed down into the sand as the rover drives over them, substantially mitigating the force they apply to the wheels. Neither of the MERs ever drove over bedrock like this for any substantial amount of time.
With the MSL wheel design the rover can drive on, even if a wheel gets hooked in sharp rocks, by sacrificing part of her beauty. The actuators and structural components are strong enough.
With more robust wheels the probability, that a wheel gets stuck in sharp rocks may be reduced, but likely not to zero. So if a wheel of a potential more robust design gets stuck, nevertheless, how does it get disentangled?
A better design may be possible, but it's better to think twice, before changing a design, which is doing its job, although maybe not perfectly in every aspect.
I was wondering what happens if cracks propagate all the way across, particularly at several points around the circumference. Does it still hold together?
Yes, it holds together unless the crack propagates across the cleats along almost all the circumference.
A few posts earlier (Post #217) I've added a link to a video showing were the limits are.
Here is an image from SOL-696 that caught my eye.
I've followed this thread since it first started, when the first holes started appearing in the wheels. And I've had a question from the beginning that I hoped would have been mentioned or answered by now. Now that we have gotten to the Hidden Valley, I am just going to ask it:
Do the holes in the surface of the wheel affect mobility on a sandy surface like Hidden Valley? At what point do holes in the thin aluminum surface start to affect driving over 'dune-like' conditions? I know JPL is spelled out in holes, but if the whole wheel surface was like that, would Curiosity have a harder time in the sand? Clearly the JPL holes interact differently with the sand than the rest of the wheel judging by the tracks left in the sand.
There has been many posts (see below for a small selection) about how the wheels will keep on driving despite the damage. I even remember reading that if a wheel was just spokes, or squared off, it would still drive. But it seems to me that the aluminum 'webbing' between the cleats probably help to float the wheel over the sand. I'm not asking to prove anybody wrong or fear-monger, obviously the wheel isn't just going to fall off, stop turning, etc.; just wondering if there's any information on webbing/sand interactions. I just looked through the thread again and didn't see anybody discuss it (is that enough disclaimers?).
Emily has written an excellent blog post http://www.planetary.org/blogs/emily-lakdawalla/2014/08190630-curiosity-wheel-damage.html with a lot of new information about this topic.
My reaction to the article is that the wheel issue seems like a manageable problem as long as the terrain doesn't get worse when we start climbing Mt Sharp. It probably means that Curiosity won't ever drive as far or last as long as Opportunity has, but it doesn't really need to given the proximity of Mt Sharp. And the lab instruments and the drill won't last for ever either.
Fortunately by 2020 there will be a new rover to replace Curiosity.
There are several drill bits, I recall. And given the paucity of uses for both it and the sample collecting instruments so far, they might well last as long as Oppy's RAT.
Rover longevity no, but mission longevity probably yes.
Paolo
I'm wondering, whether a wheel, severely damaged along the stiffening ring, needs to be the end of the wheel or the driving.
Wouldn't it be possible to intentionally split the inner two thirds completely from the outer third by patiently fatitiguing the remaining cleats (e.g. by driving back and forth over an appropriate rock a sufficiently large number of times); then driving with the outer third of the wheel through the removed inner two thirds, again using Martian rocks as tools?
The journey could be continued with the outer third of the wheel.
Certainly a (crazy) challenge, but did anyone try?
In testing, they have found that the inner 2/3 of the wheel does, in fact, rapidly shred off of the rest of the wheel once all the chevron-shaped grousers have broken through. They are currently testing driving on the remaining 1/3 of the wheel, which does work. The problem is that to get to the 1/3 wheel state you have to go through a state where the inner 2/3 flaps around while you're driving, endangering the cable bundle that runs along the top of the wheel strut. If a sharp edge of shredded wheel slices into that cable, not only will the wheel possibly become unusable, but the short could affect the motor controller -- which runs wheels, HGA, and mast. Needless to say, they will not take any action that would knowingly risk failure of the motor controller.
My hope has been, that the risk could be handled by staying at a well-known location, driving forth and back just several centimeters, plus steering, such that cables remain in safe distance from wheel shreds, until this intermediate state is overcome.
Damage to cables aside, it's not clear how you could drive the outer 1/3 through the inner 2/3. To be able to do that, you'd need to slice the inner 2/3 open, so it could be at least partially "unwrapped" along its circumference. For example, you could slice between two odometry grousers. But to completely slice through the inner 2/3, you'd need to slice through the inner rim. Most damage is away from the inner rim.
Maybe you could target the inner rim for damage. But then it's not clear if you'd be able to unwrap the inner 2/3 since once it's complely loose you'd be very limited in the forces you could apply to it.
That's probably the more tricky ("crazy") part.
An idea would be to use a rock as a tool to slip the 2/3 over the 1/3 ("driving through"). For this to work, the 2/3 needs to be stretched (assuming it cannot be sliced).
The acute angle and the relatively low coefficient of friction between the two wheel parts should help to amplify the torque of the wheel actuator.
The first step would be to find out, whether this experiment is physically possible respecting the material parameters of the alloy and the torque of the actuators.
If it turns out to be physically possible, it's necessary to find out, whether the experiment can be executed in a reliable way.
Since the wheels have been constructed to dampen the landing, and the actuators are rather strong, I'd consider the idea as physically possible, but anything beyond is guesswork, without experiments. That's why I've asked, whether there exists already some experimental experience.
Somehow I think the extremely competent mission engineers, having access to a wealth of empirical trials data and theoretical considerations will have this matter well in hand and will have considered all options. However the capacity for mitigation is pretty limited and the main value will be in lessons learned and the reminder for future designs that no plan survives contact with the enemy (the enemy in this case being the Martian terrain). However perhaps we should also remind ourselves that the MSL fulfilled the last outstanding mission success criteria when it lasted one year on Mars. Possibly we have all been spoiled by the amazing longevity and transit distance achieved by Opportunity. However Opportunity's achievement should also be considered in light of the nail biting near failure of Spirit in the first few days which was rectified only because some very smart people provided for a low data rate communications back door. This enabled the problem to be identified and rectified in both Spirit and Opportunity. All in all the MSL wheels have done pretty well.
I would think the use of a nuclear generator would be a function of the requirement for a stable power level and invulnerability to dust storms rather than longevity. Regardless, if any mission critical part of the MSL gave up the ghost tomorrow the mission would have to be classified as a success having fulfilled prime mission requirements. Still there will be some pretty interesting risk analysis being undertaken in considering the alternatives of driving over hidden valley sand or the wheel damaging environment associated with bypassing the valley.
We're years away from wheel disintegration at this point, and it might never happen if the rover is lucky with the terrain. What worries me more is what the project might do to preserve the wheels. Wheel damage is a slow, degenerative disease, but getting stuck in soft sand could stop a mission overnight. Or the rover might get slowed down so much that all the instruments have packed up before we have finished on Mt Sharp.
People praise Opportunity, but they overlook that two of the instruments have gone and their loss means the rover can no longer detect clay minerals, which is a real problem when you are trying to explore clay rich regions.
The reason for the nuclear generator was to allow a wider choice of landing sites, in particular southerly sites like Eberswalde. It also simplifies operations, and makes the rover immune to planet wide dust storms.
Is current to the wheel motors monitored, or possibly some other means (slip signature?) of determining when one of the rover wheels is likely pinned against a rock? If so, could the rover do a little sidestep of some kind?
Yes. Here an excerpt of http://www.planetary.org/blogs/emily-lakdawalla/2014/08190630-curiosity-wheel-damage.html:
That'll teach me not to fall behind on Emily's blog.
Gentle mod note: Guys, MER solar panel cleaning has been exhaustively discussed for years on many, many threads. Let's keep posts relevant to the topic at hand; thanks!
EDIT: Per mcaplinger's suggestion, new topic created http://www.unmannedspaceflight.com/index.php?showtopic=7879 for solar-powered Mars rover issues.
I read in earlier posts that the wheels suffered catastrophic failure when the treads had basically been damaged across the entire circumference, and that the wheels would basically split into two parts, one third and two thirds the wheel width.
I have noticed in recent sols that the profile of the stiffening ring/flexure rim is becoming more pronounced as seen from the wheel exterior.
It would seem that subject to exterior pressures this area is indeed a point of weakness and potential tearing, and would therefore bear out the testiing results.
http://www.midnightplanets.com/web/MSL/image/00463/0463MH0262000000E1_DXXX.html I think one of the best pieces of news about the testing program I've heard lately is that they've done such a good job recreating the problem on Earth. That shows they understand the causes, and suggests that mitigation methods that work on Earth to prevent further damage might also work on Mars.
As I said, this would bear out the testing results.
Does the ambient temperature affect the strength/ductility/brittleness of the aluminum wheels much? There can be more than a 100°C swing from day to night temperature.
EDIT: found this http://www.aluminiumdesign.net/why-aluminium/properties-of-aluminium/:
Sounds like you're looking at some data. What alloy are the wheels made of?
I think (relying on memory) that it is 7075-T6 alloy.
Evidently that matters somewhat, as well as the fracture direction:
Most of the trials and data for aerospace alloys and tempers has been directed towards aircraft applications where fatigue crack growth rates get a lot of attention. But with Curiosity's wheels we are well outside normal designs and comfort zones and for the thin skin between cleats deterioration will be a function of accumulating penetrative injuries rather than crack growth. The cleats themselves seem to be hanging in there but as I think Paolo mentioned will be subject to repetitive flexing although the frequency of such is anyone's guess. Mars has thrown up an unexpected, damaging terrain that could not possibly have been anticipated from orbital imaging, but overall the mobility system has met all performance expectations. But in the temperature range at Gale there would be no wheel durability advantage in night driving.
Just a note: http://en.wikipedia.org/wiki/Fracture_toughness is not related to fatigue per se.
I really think that we have to differentiate between the deterioration of the thin skin of the wheels and the cleats. The damage to the skin occurs when an encounter with a shard of rock results in the weight on a wheel being taken completely or primarily by the thin skin rather than a cleat. This seems to result in a localised tear or deformation which weakens that particular area and any further encounter will exacerbate the damage. I stand to be corrected but I do not think that fracture growth is of particular concern given the failure mode. The cleats are a different matter in that they can initially withstand such encounters and the probability of failure (fracture break of the cleat) would seem to be a function of fatigue relating to the number of encounter cycles and encounter geometry for each particular cleat. I don't know to what extent the thin skin contributes to the structural integrity of the cleats and whether deterioration of the skin reduces the number of cycles to failure for the cleats. What I am trying to get at I guess is that even the empirical testing to failure conducted once the terrain and wheel problem was recognised is only indicative. It would be interesting to know though whether that testing indicated that the cleat failure was a catastrophic event (sudden break) or growth of an initial partial crack.
Tears and dents in right central wheel formed hole between http://mars.jpl.nasa.gov/msl-raw-images/msss/00667/mhli/0667MH0002610010203887E01_DXXX.jpg and http://mars.jpl.nasa.gov/msl-raw-images/msss/00744/mhli/0744MH0002610010204500E02_DXXX.jpg:
I just stumbled across this pic.
Amazing.
http://mars.jpl.nasa.gov/msl-raw-images/msss/00971/mhli/0971MH0002620000304268E01_DXXX.jpg
Here's a look at the left-middle wheel over time, which is the one I'm most concerned about. Although there have been changes between sol 708 and 962, they're only incremental -- I'm actually pretty pleased with how they look after the Pahrump campaign and a whole lot of driving besides. There are no broken grousers. The grousers to watch closely are the ones between fields 11 and 12 and 13 -- those areas have a lot of tears running a substantial width of the wheel, leaving the grousers with little support except at their ends. So those are the ones that will probably break first, eventually. Hopefully continued careful driving will prevent that from happening for a while.
Moved a couple of posts about Mars 2020 wheel design to a http://www.unmannedspaceflight.com/index.php?showtopic=8030 in the http://www.unmannedspaceflight.com/index.php?showforum=80.
The latest series of images from MSL / Mars Hand Lens Imager / MAHLI camera has several views of the wheels.
From Sol 1127 (40 img): http://mars.jpl.nasa.gov/msl/multimedia/raw/?s=1127&camera=MAHLI
One of the images shows a nasty looking spike of metal jutting into the wheel space. I presume the axle shaft will knock it away / back, before it becomes an issue for the wire bundle.
I was unable to find a better image of the metal spike, but here's a ghastly, tweaked & cropped version (I presume it's a spike and not an optical illusion).
From here:
http://mars.jpl.nasa.gov/msl-raw-images/msss/01127/mhli/1127MH0002640000401794E01_DXXX.jpg
That one has been developing for a while, but it does have quite the inward point. Engineers are justifiably concerned about the possibility of these sharp edges abrading the wire bundles. I actually am having trouble figuring out a scenario in which this one, ripping further, would then straighten in the right way and place to actually scrape a wire bundle; I think it gets to be a more serious problem if (when) grousers start breaking.
Yes, you're right - when it (or any others) get long enough, they will hit and be bent in/out/forward/aft - but certainly away from the centre of the wheel - which is a very good thing.
Been pretty quiet on here: any developments in 'Wheel World'?!
Dean
The driving software update appears to have slowed down the wheel degradation. There has been less driving and more science activity. And there haven't been again these sharp and strongly embedded rocks, which caused much of the damage.
I'm not really disappointed about Curiosity being fit for the trip uphill Mt. Sharp.
As wheels continue to http://www.midnightplanets.com/web/MSL/image/01386/1386MH0002640000502644E01_DXXX.html and http://www.midnightplanets.com/web/MSL/image/01386/1386MH0002640000502656E01_DXXX.html, lets hope the http://www.midnightplanets.com/web/MSL/image/01386/1386MH0002620000502657E01_DXXX.html survive or well soon end up dead!
I included this comparison in my most recent update. Degradation has progressed, but only slowly, and there was no acceleration as they went across the Naukluft plateau, as I'd feared. As long as drive distances are relatively short (less than 50 m or so), the rover drivers can prevent a lot of damage by driving around hazards they can see. Not sure how much longer the grousers on the right middle wheel are going to last, but they're hanging on for now.
Full wheel survey sol 1315:
http://planetary.s3.amazonaws.com/assets/images/spacecraft/2016/20160614_wheel_survey_sol1315.jpg
LM wheel over time:
http://planetary.s3.amazonaws.com/assets/images/spacecraft/2016/20160614_wheel_survey_lm.jpg
I thought something looked a bit odd about the LM wheel on the latest survey, from 1512. Comparing it to an earlier view, from 708, you can pretty clearly see that the grousers near the top have been bent inwards:
Oof. Well spotted. I won't have time to look back in time for a bit, but if people want to hunt for where/when this happened, there have been full wheel surveys on 1046, 1127, 1179, 1260/9, 1315, 1434, and 1471. There have also been partial (one position only) surveys on 1182, 1214, 1245, 1287, 1313, 1355, 1380, 1403, 1416, 1435, 1444, 1459, and 1482.
With thanks to Post #278 from atomoid, above, I found their mentioned link to the site http://www.midnightplanets.com/web/MSL/sols.html
I've always found the http://mars.jpl.nasa.gov/msl/multimedia/raw/ to be quite cumbersome to use - one has to open each day, from each camera, to see what imagery was taken, and then open each thumbnail to get the final image. The http://www.midnightplanets.com/web/MSL/sols.htmlsite is a much better interface and shows all images in a neat grid array (though I'm sure, bandwidth heavy). I presume it's a bit of clever coding - a front end image scraper for the main msl site. It's very good, and, after all these years, I've only just stumbled across it.
Here are the links to the useful MAHLI (and others) images for full wheel surveys days (thanks to E Lakdawalla for pointing them out).
http://www.midnightplanets.com/web/MSL/sol/01046.html http://www.midnightplanets.com/web/MSL/sol/01127.html http://www.midnightplanets.com/web/MSL/sol/01179.html http://www.midnightplanets.com/web/MSL/sol/01260.html http://www.midnightplanets.com/web/MSL/sol/01269.html http://www.midnightplanets.com/web/MSL/sol/01315.html
http://www.midnightplanets.com/web/MSL/sol/01434.html http://www.midnightplanets.com/web/MSL/sol/01471.html
The partial surveys are here:
http://www.midnightplanets.com/web/MSL/sol/01182.html http://www.midnightplanets.com/web/MSL/sol/01214.html http://www.midnightplanets.com/web/MSL/sol/01245.html
http://www.midnightplanets.com/web/MSL/sol/01287.html http://www.midnightplanets.com/web/MSL/sol/01313.html http://www.midnightplanets.com/web/MSL/sol/01355.html
http://www.midnightplanets.com/web/MSL/sol/01380.html http://www.midnightplanets.com/web/MSL/sol/01403.html http://www.midnightplanets.com/web/MSL/sol/01416.html
http://www.midnightplanets.com/web/MSL/sol/01435.html http://www.midnightplanets.com/web/MSL/sol/01444.html http://www.midnightplanets.com/web/MSL/sol/01459.html
http://www.midnightplanets.com/web/MSL/sol/01482.html
The area dented inwards appears to be section 12/13/14.
And now the first broken grouser, seems to be between 12-13 (as predicted in Post #271!)
https://mars.nasa.gov/news/2017/breaks-observed-in-rover-wheel-treads
https://mars.jpl.nasa.gov/multimedia/images/2017/break-in-raised-tread-on-curiosity-wheel
Images here.
https://mars.nasa.gov/msl/multimedia/raw/?s=1641&camera=MAHLI
This is a very interesting event.
A different view of the http://www.midnightplanets.com/web/MSL/image/01641/1641MH0002640000602970E01_DXXX.html: one looks somewhat pushed into the wheel and is slightly severed just outside the hole to the right. Below it a second grouser is severed and displaced quite a bit and is probably the one sticking up in the original image. These are also visible lower down in the next http://www.midnightplanets.com/web/MSL/image/01641/1641MH0002640000602974E01_DXXX.html and looks about right to put the lower one in the right place to peek up over the top in the https://mars.nasa.gov/news/2017/breaks-observed-in-rover-wheel-treads. its sort of grimly funny how the middle wheels take the brunt of the damage, more load-bearing perhaps..
An Algorithm Helps Protect Mars Curiosity's Wheels
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