Curiosity Mars rover tire/wheel damage and design.

Panza · Apr 1, 2015

I just wonder what you think about the design of the wheels of the Mars Rover Curiosity ?
They are sustaining some serious damage from driving over rocks.

The wheels are machined from aluminium and the thin parts where there are no "threads" are 0,75mm thick. There is a thicker ring inside where the spokes are attached.

It's easy to say after the damage has occurred, but I say the design is pretty poor. Seems like some pretty obvious things have been overlooked.
For starters I wouldn't use aluminium where there is going to be flexing all the time. Then those machined stress-risers ?

Undamaged tire/wheel which shows the design:

Damaged wheel:

pri0ritize · Apr 1, 2015

Panza said:
It's easy to say after the damage has occurred, but I say the design is pretty poor.

You need to understand something called "scope". The original design of the Mars Rover was to last approximately 90 days. It's been operating since 2004...I'd say the design of the wheel is downright amazing.

Royldean · Apr 1, 2015

Design was for 687 martian days, and it's at 943 and still going. What's that thing Colin Chapman used to say about racecars? Something about them falling apart after rolling over the finish line.....

[edit] perhaps I misunderstood the wiki page regarding the mission length, but regardless.... point is proven.
[edit 2] pri0ritize, I think you are confusing the curiosity with other rovers... it landed in ~2012

kenh · Apr 1, 2015

Just a wee bit of damage, but it "kept on truckin'"

One Racer statement is the engine should blow as soon as you cross the finish line.

CountryBoy19 · Apr 1, 2015

pri0ritize said:
You need to understand something called "scope". The original design of the Mars Rover was to last approximately 90 days. It's been operating since 2004...I'd say the design of the wheel is downright amazing.

Curiosity landed in Aug 2012 and according to what I found had an initial mission of 2 years. But that mission has been extended indefinitely (I'm guessing until a critical failure takes it out of the game). Yes, the wheels lasted as long as the original mission but I would say that they skimped a little too much. A couple more pounds of AL in a well design support rib pattern, or a different material altogether would have been better. The dang thing weighs over 2,000 pounds and they're using 4 tiny AL wheels that have a thickness of less than 1 mm....

adama · Apr 1, 2015

So just what would you use? Have you considered the uv levels - radiation and other chemical aspects? Mars is not the place for your typical rubber tyre, thats before you get into weight restrictions that would kinda rule out your typical hardox or similar tripple grouser as used on plant in quarries that have this kinda rock here on earth.

If you have been following the problem your no doubt aware they have encountered a lot more hard - sharp little rocky areas than the other rovers have encountered, this is not visible from orbit with anything thats circling mars right now, theirs just not the definition to see that small a objects - surface textures. Combined with the increased weight, its not exactly surprising its shredding the wheels a bit. That said, if you look at the wheel you kinda realize the damage is not going to make all that much difference to the design. Equally every tread is filleted at the bottom. The short on drilling is possibly the far bigger risk for its future right now.

Its opportunity i feel sorry for, that little buggers done real well, both distance and life span, curiosity has a long way to go to match it as yet too! Heres hopeing they find the budget to keep it rolling and can fix the memory issues. I think its pretty awsome what that’s achieved, especially for the cost of it.

lathefan · Apr 1, 2015

Milland · Apr 1, 2015

lathefan said:

Yeah, but NASA could only afford the 100 mile towing level. Do you have a guess for the charge for the remaining 139,999,900 miles??

JNieman · Apr 1, 2015

It's beyond me to criticize their design. I'm nowhere near their level. I accept that if it were me, my wheel would have probably failed the landing, let alone exceeded initial design parameters.

I think the Opportunity rover is putting peoples expectations of NASA rovers way beyond reason lol. 400x expected mission life and counting... so I can see how ONLY 1.5x (and counting) could be seen as a disappointment.

They're all gonna die, man, it's just a matter of accomplishing the goals before they do. Just like the race car comments people made before me.

ewlsey · Apr 1, 2015

Is that a steer tire? If not, I'd go for a retread.

gbent · Apr 1, 2015

CountryBoy19 said:
The dang thing weighs over 2,000 pounds

Here or there? Martian gravity is only 38% of earth.

The proof of the pudding is in the tasting. I'd say they did quite well.

lathefan · Apr 1, 2015

Milland said:
Yeah, but NASA could only afford the 100 mile towing level. Do you have a guess for the charge for the remaining 139,999,900 mile??

...if it's like around here...five bucks a mile...

Rstewart · Apr 1, 2015

They should have used AeroSpace Grade AA Billet, Silly engineers

Antarctica · Apr 1, 2015

+1 on the post above that cited UV. I haven't read anymore than this post but I would guess that was a major factor in the failure - if you can even call it failure since its far exceeded its life expectancy. I've seen one of these wheels first hand (at a NASA exhibit at AGU) and I can't see it failing at the low speed curiosity operates at without an additional factor of UV breakdown or something similar.

And I'm not about to play second chair quarterback to anything JPL designs. Their shit is brilliant. Because their people are. As with almost any engineering design, its easy to point out a problem or something that might have been done different (I won't even say better here) in hindsight - but its altogether different to be at the front of a design looking forward and trying to mitigate 10000 problems.

My guess is that this design did just that - few of which will ever even cross most peoples' minds…

Brent

Antarctica · Apr 1, 2015

Followup question - quasi related.

Does rubber outgas in a vacuum? Inquiring minds….

Brent

CountryBoy19 · Apr 1, 2015

adama said:
So just what would you use? Have you considered the uv levels - radiation and other chemical aspects? Mars is not the place for your typical rubber tyre, thats before you get into weight restrictions that would kinda rule out your typical hardox or similar tripple grouser as used on plant in quarries that have this kinda rock here on earth.

I'm not saying AL isn't the best material, but certainly NASA, of all people, has the ability to access materials that we may not. I certainly wasn't suggesting rubber. I really was thinking a small design change to include some circumferential ribs on the inside would have done a great deal in making the wheel last longer.

adama said:
If you have been following the problem your no doubt aware they have encountered a lot more hard - sharp little rocky areas than the other rovers have encountered, this is not visible from orbit with anything thats circling mars right now, theirs just not the definition to see that small a objects - surface textures. Combined with the increased weight, its not exactly surprising its shredding the wheels a bit. That said, if you look at the wheel you kinda realize the damage is not going to make all that much difference to the design.

I know it's easy to arm-chair quarter-back something that was designed 5 years ago, was sent through space for almost a year, and now reside on a planet that is for all intensive purposes uninhabitable. But you would think that they could at least foresee that the terrain COULD BE more rocky than anticipated and design a better wheel? I disagree with you that the damage won't make much difference in design. Look at the design, there is NO thicker metal to stop those holes from growing out to the edge of the wheel. After they propagate through to the edge the wheel loses a significant amount of strength (essentially flopping around) and the wheel will quickly disintegrate down to the strengthening rib shortly there-after. Look at the portion where the internal strengthening rib is (for spoke attachment), that has held up remarkably well. A few more smaller ribs running circumferentially between that large rib and the outside edge of the wheel would have added maybe10-20% weight increase on the wheels but would add a strengthening rib that not only helps prevent damage but also stops it's propagation if damage were to happen. I would think a wheel like that could survive a great deal longer.

Milland · Apr 1, 2015

Yes, generally all rubbers will outgas some amount of material when in a vacuum or subjected to high temperature. Maybe some exotic "rubbers" (that never had anything to do with an actual tree) have low enough numbers for prolonged work in some harsh environments, but even they will degrade. Check out what Kalrez o-rings go for if you want a nose bleed...

Krutch · Apr 1, 2015

CountryBoy,
Weight is a compromising factor on anything sent into space. Every item is weighed and the total is what determines the fuel, which has it's own weight allowances, needed to send crap into orbit and out of orbit. Plus landing on Mars is not as easy as earth. Martian atmosphere is not as dense and parachutes need to be much larger, also adding weight. All factors affect the mission. Many I have not mentioned, mostly because I don't know all of them. That the wheels held up this long is a plus. The rover was limited in scope, mission, and ability. It has out lived it's projected life. Pretty good for millions of miles from a service station, I'd say.

Panza · Apr 1, 2015

Antarctica said:
+1 on the post above that cited UV. I haven't read anymore than this post but I would guess that was a major factor in the failure - if you can even call it failure since its far exceeded its life expectancy. I've seen one of these wheels first hand (at a NASA exhibit at AGU) and I can't see it failing at the low speed curiosity operates at without an additional factor of UV breakdown or something similar.

And I'm not about to play second chair quarterback to anything JPL designs. Their shit is brilliant. Because their people are. As with almost any engineering design, its easy to point out a problem or something that might have been done different (I won't even say better here) in hindsight - but its altogether different to be at the front of a design looking forward and trying to mitigate 10000 problems.

My guess is that this design did just that - few of which will ever even cross most peoples' minds…

Brent

You can easily see where the cracks has started: At the machined threads. Because they are serious stress risers. If that isn't a basic design flaw I don't know what is.
And I bet that those that designed the wheels thought they would last more than 8km in semi-rocky terrain.

rwbaldwin · Apr 1, 2015

lathefan said:

The member has to be there with the vehicle when AAA arrive

Curiosity Mars rover tire/wheel damage and design.

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