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Rough Roving: Curiosity's Wheels Show Damage

Soulskill posted about a year ago | from the pit-stop-unlikely dept.

Mars 78

astroengine writes "In a recent batch of images beamed back to Earth from Mars rover Curiosity's MAHLI camera, obvious signs of wear and tear could be seen in the 'skin' of the robot's wheels. Considering Curiosity is only 281 sols (Mars days) into its mission and roved less than a kilometer after landing, surely this doesn't bode well? Fortunately, there's good news. 'The wear in the wheels is expected,' Matt Heverly, lead rover driver for the MSL mission at NASA's Jet Propulsion Laboratory in Pasadena, Calif., told Discovery News. 'We will continue to characterize the wheels both on Mars and in the Marsyard, but we don't expect the wear to impact our ability to get to Mt. Sharp.'"

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Fun fact (4, Interesting)

funky49 (182835) | about a year ago | (#43798565)

There's a fun fact about the wheels of Curiosity. They spell out "JPL" in Morse Code in the sand of Mars. :)

Re:Fun fact (0)

Anonymous Coward | about a year ago | (#43798601)

As someone who has his online degree in chemical mathematics again, I can say that this is, without doubt, valid science.

Re:Fun fact (1)

EETech1 (1179269) | about a year ago | (#43799131)

I wonder if this impacts the strength of the wheel any with all those dashes, perhaps just saying hi would make them more durable.

Re:Fun fact (1)

aliquis (678370) | about a year ago | (#43799365)

"I WAS HERE!"

Re:Fun fact (1)

Anonymous Coward | about a year ago | (#43800437)

Should have gone with Michelin. Because so much (money) is riding on your tires.

Re:Fun fact (1)

Mr. Freeman (933986) | about a year ago | (#43801001)

These guys are NASA engineers. I'm sure they've considered that. If there were any structural benefits to be gained from removing the pattern then they would have done so. That said, the design of the wheels is quite interesting. The "JPL" Morse code sections have holes through the wheels whereas the rest of the wheel is simply a solid tread pattern. The addition of holes is very interesting and I'd be interested to hear the rational for incorporating such sections into the wheels.

Re:Fun fact (1)

ozmanjusri (601766) | about a year ago | (#43801693)

The addition of holes is very interesting and I'd be interested to hear the rational for incorporating such sections into the wheels.

To drop any sand or grit out once per revolution. You wouldn't want it to build up.

Re:Fun fact (1)

camperdave (969942) | about a year ago | (#43809791)

I don't think that would help. The holes could let sand and gravel in as well as out (although I don't see any sand/gravel/grit in the wheels). If I were designing the wheels, I'd make the inside slope from the center out to the edge, so that as the wheel turned, any sand or grit would gradually work its way out of the wheel.

A Journey on Mars (0)

Anonymous Coward | about a year ago | (#43803533)

Oh, the wheel in the sky keeps on turnin'
Don't know where I'll be tomorrow.
Oh the wheel in the sky keeps me yearning...
For tomorrow!

Re:Fun fact (2)

Taco Cowboy (5327) | about a year ago | (#43799313)

I learn something new today. Thanks !

BTW, looking at the picture ( @ http://upload.wikimedia.org/wikipedia/commons/3/37/Curiosity_wheel_pattern_morse_code.png [wikimedia.org] ) I am totally surprised at the sheer thinness of Curiosity's wheel !

How can they expect Curiosity to last long with such thin wheel ??

Re:Fun fact (3, Insightful)

Charliemopps (1157495) | about a year ago | (#43800015)

Because the project managers were given criteria. 1. it had to last for X months... 2. it had to be under X kilos. Which do you think was a harder goal? I think it's pretty obvious. Making things that last forever is easy. Making things that are light is easy. Making things that are both? Little bit more difficult.

Re:Fun fact (1)

jordan_robot (1830144) | about a year ago | (#43808011)

Really look at the wheels; they are actually a very well designed machine component. The main design strengths are graceful degradation (inherently long working life), and an excellent balance of material conservation/functionality . A breakdown follows:

1. The center ribs of the wheel are the first structural element, transmitting the forces exerted on the wheel to the hub.

2. The treads are thicker material that provide several functions: provide traction, transmit the forces from the wheels' skin to the center ribs, and lend structure to the center ribs.

3. The skin of the wheel looks to be slightly cambered. Bending the skin of the wheel in such a manner actually creates a suprisingly stable structure that is also slighly flexible. That slight flex means the wheel will survive impacts better a very rigid arrangement. The thin skin also reduces weight. As the wheel skin is dented and punctured, it actually will provide better traction as time goes on. Even when the skin finally begins "fall apart" the arrangement of the tread ribs and center ribs will continue to work as a fully functional "wheel".

These wheels would work even if there weren't any skin on them, they just wouldn't work as long.

Re:Fun fact (0)

Anonymous Coward | about a year ago | (#43801131)

Which is Martian for "Follow me."

Re:Fun fact (1)

Squidlips (1206004) | about a year ago | (#43804721)

The engineered holes spelling out JPL may sound like a great idea, but it is not. Those holes will be a detriment if MSL finds itself in a soft powdery dust dune, i.e. the same stuff that trapped Spirit and Opportunity. Spirit never got out. The wheels are the one major design flaw in all these rovers. Here on Earth, when you drive through soft sand, you want large soft, and smooth tires-- the exact opposite of what is used on these rovers.

Lss Schwab (1)

TechyImmigrant (175943) | about a year ago | (#43798615)

If they find a Les Schwab center to fix the tires, we'll know there's no intelligent life on mars.

Re:Lss Schwab (1)

game kid (805301) | about a year ago | (#43798723)

Out there in Mars, that rover's more likely to find a Charles Schwab center and end up owing a consultant money.

Re:Lss Schwab (1)

TechyImmigrant (175943) | about a year ago | (#43799009)

>Out there in Mars, that rover's more likely to find a Charles Schwab center and end up owing a consultant money.

$7.95 per turn of the wheel, in either direction.

Re:Lss Schwab (1)

EETech1 (1179269) | about a year ago | (#43799779)

Quick someone figure out the cost per revolution of a wheel if the rover only completes the primary mission...

Please

Wheel wearing (4, Informative)

girlintraining (1395911) | about a year ago | (#43798643)

These wheels aren't like your normal car wheels. The very thin atmosphere means that the soil is more like lunar soil than Earth soil. Atmospheric erosion tends to smooth out sand particulate so it has a rounder shape -- it is less sharp. Lunar soil is incredibly corrosive. Think of all the problems our troops had operating in Iraq with their equipment, now multiply that by a hundred. It's like walking on microscopic needles. Martian soil isn't quite as bad, thanks to having had an atmosphere at one point, and retains a minimal one now, but it's still inhospitable.

The rover was designed with multiple wheel-sets to operate independently, and the wheels themselves designed to wear somewhat more gracefully in the face of these obstacles. But yes, they're going to look ugly fast.

Re:Wheel wearing (1)

Anonymous Coward | about a year ago | (#43798933)

Despite its thin atmosphere, Mars regularly experiences massive sandstorms, so there should be plenty of erosion going on.

Re:Wheel wearing (4, Insightful)

Anonymous Coward | about a year ago | (#43799061)

I think you are confusing abrasive with corrosive.

Re:Wheel wearing (0)

Anonymous Coward | about a year ago | (#43799227)

I have an alternate theory sir! If there was severe abrasion by sand particles, we would have seen it in the other rovers and on their bodies. We don't. And since Mars has a very low air pressure (~0.5 - 1% of Earth's), it is hard to pick up sand with enough mass to cause significant damage (but it can still block out the Sun). But there is one variable that has changed: the mass of the rover. This new rover is over 5 times as massive (900 kg). At 38% of the gravity of Mars this would be 3340 N or 750 lbs. Let's assume stationary forces to start. This could be 560 N or 125 lbs per wheel. Add in dynamic forces and it might be enough for a rotating highly loaded wheel to have an angled rock (where all the weight is concentrated for a moment) punch through it.

Re:Wheel wearing (1)

Anonymous Coward | about a year ago | (#43799381)

Oh, my apologies. I didn't look at your username before I called you 'sir'. I was initially going to go for a Dr. Strangelove reference but changed it at the last moment. Sorry about that, no insult was intended.

Re:Wheel wearing (1)

Anonymous Coward | about a year ago | (#43800621)

Oh, my apologies. I didn't look at your username before I called you 'sir'.

He's a girl in training; he won't be a girl until he graduates.

Re:Wheel wearing (0)

Anonymous Coward | about a year ago | (#43800771)

One thing that changed? That's just utterly ridiculous, the wheels are also totally different from the ones on the MER. In fact, I'm rather convinced that the wheel bruising was anticipated. A few dents isn't a big deal.

Re:Wheel wearing (2)

Max_W (812974) | about a year ago | (#43800953)

Add to this radiation. There is no magnetic field around Mars.

Rough Landing (1)

illestov (945762) | about a year ago | (#43798653)

false freak out alert. I fail to see similar level of damage anywhere else on the wheels so maybe its just one area on the wheel that got dented during the landing.

Re:Rough Landing (4, Insightful)

camperdave (969942) | about a year ago | (#43798813)

If it was from the landing, it would have been noticed long before now. Curiosity went through a rigorous self check before it started on its primary mission of exploring the planet.

Re:Rough Landing (1)

illestov (945762) | about a year ago | (#43799129)

i was there and saw it happen

Re:Rough Landing (1)

kuhnto (1904624) | about a year ago | (#43801773)

But if you look at the pictures more closely, it looks like the dents were formed from the interior side of the wheel. I am not sure how terrain could cause that to happen.

Re:Rough Landing (1)

camperdave (969942) | about a year ago | (#43805005)

But if you look at the pictures more closely, it looks like the dents were formed from the interior side of the wheel. I am not sure how terrain could cause that to happen.

Me either. I just hope it's not some innate metallurgical or manufacturing flaw that would cut the mission short.

They should have used... (1)

amightywind (691887) | about a year ago | (#43798691)

Maybe they should have used a more advanced material on the tires to resist denting, like rubber.

Spirit and Opportunity set unrealistic expectation (5, Insightful)

Anonymous Coward | about a year ago | (#43798731)

Since those 2 rovers outlasted their expected mission life by a factor of 20ish, everyone now expects every science mission to do similar. When they last for the amount of time they were engineered for people are disappointed. That's the danger in overachieving and the reason people feel compelled to use their full budget each year - if they're frugal for a year people expect that they'll be able to do the same every year and cut the budget. Some aspects of human nature stink.

Re:Spirit and Opportunity set unrealistic expectat (4, Interesting)

hairyfeet (841228) | about a year ago | (#43799133)

Really? I think its more a testament to just how well NASA over-engineers and builds everything for the absolute worst case scenario that we get so much extra use out of these things. I mean look at how long Voyager has lasted way the hell out in the cold depths, that's a tough built ship right there.

But this is why I've always supported the robotics space exploration programs, with our current tech "meatbags in spaaace!" really doesn't make much sense. I mean when you figure in what it would take to get a crew of five to mars and back its just insanity, I remember seeing a video where they did the math and for a 3 month stay on the ground and round trip from here to there you'd have needed a ship bigger than the empire state building just to carry all the consumables and fuel needed, I don't even want to know how much it would cost for a stay as long as these rovers have had there. At the end of the day we can just get more done with the machine than we can with the man, our tech just isn't good enough right now to make "meatbags in spaace!" viable.

Re:Spirit and Opportunity set unrealistic expectat (3, Insightful)

SuperKendall (25149) | about a year ago | (#43800281)

I remember seeing a video where they did the math and for a 3 month stay on the ground and round trip from here to there you'd have needed a ship bigger than the empire state building

Your "math" is incredibly bad. Read any book on Mars from Zubrin and become educated.

What you are overlooking is that one human in one day could day about 100x the total research done so far by all of the rovers combined. What doesn't make sense is to continue to send very expensive robots to learn less and less... we've reached the point where we simply need to send humans to really study the place.

Re:Spirit and Opportunity set unrealistic expectat (0)

Anonymous Coward | about a year ago | (#43802021)

sure, humans would be productive, but orbital mechanics, assuming current and near term rockets, means that you're still looking at 8-9 months on the way out there, and 8-9 months on the way back plus the year or more on the ground while you wait for Mars to get back into the right position for the short trip back to Earth.

  You leave about 4-5 months before closest approach and get there 4-5 months after. It's another 2 years until the next closest approach.

there's no "zip out to the moon in 3 days and zip back in another 3 days and hope there's no solar flares that week" kind of thing possible.

Re:Spirit and Opportunity set unrealistic expectat (0)

Anonymous Coward | about a year ago | (#43803315)

You're still talking about a period of time much shorter than a PhD.

Why are you so focused on Back? (1)

SuperKendall (25149) | about a year ago | (#43809843)

sure, humans would be productive, but orbital mechanics, assuming current and near term rockets, means that you're still looking at 8-9 months on the way out there, and 8-9 months on the way back plus the year or more on the ground while you wait for Mars to get back

Back back back back back.

It's pretty damn obvious at this point there is no "back" for the first people going. When you ignore that part, especially having to launch from the surface, the whole trip is far simpler and cheaper even if you plan for what are essentially colonists to try and stay for 10 years.

There are more than enough people perfectly willing to go so lets do what makes the most sense here.

Re:Spirit and Opportunity set unrealistic expectat (1)

CanadianRealist (1258974) | about a year ago | (#43804235)

But for the same cost as sending a human on a round trip to Mars you could build a fleet of rovers. Design and testing is a significant part of the cost so building extra rovers lowers the average cost dramatically.

A human can do 100x more in a day? For the same cost I'd bet you could send may more than 100 rovers and explore a much larger area of Mars.

Re:Spirit and Opportunity set unrealistic expectat (1)

cusco (717999) | about a year ago | (#43800393)

It's taken nine years for the Opportunity rover to equal the distance traveled by the astronauts on the final Apollo mission in under a week. A human can turn over a rock, dig more than four inches deep, climb on top of a boulder, recognize when something looks unusual and should be investigated, or cobble together an experiment from duct tape and cleaning materials.

Perhaps the most important reason for humans to go exploring is because the only way to learn how to live in space is to do it.

Re:Spirit and Opportunity set unrealistic expectat (2)

Bongo (13261) | about a year ago | (#43801653)

So robot bodies are durable but slow, human bodies versatile but fragile...

can't we send zombies?

Re:Spirit and Opportunity set unrealistic expectat (0)

Anonymous Coward | about a year ago | (#43800985)

The amount of research and observation the rovers did in all these years is ridiculously small compared to what one person on site could have done in one single day. Just the fact that there is no 40 minute roundtrip for every single little command, like with the rovers, is a HUGE advantage of someone being there vs. remote-controlling a rover.

Re:Spirit and Opportunity set unrealistic expectat (0)

Anonymous Coward | about a year ago | (#43801231)

If the command loop is too long, then send the astronauts to orbit and control rather than land - the fuel used to leave mars is orders of magnitude more than that required for Apollo so unless we plan to return large amounts of samples from Mars to Earth, it makes little sense to land a human. Better to send improved rovers - with the increased capability of terrestrial robots, our explorers should have similar increases in capability in the near term.

Re:Spirit and Opportunity set unrealistic expectat (3, Funny)

skegg (666571) | about a year ago | (#43801717)

I mean look at how long Voyager has lasted way the hell out in the cold depths, that's a tough built ship right there.

Dude, relax, it's just science fiction. There was no caretaker, and no one was pulled into the Delta quadrant.

Re:Spirit and Opportunity set unrealistic expectat (1)

KernelMuncher (989766) | about a year ago | (#43803517)

Yes but robots don't inspire the public nearly as much as sending a "Joe" or "Jane". That's how an agency survives - by being relevant to all those people who pay taxes and will write their Congressmen to keep funding NASA.

Glad it's expected. (3, Funny)

sconeu (64226) | about a year ago | (#43798855)

Otherwise, it's a hell of a long wait for the AAA. And who's going to to stand there next to the rover with their card?

Re:Glad it's expected. (0)

Anonymous Coward | about a year ago | (#43799221)

I think that 30,000 people have volunteered to do just that.

http://www.bbc.co.uk/news/science-environment-22360228

Of course, they're milking the system here -- some of them going are GOING TO BE the AAA workers as well as passengers. OTOH, "the check is in the mail" and SnailMail just got a Whole New Meaning.

Mass and Weight are different (5, Interesting)

Excelcia (906188) | about a year ago | (#43798947)

From the article:

“We have the same wheels on our Scarecrow test rover, which weighs the same on Earth as Curiosity weighs on Mars,” Heverly added. “We have driven Scarecrow about 12 kilometers (7.5 miles) in the Marsyard over rocks and slopes much harsher than we expect for Curiosity. There are some dents and holes in these wheels, but the rover is still performing well.”

This sounds an idea from the same people that brought us the Mars Climate Orbiter crater.

The problem with this is that Curiosity weighs 342kg but masses 900kg. Scarecrow weighs and masses 342kg. Whatever Curiosity weighs, it hitting a rock at 1m/s is still 900 newtons of force. Scarecrow hitting a rock at 1m/s is 342 newtons. The fact it drove 12km and has serviceable wheels does not make me feel better.

Re:Mass and Weight are different (1)

Anonymous Coward | about a year ago | (#43799101)

The same force from gravity is exerted on Curiosity's/Scarecrow's wheels. I would think that, rather than impacts, would be the bulk of the wear and tear on the wheels.

Re:Mass and Weight are different (4, Insightful)

TrekkieGod (627867) | about a year ago | (#43799195)

Whatever Curiosity weighs, it hitting a rock at 1m/s is still 900 newtons of force. Scarecrow hitting a rock at 1m/s is 342 newtons.

Stop accusing NASA scientists of not understanding their job when you don't remember basic physics.

F = m * a, not F = m * v. In this case a is the acceleration due to gravity. In addition, mass is measured in kg, weight is measured in Newtons, because weight is a force. The newtons are exactly the same between those two rovers.

Re:Mass and Weight are different (3, Interesting)

complete loony (663508) | about a year ago | (#43799437)

F = m * a

Look it's right there, force equals *mass* times acceleration. On earth, Scarecrow is 342kg * 1g when stationary. On mars Curiosity is 900kg * 1mars-g *when stationary*. Sure the vertical force on the tires is the same when standing still, but what about the force required to stop 342kg vs 900kg of inertia if you hit a large pointy rock at 1m/s?. In this case, with the same initial velocity, the acceleration would be the same but the force experienced by Curiosity's tires would be ~3x larger (ignoring any shock absorption).

Re:Mass and Weight are different (2)

TrekkieGod (627867) | about a year ago | (#43800139)

Sure the vertical force on the tires is the same when standing still, but what about the force required to stop 342kg vs 900kg of inertia if you hit a large pointy rock at 1m/s?

Who says the rover is stopping when it encounters a rock? Either the 342 kg one or the 900 kg one? The same amount of force will stop both, but the force will need to be applied for longer in the 900 kg rover. The term you're looking for is momentum, not force. The 900kg, assuming it's moving at the same speed as the 342 kg one, has more momentum.

Mass would certainly matter if they crashed the rover and transferred all that momentum, assuming they were moving at the same speed as the equivalent one is here (which I'm not convinced is a good assumption. They could have increased the driving speed of their Earth-equivalent in order to make momentum equal too). Either way, the reason this would matter, is because if you crash the rover against a wall, it would stop at the same rate as crashing the lighter rover into a wall on earth. In order to stop it at the same rate, more force needs to be applied. More importantly, the rover had 1/2 * m * v^2 of energy, which all had to be dissipated somewhere when v went to zero. But this isn't what is happening when the rover is driving around. The traction it gets is equal to the coefficient of traction times weight, the forces are exactly the same, and the rover merely decelerates slower when it encounters resistance, making the amount of energy dissipated the same because the difference in v is proportionally less.

Re:Mass and Weight are different (2)

hankwang (413283) | about a year ago | (#43800779)

force equals *mass* times acceleration. ... the acceleration would be the same but the force experienced by Curiosity's tires would be ~3x larger (ignoring any shock absorption).

You do have a point -- I don't agree with some of the other responders who talk about traction forces being smaller as well. Just to make it clear: what you say applies to a cart on wheels, having constant horizontal velocity and approaching a bump in an otherwise flat surface. A larger mass of the cart will result in a larger force at the wheels the moment the cart hits the bump, regardless of gravity.

However, this force is roughly F = m v^2/L, where v is the horizontal velocity of the cart, L is the travel of the suspension, and m is the moving mass. The moving mass can be just a single wheel; in that case L is the leeway in the tire rubber (less than a millimeter), or m can refer to the entire car, with L the travel of the wheel suspension.

Now, the issue of inertia is only relevant if the instantaneous extra force is larger than the gravitational force. Given that this Mars Rover has a maximum speed of 0.025 m/s [wikipedia.org] , the maximum inertia-driven acceleration is about 1 m/s^2, even assuming only 0.5 mm of suspension travel. This is much less than the gravitational acceleration (10 m/s^2); therefore inertia does not make a significant difference in the wear on the wheels.

Re:Mass and Weight are different (1)

wonkey_monkey (2592601) | about a year ago | (#43801683)

Scarecrow is 342kg * 1g

Ow, my units!

Re:Mass and Weight are different (2)

necro81 (917438) | about a year ago | (#43802099)

Sure the vertical force on the tires is the same when standing still, but what about the force required to stop 342kg vs 900kg of inertia if you hit a large pointy rock at 1m/s?

That's what's referred to as dynamic acceleration. Rolling along at 1 m/s and then coming to a sudden stop by running into a rock would indeed produce some big accelerations, and the difference in mass between Curiosity and Scarecrow would be pretty significant.

However, the scenario that you and an earlier comment are talking about - coming to an abrupt, rocky stop from 1 m/s - simply does not happen. You might be envisioning Curiosity as some sort of Martian ATV bouncing off the landscape and doing power slides, but the reality is far more prosaic. Curiosity's top speed on flat, hard soil is about 0.04 m/s, not 1 m/s. Let's say that, for whatever reason, Curiosity came to a dead stop from it's top speed in, say, 100 ms (the suspension ensures the stop is not instantaneous). That's an acceleration of 0.4 m/s^2. The static acceleration due to gravity on Mars is 3.7 m/s^2, or about 10x that.

In other words, the dynamic loading is going to be small compared to the static loading.

What is more: Curiosity has about a dozen people planning out its path, specifically to avoid running into things. Even beyond that: Curiosity has hazard avoidance cameras and autonomous algorithms that will slow or stop it before it hits anything.

1m/s? Are you kidding me? (1)

AC-x (735297) | about a year ago | (#43802131)

Sure the vertical force on the tires is the same when standing still, but what about the force required to stop 342kg vs 900kg of inertia if you hit a large pointy rock at 1m/s?.

1 m/s? Are you kidding? Curiosity has a top speed of less than 0.04 m/s on flat ground, it literally crawls along. Force due to gravity will be by far the dominant force on the rover's wheels.

Re:Mass and Weight are different (0)

Excelcia (906188) | about a year ago | (#43799471)

First of all I will concede that yes, you are right that weight is properly measured in newtons. I used the common reference of weight most people think of. However it seems I need to explain a little bit about inertia. I'll try to use small words so even NASA engineers can understand:

Curiosity wheel encounters rock. Wheel exerts force to lift itself over rock. To do this, wheel must lift all of Curiosity. Curiosity masses 900kg. Object at rest tends to stay at rest. Curiosity tends to stay at rest. Curiosity wheel has much inertia to overcome to make Curiosity start moving up and then over rock.

NASA test robot masses 342kg. Test robot wheel encounters rock. Test robot exerts force to lift itself over rock. Test robot has much less inertia to overcome to make test robot start moving up and then over rock. Test robot has few dings. NASA engineers cheer.

Re:Mass and Weight are different (2)

TrekkieGod (627867) | about a year ago | (#43800037)

Curiosity wheel encounters rock. Wheel exerts force to lift itself over rock. To do this, wheel must lift all of Curiosity. Curiosity masses 900kg. Object at rest tends to stay at rest. Curiosity tends to stay at rest. Curiosity wheel has much inertia to overcome to make Curiosity start moving up and then over rock.

You're still incorrect. Yes, the 900 kg rover has more inertia. Inertia doesn't matter as far as how much force is being applied to the wheels, though. It means the same force will be applied as to the equivalent lower mass rover on Earth, and because of its higher inertia the rover on mars will accelerate slower while that same force is being applied.

Write the force diagram yourself. Think about what it takes to move a vehicle on wheels. How much traction do you get? the coefficient of traction times the weight [wikipedia.org] . Because the only thing keeping that 900 kg vehicle on the ground to interact with those rocks as the wheel spins is the force of gravity of mars. Every action has an equal and opposite reaction: those rocks can't exert more force on the rover than the rover can exert on them, and those 900 kg are only worth on mars what the 342 kg one is here. The inertia only matters when it comes to acceleration, not when it comes to the force the wheels experience.

Now, it's entirely possible that the mars terrain is more abrasive than they expected, and it doesn't match their equivalent here on Earth. I'm willing to bet they thought about that and built in some safety margins. I'm also willing to bet they've been looking at the damage to the wheels and have by now gone through the numbers and figured out if it's going to be a problem or not. Based on what they've said, it's not going to be a problem.

Re:Mass and Weight are different (1)

camperdave (969942) | about a year ago | (#43809943)

Curiosity wheel encounters rock. Wheel exerts force to lift itself over rock. To do this, wheel must lift all of Curiosity.

False. The rocker-bogie system allows the wheels to move vertically with very little problem. Weight is distributed all the wheels equally under normal circumstances. The most that a wheel might experience would be half the weight, and that would only happen if two of the three wheels on the rocker-bogie were off the ground. That's not going to happen because the onboard hazard avoidance and the NASA route planners wouldn't get the rover into such a predicament. So, the most that Curiosities wheels would face would be a sixth of the rover's weight.

Re:Mass and Weight are different (1)

hazeii (5702) | about a year ago | (#43801791)

The force due to gravity is the same, however on impact the forces will be different (or would you argue the force would be zero in space, since a=0?).

If I was the bump in the way, I would far sooner be hit by a 342kg mass than a 900kg one - and similarly the damage I'd inflict on the mass would be less.

Re:Mass and Weight are different (1)

Anonymous Coward | about a year ago | (#43800019)

except that Curiosity goes nowhere near 1 m/s... more like a few cm/sec so gravity loads far exceed acceleration loads.

Re:Mass and Weight are different (2)

necro81 (917438) | about a year ago | (#43801901)

The problem with this is that Curiosity weighs 342kg but masses 900kg. Scarecrow weighs and masses 342kg. Whatever Curiosity weighs, it hitting a rock at 1m/s is still 900 newtons of force. Scarecrow hitting a rock at 1m/s is 342 newtons. The fact it drove 12km and has serviceable wheels does not make me feel better.

That distinction is really only revelant in the case of dynamic loading: hitting things at speed, rapid straightline accerelation, or quick turning. Whether Curiosity on Mars or Scarecrow on Earth, there really isn't any of that going on. For the most part, the only loading going on is the static loading due to gravity, which they have accounted for.

You talk about hitting a rock at 1 m/s, but Curiosity's top speed on hard, flat ground is 1.5 in/sec [google.com] , or about 4 cm/sec (0.14 km/h). That's only 1/25th the speed you use in your bungled calculations; 1/625 as much kinetic energy. At that slow crawl of a speed, the difference in dynamic loading between Curiosity and Scarecrow is negligible. In any event, the rover is by an large prevented from hitting anything by the route planners here on Earth and its autonomous hazard avoidance algorithms.

In other words: I trust the engineers at JPL to understand these things and account for them better than a random user on /.

Re:Mass and Weight are different (0)

Anonymous Coward | about a year ago | (#43804615)

Great. Another fucking armchair rocket scientist.

What about the landing? (1)

MichaelSmith (789609) | about a year ago | (#43799001)

It must have been rougher than normal driving. Can a comparison be made with images taken right after landing?

They did. (1)

dutchwhizzman (817898) | about a year ago | (#43800421)

They checked the wheels. This is not from the landing, this is anticipated normal wear.

the words we choose. (1)

NetGyver (201322) | about a year ago | (#43799007)

My tire-skin brings all the rovers to the marsyard
And they're like,
Its worse than yours,
Damn right, much worse than yours
I can teach you,
But I'll eat your sols

Re:the words we choose. (0, Funny)

Anonymous Coward | about a year ago | (#43799833)

My tire-skin brings all the rovers to the marsyard
And they're like,
Its worse than yours,
Damn right, much worse than yours
I can teach you,
But I'll eat your sols

Pondering the fate of Slashdot Parodist Unit 201322, K'Breel spake thus: "You. You funny. I like you. Your gelsacs may remain safely attached, in fact, I'd give one of mine for mod points right about now, but the Slashdot powers that be have no use for the Speaker's gelsacs."

Wait, what? (1)

dutchwhizzman (817898) | about a year ago | (#43800425)

They have a marsyard? Where can we get one?

So.... (1)

FaxeTheCat (1394763) | about a year ago | (#43800835)

the wheels wear as expected...

In other news: Car tire worn out. "To be expected" claims manufacturer.

Re: So.... (0)

Anonymous Coward | about a year ago | (#43803289)

Hopefully NASA is working on new rover designs that incorporate legs instead of wheels. It seems one built like an ant would be much more agile and rugged.

Re: So.... (1)

camperdave (969942) | about a year ago | (#43809959)

Wheels take far less power to move than legs. However, check out ATHLETE [nasa.gov] , the best of both worlds.

Punctured from the inside out? (1)

cronostitan (573676) | about a year ago | (#43800925)

Doesn't anybody find it curious that it looks in one of the shots that the holes go from the inside to out? How is that even possible? I mean, dents on the outside are reasonable but how did the ones (and there are several deep ones) on the inside happen?

Re:Punctured from the inside out? (2)

ledow (319597) | about a year ago | (#43800959)

Not really. Work in a garage for a month, you see all kinds of weird damage come in.

And this wheel is basically a cut-open barrel. Punch it on the outside and it makes a dent on the inside. It's rolling across a rocky landscape, after being basically dropped onto the planet. It probably bumps down a lot more rocks than you realise and even more than NASA ever plan, the chances of finding a level surface to wander over that doesn't have a hidden 10cm drop onto rock for at least one of the wheels hidden behind is slim. And it weighs quite a bit. Not to mention loose things getting inside the wheels and basically being inside a small tumble-dryer.

A dent in the wheel would be the least of my worries, to be honest. And there's no way you can actually tell that the dents go from inside-out or outside-in, it's an very common optical illusion. And even if the dents go "the other way", there's no way to tell from the photos that they line up - those wheels are basically taking the shape of whatever they roll over so you might find the dent going "in" is right next to a similar bend in the metal going "out".

But never let the facts stand in the way of some mad conspiracy theory, eh?

Optical illusion (1)

AC-x (735297) | about a year ago | (#43802163)

Could be an optical illusion, all the dents I can see on the images go from the outside in.

Re:Punctured from the inside out? (1)

TheSkepticalOptimist (898384) | about a year ago | (#43816835)

This was my first through.

I mean, the thing does not travel fast enough to warrant getting a stone to punch through from the outside in,

However, look at the "Speed Holes" on the wheel surface, I am sure stones caught caught up IN the wheel and then tumbled down to dent the wheel from the inside out.

I mean, come on, you got big open wheels on a rocky surface, this ain't rocket science.

Can't repeat the blunder... (1)

SharpFang (651121) | about a year ago | (#43801039)

Don't worry, it's all according to the plan.

Considering the continued cost of maintaining Opportunity (and until not so long ago, Spirit) still running strong many years past expected "expiration date", all new mars rovers have "planned obsolescence" features built in; they are designed to break soon after their planned mission time is past. /tinfoilhat

Typical auto industry (1)

Wesley Felter (138342) | about a year ago | (#43807265)

The rover loses 30% of its value as soon as you drive it off the lot. And if NASA tries to trade it in I bet a lot of "damage" will be discovered to drive down the price.

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