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Rough Roving: Curiosity's Wheel Damage 'Accelerated'

timothy posted about 10 months ago | from the when-it-rains-it-pours dept.

Mars 157

astroengine writes "Despite the assurances that the holes seen in Mars rover Curiosity's wheels were just a part of the mission, there seems to be increasing concern for the wheels' worsening condition after the one-ton robot rolled over some craggy terrain. In an upcoming drive, rover drivers will monitor the six wheels over some smooth terrain to assess their condition. "We want to take a full inventory of the condition of the wheels," said Jim Erickson, project manager for the NASA Mars Science Laboratory at NASA's Jet Propulsion Laboratory, Pasadena, Calif. 'Dents and holes were anticipated, but the amount of wear appears to have accelerated in the past month or so.' Although the wheels are designed to sustain significant damage without impairing driving activities, the monitoring of the situation is essential for future planning."

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Please pray with me for Curiosity's wheels. (4, Funny)

Anonymous Coward | about 10 months ago | (#45751245)

Dear Lord, Father in Heaven, we pray together for the safekeeping of Rover Curiosity's wheels. Although it may be a tool of science, and its discoveries a complete threat to religious doctrine everywhere, she is but a rover on a mission of Peace and Goodness. In your ever forgiving heart, please bless her wheels with durability and robustness.

Amen.

Re:Please pray with me for Curiosity's wheels. (3)

Sam36 (1065410) | about 10 months ago | (#45751693)

I don't see how what He made is a threat.

And he is before all things, and by him all things consist. --Colossians 1:17

Perhaps God will inspire the Chinese ... (1)

Taco Cowboy (5327) | about 10 months ago | (#45752427)

In this age, whatever failure the other parties has met with is the lesson that one picks up.

The lesson whereby the failure of Nasa to better equip the Curiosity's wheels against abrasion / wear and tear may mean that the only country left on this world that has the will and the financial might to forge ahead with their space aspiration (China) surely benefit.

I bet if they are to send up any more space equipment (rover, dune buggy or whatever) they will put more emphasis on the parts that might face the issue of wear and tear / abrasion / friction.

Re:Please pray with me for Curiosity's wheels. (0)

Anonymous Coward | about 10 months ago | (#45751699)

I hear the cry of the machine spirits! In the name of the Machine God, ring the bell twice!

Re:Please pray with me for Curiosity's wheels. (0)

Anonymous Coward | about 10 months ago | (#45752099)

Dear Lord, Father in Heaven, we pray together for the safekeeping of Rover Curiosity's wheels. Although it may be a tool of science, and its discoveries a complete threat to religious doctrine everywhere, she is but a rover on a mission of Peace and Goodness. In your ever forgiving heart, please bless her wheels with durability and robustness.

HERESY. GEL FOR THE GEL GOD, SACS FOR THE SAC THRONE!
- K'Breel, on behalf of the Council.

Re:Please pray with me for Curiosity's wheels. (0)

JWSmythe (446288) | about 10 months ago | (#45752601)

Who are you talking to?

You know, talking to yourself may be a symptom of an underlying disorder. Have you talked with your psychiatrist lately?

Re:Please pray with me for Curiosity's wheels. (0)

Anonymous Coward | about 10 months ago | (#45752931)

Who are you talking to?

You know, talking to yourself may be a symptom of an underlying disorder. Have you talked with your psychiatrist lately?

Jerry Landers: Maybe, sometimes... couldnt we just talk?

God: I'll tell you what. You talk... Ill listen.

Re: Please pray with me for Curiosity's wheels. (0)

Anonymous Coward | about 10 months ago | (#45753067)

Hey, pray to your own FSM god! No fair borrowing mine just because yours let you down.

Re:Please pray with me for Curiosity's wheels. (2)

enzo1 (931050) | about 10 months ago | (#45753545)

It is not remotely a threat to religious doctrine because it will never find life.

Typical (-1)

Anonymous Coward | about 10 months ago | (#45751247)

Half assed and built by the lowest bidder. Fucking america, I hate this country

Re:Typical (0)

Anonymous Coward | about 10 months ago | (#45751277)

Agreed, this is pretty goddamn lame. Cut corners somewhere else, not on the fucking MSL rover, kthxbai.

Re:Typical (5, Informative)

Anonymous Coward | about 10 months ago | (#45751361)

The thinness of the rovers wheels isnt so much about saving money as it is about saving weight.

Every ounce the wheels dont weigh is another ounce for science equipment or batteries.

So im sure they made them absolutely as thin & lightweight as they thought they could get away with.

Re:Typical (2)

jtownatpunk.net (245670) | about 10 months ago | (#45751731)

So im sure they made them absolutely as thin & lightweight as they thought they could get away with.

Missed it by that much.

Re:Typical (2)

ihtoit (3393327) | about 10 months ago | (#45752543)

The thinness of the rovers wheels isnt so much about saving money as it is about saving weight.

Every ounce the wheels dont weigh is another ounce for science equipment or batteries.

So im sure they made them absolutely as thin & lightweight as they thought they could get away with.

...and every ounce the probe doesn't weigh is another few hundred pounds saved in fuel for the launch vehicle.

This is reflected in the amount of power the Voyager probes put out - not even enough to power a digital watch, yet we're still getting science from them. The legwork is done on Earth, with vast arrays of massive radio telescopes gathering and filtering the signals. To put out enough power for an amateur radio astronomer to be able to pick out of the cosmic background... we'd probably have had to launch each probe with a Sizewell-B sized reactor. That's 1.1GW for those not versed in "How many football fields is that?" units of measurement. Obviously not practical in terms of escaping the gravity well.

Personally, I wouldn't worry about it until two wheels on the same side develop mission-fail flat spots. This is probably why it's got six wheels - a four wheeled vehicle would be at mission end with the failure of any one wheel. This puppy can withstand two failures and keep on truckin'.

Re:Typical (2)

JWSmythe (446288) | about 10 months ago | (#45752653)

fuel for the launch vehicle.

That's the #1 reason. If we had infinite thrust with no fuel consumption, we could put up ... well, some really cool stuff. Spacecraft wouldn't need to be concerned with stuff hitting them, if they could put a mile of dirt around a steel reinforced concrete floating bunker. :) And we'd probably have a few Stanford Torus' or Bishop Rings in orbit already.

This puppy can withstand two failures and keep on truckin

Looking at the design, and the images, the front left wheel is actually pretty rough. In the linked story, look at the bottom half of the 9th picture. The metal has split almost half way across. It may end up digging into the softer sand, and could catch on rocks.

They'd have a better chance driving it backwards, letting that wheel drag along. That won't work very well though, since all the gear is on the front.

Re:Typical (2, Informative)

Anonymous Coward | about 10 months ago | (#45751285)

Yep, just give it to the highest bidder for equally shitty work.

Actually, most of the rover was built in-house.

Re:Typical (0)

Anonymous Coward | about 10 months ago | (#45752101)

Right, I mean, spirit and opportunity didn't last 10 times longer than they were meant to. One rover lasts only as long as it was planned to, and suddenly america sucks at producing anything.

Re:Typical (0)

Anonymous Coward | about 10 months ago | (#45752887)

Actually, you hate your life, and are projecting that on America.

You know I am right.

They didn't pack a 3D printer? (0)

Anonymous Coward | about 10 months ago | (#45751305)

It could have 3D printed replacement parts!

And before the Nutters come in with their usual blather abound sending people, we can barely make WHEELS that survive going 2 miles per hour there! What makes you think we'll have life support machinery and food making equipment and housing and clothes that will survive for months there?????

Re:They didn't pack a 3D printer? (1)

MichaelSmith (789609) | about 10 months ago | (#45752145)

we can barely make WHEELS that survive going 2 miles per hour there!

The rover masses 1000kg so there is 50kg of force on every wheel. Thats pretty substancial, about the same pressure as a mountain bike wheel, and mountain bikers lose a lot of tires to rough terrain.

Re:They didn't pack a 3D printer? (1)

lxs (131946) | about 10 months ago | (#45752209)

I agree. The rover only has itself to blame. It should go on a diet and stop complaining about sore feet.

Re:They didn't pack a 3D printer? (2)

ihtoit (3393327) | about 10 months ago | (#45752595)

how much science has gone in to building the Rover wheels? Mountain bike wheels have been using the same technology for decades - a steel hub, steel spokes, steel rim, and air-filled rubber tyres. With the Mars Rover, they had to think about:

Tyres: no good in such a rarefied atmosphere - they'd explode, that's if they didn't explode on the way. Plus there's no way to stop and repair a puncture. Solids are making a comeback (again), but you run in to weight issues (I know, I've had newtech solids and they are *heavy*). Tyres are a necessity in any vehicle expected to roll across the surface of any body, but do they have to be solid? They're only there for grip and suspension, you can get the same effect using sprung metal cantilevers.
Rims: here we have steel and several alloys, and recently carbon composites have made an appearance. Weight is again an issue with all of these, and consider the fact that carbon composites don't react well to UV, that's those out. You've got to develop light and strong alloys.
Hub: With the number of moving parts in a hub (the average bike wheel has over fifty!) any one of those failing can end a mission. Here they had to think about a fail-proof redesign of bearings that not only had to be maintenance-free, they also had to have as close to zero failure probability as possible. Something which can only be achieved by reducing the number of parts to the point where you can not only predict when a part is going to fail and under what conditions, but also what can be done to mitigate that probability.

The short of it is, this all comes down to mass. The Mars Rover was lucky to have been equipped with SIX wheels. If the launch systems engineers had gotten their way, the mission would have been equipped with four wheels and been over long ago (probably not even having fulfilled the mission parameters - MR is on its own clock now, everything it sends back is just icing) and the LSEs would be up a few hundred kg of fuel for the next launch. How inconvenient, they have to fabricate some more!

Re:They didn't pack a 3D printer? (1)

MichaelSmith (789609) | about 10 months ago | (#45752729)

The hand cart on apollo 14 used pneumatic tires at 10 psi. It was probably inflated in a vacuum chamber. Though I think Curiosity is fine with the wheels it has.

Re:They didn't pack a 3D printer? (1)

the_other_chewey (1119125) | about 10 months ago | (#45752671)

The rover masses 1000kg so there is 50kg of force on every wheel.

Where does it hide the other 14 wheels?

Re:They didn't pack a 3D printer? (1)

MichaelSmith (789609) | about 10 months ago | (#45752721)

1000kg mass. 300kg weight. Six wheels, each carrying 50kg.

Re:They didn't pack a 3D printer? (4, Interesting)

Jarik C-Bol (894741) | about 10 months ago | (#45752763)

By my calculations, 1000kg distributed across 6 wheels is 166kg on earth, which translates to 62kg on mars. What surprises me about the damage is that a copy of the rover was stress tested in death valley, so this level of wear and tear should have been anticipated, as the force on the wheels there was much higher. I wonder if another environmental factor, like mars' extreme cold, or increased radiation due to lack of magnetosphere is affecting the materials in the wheels.

Re:They didn't pack a 3D printer? (1)

bhspencer (2523290) | about 10 months ago | (#45753291)

"50kg of force on every wheel" How do you get that? Since when was force measured in kg.

NASA is an ugly place for a grading curve. (1, Insightful)

rmdingler (1955220) | about 10 months ago | (#45751355)

"Monitoring of the situation is essential for future planning."

As A poor young man driving a $500 '73 Ford Pickup, I remember carefully monitoring oil consumption, water level, and tread wear on the five dollar maypops I could afford to put on my baby's feet.

It is common knowledge that NASA has one initial too many for the Brobdingnagian budget, but I was poor as two Mongolian goat herders.

Re:NASA is an ugly place for a grading curve. (1)

cr0nj0b (20813) | about 10 months ago | (#45753333)

So NASA Should Change it's name to U.S.A.?

USA Space Agency?

Re:NASA is an ugly place for a grading curve. (1)

rmdingler (1955220) | about 10 months ago | (#45753409)

Perhaps I misunderstand you, but my meaning was if you subtract the 'A' from NASA, you are left with NSA and presumably a larger budget.

Really? (-1, Flamebait)

countach (534280) | about 10 months ago | (#45751365)

I know weight is important and all, but .75mm of aluminium? Really? Maybe they should have less scientists over there at NASA and more people with common sense who can raise their eyebrows.

Re:Really? (2, Insightful)

Anonymous Coward | about 10 months ago | (#45751421)

Yeah, let's just toss out a few instruments and batteries so we can have wheels that last 5 instead of 3 times the planned driving distance.
Gotta love armchair engineers.

Re:Really? (0)

jjjhs (2009156) | about 10 months ago | (#45751595)

The wheels aren't in the way of the instruments and batteries. /armchair engineer

Re:Really? (1)

Anonymous Coward | about 10 months ago | (#45751629)

In terms of total mass, yes they are.

Re:Really? (1)

jjjhs (2009156) | about 10 months ago | (#45751815)

So? Was there an arbitrary weight limit? What's a few more pounds for proper tires? Was there some reason that it had to be exactly 1,980lb? I find that very hard to believe. Cars have proper tires, at first what look like bicycle tires but they get bigger and heavier so do the tires and suspension. Buildings get taller, so they have foundations to support them. I think that is common sense. We can have our heavier cars loaded with more gizmos and the tires are designed to handle that and extra cargo, so why did they cheap out on Curiosity's tires? Are you telling they COULD NOT make the tires thicker or use a stronger and perhaps heavier metal while keeping everything they wanted, or they didn't WANT TO?

Re:Really? (1)

Anonymous Coward | about 10 months ago | (#45751861)

"So? Was there an arbitrary weight limit?"

Yes, it's called a launch vehicle. This isn't Star Trek where you can touch your nipple and talk to the blind guy in the engine room to whip you up a magical force field to float that shit up into space.

"What's a few more pounds for proper tires?"

I eagerly await your formulation for flexible rubber or plastic that can survive the vacuum of space for months, then the harsh unfiltered UV on the surface of Mars and wild swings of temperature as the wheel turns between light and shadow. Oh and one last thing, Mars seems to have a surface that CAN PUNCTURE 0.75MM OF SHEET METAL. So don't forget to pack a self-inflating (in a vacuum?) system or a run-flat system, that of course won't raise the failure rate of system and still provide the traction we expect. And another last thing, please characterize your magical substance to make sure it has the same traction at the end of the mission as at the start: you don't want to suddenly need the motors to supply more power to the wheels just as all parts are at their life limit?

But do tell, Mr Internet Engineer!

Re: Really? (1)

Anonymous Coward | about 10 months ago | (#45752051)

Would 5 grams of TiN ceramic coating really have impacted launch so terribly, AC?

Because they really only need about .0005 inch thick coating of the stuff outside the existing design part to radically increase the surface wear characteristics of the solid wheel design they already have.

We've solved the problem with mechanical erosion a long time ago on CNC cutting tools, where tolerances tighter than a nuns's cunt prevail, and where graceful transition on surface friction over tool life is a must to preserve many millions of dollars in equipment costs.

Just treat those solid wall wheels like a cutting tool, and you're golden. (In the case of TiN coating, quite literally. It's a lovely metallic gold color.)

Re: Really? (0)

Anonymous Coward | about 10 months ago | (#45752113)

5lb of ceramic coating needs 20lb of fuel to get it into the transfer orbit, which in turn, needs 100lb of fuel to get it into low earth orbit. Every lb you add to the final stage gets added to the first stage many many times over.

Re: Really? (0)

Anonymous Coward | about 10 months ago | (#45752157)

there is a very big difference between 5 GRAMS and 5 POUNDS.

(hint, 5 grams is the weight of 5 droplets of water.)

Re: Really? (1)

Ultracrepidarian (576183) | about 10 months ago | (#45752435)

Make that 100 drops of water. 20 drops per gram.

Re: Really? (0)

Anonymous Coward | about 10 months ago | (#45752565)

wow. i looked that up and its right, assuming the .05ml/drop ratio is actually correct.

regardless, it isnt a whole lot of weight.

Re: Really? (0)

Anonymous Coward | about 10 months ago | (#45752165)

Hello - Parent AC said 5 *grams* of ceramic coating, not 5 lbs.

Did you used to work for NASA on the Mars Climate Orbiter? Just wondering....

http://en.wikipedia.org/wiki/Mars_Climate_Orbiter [wikipedia.org]

Fo Reals (0)

Anonymous Coward | about 10 months ago | (#45752197)

Hey, petty attacks aside, call us if you have the expertise and experience to safely land a 1-ton nuclear powered vehicle on Mars.

If not...you're still soooo cuuuute when you get all passive-aggressive in your little AC engineering armchair!

-JPL

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45751863)

Are you telling they COULD NOT make the tires thicker or use a stronger and perhaps heavier metal while keeping everything they wanted, or they didn't WANT TO?

They had to lift all of that to MARS, dude. Try dragging a 1985 Honda Civic up Mt. Everest 50 million times. Then tell me you wouldn't toss out the spare tire in the first 50 feet.

Re:Really? (1, Troll)

jjjhs (2009156) | about 10 months ago | (#45751999)

Yes, it's called a launch vehicle. This isn't Star Trek where you can touch your nipple and talk to the blind guy in the engine room to whip you up a magical force field to float that shit up into space.

They had to lift all of that to MARS, dude. Try dragging a 1985 Honda Civic up Mt. Everest 50 million times. Then tell me you wouldn't toss out the spare tire in the first 50 feet.

So, what, it takes infinitely more energy for an extra few mm of sheet metal to launch that thing? A launch vehicle the size of the moon for slightly thicker tires versus the one they initially used? Apparently the Atlas V was used, and from what I am reading it is very much capable of launching the rover with a few more pounds/thicker tires and still grossly overpowered to deliver the payload. Also I never said anything about changing the tires to rubber or plastic! But alas I am just a armchair internet engineer. I don't have an engineer degree so I must just be another stupid hick.

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45752055)

You asked for "proper tires". Please elaborate on what you meant then.

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45752215)

It wasn't just the rover, chief.

"Curiosity comprised 23 percent of the mass of the 3,893 kg (8,580 lb) Mars Science Laboratory (MSL) spacecraft, which had the sole mission of delivering the rover safely across space from Earth to a soft landing on the surface of Mars."

That's about what the Atlas V can take to GTO. I don't know how that translates to "grossly overpowered" in your simple world.

So you make the wheels heavier, so now you need stronger motors, that need a bigger RTG to power them...

Now you need to make the MSL bigger to be able to support the heavier rover through all stages of the mission... Which now needs more fuel to maneuver the heavier rover around.... Hmm, but I'm sure you've solved that too?

But let's see, you seem to know a lot about tires on spacecraft that go on other planets AND the rockets we should be using to launch them there!

Send your CV here:

http://www.nasa.gov/about/career/index.html#.UrUtlOLtd0Q [nasa.gov]

http://www.spacex.com/careers/list [spacex.com]

I think you're pretty much guaranteed a job if you know as much as you seem to. Tell those pointy-headed PhDs a thing or two about common sense!!

Re: Really? (0)

Anonymous Coward | about 10 months ago | (#45752275)

As an aerospace engineer, "common sense" says that anything thinner than .04 inches thick will have a high scrap rate due to material deformation issues during cutting, and that use of thin walled aluminum without even a token gesture toward an abrasion resistant coating for use on an environment KNOWN to contain loose grans of iron and aluminum oxide powder (its fucking emery dust dumbasses!) Is going to result in premature failure.

Refusing to at least put an anti-abrasive coating on the wheels is inexcusable.

(Hint, we can drive a cutting tool at 3000rpm at over 40in/min, through metal, for HUNDREDS OF HOURS, with a tool that has a ceramic coating just .0005 inches thick on the cutting flutes. Your wheels not getting a coating really is bullshit stupid.)

re: (0)

Anonymous Coward | about 10 months ago | (#45752691)

Well, I was going to suggest you start an engineering career at NASA but the GP appears to have done that for me.

There's a cliche about being thought a fool, then opening one's mouth and confirming it. That applies here quite well: shut your mouth; we already know you're a fool.

Re: (1)

Christian Smith (3497) | about 10 months ago | (#45752869)

Wasn't it "aerospace engineers" working in non-metric units that lost the Mars Climate Orbiter [wikipedia.org] ?

I don't think NASA would employ someone still working in inches.

Re: Really? (1)

trout007 (975317) | about 10 months ago | (#45753173)

It looks like those wheels have a Type III Anodizing. That's pretty wear resistant. You are talking about TiN coating on steel or carbide cutters. There is a bid difference. This doesn't look like wear but puncture damage. A coating isn't going to protect against that.

Re:Really? (1)

RightwingNutjob (1302813) | about 10 months ago | (#45751433)

Agreed. Also, six rigid wheels was fine for Pathfinder, Spirit, and Opportunity, but now you've got what, one ton? of rover, and still six rigid wheels. Eight or twelve smaller wheels might be a good idea for the next similarly-sized rover.

Re: Really? (1)

Anonymous Coward | about 10 months ago | (#45752033)

The wheels aren't showing signs of fatigue, they are showing erosion damage. More wheels means increased contact surface, and greater wear rates.

The better idea is to put a generous coating of a hard ceramic on the wheels, like TiN. (Titanium Nitride.)

There is no compelling reason why they couldn't coat the wheels with TiN after machining them, and before assembling them. It gets applied in a vacuum chamber, and can be precision applied with a vapor deposition process.

A coating just .0005 inches thick would radically improve the erosion resistance of the contact surface of the wheels.

nope (1)

Anonymous Coward | about 10 months ago | (#45752183)

"More wheels means increased contact surface, and greater wear rates."

Well, no.

The controlling variable with respect to vehicle mass vs. number of wheels is the pressure resolved on the wheel. Pressure is force/area. So having more wheels (of the same geometry, of course), means lower pressure loading, which means lower erosion. It can be a very nonlinear effect if the increase in load bearing area drops the pressure below a plastic deformation threshold.

From a simple wheel erosion POV, more wheels = lower erosion. From the whole mission engineering POV, it's much more complicated.

Re:Really? (1)

BringsApples (3418089) | about 10 months ago | (#45751447)

Maybe they should have less scientists over there at NASA and more people with common sense who can raise their eyebrows.

Yes, that's exactly what they should do. This is, of course, if by "common sense" you mean common knowledge of the terrain on Mars. I'm sure that there are lots of non-scientists with such, as you say, "common" sense.

Re:Really? (1)

Anonymous Coward | about 10 months ago | (#45751619)

The thing I'm wondering about is why they didn't use something stronger than aluminum like titanium -- lighter too!

Re:Really? (3, Interesting)

ShanghaiBill (739463) | about 10 months ago | (#45751819)

The thing I'm wondering about is why they didn't use something stronger than aluminum like titanium -- lighter too!

Density of titanium: 4.5
Density of aluminum: 2.7
So no, not lighter.

Re:Really? (3, Interesting)

ArbitraryName (3391191) | about 10 months ago | (#45752077)

Titanium has a strength to weight ratio of 288 kNm/kg and aluminum 214 kNm/kg. So yes, lighter for a given load and stronger for a given weight.

Re:Really? (4, Insightful)

ColdWetDog (752185) | about 10 months ago | (#45752239)

And tends towards brittleness and is a PITA to machine.

I'm rather sure the nice folks at JPL thought this one through.

Re:Really? (5, Insightful)

Kwyj1b0 (2757125) | about 10 months ago | (#45751707)

I know weight is important and all, but .75mm of aluminium? Really? Maybe they should have less scientists over there at NASA and more people with common sense who can raise their eyebrows.

Yes, every time something goes wrong, let us point out how "stoopid" those scientists are in hindsight and claim that the "common sense" solution would have worked. Of course, it couldn't be that the people there did a lot of simulations, analysis, and decided that 0.75mm was a reasonable (not perfect - nothing is black and white) thickness and the disadvantage of thicker wheels was outweighed by the advantages of thinner wheels.

Yes, the designers took a risk - that is their job. To clearly assess the tradeoffs and come up with a good design that trades off risk and performance at an acceptable level. Something doesn't work out as you expect? Use that knowledge in the next iteration. At one extreme you have a lot of equipment with no wheels, and the other extreme you have just wheels, no equipment. You want to do the designer's job? Go ahead, show me what your "common-sense" analysis of the tradeoffs are - what equipment would you cut for thicker wheels, and back it up with a detailed discussion on how the benefits outweigh the disadvantages.

Re:Really? (1)

Shavano (2541114) | about 10 months ago | (#45751867)

I'd say that the material itself is questionable for something designed to roll over rocks. Why not titanium?

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45751913)

Titanium is harder, but more prone to fracture and shattering. It can't handle deflectional or tortional stress well at all. Especially heat treated titanium.

Since corrosion is unlikely to be a problem, i'd say condition T6 2025 alum would probably be fine, but given the weight of the rover I wouldn't be happy with less than .08 inch material. (That's a little over 2mm.)

T6 2025 alloy has a stat sheet pretty comparable to mild steel.

Re:Really? (4, Informative)

Anonymous Coward | about 10 months ago | (#45751979)

In reply to the GGP, here's what I would suggest, and why:
(Note, I work in aerospace)

I would suggest a minimum wheel skin thickness of .08 inches (a little over 2mm, it's a standard sheetmetal thickness) made of structural aluminum alloy (say 2025, or 7075, whichever is most electrically compatible with the suspension, given the pesence of perchlorate in the environment. 7075 is probably the better bet between the two, but 6Al4V might be a good choice too.) With a very generous plating of titanium nitride.

To make up the weight, (which would amount to only about 100 grams on the high side, give or take) I would look at using smaller radii on the machined parts of the suspension, using lighter gauge insulation on low voltage data wires in the electrical system, and laternative solder formulations. Also, replacing components that don't experiences constant drive or levering forces with ones made of titanium. (Parts of the arm near the wrist, parts of the camera mast, parts of the outer skin, etc.)

Re:Really? (1)

MichaelSmith (789609) | about 10 months ago | (#45752151)

But is the sheet aluminum even structural? Maybe the mission will finish with just the ribs which make the wheels rigid, but that may be enough.

Re: Really? (0)

Anonymous Coward | about 10 months ago | (#45752205)

Looking at the curiosity rover's monolithic wheel design, it is essentially a solid block of round aluminum stock that gets cut on a cnc lathe machine, and has the "ribs" as physical parts of the outer surface. (Think, "textured", like diamond plate pattern aluminum plate.)

It is not actually "sheet metal". I was mentioning that .08 inches thick is a well known thickness in industry, with well understood properties.

The issue I really see here is that a thickness of .75mm will be "absurdly hard to machine", let alone hold up to actual use on a harsh, abrasive environment.

Anything thinner than .04 inches thick has bad habits of deforming under the contact pressure of the cutting tools! They would have to cut the textured features of these wheels FIRST, THEN turn out the lathe cut interior of the rim, or the wheels would get holes in them during manufacturing!

They are stiffened somewhat by being a cylendar wall, but that only buys you so much.

That they didn't even give them an abrasion resistant coating tells me that you had beancounters making engineering desicions.

Re: Really? (2)

khallow (566160) | about 10 months ago | (#45752291)

That they didn't even give them an abrasion resistant coating tells me that you had beancounters making engineering desicions.

It's the nature of the beast. The launch costs were just shy of $195 million. The mass of the vehicle ended up being 900 kg. That's roughly $215,000 per kg or $100,000 per pound. That's just the ante for putting something on the surface of Mars. Shaving off a mere 5 grams saves you more than $1000 just in launch costs. You then have to add in the testing to make sure the coating actually stays on and such.

Given that this decision didn't actually endanger the mission's success, it was a successful gamble too. That indicates to me that the bean counters were actually engineers.

Re: Really? (0)

Anonymous Coward | about 10 months ago | (#45752357)

maybe i'm just biased about being cost effective to manufacture, vs cost effective to launch. (favors reproduction, vs favoring 1-off production.)

still, the coating I would have suggested is well understood to be very chemically compatible with aluminum alloys, and is quite inexpensive. you see it on blades for hedge trimmers and such all the time. i really am serious here. it would most likely have doubled the effective service life of thier existing wheel design.

Re: Really? (1)

torsmo (1301691) | about 10 months ago | (#45752675)

It is understandable why the good folks at NASA/JPL made the choices that they did. But if increased weight was a factor which stopped them from putting in more robust wheels, couldn't they have used something similar to what the Indian mars mission did, and launch the vehicle into a polar orbit, and from thereon, perform a Hohmann transfer?

Re: Really? (1)

trout007 (975317) | about 10 months ago | (#45753191)

If I were building them I'd CNC cut the outside on a 5-axis mill. There is plenty of support material with no deflection. Then wire EDM the inside out. No cutting forces.

Re:Really? (1)

ridgecritter (934252) | about 10 months ago | (#45752187)

Interesting, thanks. Wish I had mod points today.

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45752717)

I think you have missed the big important detail that there is less gravity on mars, and thus the material will experience less strain than here on earth.

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45753195)

Okay, so did they, nasa, mount this in the orbiter upside down, to avoid launch stresses? or was it launched in a standing position, Just as in landing position for deployment? Reasoning for a smaller wheel, less caution if upside down, but then, have to reenforce the case upper regions to withstand initial deformatioon at launch.

Re:Really? (1)

TubeSteak (669689) | about 10 months ago | (#45751875)

The internet says that the wheels and suspension are made of aluminum and " fittings made of titanium where ever they are needed"

Obviously cost wasn't an issue, so I'm curious about the alloy of Aluminum they used and why they picked that over lots of other more exotic possibilities.

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45751931)

Young modulous most likely.

Harder materials handle abrasion better, but they can't handle getting hit hard and suddenly, or being put under constant bending or tortional stresses.

What I personally think they should have done:

2mm thick 2025 or 7057 alloy aluminum wheel skins (T4 to T6 cond), with a fairly thick coating of titanium nitride anti abrasion coating.

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45752063)

Took a risk? I seriously question your definition of risk, sorry.

Curiosity had a total cost of 2.5 billion dollars, and yes, that money represented years of work, but it was supposed to buy the most advanced tech on Earth, not something that amounted to a simple 'risk' and "oh, well, better luck next time". They made the most stringent promises in order to secure that budget - now we're faced with it being nothing more than another beta and chain of more requests for funding. After all, if it worked, they'd be done and have to pack up and go home.

Any benefits NASA weighed were in their interest towards staying employed. Nothing new there, and sadly, the money pit they are doesn't look to change any time soon. Meanwhile, China has a long term plan and is working solidly towards their goals, free from the creaky bodkins that feed from the trough here in the US.

Re:Really? (0)

Anonymous Coward | about 10 months ago | (#45753655)

The moon rovers actually put a wire mesh over the wheels.

http://www.armaghplanet.com/blog/wp-content/uploads/2013/01/image_of-wiremesh-tyre.jpg

Re:Really? (1)

khallow (566160) | about 10 months ago | (#45752255)

I know weight is important and all, but .75mm of aluminium?

It's already been pointed out that the mission and those wheels exceeded the mission parameters. That means that 0.75 mm of aluminum was indeed enough. The common sense, eye-brow raising people are done here.

Your worry IMHO completely misses the point. In the real world, when someone screws up a prototype badly, they just make another cheap prototype which eliminates that failure mode and come up with more advanced and sophisticated screw ups. If 0.75 mm wheels weren't enough, then make the next generation of wheels a bit thicker.

But in the NASA world, who and what will use this knowledge? In my view, there won't be a lot of NASA Mars-oriented projects altogether, much less rover designs which can use this knowledge. NASA is notorious for spending vast sums of money, inching along over painfully long periods of time, and squandering the talent of generations of engineers and scientists, only to abandon the results when the activity can no longer be politically sustained. I believe that will happen here.

Sometimes, the results are sufficiently useful that other parties can use them. But this is remarkably poor return on what NASA consumes.

Engineer the entire system (2)

tomhath (637240) | about 10 months ago | (#45752449)

The rover is designed to perform a certain mission for a certain length of time. There's no point in putting tires on it that outlast the instruments. Everything is designed to have roughly the same lifespan - so yea, the tires will be worn out by the end of the rover's mission. That's all they need.

Future planning? (0)

BringsApples (3418089) | about 10 months ago | (#45751367)

...the monitoring of the situation is essential for future planning

They mean when the rover is near it's death, they pause it, and send more rovers. After they get like 8 up there, they'll fight them, like on BattleBots. You know, get Mars ready for humans and their wars.

...the monitoring of the situation is essential for future planning

We all know that those rovers are up there cutting up large rocks and stacking them into pyramidal shapes that regulate the atmosphere in preparation for humans to arrive, only to try to cover up the pyramid's real identity so that the future race of beings don't know their real history.

...the monitoring of the situation is essential for future planning

obligatory future for this rover [xkcd.com]

Re:Future planning? (2)

John Bodin (189895) | about 10 months ago | (#45751445)

As part of planning to send people to the other planets, I am surprised that they do not try to figure out a way to get something back from the landers. I would think that seeing how the materials held up to the conditions it went through would be important data to have.

Re:Future planning? (1)

BringsApples (3418089) | about 10 months ago | (#45751479)

I think it'll be interesting to see what happens to a human once they leave the magnetic environment of their home planet.

Re:Future planning? (0)

Anonymous Coward | about 10 months ago | (#45751535)

Maybe they could make the wheels out of extra apostrophes? Those things seem indestructible.

China to the rescue! (0)

Anonymous Coward | about 10 months ago | (#45751675)

Maybe Jade Rabbit can hop over to Mars and help Curiosity out...

Next time... (1)

Anonymous Coward | about 10 months ago | (#45751725)

they should not go with Pirelli...

Re:Next time... (1)

ihtoit (3393327) | about 10 months ago | (#45752605)

snap!

AAA? (0)

Anonymous Coward | about 10 months ago | (#45751825)

Maybe they should have considered a AAA membership. Or I guess it would be MAA...

Re:AAA? (1)

gapagos (1264716) | about 10 months ago | (#45752175)

I don't know about MAA, but my CAA policy states that it doesn't cover off-road driving incidents, and I believe Mars is off-road, so...

It always sucks to get tire damage (1)

Ukab the Great (87152) | about 10 months ago | (#45751941)

that gets you stranded in a bad neighborhood.

Sad. (-1, Troll)

ApplePy (2703131) | about 10 months ago | (#45752153)

How far has this thing managed to go now? Couple miles?

Tires are stupid anyway. Hey, news flash, PhD eggheads... try these things called "tracks". I'm pretty sure they'll work on Mars.

NASA (and whatever monkeyshine outfit built this piece of shit) has too many Pee Haych Dees, and not enough people with mechanical skill and common sense.

Here's government for ya. A multi-billion-dollar whiz-bang rover with the world's best scientific equipment... off on the shoulder with a flat tire. Wonder how long it'll take Triple-A to get there?

Re:Sad. (2)

bobthesungeek76036 (2697689) | about 10 months ago | (#45752207)

How far has this thing managed to go now? Couple miles?

Tires are stupid anyway. Hey, news flash, PhD eggheads... try these things called "tracks". I'm pretty sure they'll work on Mars...

There would probably be a weight issue with tracks...

Re:Sad. (5, Funny)

Trepidity (597) | about 10 months ago | (#45752297)

Hey man we don't need none of yo science, we got Common Sense Internet Man here, who read 4 sentences on the topic and is gonna design him a better rover than all them eggheads!

Re:Sad. (1)

ihtoit (3393327) | about 10 months ago | (#45752613)

there'd be an issue with MPF (moving parts failure) as well, how many moving parts per inch of track? Half a dozen? On a wheelbase of three feet? Couple hundred? The failure of any ONE of which would end the mission.

Probably why they opted for six independent wheels - so the failure of any two on opposite sides would not be a mission ender. On a four wheeled vehicle, the failure of just one wheel would end the mission.

Re:Sad. (0)

Anonymous Coward | about 10 months ago | (#45752331)

Tires are stupid anyway. Hey, news flash, PhD eggheads... try these things called "tracks". I'm pretty sure they'll work on Mars.

Wow! You must be really smart! To think, none of those PhD eggheads or engineers working at NASA had thought of tracks. Now it all makes sense. I mean, they probably had considered tracks, done a whole lotta calculations and testing and simulations that weighed the advantages and disadvantages of all sorts of different kinds of tracks and wheels, and made a very educated decision to use the type of wheels they did based on evidence, data, risks, etc. But clearly they were wrong, because you say so.

Man, it would have saved them so much time if they had just hired you. You wouldn't have had to do all that testing, running all those simulations, calculations, factoring in the extra weight of tracks and all that, you are just such a genius that you can just know without even laying eyes on the thing! Man, you really ought to consider putting in an application to NASA, I'm sure after seeing your post they'd hire you in a heartbeat!

Rough rovin', or rovin dirty? (1)

Anonymous Coward | about 10 months ago | (#45752437)

Maybe the wheels are just dirty?

They see me rovin'
They hatin'

Amazing machine! (1)

bradley13 (1118935) | about 10 months ago | (#45752497)

I don't get all the people bashing the design?

Just think how long the rover has been on Mars - far longer than ever expected. It has a few dings in the wheels. Amazing machine!

Re:Amazing machine! (0)

Anonymous Coward | about 10 months ago | (#45752711)

You're thinking of Opportunity. Curiosity has been on Mars just a little over a year.

Should we call those photographs ... (1)

Alain Williams (2972) | about 10 months ago | (#45752579)

selfies [wikipedia.org] ?

Hasn't it already met most of its goals? (1)

TomGreenhaw (929233) | about 10 months ago | (#45753189)

From the reading I've done, it's met most of its objectives. Many of the goals and experiments don't need mobility anyway. It's not like it can't move either even with the existing and anticipated state of wear.

It does raise an interesting question though. Due to the cost of getting stuff there, should future missions include repair robots to reuse or recycle the stuff already on site?

Should have tested them (0)

Anonymous Coward | about 10 months ago | (#45753331)

Shoulda tested them on Minneapolis's potholes.

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