Slashdot Mirror
Wheel Damage Adding Up Quickly For Mars Rover Curiosity
An anonymous reader writes: The folks in charge of the Mars rover Curiosity have been trying to solve an increasingly urgent problem: what to do about unexpected wheel damage. The team knew from the start that wear and tear on the wheels would slowly accumulate, but they've been surprised at how quickly the wheels have degraded over the past year. Emily Lakdawalla at the Planetary Society blog has posted a detailed report on the team's conclusions as to what's causing the damage and how they can mitigate it going forward. Quoting: "The tears result from fatigue. You know how if you bend a metal paper clip back and forth repeatedly, it eventually snaps? Well, when the wheels are driving over a very hard rock surface — one with no sand — the thin skin of the wheels repeatedly bends. The wheels were designed to bend quite a lot, and return to their original shape. But the repeated bending and straightening is fatiguing the skin, causing it to fracture in a brittle way. The bending doesn't happen (or doesn't happen as much) if the ground gives way under the rover's weight, as it does if it's got the slightest coating of sand on top of rock. It only happens when the ground is utterly impervious to the rover's weight — hard bedrock. The stresses from metal fatigue are highest near the tips of the chevron features, and indeed a lot of tears seem to initiate close to the chevron features."
The things are the thinnest element in the entire lander. When I first saw those wheels, I just shrugged and figured they knew what they were doing. But the reality seems to be that they stuck with some sort of legacy design and somehow nobody ever asked the obvious question about those miserably thin wheels.
Though maybe I should instead be celebrating the fact that they didn't get their metric crossed with their imperial.
The Opportunity (MER-B) Rover landed on Mars January 25, 2004. More than 10 years later, it is still going strong even though it, too, was only expected to perform a 3 month (90 day) mission.
The success and longevity of the earlier Mars rover missions sort of sets expectations that future missions will last just as long....
We of course realise that is not possible. Plenty of missions end early, Spirit (MER-A) got its wheel stuck and got in trouble years ago but Opportunity keeps on running and sets unrealistically high expectations of Curiosity and future missions.
You can tell how powerful someone is by the magnitude of the crime they can commit and be able to get away with.
The planned mission duration was 2 years not 3 months.
http://en.wikipedia.org/wiki/Curiosity_%28rover%29
You are thinking about Spirit and Opportunity, whom both enormously exceeded their planned mission duration.
Solarpanels ? Curiosity is powered by an RTG not solarpanels.
http://en.wikipedia.org/wiki/Curiosity_%28rover%29
You are thinking about Spirit and Opportunity, whom both have solarpanels.
Spirit
Obligatory, because it's beautiful.
Seriously, Spare Tires? Or spare belts for tires so that the rover can re-tread itself.
Simply build a wheel changing robot and launch it to Mars.
If it's too difficult, I can't understand it !
Pic of the wheel ...
http://www.garrettbelmont.com/...
The first time when I saw the wheels I was wondering why the hell they spend so much money to send up a robot to Mars and then equip that thing with such flimsy wheels
And I did post question here on /, and there were people (NASA fanbois, perhaps) defending those flimsy wheels
Muchas Gracias, Señor Edward Snowden !
I am guessing that part of the reason for an all-metal milled wheel is because of the (largely) unshielded RTG power source which Curiosity uses may seriously degrade organic-based materials.
Could someone with more knowledge of materials near RTG sources comment?
No sig. Move along - nothing to see here.
Curiosity is not spirit or opportunity. This is a much heavier rover. Plus, it consumes way more power and moves faster. The forces on the wheel are much much rougher than on the MER rovers.
A fool and his hard drive are soon parted.
The thousands of microscopic missiles launched at the rover to stop it anhialating more of their tiny cities is finally paying off. If one of them only had an old macbook and some way of getting to its core....
Aluminum does not have a fatigue limit. That is, no matter how beefy you make an aluminum part, after enough cyclic stresses it will suffer fatigue failure. This is why airframes are retired after about 100,000 pressurization cycles - to avoid the fate which befell the de Havilland Comet.
Other materials like steel or titanium can be designed so it can withstand an infinite number of stress cycles and not fatigue. Given the nature of the mission and power source (multi-year if not multi-decade operation on another planet with no hope of human intervention if something should go wrong), they really should have allocated sufficient weight budget for non-aluminum wheels. This is basic materials science that every undergrad mechanical engineer learns. I was very surprised when I heard they were going with thin aluminum wheels on this rover.
You've confused your different Mars Rovers. Curiosity was launched from Earth on November 26, 2011.
You can't be ahead of the curve, if you're stuck in a loop.
Don't forget the thing weighs a ton.
My thought exactly ...
"Oh, no! The item we built is starting to fail after it's had 40 times the planned usage!"
That's not a poor design choice ... that's a *fantastic* problem to be having.
Build it, and they will come^Hplain.
To all you idiots who think you could have done do a better job, read Emily's article. There were serious weight constraints for the wheels that effected everything from EDL to operations. Any huge engineering project is full of tradeoffs. Hindsight is 20/20.
Launch and land a "pep boys" on mars...
Do not look at laser with remaining good eye.
Plastics don't do very well in a vacuum like atmosphere full of radiation with wide temperature swings in the long term. Plus the low average surface temperature of -82F/-63C makes plastics less malleable and in many cases, brittle.
In the low atmosphere they can become brittle from outgassing and are susceptible to cracking and can simply shatter like glass. Nylon wire ties in a vacuum chamber simply fall apart after a few months. Though the 6 mbar (4.5 Torr) Atmospheric pressure of Mars isn't a hard vacuum, it is still 0.6% That of Earth's average sea level pressure.
Then you have radiation degrading the plastics which again makes them brittle. A friend worked on RHIC out in Brookhaven National Labs and since he was small and skinny he was tasked with changing out a lot of the sensor cables on the ring. The insulation simply disintegrated from radiation. There was nothing they could do about it save for bulky shielding which would have made servicing impossible.
In the end, metals are simply more suited to the task.
The biggest problem is the curvature of the wheels is concentrating all of the weight of the vehicle on the center of the wheel, and not only that, but with the tread design, all the force is concentrated on a spot about 2 square millimeters. They just need to add a rib going down the middle like bicycle tires.
I love how the retards are bitching because the probe that got launched to Mars is starting to have problems after exceeding the design life.
As an embedded systems (electronics/firmware) engineer, I was going to half-jokingly, half-seriously say, "Well, we'll just send a new firmware update to Curiosity to help with the problem." And then of course as I read the article, that was one of the proposed mitigations:
I've been developing embedded systems for more than half my life, and I never get bored...
And you can't use the average temperature as a primary guide. The landing area temperature range from minus 127 C to positive 40 C
The Kruger Dunning explains most post on
Nowhere on Mars has ever been +40 C.
This space intentionally left blank
No, what this actually says is that mission goals of a specific time are a nebulous, silly concept that are foisted off on the Power Point People because it's simpler than explaining complex physics and material sciences. It avoids icky concepts like engineering trade offs, probabilities, risk ratios and mathematical feats more complicated than 'next slide'.
Faster! Faster! Faster would be better!
Curiosity does have a bunch of 'nylon tie' like objects on the top of the rover, holding bundles of cables together. Wonder what they're made out of. A quick search found lots of documentation on exactly how to run the cables (fun factoid - they still use knots on cord) but not much on what the stuff was made out of.
Faster! Faster! Faster would be better!
According to a JPL article, "During their exploration of Mars, the rovers have recorded temperatures ranging from midday highs of about 35 degrees C" (Source link). Making the range a round number like 40 C seems reasonable in this instance.
Spirit recorded temperatures of +35C - http://mars.jpl.nasa.gov/mer/s....
You are claiming that in say the last 10,000 years nowhere on the planet has ever managed to get just 5C higher than what was measured in an arbitrary few year window?
I don't get what's so hard. Just have Jebidiah Kerman exit the rover and fix the wheel.
They did. And they designed it really well. So far has gone well beyond what the primary mission required of it. They are now trying to find ways to boost its life even further.
Why is it so hard to only have politicians for a few years, then have them go away?
My guess is the metal fatigue is being cause by radiation. Mars does not have the atmosphere and magnetosphere of Earth (no news flash here). So maybe it's just a case where cosmic radiation causes metal fatigue and we didn't know that -- or perhaps it's SPECIFIC to the type of allow being used.
>>"ad space available -- low rates!!!"
Plenty of missions end early, Spirit (MER-A)
Er what?
Spirit
Original Mission Parameters: 90 Mars days (sols)
Actual Mission Length: 2210 sols (lost contact)
I wouldn't say Spirit's mission ended early. It went 2100 sols past mission date. It didn't last as long as Opportunity though.
Well, there's spam egg sausage and spam, that's not got much spam in it.
The original mission duration was 668 sols for Curiosity. It is on 723 sols or so.
Well, there's spam egg sausage and spam, that's not got much spam in it.
http://en.wikipedia.org/wiki/A... I wonder why none thought of those...they look much sturdier and if that mesh fails it will be in spots only... plus with 50years later materials.... look to me they could have done a maybe better job....
What is being done to improve future wheels on rovers and others?
Ant(Dude) @ Quality Foraged Links (AQFL.net) & The Ant Farm (antfarm.ma.cx / antfarm.home.dhs.org).
For a three month mission, this rover is performing fantastically beyond expectations.
Save it, nobody's buying it. Spirit and Opportunity set a higher bar than that.
Hey, Spirit and Opportunity went beyond expectations... way better than Hope and Change, that failed almost instantly.
Well, the leading alternative was Smith and Wesson, but voters weren't quite ready to pull that trigger.
my, your, his/her/its, our, your, their
I'm, you're, he's/she's/it's, we're, you're, they're
It's not "bad luck", it's why you explore. If you send out a scout to the east, and he comes back with an arrow in his back, bummer for the scout, but at least you now know the east is dangerous before sending the rest of the troops to the east.
Better we find out about stiff rocks now instead of when humans are driving a rover there, without AAA.
Note this rover is better able to handle sand based on lessons from the last rovers.
Table-ized A.I.
But, they are moving slower than expected, in part because of the wheel worries.
Table-ized A.I.
Historically cable lacing was done with waxed cotton. Since WWII more nylon and polyester, as they wear harder and don't burn as good, don't like water, etc.
I'd imagine NASA uses some kind of space age stuff.. polyimide or some sort of fluoropolymer, but who knows, maybe cotton has better extreme cold weather performance.
Sent from my PDP-11