
Breaks Observed in Rover Wheel Treads - andyjohnson0
https://www.jpl.nasa.gov/news/news.php?feature=6785
======
mentos
Always loved the name of the Curiosity rover, was just reading the wikipedia
article, apparently it was crowd sourced from 9,000 proposals and the selected
name was from a 12 year old student. Very cool

"A NASA panel selected the name Curiosity following a nationwide student
contest that attracted more than 9,000 proposals via the Internet and mail. A
sixth-grade student from Kansas, twelve-year-old Clara Ma from Sunflower
Elementary School in Lenexa, Kansas, submitted the winning entry. As her
prize, Ma won a trip to NASA's Jet Propulsion Laboratory (JPL) in Pasadena,
California, where she signed her name directly onto the rover as it was being
assembled.

Ma wrote in her winning essay:

Curiosity is an everlasting flame that burns in everyone's mind. It makes me
get out of bed in the morning and wonder what surprises life will throw at me
that day. Curiosity is such a powerful force. Without it, we wouldn't be who
we are today. Curiosity is the passion that drives us through our everyday
lives. We have become explorers and scientists with our need to ask questions
and to wonder."

[https://en.wikipedia.org/wiki/Curiosity_(rover)](https://en.wikipedia.org/wiki/Curiosity_\(rover\))

~~~
abandonliberty
I'm very happy that we're involving students and helping increase passion for
space.

Is it crowd-sourcing when the result is selected? If infinite monkeys give us
Shakespeare, 9000 students should generate a pretty dense set of data given
student vocabulary.

Cynicism:

1\. Know what you want to call it

2\. Canvass 9000 people

3\. Pick the best one that agrees with you (because there must have been
collisions)

~~~
vkou
If you know what result you want, why not just have a patsy write your
suggestion in, so that you can select it?

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JetDogRush
This seems dramatic, but there is a ton of life left in the wheels. Some of my
colleagues performed life testing on the wheels after we first discovered the
cracks and found the rover is capable of driving around on the titanium
support struts even after the aluminum wheels have completely disintegrated.
We've got a long way to go yet!

~~~
kahnpro
If Kerbal Space Program taught be anything about space, it's that most
problems can be solved with struts.

~~~
JetDogRush
If only Curiosity were as fast as the KSP rovers... top speed is somewhere
around 100 meters/hour, and usually more like 40!

~~~
TeMPOraL
Should have strapped an SRB on the rover.

Reminds me; I wonder just how much ion engines are overpowered in KSP compared
to their real-life equivalents. Or, put differently, if one could replicate a
hovering Minmus rover I made in KSP (which used ion engines to stay afloat for
a long time).

~~~
jerf
Minmus surface gravity is 0.491 m/s^2; current ion drives thrust with a couple
hundred millinewtons, so I don't think a drive could even support itself
against that level of gravity let alone with power and a ship attached.

However, we currently design our ion drives for power-to-thrust efficiency and
long-term effectiveness. I'm not sure what we could get if we designed them
for maximal thrust. Especially since in real life, right now the answer to "Do
you want a 'maximal thrust' ion drive?" is pretty much "Well, have you
considered using... _not_ an ion drive?", so I'm not sure I've ever seen a
treatment of that question based on current tech.

~~~
creshal
> I'm not sure what we could get if we designed them for maximal thrust.

Probably something with a worse specific impulse than a chemical engine.

------
dayjah
This appears to be a brilliant case of reliability engineering. I'm always
super impressed with these sorts of tales; given how NASAs budget always seems
to be concern seeing them deliver solutions which have just enough wiggle room
in them to deliver the intended results without going too far into gold
plating their solutions really leaves the software infrastructure engineer in
me in awe. Even more so when you consider the time spans involved in this; I
personally believe we've a ton to learn in the software space from practices
like this.

~~~
jeremiep
I think we also have a ton to learn in the software project management space.
Agile for example would be quickly laughed off and dismissed.

Our field is currently full of cargo-cult practices, studies and best
practices without any empirical research, java schools, a strong focus on
"awesome" and easy to get started instead of useful and simple; we're still a
pop culture for the most part.

~~~
komali2
To be fair, NASA software engineers don't exactly act like your average agile
start-up team,because once the "product" is out, patching is really feasible.
Whereas for your average webapp, it's more strategic to iterate based on
feedback.

~~~
komali2
Whoops too late to edit. Should be "patching _isn 't_ really feasible".

~~~
greglindahl
Except they DO send out patches. Just not very often.

~~~
komali2
Well, my point was it's a bit more trouble to patch something on another
planet that it is to `heroku push.`

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6DM
Breaking after a mere 10 miles, to me sounded really awful, but apparently
they planned on this. The construction must have been to save on weight,
making the wheels no more reliable than the exact distance they wanted to
travel: "...milled out of solid aluminum. The wheels contact ground with a
skin that's about half as thick as a U.S. dime, except at thicker treads."

~~~
jakobegger
I thought NASA used metric units; would be nice if their press releases did
too. I have no clue what "half as thick as a U.S. dime" means.

~~~
tossaway1
That's a description that most Americans can more easily picture than
something like 0.68 mm (including people who are comfortable with metric units
like myself) and they seem to be focusing a lot in recent years on making the
information they provide more accessible to average Americans, undoubtedly to
help drive interest in and support for what they're doing.

~~~
bumblebeard
I'd prefer if they wrote something like "0.68 mm (about half as thick as a US
dime)." That way the number is still there for people who don't want to look
up how thick a dime is.

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DanBC
This comment from a while ago links to a really good blog about the wheels:
[https://news.ycombinator.com/item?id=8206378](https://news.ycombinator.com/item?id=8206378)

Here's a direct link to the 2014 blog talking about damage to the wheels:
[http://www.planetary.org/blogs/emily-
lakdawalla/2014/0819063...](http://www.planetary.org/blogs/emily-
lakdawalla/2014/08190630-curiosity-wheel-damage.html)

------
yread
Apparently the new rover - Mars 2020 - will have narrower, thicker wheels with
more growsers with a different shape
[https://mars.nasa.gov/mars2020/mission/rover/wheels/](https://mars.nasa.gov/mars2020/mission/rover/wheels/)

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kirykl
NASA is funded by Americans, and this is a press release not a scientific
paper. US customary units and dimes is intentional for the audience.

~~~
JackFr
Also very descriptive, since dimes are also noticeably thinner than our other
coins.

------
overcast
The wear patterns on these wheels always seemed so strange to me, considering
the extremely slow pace at which this thing moves. The wheels look like
they've been hit by shrapnel. Obviously I have no context as to what
conditions are like on Mars, but it just seems strange that driving over rock,
slowly produces wear like that. Seems like they were never strong enough to
support the weight, over something sharp.

~~~
JetDogRush
There are two major factors - fatigue (think bending a paper clip repeatedly)
due to driving over tons of small rocks, and the the mechanics of having six
wheels contributing additional damage to the front and middle wheels. Think of
pushing a rolling suitcase versus pulling one - when hitting an obstacle it
tends to dig in instead of easy popping up. The front and middle wheels are in
front of their pivots, and so tend to get driven in to rocks by the other
wheels.

~~~
mnw21cam
In terms of metal fatigue, aluminium doesn't last very long at all. That's one
reason why you want electric cables made of copper, not aluminium.

~~~
JetDogRush
True! The actual induced strain is not particularly high (the wheels do not
visibly deform) but it's the cycle count that will get you. The chevron-shaped
grousers also act as stress concentrators, which is why the cracks are all
starting at those tips.

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typetypetype
Tangential, but the quality and resolution of that image is incredible.

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JKCalhoun
Are the materials used in the rover wheels _too_ exotic? I'm metallurgist, but
I know that steel, though heavy, is malleable and, if correctly tempered,
unlikely to break like the rover's wheels. At what cost ultralight, exotic
metals?

Edit: Are they really made of aluminum? If so, while hardly exotic, definitely
more brittle than steel. I know steel is heavy as hell, but of course you can
use a thinner steel for an equivalent strength (still heavier I suppose).

~~~
MadManE
One of the first things that I got told in my materials class was that for the
strength and weight, carbon steel and aluminum are essentially the same. Steel
is about 3x as dense, but also 3x as strong, and does not fatigue like
aluminum.

I'm assuming that NASA knows this, and chose aluminum for another reason that
I'm not aware of.

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Splendor
I would love to see a write-up of everything we've learned about wheel
engineering from the Mars rovers. What would the team(s) responsible for
Curiousity's wheels do different now? (I don't mean to imply that their design
is not successful -- just that I'm sure they've learned from this iteration)

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danaliv
Fun little bit of trivia: those slots in the wheels are Morse code, and they
spell out "JPL." The original design had the letters JPL emblazoned on the
wheels but they felt this was a little too tooting-your-own-horn, so they made
them Morse code instead.[0]

0\. Personal communication from MSL engineer

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JoeAltmaier
Would be less confusion in this thread, if the title added "as predicted and
on schedule for successful mission completion"

~~~
anotheryou
as predicted after more tests. they where surprised about the ammount of
damage initially.

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pfortuny
So ir broke after how many years of life longer than the expected utility?
Like forever, iirc...

~~~
krallja
You're probably thinking of Spirit and Opportunity, the smaller rovers which
landed in the early 2000s and long outlived their primary scientific missions.
This is Curiosity, the SUV-sized rover which landed in 2012, and is still in
its primary mission.

~~~
JetDogRush
Not quite - primary mission was two years (one Martian year). We are in
Extended Mission #2.

~~~
krallja
Oops, you're right! Thanks.

------
gregcohn
Did you know the wheels have morse code embedded in their tread?
[https://www.jpl.nasa.gov/news/news.php?feature=3497](https://www.jpl.nasa.gov/news/news.php?feature=3497)

------
theandrewbailey
Meanwhile, Opportunity keeps going after 13 years.

[https://mars.nasa.gov/mer/mission/status.html](https://mars.nasa.gov/mer/mission/status.html)

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gene-h
It's a shame that the trend in increasing rover size probably won't continue.
If scaling does continue, we might expect to have rovers the size of monster
trucks on Mars by 2030.

------
ianai
Am I the only one that thought they meant the tracks left on the ground?

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awinter-py
even blizzak coatings last more than 10 miles

this doesn't bode well for their JD Power rating

I guess if you start the odometer at launch their numbers look a little better

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postit
What surprises me is that the wheels aren't covered with a honeycomb-like
texture instead of these longitudinals M's

------
jcoffland
The spin machine is always on at NASA. It's not that the wheel is failing it's
"nearing a wheel-wear milestone." Still it's impressive what they have
achieved.

------
mrfusion
How's it possible to get all that wear in ten miles? That's just a trip to
church. My car tires don't even register that.

~~~
olex
Your car tires are rubber, and designed to last for a long time at speed.
Curiosity's tires are aluminum, and are designed for much less and much slower
driving. That seems weird, but the important point is their mass: they only
weigh 3 lbs (~1,4kg) per wheel, compared to over 20 lbs for the tire alone
(without the rim) on a normal car. Mass budgets are extremely tight on space
missions, every pound saved can either go towards more scientific payload or
significantly decrease launch costs.

~~~
ianai
Car tires also have the benefit of a nearby support system. They were looking
for wheels that would do the job with 100% certainty of never being able to be
replaced.

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wintom
Martians popping our tires?

In all seriousness its unclear to me how this could happen so quickly? The
article does not really explain why they didn't think through this.

~~~
AnkhMorporkian
They did think through it, but the rover has already exceeded its planned
mission time by over 2.5 years! Wheels can't last indefinitely, and more than
doubling the time of a 2 year mission before they see any wear is pretty
incredible.

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nanodano
Does anyone else think it's odd that the treads are wearing like that after
TEN miles? They probably could have done better by sticking a Goodyear on it.

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redcalx
I assume they're titanium. I wonder though if they use titanium crystals as
per jet engine turbine blades?

~~~
jordanb
Turbine blades are made from inconel. And all solid metal is crystalline.

~~~
SEJeff
SpaceX "3D Prints" their merlin engine chambers from the same alloy, inconel.

[http://www.spacex.com/news/2014/07/31/spacex-
launches-3d-pri...](http://www.spacex.com/news/2014/07/31/spacex-
launches-3d-printed-part-space-creates-printed-engine-chamber-crewed)

~~~
greglindahl
SpaceX's entire Super Draco rocket engine is 3d printed, too.

