Breaks Observed in Rover Wheel Treads

Re:Breaks Observed in Rover Wheel Treads by gambiting on Wednesday March 22, 2017 @11:49AM (#13931867)

I'm curious(and this is in no way meant to belittle the work they've done) - if you drove a normal Earth car on the surface of Mars, how would the wheels and tyres behave in Martian conditions? Obviously we have off-road tyres here on Earth which can withstand some extreme abuse, so I'm just wondering - is Martian soil just full of sharp objects? Or is something else going on here?

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Re:Breaks Observed in Rover Wheel Treads by brians on Wednesday March 22, 2017 @12:01PM (#13931994)

It does have sharp objects, but ordinary truck balloon tires would handle those relatively well. But at night, the temperatures drop to -100 °C, and your rubber tires freeze and shatter.

Also, rubber's much heavier, and they just couldn't bring that weight. They really couldn't drop that weight from the sky crane, not without increasing the shock absorbers in the legs... which would have meant more weight, and the plan's just impossible.

It also has horrifically abrasive dust, much worse than anyplace on earth. The abrasion from that would wreck a balloon tire seal---hard to predict how quickly.

A balloon tire also goes from "fine" to "useless" with one puncture. Apparently they got surprised by the sharp rocks: http://www.planetary.org/blogs/emily-lakdawalla/2014/0819063... , not having seen anything like that from previous missions.

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Re:Breaks Observed in Rover Wheel Treads by andygates on Thursday March 23, 2017 @10:02AM (#13939780)

Well, the tyre will almost instantly go soft as the inflating gas reduces in volume due to the cold. Then the tyre will go flat as the gas escapes (try driving for a couple of years without pumping your car tyres up). And the rubber will freeze and crack, and get UV perishment and low-pressure outgassing of its own.

The balloon-like tyre of choice is a springy basket mesh, as seen on the Lunar rover. But that's only needed because we wanted to drive around at human-acceptable speeds (to get to interesting places before the humans had to go home). With a teleoperated robot, we can take our time, and that means we don't need bouncy suspension. Which is good, because big wire tyres are quite heavy.

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Re:Breaks Observed in Rover Wheel Treads by tropo on Wednesday March 22, 2017 @06:53PM (#13935802)

That is the best solution for Mars, but you might need to build the rover in a freezer. Tires that would be soft at Mars temperatures would be liquid or worse at Earth temperatures. For example, you might fill a normal tire mold with diesel, then cool it with liquid nitrogen and there you go -- a lovely tire for Mars that will melt at normal Earth temperatures.

You'd still want to go airless probably, due to a lack of repair shops.

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Re:Breaks Observed in Rover Wheel Treads by jonknee on Wednesday March 22, 2017 @11:58AM (#13931956)

I think low temperatures alone would wreck Earth tires (and the rest of the car, but that's a different story).

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Re:Breaks Observed in Rover Wheel Treads by passivepinetree on Wednesday March 22, 2017 @11:55AM (#13931931)

Well, regardless of how well an Earth car would perform, it'd likely be far too heavy/expensive to get to Mars in the first place. It's impressive how NASA can solve problems with the resource constraints they have.

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Re:Breaks Observed in Rover Wheel Treads by jonknee on Wednesday March 22, 2017 @12:01PM (#13931996)

It would obviously be a dumb idea, but Curiosity is in the same ballpark as a car in both size and weight (1,982 lbs). A Smart Car is ~1,800 pounds, so it's actually heavier than some Earth cars!

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Re:Breaks Observed in Rover Wheel Treads by passivepinetree on Wednesday March 22, 2017 @02:53PM (#13933633)

Interesting, I didn't know that Curiosity was that heavy! It's a ways away from Jeep Wrangler/military Humvee territory (especially if you loaded one of those up with the required scientific instruments) but it'd be cool to see NASA go with something heavier-duty for longer-range missions in the future.

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