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Rough Roving: Curiosity's Wheel Damage 'Accelerated'
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."
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.
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.
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.
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.
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.)
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.
And tends towards brittleness and is a PITA to machine.
I'm rather sure the nice folks at JPL thought this one through.
Faster! Faster! Faster would be better!
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!
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
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.
I've decided to Diversify my Holdings. I've divided my cash between my left and right pockets, instead of all in one.