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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.
Agreed, this is pretty goddamn lame. Cut corners somewhere else, not on the fucking MSL rover, kthxbai.
Yep, just give it to the highest bidder for equally shitty work.
Actually, most of the rover was built in-house.
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?????
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.
Happiness in intelligent people is the rarest thing I know.
Ernest Hemingway
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.
...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
Politics; n. : A religion whereby man is god.
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.
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.
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.
Politics; n. : A religion whereby man is god.
The wheels aren't in the way of the instruments and batteries. /armchair engineer
The thing I'm wondering about is why they didn't use something stronger than aluminum like titanium -- lighter too!
In terms of total mass, yes they are.
Maybe Jade Rabbit can hop over to Mars and help Curiosity out...
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.
they should not go with Pirelli...
So im sure they made them absolutely as thin & lightweight as they thought they could get away with.
Missed it by that much.
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?
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.
Maybe they should have considered a AAA membership. Or I guess it would be MAA...
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!
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.
I'd say that the material itself is questionable for something designed to roll over rocks. Why not titanium?
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.
[Fuck Beta]
o0t!
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.
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.
that gets you stranded in a bad neighborhood.
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.)
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.
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.
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.)
You asked for "proper tires". Please elaborate on what you meant then.
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.
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.
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.
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.
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.
http://michaelsmith.id.au
there is a very big difference between 5 GRAMS and 5 POUNDS.
(hint, 5 grams is the weight of 5 droplets of water.)
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
Comment removed based on user account deletion
"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.
Interesting, thanks. Wish I had mod points today.
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
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.
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...
Karma: Bad
"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
http://www.spacex.com/careers/list
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!!
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!
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.
"Nothing new there, and sadly, the money pit they are doesn't look to change any time soon."
Find the NASA budget in this chart:
http://www.nytimes.com/interactive/2010/02/01/us/budget.html?hp&_r=0
http://www.rootstrikers.org/
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.)
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 $1000 just in launch costs. You then have to add in the testing to make sure the coating actually stays on and such.
Given that this decision didn't actually endanger the mission's success, it was a successful gamble too. That indicates to me that the bean counters were actually engineers.
Hey man we don't need none of yo science, we got Common Sense Internet Man here, who read 4 sentences on the topic and is gonna design him a better rover than all them eggheads!
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
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!
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.
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.
Muchas Gracias, Señor Edward Snowden !
Make that 100 drops of water. 20 drops per gram.
Maybe the wheels are just dirty?
They see me rovin'
They hatin'
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.
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!
Enjoy life! This is not a dress rehearsal.
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'.
Political debates have me rolling my eyes so much I think I got optical whiplash. I should sue. - Foamy The Squirrel
wow. i looked that up and its right, assuming the .05ml/drop ratio is actually correct.
regardless, it isnt a whole lot of weight.
selfies ?
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.
Political debates have me rolling my eyes so much I think I got optical whiplash. I should sue. - Foamy The Squirrel
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.
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.
Serious? Seriousness is well above my pay grade.
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?
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.
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.
Wasn't it "aerospace engineers" working in non-metric units that lost the Mars Climate Orbiter?
I don't think NASA would employ someone still working in inches.
Actually, you hate your life, and are projecting that on America.
You know I am right.
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.
I love Jesus, except for his foreign policy.
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?
Greed is the root of all evil.
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.
I love Jesus, except for his foreign policy.
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.
Shoulda tested them on Minneapolis's potholes.
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
I wonder how it behaves at -80 or -100C, compared to aluminum?
The MSL wheels are machined out of one solid billet, not made from sheet (just like MER and Pathfinder).
The problem with the 100 grams is that at the beginning of the project you have a particular mass budget, and it gets allocated into all the little smaller buckets, so that each team can go off and do their designs essentially independently: there's probably 10,000 people involved in making MSL, and some division into independent chunks is needed. You can't have the wheel designer calling up one of the people making a science instrument and saying "hey, can you give up 10 grams?". What's to stop the spectrometer guy asking for 10 grams from the wheels?
There's also a schedule issue: by the time you decide you need a heavier wheel, a lot of that other stuff is already built. MSL took about 4-5 years to build, it's not like lots of people were hanging around with nothing to do waiting for something. They were running double shifts to get it ready.
So at each step of the process, you take your best shot, and move forward.
As far as component sizes go.. There's standard design margins used, and you design on the basis of the expected loads (often for something that's not physically in existence yet, so there's some allowance for not hitting the target, as well). A lot of times, a structural member will be the size it is because it matches a bunch of other members, and it's easier to make them all 20mm rather than individually optimizing (not that they are interchangeable, but that means you can do a test or analysis once, which saves time). Same reason we don't make every resistor the optimum value, but use "standard values".
Insulation thickness on the wires are already at the minimum (that's an easy mass savings, and was taken out decades ago). It's not just the voltage rating, of course, but more about abrasion resistance and ruggedness during assembly. Solder formulations are chosen for reliability and process control, and I doubt that changing it would change the mass much. There is persistent talk about going to wireless interconnects to replace the substantial wire harness mass, but there's some untried technology there (parts that are radiation tolerant, non-deterministic links, potential EMI/EMC), and on a 1B+ mission, one tends not to take risks with the "infrastructure".
There are a lot of titanium parts on MSL, but some of those were exceedingly troublesome: acutator gear trains were changed from SS with wet lube to Ti and dry lube, and caused problems: http://www.thespacereview.com/article/1319/1
But ultimately, it's because it's a huge project, and you are inevitably going to have excess capacity/margin in all areas, to allow for the folks who burn their entire margin in theirs. Not every tradeoff is possible within the time constraint to get the darn thing launched.
Check out this gash/puncture taken from the mast camera. A whole set of images from the MAHLI "hand lens" camera on the arm, which lets them look under the rover. Lots of dents, and quite a few punctures. The ridges that form the treads seem to be holding out, though.
i'm amazed that Curiosity is still running on Mars. Modern technology is amazing. I thought Curiosity died. Or maybe I am thinking of another rover.
Ouch, that's a lot of EDM time. I presume the wheels were built to do some deformation, anyway.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
How far has the rover driven? A kilometer? Less?
Was the rover built by the lowest bidder?
The next Mars rover mission is planned for 2020. It's quite likely the lessons learned from Curiosity will be applied.
Somehow, you got modded Insightful for some drivel best modded "faux intellectual sarcastic wanna-be know-it-all nonsense".
You know how many of those brilliant egghead scientists can't tie their own fucking shoelaces, or change a tire on their cars? Huh? I do.
I know plenty of the type, and I know full well how incompetent they are at everything but what their degree says. The Renaissance Man, the Jack-of-all-trades -- they are not. He be a rare creature indeed. Sure, I want brilliant scientists designing the test equipment, the rockets, etc.
So... let's think about this: the eggheads knew, from previous Mars missions, that Mars has sharp rocks. They built a machine with wheels that are vulnerable to sharp rocks!
Even the dumbest hillbilly doesn't go 4-wheeling with drag slicks, fergawshsakes.
So, umm... who's the idiot(s) here?
Hey, remember that one Mars mission that crashed & burned, because the brilliant scientists forgot to convert SAE units to metric (or vice-versa, I forgot)? I guess I'll concede there was a bit less derp this time. But would "Common Sense Internet Man" make a mistake like that?
Nah. That takes a team of highly educated geniuses.
That I'm right, and you don't like it, doesn't mean I'm a troll.
except grams is not a unit of weight or force. The kilogram is a unit of mass. If you want to say weight (force due to gravity) then kindly use Newtons (N).
In my misspent youth, I spent a number of years operating heavy machines, many with tracks. Anything from rubber-tracked skidloaders, to D10 bulldozers... in the Rocky Mountains.
I experienced and saw many tire/wheel failures... but never a track failure. It happens, but it's considerably more rare. Tracks not only provide better traction, better maneuverability, better stability, better slope capability, and lower ground pressure/better flotation, but they are more durable in rough/rocky conditions.
Just for your edification, it does require multiple part failures on one link to achieve track failure. If tracks on machinery were as vulnerable as you seem to think, there would be no bulldozers. Go look at a diagram of how they're made.
Give a country boy a little credit.
six independent wheels - so the failure of any two on opposite sides would not be a mission ender.
The odds are exactly the same that you'd lose two wheels on one side, as one on two sides. 2/6 wheels == 2/6 wheels.
That I'm right, and you don't like it, doesn't mean I'm a troll.
I'm sure those lessons will be applied. There might be another rover after that one, and maybe even one after that. So the lessons learned from Curiosity probably will be applied a few times. I'll just note that NASA could have built, launched, and operated a number of Mars Exploration Rovers for the total cost of Curiosity and apply the lessons of the MERs to more rovers by now than Curiosity will ever help.
So, umm... who's the idiot(s) here?
It's you, hillbilly.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
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?
They could, but it'd require more delta v and result in less payload. Putting the vehicle into a polar orbit is already less efficient because it takes more delta v to do that than to put the vehicle into a near equatorial orbit (especially from India). And then transitioning from that orbit to a Mars transfer orbit (or MTO, the Hohmann transfer you speak of) is another delta v cost.
Instead, launching almost directly (I understand there is a somewhat later boost after the vehicle drops the first stage) to MTO (as Curiosity did) is relatively efficient delta v-wise.
still, the coating I would have suggested is well understood to be very chemically compatible with aluminum alloys, and is quite inexpensive.
And it is untested in a Martian environment. It's also worth noting here that Curiosity's tires experience considerable flexing as part of normal operation. A coated saw blade just doesn't see that kind of flexing.
Having said that, if I were running the unmanned Martian exploration program, I would be deploying a large number of much smaller rovers. For example, the Mars Exploration Rovers are proven technology. I would be launching several of them every two years to different locations on Mars using the Delta II, Atlas 5, and Falcon 9 rockets (I'd also consider foreign launchers, if the restriction on US-only launchers was lifted).
In that case where there's a lot of vehicles being manufactured rather than a few one-offs, it would make sense to investigate and use off-the-shelf technologies that could be applied to reduce manufacturing cost.
Why are the photos from Chang'e 3 so dreadful in quality compared to these photos comingn all the way from Mars? Do the Chinese want their moon mission to look like it's using 20 year old camera technology?
"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."
Ahem... effective and robust wheels to survive those conditions -- at a pretty darned good rate of speed, with 2 human passengers -- were built about 40 years ago for the lunar rovers.
How quickly we forget.
"Curiosity's tires"
What tyres (UK spelling) are you talking about? It doesn't HAVE any tyres, it only has WHEELS - without tyres.
"Eight or twelve smaller wheels might be a good idea for the next similarly-sized rover."
No. The diameter of the wheels has a very large effect on the terrain the vehicle can navigate without strain or damage.
To illustrate: ride a bike with a 28" wheel over a sidewalk curb. Then try the same thing on a skateboard with 3" wheels. See how far you get.
I though Curiosity had airless tires.
PhD eggheads... try these things called "tracks". I'm pretty sure they'll work on Mars.
That's a lot of moving parts to go wrong. Doesn't matter here on Earth so much because there are typically tank mechanics within driving range.
Wasn't it "aerospace engineers" working in non-metric units that lost the Mars Climate Orbiter? I don't think NASA would employ someone still working in inches.
That old canard. NASA does everything in metric. They hired a subcontractor, some very popular these days among the anti-government groups. The contractor use imperial units. NASA engineers didn't realize until too late.
Yep and a lot of wire. Nice cut though.
I love Jesus, except for his foreign policy.
OMG... seriously? Another one?
Think about the whole drivetrain for a moment. Two drive motors instead of six. Steering by differential motor speeds, not steering motors or servos. Etc, etc, etc. Fewer motors, less wiring, fewer joints, fewer electronics, lighter weight all round... in exchange for some more moving parts on a track -- whose parts barely move, and are far less complex than motors, electronics, or steering knuckles. Yes, there are many parts in a track system. SIMPLE parts. It's a SIMPLE system. SIMPLE is less prone to failure on any planet.
My god... have some of you people never been around anything mechanical? Or just not heard of "KISS"? Or maybe you work for NAySAy.
Just got off the phone with one of my cousins who's working on a project for NASA. He says they run away from simplicity. What's wrong with simplicity? There's so bloody much to go wrong with Curiosity that it's a bloody miracle it's still working.
Do we, anywhere on Earth, need vehicles with 6 independently driven and steered wheels? No! Earth has dust, dirt, rocks, and cold and hot temperatures. So does Mars. We don't need to invent new forms of locomotion for it! (Unless you're trying to justify an enormous pork-ridden budget, I reckon.) We have figured out how to reliably transport stuff over the same terrain and conditions (Antarctica, Arizona), right here at home.
One thing is for sure: if SpaceX or Scaled Composites or Virgin Galactic were sending a rover to Mars, it would be better and cheaper. They'd choose things that work instead of things that make the most money for defense contractors.
I used to operate bulldozers for a living. There were times, ripping rock, when I was pretty sure *I* went home broken into little pieces at the end of a day... dozer would be fine. If it were the failure-prone locomotion method some of you seem to think it is, Caterpillar wouldn't have been using it for a century already.
That I'm right, and you don't like it, doesn't mean I'm a troll.
Given your description, Common Sense Internet Man has sight that comes out of his (be)hind.
Since he also should be a good oracle for SHA256 inversion in addition to all the other stuff you think he can do, you should be making a bundle in BTC right now, eh?
The odds are exactly the same that you'd lose two wheels on one side, as one on two sides. 2/6 wheels == 2/6 wheels.
Nope.
Assuming wheel failures are completely random, the odds for losing 2 wheels on the same side are 40%.
Assuming wheel failures are biased some way, you can't say without knowing the bias.
hmmm... nope again. Assuming all things equal (ie common cause probability), the odds of losing one wheel=1/6
The odds of losing another wheel are still 1/6 (because you still have six wheels)
the odds of the second wheel being on the same side as the first wheel: 3/6 (6 possible positions, 3 condition-meeting outcomes)
If you're going to bias the odds in some way, ie by excluding one axle just because a wheel has already failed, then you have to exclude that axle at the start knowing for certain that it is going to fail. Or, you don't *ever* exclude it just because it has met a failure condition. This would be like excluding a coin toss outcome just because it has been met x number of times in y tosses.
Political debates have me rolling my eyes so much I think I got optical whiplash. I should sue. - Foamy The Squirrel
They've been planning a return mission for decades. A Mars sample return mission would be the most elaborate and expensive NASA had ever planned, not including new technology cost overruns which nearly doubled Curiosity's cost, and delayed it one launch cycle. The Mars exploration program was even terminated from NASA's budget last year as a punishment, untill partially restored.
The latest proposed sample mission would invovle three sub-missions; (1) A lander-rover to collect the rockets; (2) a lander-launcher to collect the samples and put them in orbit; (3) A third slingshot mission to retrieve the orbiter. This would involve less fuel weight cost than an all-in-one mission. We dont even have a powerful enough enough rocket to launch an all-in-one mission. A probablem with tis elaborate mission is more new technology to develop with unpredicatable cost. And more steps that could fail.
NASA and the space community classify proposed missions into three categories: (1) grand over $2B, (2) quick ($1/3B), and average (inbetween). They had about a hundred excellent missions of all kinds proposed in the most recent decadanal planning. But were unable to fund even a single grand, and just a couple average.
China may do it first.
He said five GRAMS, not five POUNDS. So that's 100g of additional fuel. Less than a kilogram. Even if it were pounds, 100 pounds of fuel is miniscule in the perspective of a 6.5-MILLION-pound[1] craft.
[1] - Saturn-V used for sake of argument.
I sincerely hope that this was as I read it...as a "Men In Tights" reference :D
What else can happen when an unstoppable force collides with an immovable object?
See my posting above concerning the erosion of diamond-coated drill bits by chalk (trigonal calcium carbonate). Diamond is hard, sure. And tough. But Chalk can be much softer, and tougher.
Birds are not dinosaur descendants;birds are dinosaurs, for all useful meanings of "birds", "are" and "dinosaurs"
Please record this result. I do not wish to repeat the experiment..
Birds are not dinosaur descendants;birds are dinosaurs, for all useful meanings of "birds", "are" and "dinosaurs"
Agent 86