Now where is the ...
JATO bottle when you really need it!
Power, baby! Power!!
NASA scientists are preparing to put Curiosity through its toughest challenge yet, scaling a meter-high sand dune that could leave the Mars rover stranded, immobilized. Dingo Gap Let's go off-road! The boffins behind Curiosity are looking for the best possible route to the rover's next goal, Mount Sharp, but the two routes …
... and now find there's only 3 ways out, two are escarpments and the other is blocked by sand? Not exactly an exit ramp from the freeway then.
1) Fire the harpoon to stick in the ground on the other side and winch Curiosity out... err.. no.. it's rock or sand and there's no harpoon.
2) Hook up the dozer blade and make a path.... err.. no... no dozer blade.
3) JATO is out.
4) Put on the sand tires to paddlewheel their way up the dune... err.. nope.
Doesn't look good from here but hopefully, that sand is hardpack and it can climb out instead of all loose and fluffy and bog it down. Time to get some popcorn and see what happens.
Something that has always confused me: why didn't they fit nice big, soft(ish) rubber wheels to the buggy? Wouldn't that be less prone to damage than aluminium wheels? And make it easier to drive it around on the rocky surface?
Something like these: http://upload.wikimedia.org/wikipedia/commons/e/ed/Apollo15LunarRover.jpg
..Because rubber will behave very strangely in space / on Mars (Not to speak of the problems with de-pressurizing and re-pressurizing them).
You get degassing, temperature effects etc.
The moon rover wheels were not made of rubber. They were made of metal wire and plate:
The engineers aren't overly worried about the wheels getting a bit dog-eared because the torque is so high that even square wheels would allow the rover to travel about.
And yeah, and Holtsmark has noted, a combination of aluminium wheels, adhesive and a rubber-like material would introduce far more variables than just aluminium alone.
Your question has made me wonder "Why aluminium and titanium?". Though I can't find a quote from a JPL engineer on the internet, the answers given on the internet are plausible... for example, forming aluminium is a very mature technology, and denser (and thus thinner) titanium wheels would be more prone to point stress.
The damage to the wheels makes me wonder, "Why not steel?" But I already know the answer: with NASA's prior rover experience, aluminum wheels seemed like a sure bet. I would've stuck to proven wheel materials, too.
Still, in the future I'd give steels another look. There are some nice precipitation-hardened stainless steels popular in the aerospace industry (like 15-5, 17-4, 17-7, etc.) that have great strength (much better than aluminum and, yes, titanium alloys, which are over-rated); good hardness (again, well beyond Al and Ti alloys); great wear resistance (something Al and Ti aren't known for); good toughness (though I'd have to check to compare to Al and Ti alloys); and they retain those properties to cryogenic temperatures well below anything seen on Mars. There's also a lot of industry experience in shaping those stainless steels.
Actually, since corrosion probably isn't much of an issue on Mars, I'd also want to poke into some of the lower strength, higher toughness maraging and Aermet steels. Stainless steels are nice, but they compromise their properties some to stay shiny. Beasts like maraging and Aermet alloys don't bother staying pretty for the public.
Because of the point loading issue Dave 126 brought up, you'd want the wheels to be thick (about the same as the current aluminum wheels) so there'd be a weight penalty. But a weight penalty in a mission-critical item like your wheels isn't necessarily a vice.
The typical high on Mars if 68 degrees Fahrenheit. Rubber doesn't have an issue with that, but it will at say at -67 degrees Fahrenheit. Then you also have other environmental issues since Mars doesn't have an Ozone layer nor a magnetic field to protect it from radiation. A pressurized tire is also acceptable to punctures. They also wear as well. A metallic tire has a much better chance or surviving longer than a rubber tire. Oh, extreme cold can cause a rubber tire to become brittle. Mars has a temp fluctuation of 100 degrees, so making a tire to cope with that and durable would be a bit of a challenge.
Re the 'wet looking sand' - firstly I'm not sure about the particulate size, but I think it's an illusion mainly because it's difficult to grasp the scale of these images. Bear in mind the wheels in that picture are half a metre across. That's why the tracks it leaves have such clear definition - because they're so damn big!
From Wikipedia: "Dimensions:... The rover is 2.9 m (9.5 ft) long by 2.7 m (8.9 ft) wide by 2.2 m (7.2 ft) in height //...// Mobility systems: Curiosity is equipped with six 50 cm (20 in) diameter wheels in a rocker-bogie suspension."
My feeling is that the top layer is either sun bleached and so darker underneath like on the moon or maybe it's only the ultra-fine particulates on the surface, ie the stuff capable of being moved by the storms in that very, very tenuous atmosphere,which is lighter in colour than the bigger sand grains underneath.
I suppose it looks wet because the impressions are sharper.
I believe the maximum gradient of a heap of sand is a function of the cohesiveness of the sand and the strength of gravity. Wet sand takes sharper impressions because it's cohesive so the micro-structures that constitute the impression have steeper edges. Impressions in Martian sand are sharper because of the lower gravity.
It's also possible that impressions in dry sand are rapidly blurred by air movement. The thin atmosphere on Mars would reduce this effect.
Disclaimer: I know absolutely nothing about soil science and I'm making this up as I go along
ref Your esteamed article on the Mars rover and the snap of it manoeuvring in the dust:
I am, for my many sins, occasionally tasked with inspecting electrical wiring in its finished state.
Kindly forgive my relapses into high technical language below.
Wot appears to be std* cable ties used and they fixed tight/near
Single, but for x1 fix point seen, std* thin ones used.
All on wot appears to be a mixture of cables and sleeved cable bundles, and poss' pipes - ?
'Tis likely that ye 'affecting elements' will degrade stressed placcy' bits no matter how good they are.
Kindly apply the below to situation as is.
I humbly recommend:
1.1: At least use wider type 'bundle' ties and they be doubled/ paired together.
Don't over-tighten !
(A dab of super-glue on ONE cable/ sleeve outer will fix the tie there and stop it slipping)
1.2: If indeed cables are wot is seen, over-sleeve cable bundles with a lightly shrink wrapped sleeve
Transparent ones are available if you want to watch the cables move under.
Seal the sleeve ends with some decent caulking (not that stuff from B&Q)
and shrink tight-ish here so the muck won't get in the sleeve.
2.1: Lub between the adjacent cables in bundle if that not done
(Std WD 40 should do it -
Sparky's posh silicone grease would pick the dust up)
. . . ..................
and you'll get your Sparky Badge.
3.1: If you want any more:
See Windmill Products
Birdhall Lane, Cheadle Heath, Stockport
for other nice cable tying thingies various.
Inter-Voice (or wotever they're calling themselves this week)
at Gatley, Stockport
for how to rig cables proper.
I haven't the time, the inclination or the bus fare to go over to Yankishire and fuck the fucking gormless fucking twats who half rigged that glorified handcart.
Kindly pass my humble observations on to them.
Gods Right Hand.
+ + +
1: ref *'Std' above:
Do hope the ties and all other exposed cable surfaces are
posh anti-UV&everything else std - ??????
2: Parting Overview:
Orrrrrr . . . ...... etc . . ............
Have they sent a mechanic with it ?
(Phone Kerry at Project Camelot - she'll know)
+ + +
Did I mention the exposed fixings to gear other various ?
Top Tips again:
A dab of super-glue in the cable closure box when fixed and the cable tail trimmed-off
ensures the very occasional occurrence of lock-fin failure is obviated.
+ + +
I'm going for a wee and a cup of tea now.
+ + + + + +
"The Sol 533 toe dip went well, leaving the rover's front wheels on the crest of the dune. The Sol 534 plan was to drive over dune into Dingo Gap, but late in the day it was cancelled. The Rover Drivers had some concerns about the terrain and it was decided that delay the drive to Sol 535 in order to give them more time to plan the drive."
Here is a panorama of the lovely strata to the left of dingo gap. Notice that is you do no processing at all of Curiosity photos then the sky is blue. Perhaps Mars photos are realy taken in Arizona after all. The conglomerate and sandstone beds in this view certainly look very Earth like.
Cracking image that.
I wonder what caused the corral (or stalagmite/tite) shaped rocks centre of frame (look at the large grey slab and then up about the same distance as the slab is long). I expect it is just normal erosion but this is the internet...
Another thing that confuses me is the depth of field, to eyes used to Earth's atmosphere the focus seems to suddenly drop at the back.
Hyperfocal meets Mars.
The blurry hill behind the outcrop is Mount Sharp/Aolis Mons which is Curiosity's eventual destination and is still about 5 km away. Presumably it is blurry because Curiosity's camera was focussed on a point about 5m away. One thing to remember is that distant views on Mars can be blurry even when the camera is focussed on infinity because of dust in the atmosphere.
PS: If you want proof that Curiosity has crossed the Dingo Gap dune on Mars/Arizona, here it is: