The stuck wheel has been key to most of Spirit's most important discoveries. Should future rover designs include a scoop which can be dragged behind the rover to turn over the soil? It could be on an arm with just one motor/degree of freedom--up or down. The scoop/plow could be on a flexible arm so if it snagged a rock, it would deflect away. Since everything on mars is covered with a layer of dust, you need something to continuously trench to find sulfates, silica or the next unexpected thing. The arm could be very light if you had a little scoop/rake at the end of a flexible fiberglass pole. Maybe you could add some type of simple sensor to the scoop to determine the crude spectral properties of the freshly exposed soil. Lots of possibilities.
What do you think--is a scoop/plow/rake a worthwhile rover tool? What is your design?
A simpler design would be to have the scoop hanging on the underside of the rover, then it could just drop straight down. As far as it snagging on something, you could just have the software check for some limit on extra friction and stop moving if the force is too high.
My philosophy is that an "Space hand" is of vital importance in order to increase the survival of spacecraft as the main objective and also taking the advantage of its own characteristics.
Let us suppose about the problem of Spirit, the arm would assist to improve the motion. For Opportunity, the arm would help it to go closer to rocks and lower to bottom of Victoria and also to climb on sandy surface. Overcome any accident such as one with more than one month sand stuck to Opportunity. Anyway, this arm would help both rovers to improve the science by snagging any interesting stone, rock, dig the surface, etc.
You can see this example with the Shuttle's own long and powerful arm that help to improve the security and survival of spacecraft.
However, I think that this facility, will lead a much increase the budget to the program since the engineering to build an intelligent arm is very expensive as I know about the Shuttle's arm. Sophisticated software, very light material and strong, more video camera, incorporated laser for measuring the distance, etc., etc.
Finally, it would be a one of the top wishlist for MSL since it can supply electrical power with more prediction. At this point, I cannot further comment about the trade between benefit and costs by incorporating an intelligent arm to MSL project. However, for the philosophy of survival, it must be a "yes" or "yes" choice.
I have been frustrated the entire MER mission, since before landing, at the lack of any capability to observe the intact stratigraphy of the soils. Yes, Yes, Yes, what would you remove from the MER's to include, blah, blah, blah. But MSL REALLY should have something. ... And ExoMars.
I've thought that a very simple, 1 degree of freedom plow could be very revealing. A simple arm, spring loaded, with a single up-down motor. At the end is some equivalent of a (I think the term maybe moldboard) plow.. essentially a single-sided plow, designed to cut into the surface, leaving a 45 or 60 degree slice-exposed and relatively undisturbed soil slope, and turn-over the soils of the opposing surface. The angle should be less than the angle of repose for loose soils... maybe that's less than 45 deg. (I'm too lazy to google and check)
The plow blade should be sping-loaded-hinged so that if it catches it's leading edge on something that resists too much, it simply pivots to the rear and slides over the whatever.
The whole idea is that this thing would be very light, KISS designed (keep it simple, stupid), with one exception. In case of failure of the lower/raise motor, it should have 1 backup, maybe pyro initiated, forced retraction ability so as to not cause rover mobility problems with an un-retracted plow.
How deep a furrow?
Edit: This proves it. nprev and I must both be dreaming in lockstep.
Ed, man...take a pill! Understand you're bolstering for criticism, but I'm with you; good idea.
Trenching the martian soil clearly is scientifically valuable, which was completely unexpected until Spirit's wheel failure; this will surely be recorded as one of the great incidences of serendipity in modern science.
Your schema sounds very practical, and like the fail-safe mode; well done!
DJEllison: " We got some fairly good trenches that way. "
Sorry. We didn't. We got churned up holes in the ground with practically all tracesof stratigraphy removed.
Nprev: "Trenching the martian soil clearly is scientifically valuable, which was completely unexpected until Spirit's wheel failure"
DJEllison: "What Spirit may have shown us is that there is a lot more value in playing scratch-and-sniff than we ever thought possibl"
We had clear signs from Vikings that there was "interesting" structure in the soils, most specifically "duricrusts" at both landing sites, plus drifts and more indurated soils. Spirit didn't see too much till it reached the hills, but did spot at least one patch of light salts on the long drive southeast, then hit (as I recall) some light salts on the climb to the summit, then hit a major patch of multi-colored salts on the drive south from el Dorado toward Home Plate. The wheel lockup just forced us to see how much interesting geology there was in the soils.
As I argued, a very simple trencher plow, normally kept retracted, AND WITH REDUNDANT RETRACTION CAPABILITY, would do a far better job of slicing a stable, stratigraphy revealing cut in the ground than just grinding your way down with churning treads.
I just don't see it working - I don't see it producing any soil stratigraphic record at all. I see it making a little furrow of mixed soil, in essence no better or worse than spirit's FR wheel.
If you want soil stratigraphy - do a vertical mission - a big arm - Phoenix style, or a drill or even just a more simple sampling tool (Pluto was good on Beagle 2).
Worth investigating - worth doing some tests on - but I don't think it's the right way of doing it and I just can't see it achieving what you want it to.
Doug
and don't forget that they were trenching with the wheels before Spirit's got stuck - they were deliberately making wheel trenches in Eagle Crater.
But it was Spirit's stuck wheel that really showed the extent
of what lay unseen just beneath the surface. Some big
discoveries would not have been made but for that wheel.
Just think, as MSL rolls happily along, who will not wonder
on occasion what we're missing.
I like the plow idea. However, I did a fair amount of pulling plows with tractors as a teenager. It takes a LOT of force to pull a plow (which is why our neolithic ancestors hitched them to big animals), and I just don't see this amount of force being available. My own experience was with with sandy soil, which was trouble enough. On Mars this would be through regolith with lot's of rocks of many sizes mixed in - it strikes me as a very difficult proposition. On the other hand a simple arm designed for the purpose - perhaps even designed to take advantage of the strength of the wheel motors - seems easily doable.
algorimancer--It all depends upon the size of the plow as to how hard it is to pull. hendric made that point in a near simultaneous post. I was also thinking small, but such a tool would require some sand/mars box testing to get a design that was not too hard to pull and cleanly turned over 2" -3'' of soil.
Given the weight budget I feel that any needs analysis would classify a plow as a 'nice to have' and reject it in favour of more productive instrumentation. The broken wheel certainly churned up the regolith, but the first evidence of salt deposits came from Paso Robles when all wheels were operating. Given Opportunities experiences with soft soils is there any reason to suspect that Tyrone would have not been exposed regardless of the broken wheel since all wheels churned the salt up? Same with Gertrude Weise. Sure the dragging wheel made the salt very evident but is a plow really a good tradeoff - what would you take off to compensate?
Weight is critical in the cost benefit analysis. Does anyone have figures for the weight of the RAT and other instruments? If plow weighed 10 kg, no way. 1 kg, maybe. 0.1 kg, sure, but probably very difficult build it this light. What is the minimum weight of a motor/joint, fiberglass pole, and a very simple rake/plow/bit of curved plastic? Isn't its possible to construct a simple system at under 0.3 kg?
Perhaps we could just employ the Swiss version of the Rover.
Now that is really cool!
I'm lauging so hard I can't see what I'm typing.
What we need is to change the labor laws to make Mars a right-to-work state!
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