Getting Unstuck in West Valley Options

[alan]

I think the pointy rock has been shifted from its original position. I don't see a pointy rock in the right spot in the 1870 navcam.



Hopefully that means if its in contact with the the WEB it isn't able to support much weight.

The rock in front of the left middle wheel looks like a problem though.
Can Spirit climb over a rock nearly the height of its wheel when the other wheels are dug in?

[Astro0]

As RoverDriver noted, Spirit is sitting at an angle of 12degrees.
Here's the two MIs in that orientation.
Pointy Rock now becomes 'Flat Rock with Pointy End'.


I think we need a few of our rockhounds to take the available navcams and identifiy each rock. Any takers?

[RoverDriver]

The new set of MIs don't stitch together well.
...

That was intentional. The MIs are 10 deg apart except in the center where the images are 5 deg apart. The rationale was to have images with more overlap and do stereo on them. The pivot point is behind the CCD and therefore there is a translation of the optical center corresponding to each rotation. A colleague of mine did triangulation and determined the position and size of the rock.

Paolo

[RoverDriver]

I suspect we'll see a raft of additional images, from several positions, maybe even trying to edge the IDD further under the rover to help refine our understanding of the situation here. Are the people at JPL at least of the belief that this is a substantial rock and not a soft mound with perhaps a sharp stone poised at the top?

Don't know. Since we drove straight over it I think it is quite firmly set in the soil.

Paolo

[fredk]

I think I've got many of the rocks identified, including the "pointy rock" that we may be high-centred on. First of all, I agree with Alan's identification in his most recent post. To get there I followed a trail of rocks, comparing the sol 1870 navcam with the 1897 hazcam. In this composite, the white lines are identifications, and black lines identifications between rocks that have been moved somewhat by the rover wheels:

Next, to identify the high-centre rock, it helped a lot to look at stereo imagery. Here is a comparison between the sol 1367 pancam view from HP and the 1870 navcam, both in stereo, with some rocks identified:

The white ellipse indicates the rock we're high-centred on. Notice that it doesn't stand out very well in the single-frame navcam from sol 1870. The anaglyph really brings it out. The 1367 view shows it to be a pretty substantial rock.

Finally, compare the circled rock in the 1870 navcam with the rock we appear to be high-centred on in the MI view (cropped from Astro0's mosaic):

The shape is quite similar, including the notch on the right side (although it may have shifted if the wheels disturbed it).

[alan]

I agree with your identifications. Its surprising how insignificant the pointy rock looks in the 1870 navcam compared to how large it looks in the 1367 pancam

edit: I see now why I was having trouble matching the two views before, I was seeing two small rocks in the individual 1870 navcam images instead of one large one with a notch on the right side.

[RoverDriver]

I think I've got many of the rocks identified, including the "pointy rock" that we may be high-centred on. ...

Thank you! That really helps. I was planning to do the same analysis, but this is really great!

Paolo

[RoverDriver]

In a private message I was asked the following question, which I think might be interesting to some of you as well.

I have been wondering for several years now what you guys do to compensate in the test bed for .38 g on Mars.

I assume it's easy to lower the mass of the test rover, but what about the soil mechanics? Does the sand and soil not behave differently in that lower g environment? When you take an MI pan of the soil particle to reconstruct a similar mixture in Pasadena, how do you compensate for the soil particles' behavior in the lower gravity? Do you have a study of sands and their particle density characteristics that allows you to come up with an inventory of choices that behaves the same as the martian soil behaves in .38g? or is the gravity effect on the soil mechanics insignificant under these conditions? It's clear to me from old Apollo videos that lunar soil behaves far differently so there must be some threshold where you need to take the gravity into account.

This is an excellent question! We have two vehicles we can use for testing: SSTB1 a full size replica of the MER vehicles, minor some minor differences (no solar panels, some temperature probes are missing...) which of course has the same mass as MER and higher weight on Earth than MER has on Mars; and SSTB Lite, a stripped down vehicle with same wheel size, actuators and suspension system, same WEB size but major components like the IDD and others are missing. This vehicle has a weight on Earth that is similar to the weight of MER on Mars. For Purgatory and for this event we are going to use the SSTB1, not the SSTB Lite.

We are still in the process of soil simulant selection and we are following the same principle we followed during Purgatory: we try to replicate the vehicle performance during the embedding event. In Purgatory no matter what we tried, we could not get the SSTB Lite to embed in the soil. The soil we used was too heavy. Fortunately we were able to replicate the embedding event with the SSTB1, not perfectly, but close.

We really can't try to replicate the exact soil characteristics we measure with spectrometers and MIs but try to replicate how the vehicle behaves during the embedding event and hope it will be representative enough for testing the extrication maneuvers. We use some of the information we get on particle size, but ultimately the vehicle is the best instrument we have to select the soil simulant.

Paolo

[Fred B]

Here's my deconvolution, optimized for distances near the "fulcrum". Almost looks as if the rock scraped some dust off the bottom of the rover!

Attached thumbnail(s)

 

[ElkGroveDan]

In Purgatory no matter what we tried, we could not get the SSTB Lite to embed in the soil. The soil we used was too heavy.

I know that now I'm going to spend the next few days day dreaming trying to think of light soil mixtures. Things like ground pumice, mica, asbestos, balsa wood chips, styrofoam balls etc. Its a good thing I'm not retired yet or I probably would have built my own rover test bed in the garage by now.

[centsworth_II]

I wonder if there is much difference between the mechanics of an Earth-weight rover tested in Earth-weight soil as opposed to a Mars-weight (lite) rover tested in Mars-weight soil. Is it possible that the Earth-weight rover and soil may even give a better idea of how the rover will react on Mars?

[Burmese]

Can we get some nice pics of the exposed surface of the WEB as seen while still on earth, so as to be aware of how smooth it is and whether there are any spots where a sharp rock dragging across the bottom might snag or even cause damage.

[fredk]

Some interesting comments in a New Scientist story:

"It certainly doesn't look like the rover is bearing its weight on a mound of rocks, which was one of our early concerns," Callas told New Scientist.

The images did reveal one possible obstruction – a rock or mound of dirt near the middle of the rover. But it is not clear whether the object is actually touching the rover's belly. "We can't tell if it's underneath the lowest part of the belly pan or in front of it," Callas says. The team plans to take pictures at different angles to get a better sense of the shape and location of the obstruction.

Also, in case anyone has missed it, they're calling our location Troy.

[SpaceListener]

During her intent to pull out, it is very probably that the rover will continue slipping the wheels. The belly surface height will lower and will eventually rest on a rock. Then, depending upon to the center of gravity of contact point, any of the surface sides (I think on the right side) will have more contact pressure. Hence, these spinning wheels will deep into the surface and hope that it will pick up any hidden stone or more compact soil. These change of soil consistency or any small stone will eventually help to improve the wheels traction to pull out.

In order to avoid in making a hole by the wheels spin is that the wheel spin must be spinning alternating forward and backward and increasing the distance between sides: Example

1st intent : 5 rev backward and 5 revs forward.
2nd intent: 10 rev backward and 10 revs forward.
3rd ....

Cross fingers

[RoverDriver]

...
Also, in case anyone has missed it, they're calling our location Troy.

Yep. Of all the names! I will blush each time I will talk in Italian about this anomaly.

Paolo