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InSight Surface Operations, 26 Nov 2018-
siravan
post Oct 27 2019, 11:09 PM
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I guess the soil crashed and filled the gap opening under the probe by the hammering. The properties of the regolith remind me of what Arthur C. Clarke wrote in "A Fall of Moondust": "This dust has the worst properties of solids and liquids, with none of their advantages. It won't flow when you want it to, it won't stay put when you want it to." Maybe one has to think of it as a very viscous fluid rather than a proper solid. I don't know whether the change in the season and temperature has affected the properties of the soil in any way.
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mcaplinger
post Oct 27 2019, 11:10 PM
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It's worth remembering that no one would have proposed doing the heat flow experiment this way if there had been a more straightforward drilling technique that would fit within the mission constraints.

As was pointed out earlier, even with many fewer constraints, the Apollo heat flow experiments didn't work well the first two times and Apollo 17's only got down about 2.5 meters. https://www.hq.nasa.gov/alsj/a15/a15carrier.html


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Explorer1
post Oct 28 2019, 01:55 AM
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Exactly. This is alien soil on an alien planet. We have no idea what to expect. And of course, the mole has no way of 'knowing' if it's moving in the wrong direction, so it just kept on unearthing (unmarsing?) itself until the commanded strokes ran out, right?
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Phil Stooke
post Oct 28 2019, 05:02 AM
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Not sure I can accept the explanation that high frequency drilling is the problem. Soil falls in front of the rebounding mole? That takes time, even if only a tiny increment of time, so I expect it is less likely with faster operation. But what do I know? (spoiler: nothing). Only testing is reliable, and even that is difficult when considering another world. Do we know anything about other kinds of percussion drilling that might be significant here?

Phil


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Keatah
post Oct 28 2019, 06:52 AM
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QUOTE (Phil Stooke @ Oct 28 2019, 05:02 AM) *
Do we know anything about other kinds of percussion drilling that might be significant here?
Phil


While not really percussion drilling, why not a self-contained pile driver? There would be no recoil. The mole would need to be longer and of a larger diameter of course to accommodate a weight.. And its effectiveness would diminish if it turns away from the vertical. But there would be no back-filling of material at the front tip. No vibrations to "break friction" on the sides. 100% reliant on gravity to generate the downward motion of the internal impactor. It would still be all self-contained, using mass instead of springs. And it work at 1 hit per second more or less.
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mcaplinger
post Oct 28 2019, 02:27 PM
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QUOTE (Keatah @ Oct 27 2019, 10:52 PM) *
While not really percussion drilling, why not a self-contained pile driver?

Are you sure you know how the mole works? See http://esmats.eu/amspapers/pastpapers/pdfs...grygorczuk2.pdf and https://www.geomechanics.caltech.edu/public...shall-2017a.pdf for details.

One assumes that if they could have gotten a more robust solution into the mass/volume/power box they were in, they would have done so.


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anticitizen2
post Oct 28 2019, 03:24 PM
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the difference between the successful sessions and this one was the scoop directly touching the mole vs pressing on the ground. maybe it isn't so much backfill, but the mole bouncing off the far wall, rebounding, and catching because its tilted over and levered against the far wall? maybe touching the mole stopped much of the rebound, but now it was one step forward and two steps back? the scoop was definitely pushing into a crumbling hole more than ever

the good news is the retreat slowed down in the second 150 hammers, vs the first 150 where it popped almost all the way out
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stevesliva
post Oct 28 2019, 03:29 PM
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Last week's Mars Society talk by Tom Hoffman is up on youtube:
https://www.youtube.com/watch?v=Q1yJPFRuv74

Mole / Pit of Doom discussion is around 18 minutes in.

Interestingly at about 21:45, he says "We need friction ... because we have the 100N force down and about 7N force back up. We did some experiments on earth where if we had the right conditions the mole could either bounce or come back up."
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PDP8E
post Oct 28 2019, 07:04 PM
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Holey Moley!
Looking at the images on the Insight site, the mole just popped out!
(a cascading backfill from the hole side material to the conical tip, all the way to the surface?)

I see a shovel on that arm, maybe dig a good-sized hole/trench and then put mole in there?

Wow, that was unexpected!


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mrpotatomoto
post Oct 28 2019, 08:02 PM
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What proportion of the mole is still under ground?
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Explorer1
post Oct 28 2019, 08:29 PM
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Half is still below, according to the bold text here: https://www.jpl.nasa.gov/news/news.php?feature=7519
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atomoid
post Oct 28 2019, 09:58 PM
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NASA page essentially the same details.
It seems Mars will just certainly not have any of this kind of thing going on!
Gif animation (5fps) of unsettling shennanigans seen on Sol325
Attached Image
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HSchirmer
post Oct 28 2019, 10:21 PM
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QUOTE (Phil Stooke @ Oct 28 2019, 06:02 AM) *
Not sure I can accept the explanation that high frequency drilling is the problem. Soil falls in front of the rebounding mole? That takes time, even if only a tiny increment of time, so I expect it is less likely with faster operation. But what do I know? (spoiler: nothing). Only testing is reliable, and even that is difficult when considering another world. Do we know anything about other kinds of percussion drilling that might be significant here?

Phil


Drilling alters the frictional properties of the soil.

Could be that impacts are heating up the soil and lubricating the mole.
e.g. friction generates heat, heat melts ices, melted ices and clay becomes a slippery mud.

Could be that repeatedly hammering into a conglomerate-duracrust horizon grinds the soil into a finer particles that act like ooblick and push the mole backward.

Could be like driving across a dry lake after a rain, clay covered by water is structurally stable, but if you stop and add too much force, you mix the clay and water into mud and you loose friction.
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mrpotatomoto
post Oct 28 2019, 10:31 PM
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For what it's worth (meaning: probably nothing), here's a quick impression of the probe's situation.


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Weywot
post Oct 29 2019, 05:39 PM
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In the new DLR blog entry from Tilman Spohn he's still positiv. Nothing is mentioned about a technical error. The mole itself seems fine. They want to inspect the pit and then hope to drive the mole back in. But how?
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