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Everyone knows what happened to Philae lander (Rosetta mission). It is hard to predict the reliability of anchoring points before we know surface conditions on the asteroid. On the other hand, it is hard to plan any asteroid mining mission without a plan for anchoring points. Some practical ideas would be very welcome.

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Cold Welding can bond two metals in vacuum because of the absence of gases and oxide layers. The metal atoms on the materials are able to join with one another when given enough pressure. The Galileo Spacecraft antenna did get welded to the spacecraft’s body, causing a failure.

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    $\begingroup$ I'm surprised that nobody suggested an (electro)magnet. $\endgroup$
    – JohnEye
    Feb 16, 2023 at 12:10
  • $\begingroup$ @JohnEye - Iron-Nickel core, near-zero gravity, electro magnets (keeping the mining rover from flying away) - would be the first thing to come to mind. But a substantial layer of dust and non-metallic debris on a surface of M-Type asteroids could make magnets inefficient. $\endgroup$ Feb 16, 2023 at 14:23
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    $\begingroup$ Google for "magnetic sand" and imagine your spacecraft ending up like one of those magnets. Worse, the sand/gravel/dust will probably permanently magnetize to some degree, then stick to anything vaguely ferromagnetic when you turn the electromagnet off. $\endgroup$ Feb 16, 2023 at 15:26
  • $\begingroup$ @ChristopherJamesHuff - we used to play with magnets in children's sandbox. And you would see dark fur/hair growing around the magnet. But it did not create any resistance when you pulled the magnet from the sand. It might keep the rover on the surface, but it would not be enough force to keep a drilling rig in place. $\endgroup$ Feb 16, 2023 at 15:57

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Taking the point of homogeneity, internal structure and our knowledge of so called M-type asteroids further.

Given how data has been collected for some of the larger M-type asteroids there is still some uncertainty regarding the homogeneity and internal structure of such asteroids.

One of the better indicators of the homogeneity and internal structure of a asteroid is it bulk density. The higher the density, around 8 g/cm3, the more likely its internal structure will resemble a block of metal. The density of iron is 7.87 g/cm3, steel 8 g/cm3 and copper is 8.93 g/cm3. Obtaining the bulk density of an asteroid is difficult because accurate measurements of its mass and volume are required.

A number of the large M-type asteroids have bulk densities between 3 and 4 g/cm3. This indicates such asteroids may be porous and thus more consistent with a rubble pile or they may contain silicate minerals and thus resemble stones (crystalline) - something analogous to basalt which has and average density of 2.9 g/cm3.

Returning to your question. Using a high powered nail gun on a block of metal might work if surface debris can be removed prior to using the nail gun. If used on a crystalline metal rich asteroid, a nail gun could shatter the asteroid or break it up into discrete chucks, particularly if the asteroid contain discontinuities and planes of weakness. I would not recommend considering using a nail gun on a rubble pile.

Alternatively, resin grouted rock bolts might be an option. A hole would be drilled into the asteroid, preferably under rotation, with no hammer to minimize the possibility damaging the asteroid. Clean the hole with a blast of air. Insert the anchoring bolt with a resin cartridge and rotate to break the cartridge and encase its contents around the bolt.

For the resin to set a setting agent is required. This can either be done by inserting a cartridge of resin and one of the setting agent. Alternatively single cartridges are available that contain both, each separated by a membrane. Rotating the bolt and the cartridge breaks up the cartridge and given the correct rotation time everything sets nicely. To assist with mixing the resin, the part of the anchor inside the hole would have flat "paddles" or flared out parts along its shaft.

If resin bolts aren't practical, then mechanical anchoring, where a deformable barb, or expansion shell grabs the sides of the drilled hole, securing the anchor.

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  • $\begingroup$ The idea of 'sticky' bolts seems to be promising. They will not be the most powerful anchors, but they can work in a wide variety of surface scenarios and rock composition. $\endgroup$ Feb 16, 2023 at 3:26
  • $\begingroup$ @Fred .... are there resins which work at the temperatures expected on the surface of an asteroid.? $\endgroup$
    – Woody
    Feb 24, 2023 at 1:53
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Answer: No, a nail gun can't cold weld to an asteroid.

Grappling anything in space is problematic. Partially because almost everything has angular momentum, partially because any contact with the object will produce equal and opposite momentum in the grappling spacecraft and partially because most objects you want to grapple (asteroids, debris) are either hard or friable.

One approach is to snare first, before trying to place hard anchors. See Is there an elegant method to stop an asteroid's spin? and Can space debris capture be modeled on surgical grapple baskets?

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For reference, here is a picture of a surgical snare:

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It's very unlikely "cold welding" will attach a grabble to an asteroid, especially using a nail gun. According to Wikipedia, cold welding requires "two clean, flat surfaces of similar metal" being pressed together. In conventional cold welding, high pressure is required. These requirements are unlikely to be met on the surface of an asteroid.

An alternative would be explosion welding. Like cold welding, it is a solid state welding process, but it is more tolerant of surface contamination and can weld dissimilar metals.

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  • $\begingroup$ If I understand you correctly, there will be some ultra-light rope around the circumference of the asteroid? For example, the closest candidate for asteroid mining - NEO M-Type asteroid: 1986 DA 3 kilometers in diameter. That would take a lot of rope? $\endgroup$ Feb 15, 2023 at 18:36
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    $\begingroup$ @TheMatrixEquation-balance ... It is wire, not rope, I added a graphic of a surgical snare to give the idea. The snare retains a "memory" of its shape while spooled in the spaceship. A 3 km asteroid is a bit ambitious for a first attempt. Presumably M-types exist in all sizes. The biggest are just easiest to track. $\endgroup$
    – Woody
    Feb 15, 2023 at 19:04
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    $\begingroup$ @TheMatrixEquation-balance ... according to Wikipedia, cold welding requires "two clean, flat surfaces of similar metal". These requirements are unlikely to be present on the surface of an asteroid. $\endgroup$
    – Woody
    Feb 15, 2023 at 20:21
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    $\begingroup$ @TheMatrixEquation-balance I think you are assuming that there are M type asteroids which are... I don't know the scientific words for this... but are all one piece, such that if you pull on any part of it, you'll pull the whole thing along. I wonder however if we have evidence for that. We do know that asteroids can also be rubble piles, and pulling one one piece of it will just separate that piece from the rest of it. $\endgroup$ Feb 15, 2023 at 21:57
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    $\begingroup$ You are STILL assuming M-types to contain (nontrivial) metal. (Even ordinary chondrites contain reduced metal, they’re just flecks in a matrix.) While some do, I bet, we are NOT CERTAIN that all do, or even that our claim to an “M-type” is a valid type, in a valid taxonomy. M was split from X, and the history of the split should tell you not to go assuming. But that’s assumption for you- people don’t even realize the bad assumptions are even assumptions. $\endgroup$ Feb 15, 2023 at 22:23
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“…on M-Type (metallic) asteroid)”

Which one(s)? You presume not just monolithic asteroids but a monolithic type, in a deterministic and discrete typing system. That is, you presume too much. We have already spent mucho millions on a mission, and yet we still have handwaving notions about the homogeneity, petrology, etc. of Psyche. The gravity of Psyche also falls in a weird zone, not negligible, yet different enough from Earth-Moon to be an issue, not handwavable.

“ Or are there better alternatives?”

The alternatives that are robust to failure- mechanical failure, sure, out to failure of the imagination: a surface not anticipated, because why would humans anticipate it?

Terrestrial mentality is good at terrestrial solutions to terrestrial problems. People spend time, and get paid, to not be in the rut of terrestrial thinking. It’s harder than you think (or handwave away instead of thinking, or never even bother to even bother).

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  • $\begingroup$ When you think in terms of the Space Shuttle, or NASA's Orion project - then, yes, asteroid mining is a future dream. But SpaceX Starship could easily bring several tons of equipment to a NEO Asteroid for an exploratory mission. $\endgroup$ Feb 15, 2023 at 20:44
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    $\begingroup$ When did I ever mention schedule? Humans failed to anticipate neutron stars- in effect, atomic nuclei the size of a city. We have more “unknown unknowns” about Psyche (the asteroid) and the probe (“Psyche”- couldn’t they come up with another name?) is at The Cape, about to launch. Don’t put “no asteroid mining” into my mouth, I’m working on an asteroid-resources paper. $\endgroup$ Feb 15, 2023 at 22:00
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    $\begingroup$ To clarify: our declaration of an “M-type” of asteroid will, if you dig deeper, turn out to be for the convenience of spectrophotometry. Whether M-types, K-, or certain other names within the taxonomy will actually hold up to “ground truthing” is yet to be determined. Just look at F-. And no, the existence of iron meteorites does not mean our spectrophotometers got it right. There has already been talk of subdividing M-. $\endgroup$ Feb 15, 2023 at 22:13

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