I am already aware of the concept of the fusion torch.

But I would like to consider other solutions for separation of raw materials that can be automated but are less "extreme" and closer to current technologies.

My machines are supposed to mine mostly asteroids (0g no atmosphere), moons and moonlets(low g, no atmosphere).

EDIT: As stated I am thinking at clanking replicators, not nanobot. If you want an example of material composition to use then moon regolith composition is ok: Oxygen (40%), Silicon (20%), Iron (10%), Calcium (6%), Aluminum (5%) and Magnesium (5%)

  • $\begingroup$ Can you give us details of what materials you are looking to extract? $\endgroup$ Commented May 2, 2016 at 13:58
  • $\begingroup$ Materials would be mostly in the form of regolith. The composition might vary. Lunar soil for example contains Oxygen, Silicon, Iron, Calcium, Aluminum and Magnesium. I was looking for a general system but if someone wants to propose a system designed for specific elements than the ones I named would be good. $\endgroup$ Commented May 2, 2016 at 14:12
  • $\begingroup$ When you say "self-replicating machines" do you mean nano-bots, or larger robots? If so, of what size? $\endgroup$
    – AndreiROM
    Commented May 2, 2016 at 14:59
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    $\begingroup$ Have you checked out real-world mineral separation techniques? Both gravity separation (e.g centrifugal), electrostatic separation, magnetic separation, and pyrometallurgy seems applicable to clanking bots on an asteroid. en.wikipedia.org/wiki/Mineral_processing $\endgroup$
    – Abulafia
    Commented May 18, 2016 at 8:04
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    $\begingroup$ Roots. See this answer which applies directly here too, as the model I describe is pretty much what your asking. $\endgroup$
    – JDługosz
    Commented May 18, 2016 at 11:25

2 Answers 2


Look up how a mass spectrometer works. I believe the fusion torch concept is something of a variation on this. You don't need fusion to make it work, just an abundant energy source. It could be solar powered, for example.

First you heat the substance to a very high temperature (start with a mirror based solar concentrator, then zap the pre-heated material with a laser to reach the very high temperatures). This produces positive ions because electrons (which carry negative charge) are lighter than atomic nuclei (which carry positive charge). If you heat it up enough, any molecules will break down (since molecular bonds are based on shared electrons).

Then you magnetically propel the ions along a curved trajectory. An ultra hard vacuum (like exists in space or on the lunar surface) is necessary, otherwise they would bump into too many air molecules for this to work. Heavier ions retain their forward momentum longer, causing them to be separated from lighter ones as they are magnetically deflected around the curve. On the other hand, particles with higher charge are deflected more due to higher interaction with the magnetic field. So there is separation based on the charge-mass ratio of the atoms. These atoms end up forming different "beams" of particles, one beam for each element.

This concept is discussed by Freitas as an Atomic Separator Replicator. It isn't particularly energy efficient, but this is an "omnivorous" refining strategy, which means you can take just about any material and feed it in, and get the elements that it is comprised of. For self replication in an energy rich environment (i.e. since there is a lot of solar energy in space), an all-in-one process like that plausibly makes the most sense. The main design goals would be to eliminate the need for human involvement in the construction, operation, and maintenance of the machinery. Lunar regolith (just like dirt on earth) is about 10% aluminum, but the process we use for separating it out here on earth is rather complex, relies on specific ores, and would require pressurized tanks and specialized electrodes for high temperature electrolysis.

Something you could perhaps refine more easily would be iron, which is present in small amounts throughout the lunar regolith as a result of meteor fragmentation. You would collect the iron using magnets attached to rovers. That would produce a mixture of iron oxide (rust) and nickle-iron. Heating it to remove the oxygen would result in a metallic iron-nickle alloy. Further processing with carbon would be needed to make steel, but high quality steel might not be needed for your self replicating units -- the gravity is only a sixth there.

  • $\begingroup$ ok. So once the elements have been separated with magnetic deflection how exactly are they collected or stored? In the original FT designed there were "bins" but how exactly are they supposed to work? Wouldn't gas just disperse? How do you trap them? $\endgroup$ Commented May 5, 2016 at 6:00
  • $\begingroup$ Most substances form stable solids at low enough temperature, and/or will adhere to a surface. So you might have large cryogenically cooled plates (or maybe a more spongy or fibrous structure with lots of surface area) that collect the gaseous elements and are periodically cooked to release them into a tank. $\endgroup$ Commented May 5, 2016 at 17:58
  • $\begingroup$ You might also not need to keep the typically gaseous elements for the purposes of self replication, since un-oxidized metal might be a more common structural component. You would potentially want to capture oxygen (which is extremely abundant in rocks), to avoid losing the hard vacuum conditions, for making ceramics and glass, or perhaps to serve as a disposable/abundant rocket propellant. For that you could use cryogenic trapping (it is stable as a solid in a vacuum at around 77 kelvin) or chemical trapping (let it oxidize a metal plate, then heat the plate to regenerate it). $\endgroup$ Commented May 5, 2016 at 18:31
  • $\begingroup$ I believe the real-world analogue to the fusion torch is Pyrometallurgy: en.wikipedia.org/wiki/Pyrometallurgy $\endgroup$
    – Abulafia
    Commented May 18, 2016 at 8:07
  • $\begingroup$ No, I don't think any of the four categories listed as pyrometallurgy are analogous. They do not involve plasma. $\endgroup$ Commented Oct 26, 2016 at 18:29


Mobile bots will use chainsaws/circular saws/plasma cutters to slice material up into regular blocks. They will be transported to the central processing unit, where they will be processed in grinders, until it has the granularity of powdered sugar, this will also remove any ices in the ores, which can be condensed if desired.


Materials will be sorted using a combination of hyper-spectral sensors, centrifuge and magnetic separation. Further processing at temperatures that target materials melt at and 'tapping off' this material or by exposing the resources to heated Carbon Monoxide and then extracting metals from the resultant gasses.

  • $\begingroup$ I never heard of centrifuges being used for separating solids. Can you provide a reference? $\endgroup$ Commented May 2, 2016 at 15:55
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    $\begingroup$ Oh, sorry, I was meaning that centrifuges would be loaded with plasma from super-heating the asteroid material, in a process similar to isotope separation. $\endgroup$ Commented May 2, 2016 at 16:09
  • $\begingroup$ ah ok, got it! I already knew some of these tech; I got the impression they were less than optimal for operating in 0 g and no pressure $\endgroup$ Commented May 2, 2016 at 17:28
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    $\begingroup$ Solid-solid centrifuges exist (see en.wikipedia.org/wiki/Solid_bowl_centrifuge). But you can simply reuse the ice, melt it, add the raw material (the finer the grain, the best), and voila, ready for liquid basic centrifuges. $\endgroup$
    – Uriel
    Commented May 18, 2016 at 19:18

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