Material Separation Will be Key for Long Term Space Travel

Many manufacturing industries currently use material separation due to the need to recycle and reuse materials, both from a commercial and environmental need. The material separation process has become so in demand that a whole industry has grown around it.

It is not just on Earth where the manufacturing sector looks to separate materials for reuse. Space agencies such as NASA and the European Space Agency (ESA) look to recycle and reuse materials as much as possible. This extends beyond air and water to structural components.

With this in mind, let’s look at how material separation may be both a driver for space travel development and to make the process more efficient and produce better results.

Research and Mining
In 2015, NASA published an online article talking about using to fabricate space parts for repairs to space vehicles. Dylan Carter, the author of the article, talked about using regolith (planetary body bedrock) handling devices. Here, after the regolith is collected, Carter’s theory is that useful materials could be sorted and grouped using a tribocharging technique.

Although the technology was in 2015 relatively new, Carter believes that his experiments prove that this could be an invaluable way of separating materials in space.

If this works, then humanity as a species is a step closer to mining and harvesting resources from celestial bodies.

Driving Investment
Being able to separate materials on an industrial scale has always been vital to the manufacturing sector. Given the infinite resources of space, being able to harvest these resources represent a big draw for investment. This can be seen with the rise of Space X, whose goal is to make space profitable and create a Mars colony. It has undertaken a lot of work in developing space vehicles that can be reused.

Humanity is not at the point where deep space mining is possible. Commercial space flight developments, however, could be the key to making it possible.

Commercial entities are freer to focus on singular goals, greatly speeding up the process and allocating all resources to hitting said goal. Should companies like Space X focus on this endeavor, we may see space mining a reality in the not too distant future.

Material separation processes will be an invaluable part of this process.

Space Vehicle Repairs
Collisions with debris are a real danger when traveling in space. Small punctures up until a millimeter in diameter cause problems, 10 milometers or greater can cause potentially catastrophic damage to space vehicles according to the ESA.

This is mostly due to the high velocities space debris and particles travel. What would be considered harmless on Earth is potentially lethal when in space.

Currently, vehicles such as the International Space Station uses passive techniques to avoid smaller particles.

Nonetheless, if the dream of Mars colonies and beyond are going to become a reality, then the ability of a crew to fabricate raw materials for essential repairs is mission-critical. As such, material separation technology is going to be essential to bring long-range manned space flight within humanities reach.

Currently, on Earth, material separation and recycling are possible and are being improved year on year. Soon, we may be able to do this in space, and that’s when things become really exciting.

36 thoughts on “Material Separation Will be Key for Long Term Space Travel”

  1. > consider that a complex piece of equipment is never made from just one material.

    That’s one of the reasons CHON shines for nanotech. If you can arrange the atoms in any way that physics allows with enough control, then you can make almost all of the parts from just these 4 elements. From soft polymers and foams to very hard stuff like diamond. From good insulators to excellent conductors. You can make semi-conductors with a wide range of different band-gaps. Or you can make computing parts based on other principles (mechanical, optical, spintronics, etc). And a bunch of other stuff.

    You may still need trace elements for some specialty applications, but maybe as much as 99% of the mass can be just CHON in various different arrangements. We see something similar in biology: CHON accounts for over 96% of the human body (for example). Then there’s some phosphorus for various stuff, a bunch of calcium in the bones and as charge carriers, a few other elements that are less than 1% each (some other charge carriers and some sulfur), and everything else is less than 1% combined.

    It makes sense to limit the amount of elements used, because that reduces the amount of different machinery needed to build stuff. As it happens, CHON is extremely versatile, and also is 4 of the most common elements.

  2. Sand based thermite might be useful for welding existing iron parts together? I don’t know.
    My last attempt at welding aluminium indicates that I’m very much not an expert on this.

    That’s a good point about aluminium space ships. I’m not concerned about solid Al spaceship walls reacting with dust. You need the Aluminium to be a fine powder before it’ll just go up without a lot more prodding that that.

    Something like: You load your asteroid chunks into the hold. Subsequent movement causes the rocks and gravel to grind against themselves and the walls, producing a mix of SiO2 dust and Al dust. Being vacuum the Al doesn’t produce an oxide layer…. yeah do that multiple times in a mining operation and I can see it going badly wrong at some point.

  3. That is a fun fact – but is it useful to your story, if the astronaut wants to make a metal part by casting iron?

    Maybe – you need enough heat to melt relatively pure iron and then let it gravity separate the iron from other reaction products (Al2O3 and Si for the reaction you’re proposing). I guess Al2O3 floats on liquid iron, as would SiO2, so they’d separate?

    I’d expect moon dust to already be fine enough and it is mostly (50%) silicon dioxide. I presume the pure aluminum could be made by grinding up an aluminum spare part in vacuum.

    Hmm – could an aluminum spaceship be a fire hazard? I.e. a mining ship is ready to head home, battered and scratched (exposing unoxidized Al) and covered in SiO2 dust from months of mining. It lights up engines, sparks rebounding from the asteroid surface hit the ship, and it goes up like a torch, at least briefly?

  4. “Actually, as it happens, we ALREADY have a bunch of nanotech swarms roaming the planet and attacking humans as a food source. Which is why I’m stuck at home, in quarantine, and loaded up on antivirals and pain killers.”

    And that’s the other reason why I don’t put much stock in the grey goo scenario. Bacteria has all of the ingredients for self-replication and, while they are prolific, the entire surface of Earth isn’t some desolate microbial mat either.

    Also consider that a complex piece of equipment is never made from just one material. The bulk of the structure, let’s say a 3-d printer, may be steel or aluminum or polyethylene but the inner components are silicon, whatever element they doped the silicon to be a semi-conductor, copper for wiring, rubber for insulation, etc. Nanomachines would be limited by the least plentiful element vital for its operations. All of that silicon dioxide is worthless with some germanium to go with it.

  5. He was actually trying to get water, as I recall. Hydrazine, N2H4, catalytically decomposes to N2 x 2xH2. Then he burned the hydrogen in oxygen to get water.

    His initial problem was that he accumulated too much hydrogen before he got it lit, and had a gas explosion.

  6. Fun fact: Iron oxide isn’t the only oxide that will work to power a thermite reaction. It just has to be something with sufficiently lower chemical potential than aluminium.

    Silicon fits the bill. So you can (apparently, I’ve never done it) make up your thermite with sufficiently fine sand. Which isn’t rare at all. And it’s much easier to grind sand to finer grain size than with Al2O3.

    You still need the fine aluminium powder. And ground-to-dust sand will give you a deadly lung disease if you breathe any. And thermite will kill you in half a dozen ways….

  7. Not just meat, but any organic material is a good source of CHON and other useful elements, which is good starting material for nanodevices. That’s part of why gray goo could be so dangerous.

    But nanotechnologists who’ve given the scenario plenty of thought are mostly convinced it’s not a likely scenario, especially by accident. The engineering requirements are too complex.

  8. Gold miners have a trick to get the magnetic stuff out – they put a strong magnet inside a thin non-magnetic cup, get all the iron bits on the outside of the cup, then pull the magnet out so all the iron falls off where they want them. Saves a lot of time, which would be of the essence in your story I think. Should be pretty easy to rig up something similar.

    Another interesting trick might be making thermite out of rusty iron and aluminum, to melt the iron, even in vacuum. While much of the iron retrieved would not be very (if at all) rusty, it wouldn’t be too hard to make such fine iron rust in water – heat it up and sprinkle it in, wait a bit.

    That’d also produce hydrogen, which might be useful or dangerous (as in The Martian – she could reference avoiding the mistake he made in the book/movie, though I think there he was trying for hydrogen but had too much O2 or something like that?)

  9. If your space minerals processing facility is 1% of 1% as dust covered as all the Earth based facilities I’ve been to, probably with some water or at least water vapour escapes as well, then the outside of said space facility would have layers of what is basically mud in every crevice. With some powdered Carbonaceous chondrite meteors in there as well providing everything a growing bacteria and fungus colony would need.

  10. I believe that the grey goo scenario is assuming a level of technology in the nanobots that is several generations more advanced than what we are talking about here.

    Also, you COULD make your nanobot swarm use, and home in on, a material source that has already, on Earth, been separated out.
    Virtuosity (a sadly forgotten SF film) had the nanobots use glass as their raw material. Big slabs of purified glass are common in our world (but not the moon). And actually glass is a pretty good basis. After all silicon chips and mems are in fact made from materials where silicon dioxide is the starting point.

    If you are really wanting to push the grey goo horror story, you have the ideal starting material being meat. Dead or alive.

    Actually, as it happens, we ALREADY have a bunch of nanotech swarms roaming the planet and attacking humans as a food source. Which is why I’m stuck at home, in quarantine, and loaded up on antivirals and pain killers.

  11. I wish people would make these sort of considerations when they talk about the grey goo scenario. These runaway self-replicating nanomachines are suppose to consume everything and make it into new nanomachines but what happens when your runaway self-replicating nanomachines don’t have access to the material that it’s made of?

  12. Extremophilic bacteria wouldn’t grow outside the hull. They may survive, but they won’t reproduce as there’s no material for them to incorporate.

  13. I saw a recycling plant once that sent mixed pelletised plastics through a cascade of hundreds of charged metal plates acting as electrostatic divertors. Run it through long enough, assuming even mass of pellet, and you get a decent enough separation to use the materials as feedstock. I bet the same can be applied to minerals.

  14. I’m thinking of fiction with an astronaut stuck on the moon (think “The Martian”) and to make a part to repair the mcguffin she has to troll through the soil with a hand magnet, scrape off the iron powder, and then use a broken widget as a hammer to vacuum hammer forge the powder into a useable part.

  15. Interesting – but apparently you can do a lot of useful separation on the moon with just a magnet – even easier than mining water ice.

    Maybe 5-10 kg of iron (often alloyed with nickel and cobalt) could be pulled out per cubic meter of lunar soil.

    Titanium is also available as illmenite, which is weakly magnetic – you could probably separate it from a thin stream of dust with a strong enough magnet.

    Why not go for the low-hanging fruit first?

  16. Seems like each crater of the Moon was made by a thing that MAY have been gravitationally separated before being broken up. Then not disturbed by plate movement or water. So no mineralization, but no dispersal either.

  17. I wonder how much easier it would be to do large scale mass-spec separation if you have access to multi km long separation volumes, with hard vacuum, and an existing ion stream to accelerate everything (solar wind/ pre-separated solar wind so you’ve diverted it magnetically or electrostatically so as to only get the positive or negative component).

  18. Probably the easiest chemistry for metal and metal oxide separation is via HCl: it should react with most oxides to produce the hydrated metal chloride, or with metals to produce the metal chloride and hydrogen gas.

    With electrolysis of the metal chloride, you get the metal and chlorine gas, with water remaining. Further electrolysis splits the water to oxygen and hydrogen. React the hydrogen and chlorine to get back HCl. A similar process might be possible with H2SO4, but recovering the sulfuric acid is trickier.

    Different voltages should extract different metals if you have a mix of chlorides. Or if you get a mix of metals, you can use induction heating to different melting points, as noted above. Separating alloy components is more difficult, but similar principles should apply.

  19. 4 (cont). Most of the remaining carbon can be burned by splitting water to oxygen and hydrogen. Separate the gases as in 1, then pass the CO and CO2 through Sabatier using the hydrogen part of the split water. This recovers most of the water, and produces methane, which can be converted to other hydrocarbons.

    At the end of all that, you’re left with mostly carbon-free solids. See below for those.

    5. Non-oxidized metals (usually in asteroids). Probably crush, melt at different temperatures, then separate physically (filtering, light centrifugation, etc). If you have access to the necessary supplies, can apply various chemistry to extract in the liquid or gas state. But in space you want to select a process where all your reagents can be recovered and reused.

    6. Rocky stuff (regoliths, rock fractions of asteroids, etc). This is mostly metal oxides and silicates. Vacuum reduction has been proposed here for the metal oxides. If you have access to water, hydrogen reduction should work for some oxides, recovering the water. If you have access to carbon, carbon reduction can be used for some other oxides. Electrical reduction is another option, but can be difficult with oxides. Easier if you can convert the oxide to some other salt. Once you have reduced metals, it’s back to 5. And as with 5, if you use chemistry, you’ll need to select the right process, where you can recover your reagents.

    The remaining unsorted solids can be used as radiation shielding.

  20. Even in space, you won’t have just a random mix of everything. The solar gravity and thermal gradient has separated stuff into several broad categories; chemistry has put certain things together; and on the larger bodies, their own gravity has separated things some more. So broadly speaking, there are:

    1. Gases (in various atmospheres). Relatively simple to separate by various distillation techniques or maybe by centrifugation.

    2. Occasional liquid deposits (sub-surface oceans, lakes of Titan). Separate solids by filtering or centrifugation, gasify the liquid by heating or vacuum, then see 1. If you know the composition, in some cases you can apply various chemical techniques in the liquid phase.

    3. Ices. Crush if necessary, gasify by heating, then see 1. The non-volatile remainder falls into the below categories.

    4. Carbonaceous chondrites (asteroid belt). Will usually be mixed with water ice or hydrated minerals and other solids. Crush and bake (not necessarily in that order) to release the water and low molecular-weight organics. See 1 to separate. Some of the medium molecular-weight stuff can be released similarly by further heating or by applying oil extraction techniques. The heavier stuff can be steam-cracked to lighter compounds using the water you extracted earlier.

    (continued in reply)

  21. I think that it would be helpful to distinguish between the different types of material separation. There is:
    Waste separation for recycling
    Recycling of life support chemicals
    ISRU (in-situ resource utilization)

    Waste separation for recycling could use crew or robots (think of how we choose to place plastic containers in the recycling bin).

    Life support recycling is being done fairly well on the ISS (93% of water is recovered).

    Beneficiation is a mining process of taking low-grade ore and processing it to higher grade (i.e. higher concentration). This is going to be critical to success.

    ISRU – Using local resources instead of having to ship them. Also critical but involves processing (e.g. metallurgy & machining) which does have a cost especially at small scale.

    More info:

  22. Yes, the apparatus needs to be enclosed, but the operating pressures are like 0,001 atmosphere, so it doesn’t need to be a strong pressure vessel on the Moon. You are right that eventually you are left with refractory oxides. Those would have to be separated by other methods, or just used as refractories in other processes.

    More complex processes can separate all the materials, but they need a lot of energy and high temperatures:

  23. I remember some discussion of “electrowinning” to separate out contaminant metals selectively in a nuclear reactor. A nuclear reactor could probably be used to separate individual metallic elements from an aqueous bath of salts at more reasonable energies per kilo. You’d basically be taking advantage of all that hydrothermal chemistry, fast-forwarded by your energy input. Sort of.

  24. It’s beyond just materials separation: we need to take a stable ecosystem with us when we go to space. I’ve always found boxy metal spaceships not to make much sense, aside from allowing for a more Shakespearean stage. O’Neill cylinders all the way! Biology is quite nearly the most advanced nanotechnology we will ever need.

    As for minerals and volatiles, distillation columns, spiral separators, electrostatic separators and magnetic separators are quite effective as long as you have spin gravity, for simple low-power separation. And for nickel and iron, silicon, aluminum, zirconium, tungsten, and a few others, gas phase processes have been developed (originally for IC etching/deposition/purification) which could be used for fairly easy separation of the elements or their oxides. Only issue is they use toxic gases like fluorine, chlorine, iodine or carbon monoxide typically, but this is less of an issue in space where it’s easier to isolate and would probably just help kill off any extremophilic bacteria that start growing outside your hull.

  25. Perfecting these sorts of tech is actually the greatest argument in favor of “get to space to fix the Earth” in contrast to “why go to space when Earth isn’t a utopia?”

    Get this down cold, clean, and cheap, and it gives benefits wherever humanity goes.

  26. The nice thing about that approach on the Moon is that without clouds and an atmosphere, you can heat to some pretty high temperatures just with focused sunlight.

    Thinking about your proposal, this would only work for the higher vapor pressure metals, because for the ones with lower vapor pressure, you wouldn’t get that fractional distillation effect, the metals would plate out wherever the atoms struck, unless the apparatus was at high enough temperature at that location that it would evaporate away again.

    As you get into the higher temperature metals, this really restricts what you can make your apparatus out of.

    And it does have to be a closed apparatus, because at those temperatures, the atoms would go a LONG way on ballistic trajectories in the Lunar vacuum.

    A construction technique for the Moon that I’ve mused about, would be to use electrostatics to create a beam of sand or whatever, run it through the focus of a mirror on the way to its target to melt it, and build up 3d objects by beam deposition.

  27. Nice thing is, there are a finite number of elements and isotopes you have to be concerned with, so achieving closure requires a process of finite complexity. Yes, mass spectroscopy is probably too power hungry for general use, though I bet it could be optimized a lot if we really tried.

    But you want to start with general processes, and work your way to the specific. And be prepared to use what you find, instead of demanding the best material for every job.

  28. Shale isn’t stupid and unwanted. The typical blend for Portland Cement is 5/6 limestone and 1/6 shale. You don’t want too much, of course, but you do want some. If you cook pure limestone, what you get is lime (CaO), used in mortar, but not the same as cement for concrete.

    One of the things we can do in space more easily than on Earth is “vacuum reduction”. You heat your raw soil up in a solar furnace. At a certain temperature, some of the oxygen will separate out (i.e. partial pressure > 0). You pump this away, cool it down, and store it. So long as you keep pumping it away, more will separate out.

    Any reduced metals with a non-zero vapor pressure will also leave as vapor, and can be fractionally separated by a zone of gradually reducing temperature, where they plate out.

    We don’t normally do this on Earth because it takes a lot of work to produce a vacuum which can withstand high temperatures.

  29. Darn decent answer, that. To me the whole thing is about “energy tradeoffs”. Mass-spec would deliver ‘the goods’ at pretty preposterous energy demands per kilogram of separated elements. I recall the Hanford nuclear enrichment facility was mass-spec in design, and used a whole hydroelectric dam’s worth of energy to get a handful of grams a day output. Granted, it was separating kilograms of ²³⁸U + ²³⁵U to get the 0.720% of ²³⁵U concentrated to 90%+ values. Takes a lot more energy than say separating thorium from uranium, by mass-spec. 

    But still. 

    The other thing is that the mass-spec Hanford plant was HUGE. Maybe some of that hugeness was the modest level of technology of the day, for making large electromagnets, large vacuum lines, and so on. They had no microprocessors, no computers, everything was almost manual. This’d be different today and in the upcoming future. And rare-earth magnets make it more possible in more compact ways. 

    In any case… energy of separation. 

    And maybe “synthetic hydrological processes”. Just as have been used for the last 100 years to make ‘synthetic hydrological emeralds’ and other coöperative gems. 


    GoatGuy ✓

  30. The thing is, on Earth we’re dealing with material that has already been largely segregated by hydrothermal and other processes. Whatever you’re looking for in it has already been concentrated way above primordial levels, or you’d be looking for it someplace else. So we’re used to using techniques that assume there’s one or two desirable components mixed with a disposable component. We don’t usually just dig a hole wherever we are, and want everything in the hole sorted out.

    In space, unless you’re on a planet like Mars, you’re not looking at that. You’re looking at minimally processed primordial junk, and you’re trying to get everything out of it, because you mostly don’t have ore deposits, as we know them on Earth.

    I think we need to look at the processing from that standpoint. First, bake out any volatiles, and separate them by distillation. Then run the rest through a plasma torch with an excess of hydrogen, to strip out things like oxygen, chlorine, sulfur. Distill that.

    Now you’re down to a random mix of elements with higher boiling points, that don’t form volatile compounds. Separating them starts to get more complicated. Maybe just run the whole mess through mass spectrography? Is the simplicity worth the energy cost and low throughput?

    And then, once you’ve got it all separated, I think you want to have a library of technologies that can achieve the same general end using different mixes of elements. Luck into some nickle iron? Make steel. Silicates? Ceramics.

  31. Right idea … scoop up “whatever” from asteroids, our Moon, Mars, other planetary moons; use electrical, magnetic and gas gradients, centrifugal, and yes even weak chemical affinity (i.e. oil-and-water separations, that kind of thing) to split all the lil’ bits into piles of physically more homogeneous “whatever”. Then “do stuff to it”, akin to smelting, but not really.  

    As an example of a similar end-to-end process here on Planet Dirt: making cement. 

    A quarry scoops and trucks dolomite-calcite limestone. Mother nature determines if a scoop is mostly dolomite, mostly calcite, or some blend between. Or stupid, unwanted layers of shale.

    The crunched up rock is sent to a sorter. It uses techniques outlined above to isolate the good stuff from the unwanted junk. Down conveyer, the various dolomite-calcite ‘blends’ are chucked onto enormous piles. Much easier to RE-blend for making cement. 

    With cement demand worked out, every day the stuff heads to a kiln. The carbonate rock is cooked to free CO₂. This leaves oxides of Ca and Mg. And silicates, and other stuff, all part of a good cement. Clinker (as it is known) is kept for months, waiting grinding to the powdery grey stuff that is the ‘real cement’.  

    Thus, repurposed limestone becomes sidewalks and suspension bridges. So yah… do this on asteroids!

    Just saying,
    GoatGuy ✓

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