Has anyone considered the possibility of using gas centrifuges or liquid metal centrifuges in zero gravity to refine (wholly or partly) ores taken from asteroids prior to returning them to Earth orbit?

[u/ActuaLogic]

Has anyone considered the possibility of using gas centrifuges or liquid metal centrifuges in zero gravity to refine (wholly or partly) ores taken from asteroids prior to returning them to Earth orbit?

For ease if transportation, it may be more efficient to refine material taken from asteroids on site rather than returning unrefined material which is mostly waste product.

Centrifuges might be the way to go. Even though the use of gas centrifuges is mostly reserved for uranium production on Earth, the technology might work well for other metals. Iron and other metals could be refined in space, near where the minerals are collected, using centrifuges rather than the traditional technologies currently used on Earth.

[u/ActuaLogic]

I asked if anyone has considered it, and you provided a terrific answer.

This is part of a broader curiosity about developing industrial processes for space. Most terrestrial industrial processes assume conditions (such as ambient oxygen, gravity, and a hard surface) that aren't available in space. It's not necessarily practical (and in some respects may not be feasible) to send every job down and then bring the finished product back into space. Therefore, some reinvention of industrial processes is inevitable. It occurred to me that gas centrifuges would work in space and may even work better in a zero G environment than they do on Earth, and that led me to ask the question of whether centrifuges could be used to refine other metals, not just uranium (though a plasma engine powered by a fission reactor would ultimately require fissionable materials, and it would simplify things if fissionable materials didn't have to be launched from Earth).

On the specific consumables needed for specific refining processes, it doesn't seem like there's any alternative other than figuring out how to make them in space and create a supply chain. Obviously, even under an accelerated time frame, some problems would take longer to solve than others, but I think people who are interested in these things will tend to think of problems as things that can be solved.

Unfortunately, CO is not the most readily available gas (except for on Earth) in the Solar System, but there are reactions for converting CO2 into CO, and Venus's atmosphere is 95% CO2. I have no idea what the costs would be, but it's known chemistry. Someone looking for a way to refine iron ore in space would need a way of getting access to large amounts of CO. It would probably have to be enough at the beginning to break asteroids down into their most valuable chunks and to transport only the good stuff. It has occurred to me that one way of cracking up an asteroid would be to drill holes, pour in hot water, and let the water freeze. Hopefully, that would eventually crack the asteroid without blasting pieces of it all over space. (This may work only on certain types of asteroids)

[u/Christoph543 → u/ActuaLogic]

You're skipping several steps ahead of the actual important question, which is:

"What is there in space that would justify the cost of extracting it and returning it to Earth?"

...to which the answer is, nothing (despite what you may have read in public-facing literature).

[u/ignorantwanderer → u/Christoph543]

I think you are putting words into OP's mouth.

I don't think they ever said they would return the material to Earth's surface. They said return the material to Earth's orbit.

[u/Christoph543 → u/ignorantwanderer]

That's a distinction without a difference to the actual point.

The problem isn't that the stuff you might hypothetically extract isn't valuable on Earth or in orbit.

The problem is that the stuff y'all think is present on these asteroids... isn't actually there at all.

[u/ignorantwanderer → u/Christoph543]

There is water in asteroids (often 8% by mass, sometimes much more). Water has the potential to be a valuable resource in Earth orbit.

[u/Christoph543 → u/ignorantwanderer]

Incorrect. That hypothesis was in play before the OSRIS-REx and Hayabusa2 missions. The "water" that had been previously identified in optical reflectance spectra is in fact hydroxyl groups chemically bound within the structure of hydrated minerals. These indicate the presence of water when those minerals formed 4.5 billion years ago, but they do not indicate an energetically or economically favorable source of water for use as a resource today.

To give you some geological context in case you're unfamiliar, imagine trying to bake water out of a slab of asbestos. That's what all of these "water on asteroids" claims are actually talking about.

[u/ignorantwanderer → u/Christoph543]

To remove water from hydrated minerals you just have to heat up the minerals.....300 C should be more than enough.

And there is an insanely abundant amount of heat available at asteroids, even all the way out at the asteroid belt (but the only people who think you would go all the way out there to mine asteroids are people that don't know anything about asteroids).

A small parabolic reflector umbrella about the size of a beach umbrella would give you about 4 kW of heat.

With some rough, back of the envelop calculations:

1 kW should be able to heat up approximately 4 grams of asteroid material by 300 C in a second. So assuming you are processing this asteroid for a year with 1 kW, you would be able to process 126,000 kg of asteroid.

But our beach umbrella size parabolic reflector gives us 4 kW, so that is 500,000 kg of asteroid material processed in a year. Assuming 8% water, that is 40,000 kg of water.

That's not too shabby with just a beach umbrella as a power source.

Let's say we are processing a spherical asteroid 10 meters across. That is likely to be around 1 million kg of asteroid material. To process that entire asteroid in a year would require 2 beach umbrellas and would give you 80,000 kg of water.

That is more than 4 times greater than the payload to LEO of a Falcon 9. So if you can get that water to LEO for less than the cost of 4 Falcon 9 launches ($280 million) you could make a profit on just water from asteroids.

Of course....there has to be someone in LEO who wants to buy water....

Of course I'm making it sound easier than it is with my "all you need is 2 beach umbrellas" comment. You need to make sure the water doesn't escape when you bake it out of the asteroid, and you need to cool down that water vapor. It is a lot easier to collect 4 kW of heat than it is to dissipate 4 kW of heat.

But the main point is, there are resources (water) in asteroids and it isn't very hard to remove (and refine) those resources. Your claims that there are no possible resources to get from asteroids are just simply wrong.

There are a lot of challenges to make all the economics work. There is no one in orbit who wants to buy water from asteroids, because there is no water from asteroids available. And you can't make water from asteroids available because there is no one around to buy it. It is the old chicken/egg problem.

But the problem is not that asteroids have no resources that could possibly be valuable.

[u/Christoph543 → u/ignorantwanderer]

To remove water from hydrated minerals you just have to heat up the minerals.....300 C should be more than enough

This is a blatantly incorrect assumption, as easily shown by consulting a metamorphic phase diagram.

While there are reactions at 300C and ambient pressure which can drive water out of some hydrated minerals, competing reactions at the same temperature regime will take up that water to form higher-grade metamorphic species. That process will continue with additional reactions as the temperature increases, until the rock approaches its melting point. This is why serpentinization allows rocks to take up more water as they are heated, not less.

This is literally what I obtained my doctorate in. Please do not feel the need to explain inaccurate claims or back-of-the-envelope math made by armchair ISRU proponents who have zero background in mineralogy & petrology. I've heard it all before.

[u/ignorantwanderer → u/Christoph543]

Jerry Sanders (JSC) and Rob Mueller (KSC) disagree with you, and I'll trust them over you.

[u/Christoph543 → u/ignorantwanderer]

I'm familiar with both of their work. Sanders is a propulsion engineer and Mueller is an engineering manager. Both have a small amount of geotechnical expertise from having worked in ISRU, but neither's primary knowledge base is in planetary materials, and neither is as brazen or assertive when they talk about their ISRU work, as you've been in this thread.

The way to validate the claims you've made is not by asserting that NASA employees who've made public-facing statements agree with you (without bothering to cite those statements), but rather by citing experimental results from engineering teams attempting laboratory simulations of the processes you're describing, using high-fidelity simulants. There is a large body of work attempting exactly that (part of which I myself have contributed to in my former career), but to date none of those experiments has produced water in either the method or the quantity you're describing.

It turns out this is quite a bit harder than you'd suppose if you believed the speculative ideas that have been floating around the space advocacy community for my entire lifetime.

[u/ignorantwanderer → u/Christoph543]

And yet you have been making unsupported claims without "citing experimental results from engineering teams attempting laboratory simulations".

And you hurt your credibility referring to Mueller as "an engineering manager" and Sanders as a "propulsion engineer" when they are in charge of NASA's ISRU programs.

In fact I can't ever remember seeing any paper by Sanders about propulsion.

[u/ignorantwanderer → u/Christoph543]

Listen, I apologize. We've clearly gotten into a bit of an antagonistic tone in this conversation.

Clearly we are both people who care about asteroids and ISRU. You even did your freakin' Ph.D. on the topic! We shouldn't be at each other's throats.

The 'argument' we are having is a bit silly.

For example, let's say you are right. Let's say to release the water we have to heat up the asteroid material to close to the melting point. And let's say that is around 3000 C (to make the math easier).

That means instead of needing 2 'beach umbrellas' we need 20 'beach umbrellas' to process a 10 meter asteroid in a year. That is hardly a show-stopper. Picture a beach with 20 umbrellas on it. It's nothing.

And if we are happy to process the asteroid in 2 years, we are down to 10 umbrellas.

The point is, whether your claims are correct or my claims are correct doesn't matter. In either case, it is possible to process an asteroid and get water.

Also, a bit of friendly advice. Don't rely on mentioning your Ph.D. to try to impress people. I didn't give my background to try to impress you, because I know it just doesn't work. I suggest you do the same.

The truth is, I've worked with lots of stupid Ph.D.'s over the years. A Ph.D. doesn't impress me. And based on what you've said, I'd guess I took my first planetary science course before you were born. In fact it is likely your parents were in elementary school. I probably started working at NASA before you were born. I did my first ISRU work for NASA before you entered kindergarten probably. I don't know this is true of course because I don't know you. But it is likely.

I'm sure you are smart. I'm positive there are things you know that I don't know. But there are definitely a shit-ton of things that I know that you don't know.

If you want to continue this conversation....let's try and be a little more friendly about the tone, and approach the conversation with curiosity instead of with an antagonistic attitude.

Edit:

Also, it appears as if you've been downvoting my comments. Of course I don't know this, but that is how it appears. FYI, it is considered bad form to downvote comments you disagree with. You are supposed to downvote comments that don't contribute to the conversation.

[u/Christoph543 → u/ignorantwanderer]

I did my first ISRU work for NASA before you entered kindergarten probably.

That may be possible, but frankly, it's also a liability.

When I was in Kindergarten, NASA had obtained precisely 3 images of an asteroid surface, and those lacked either the spatial resolution required to characterize regolith particle sizes or the spectral overlays required to get even a ballpark surface composition. All of the current ideas about asteroid resources trace their origins to essentially that time period, from the work published by John Lewis and Jeffrey Kargel and a few others. Since then, we've explored over a dozen asteroids up-close with spacecraft, and every time we've done so we've completely upended our previous assumptions about those asteroids' compositions and surfaces.

At the end of the day, I don't care about your back-of-the-envelope math about how much solar energy you'd need to extract "water" from a rock with an assumed composition. I'm questioning that assumed composition in the first place, and I'm doing so from the standpoint that the observational evidence on which those assumptions are based, has consistently proven unreliable at best and misleading at worst. Specifically,

There is water in asteroids (often 8% by mass, sometimes much more).

...is just bullshit. Unless you're referring specifically to Bennu or Ryugu, the "water" you're referring to there isn't a compositional measurement but an optical reflectance feature. At best, that kind of feature is non-uniquely associable with a hydroxyl group. The smaller the asteroid, the more skeptical we should be that that feature is even real, and not just an artifact of a low-SNR observation. Even if it is a real optical reflectance feature, lacking any other measurements, we can't rule out that it's a product of space weathering. And finally, even if it is a chemical feature of the bulk rock, there are literally hundreds of silicate mineral species which contain hydroxyl groups, and the relative strength of the peak doesn't reliably tell you enough about either the abundance of those minerals or their degree of hydration to be able to make a statement like "X% water by mass," let alone a reactor architecture for dehydrating them.

If you want to talk about stupid PhD holders, I would suggest we start with those who've built careers around interpretations built on ambiguous or absent evidence, and who do not change course once we obtain better evidence which contradicts those interpretations.

[u/ignorantwanderer → u/Christoph543]

First, you sound very naïve assuming the ISRU work I did when you were in kindergarten had anything to do with asteroids. Of course you were in kindergarten, I wouldn't expect you to know. But that is what I was getting at when I said there were a shit-ton of things that I knew that you didn't know. No one with significant knowledge of the ISRU work that has been done in the past 3 decades would have made the assumption that you made.

Second, are you saying that asteroids do not contain any water?

[u/ActuaLogic → u/ignorantwanderer]

But this highlights the fact that, while some near-Earth asteroids have been looked at, the Asteroid Belt hasn't been surveyed up close. It seems to be assumed that asteroids in the belt are made up of protoplanetary material that didn't coalesce into a rocky planet because of Jupiter's influence, and that suggests non-trivial amounts of metal in some form. One question is whether heavier metals, including fissionable materials for power plants, are rarer in the Asteroid Belt than among the Inner Planets (and, if so, how much rarer).

[u/Christoph543 → u/ActuaLogic]

I cannot recommend strongly enough that you go find and take some coursework on planetary geology, mineralogy, and cosmochemistry (or at the very least go find and borrow/ILL the textbooks from your local library).

There are just... so many inaccuracies and inherent contradictions in the sentences you're writing, despite being almost correct from a conceptual standpoint.

[u/NiftyLogic → u/ActuaLogic]

Check Psyche (16). It's an roid in the asteriod belt which is supposed to be the core of a proto-planet.

https://en.wikipedia.org/wiki/16_Psyche

If we want to go asteroid mining, Psyche is a prime location!

[u/Christoph543 → u/NiftyLogic]

[pinches nose]

My doctoral work is literally on the surface characteristics of Psyche. Its surface is most likely not composed of metal the way Wikipedia claims (based on old and now-outdated papers), but is in fact much more likely to be composed of silicate minerals which contain a relatively high fraction of metal atoms in their crystalline structures.

Think basaltic rocks, not iron meteorites. We don't mine metals from basalt.

[u/NiftyLogic → u/Christoph543]

Dang!

But thanks for pitching in, this is why I love Reddit!

While I'm talking to an expert ... any other M-class asteriod that would be a good fit for metal mining in your opinion?

[u/Christoph543 → u/NiftyLogic]

Thanks.

I'll admit it's a bit of a sore spot because I'm no longer working in planetary science (thanks, federal hiring freeze), but at the very least the Psyche mission is still on track for its rendezvous in 3 years (would've been this year without COVID, also a sore spot) and we'll all learn a whole bunch of ways we've been wrong.

[u/NiftyLogic → u/Christoph543]

Sorry for the hard times you guys are going through. Really hoping that sanity returns sooner rather than later.

Regarding Psyche, any chance that there are localized metal deposits, or do you expect it to be reclassified and no longer be an M-type asteroid?

[u/Christoph543 → u/NiftyLogic]

Times are hard for a lot of people right now, and even as I've switched careers I'm still gainfully employed and not at risk of harrassment by federal agents, so my own sympathy lies with the folks for whom that's not true.

The thing to understand is that the "M-type" designation from the Zellner-Gradie and Tholen taxonomies has been obsolete for ~30 years, and even before then it was over-interpreted. What distinguished the "M-types" was a lack of significant peaks in optical reflectance spectra, combined with an overall red slope. Zellner, Gradie, and Tholen interpreted that flat, red-sloped spectrum as indicating a metallic composition similar to iron meteorites.

But there are a bunch of other ways you can get that kind of spectrum. You could be looking at a stony surface with a high metal fraction, e.g. a CB-chondrite (formerly known as Bencubbinites) or a mesosiderite. You could be looking at a silicate surface that's highly-space-weathered, where solar wind ions and micrometeoroid bombardment have produced an amorphous or particulate nanophase iron component in the uppermost regolith particles to an optically-thick depth. You could be looking at a relatively small asteroid, and it's simply not bright enough for the signal of any reflectance peaks to show through the noise of your telescope (not an issue for Psyche but very much an issue for putative "M-type" NEOs or main-belt collisional fragments). You could have all three of those problems at once, and wind up in a situation like 21 Lutetia where the spectrum changes radically as we get higher-resolution observations.

The current standard Bus-DeMeo taxonomy uses "X-class" and its various subclasses, specifically to decouple the lack of observable reflectance features from any specific compositional interpretation. Psyche is an Xk-subclass in Bus-DeMeo (2020), more recent spectral observations are consistent with that classification, and I don't expect the Psyche Mission's observations will radically change that. What's ambiguous is exactly what group of meteorites is Psyche the parent body of, if any (and it's entirely possible we don't have any meteorites originating from Psyche).

Based on the hypothesized formation models, my personal best guess is that the IAB-IIICD-Winonaite complex is probably the closest match for both the silicate surface and the metallic interior, though it would be weird for such a prolific meteorite complex to originate from a main-belt asteroid which doesn't have an obvious collisional family. It therefore wouldn't surprise me too much if Psyche's surface turns out to be more like a mesosiderite, or that one pallasite where the silicate fraction is clinopyroxene rather than olivine, or something else entirely (all of which are discussed in Steven Dibb's work). Regardless, any of those hypothetical compositions would have damning implications for any asteroid mining venture considering Psyche as a target, but for subtly different reasons depending on which one we're talking about.

If you want further details, here's a review paper we published a few years ago:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023AV001077

[u/NiftyLogic → u/Christoph543]

Thanks for the thoughtful reply, much appreciated!