The practicalities of mining asteroids

Factual Questions
1

Lately I’ve seen news headlines about mining asteroids. Today there were 3.

I always think the same thought. Mining is a heavy industry and I’ve been around in some. Large equipment is required, millions of tons of ore to be processed. Lots of energy and heat required. Spare parts, equipment maintenance, fluids for the equipment, specialized help to repair the equipment. Also exactly how do they plan on getting the end product back on earth safely without it burning up ?

Am I the only one that thinks this beyond the realm of the possible ?

2

I think that is all you need say right there.
Even if you process and refine off world, unless it is all used for building a stardock etc, it has to come down to earth some time, and unless it can come down by the freight train full for cheap, does not seem feasible?

3

Just to launch the Space Shuttle cost 450 million each time. Think of the cost to just set up the operation.
All the equipment will have to be re-designed or invented to deal with vacuum, radiation and heat/cold cycles.
Then the cost of resupply.

4

Why does it have to come back to Earth? Why not use it for space stations or asteroid bases, which are the only way to work in space: without the gravity penalty.

We’re a very long way from asteroid mining. Maybe as far away as we are from fusion power. And I just did a search for those articles you mentioned. The one I found agrees with both my predictions.

5

I thought of one way to do it. Send a solar-electric thruster spacecraft to the asteroid in question. (greatly reducing the propellant needed).

Redirect it into a course that will collide with the earth. Energy-wise, it would never enter earth orbit, takes too much fuel. Put it on course to collide with a target zone in the wilds of Australia.

Give it a trajectory that puts all the pieces either into the resulting crater or drops fragments off over the Indian ocean.

So in doing so, you’ve basically just created a crater rich in platinum and iridium, and you now just mine it.

6

Is that before or after you apologize for effectively nuking Australia and New Zealand into extinction and the rest of the ensuing cataclysm the follows this large object impact?

7

By the time we learn to figure out how to make an asteroid fall exactly where we want it to, we’ll all be living on Jupiter.

8

People who float ideas for mines aren’t necessarily realistic.

I’ve seen plans for a mine in the far North that seemed simple until one started plugging in numbers.
The idea was standard: get your ore, use steel balls for grinding, then smelt and ship to civilization.

The problems were three

  1. The mine was located far away from anything, and to get there required building a railway to the nearest shore-- and building a dock. And a town, because
  2. The amounts of ore being mined were immense, such that a standard freighter ship would be filled in a day and
  3. the amount of steel balls required for grinding on a daily basis was equal to the total annual output of every company that makes them in Canada.

Needless to say, that plan was sent back to the drawing board.

9

Meteors don’t create nice neat craters full of meteorite.
Meteor Crater in Arizona.

Get yourself a nice 6 mile diameter rock and you’ve just wiped out most of life on earth.

10

Perhaps so, I was thinking maybe if the rock were ‘only’ going a little over escape velocity (7 kps) and you choose the trajectory carefully, maybe you could get a nice solid chunk of metal embedded in the ground. You’d pick a spot away from the water so no tsunami, just maybe a bit of an earthquake and dust cloud for the locals. No big deal.

And yeah, I’ve thought of part 2 of your business model. 'oh noes, hackers have stolen the control codes to our spacecraft! They’ve lined it up for New York City! I hear if you pay them a ransom in bitcoins, they’ll align it somewhere else!"

11

15,658 mph.

That’s gonna leave a mark.

12

Using the cost of the Space Shuttle to start is not a good idea. That was a hideously expensive device in every respect. There are already much cheaper alternatives to loft system into space. However they still remain silly expensive if you want to talk other world mining.

I suspect there is a difficult to problem to address here. Gold is worth about $40M per ton*. There is little chance it would be worth finding an asteroid made of pure gold mining bits of it and returning it to Earth. Now there are metals that are worth more than gold. But in many cases this is because of rarity. There is low but steady demand, and limited supply. So prices are high, but a sudden glut on the market would depress the price. So many even more valuable metals would still not be usefully mined. Diamonds are another such example. Finding an asteroid brimming over with diamonds would not be economical to recover simply because the price of diamonds is artificially maintained by a cartel.

The idea that we would mine and then refine metals in space is fanciful as well. Exactly how we would loft a machine capable of refining useful quantities of any metal from deposits in some asteroid is highly unclear.

Worst of all, asteroids are very unlikely to have undergone any of the geological processes that lead concentrations of minerals. Even if your asteroid contains thousands of tons of gold, it is all likely to be evenly distributed throughout at concentrations that even on the Earth would be considered uneconomic.

  • Space-X will loft mass to low earth orbit for about $4M per ton. If you want that in geosynchronous orbit it is going to cost a lot more. GTO is about $12M per ton, and you still need to burn fuel to circularise the orbit. It is sobering to consider that this means your payload is still costing 1/10th of its weight in gold to send into LEO, or a third of its weight in gold to get into geosynchronous orbit. Space-X suggest Mars is about another halving in payload, so we are getting perilously close to a one-to-one cost. Your spacecraft arriving at the asteroids is probably going to cost its own weight in gold to have got there (not counting the cost of the spacecraft). Now you need to make money. Any propellant you take with you has already cost its own weight in gold, so you are going to need a pretty spiffy way of using it to justify its use.
13

The point to mining asteroids has never been to return the metal to Earth. After all, the Earth has pretty much all the metals it needs. The metal mined is to be used to build things in space, thus avoiding the gravity penalty for lifting metal out of the Earth’s gravity field.

I envision the mining operations to be done with smaller machines, rather than using the sort of brute force methods used on Earth. But how much of that is unreasonable science fiction and how much of that is realistic I don’t know.

14

We know a lot about mining and refining and manufacturing here on earth where there’s gravity, air, water, fossil fuels, and people. In space, not so much. The only short term practical goal for mining asteroids is to find one that has a high concentration of gold or some other valuable element, break it into big chunks somehow, and then drop those or fly them down for recovery. One ton of gold is worth almost $40 million right now, a medium sized asteroid that’s just 10% gold would be worth quadrillions. Even then it’s a challenge to break up the asteroid, get the pieces or the whole thing close to earth, and then bring them down. We can drop reasonable sized pieces with reasonable accuracy onto land or water right now, but even that method would require us to send shielding and other recovery materials into space first and just that part may cost more than the value of the gold that can be recovered. And that pales in comparison to the cost of ever manufacturing anything in space from raw materials. Even if we knew how to do it sending the minimal equipment into space to begin the process in the first place exceeds all of our efforts in space exploration to date. And then what do we have? After we’ve bootstrapped mining, refining, and manufacturing facilities in space what are we going to do with them?

15

For many of the elements that are rare on Earth’s surface, those geological processes that concentrated them concentrated them down to the Earth’s core. In a differentiated asteroid, those same elements would be concentrated into the asteroid’s core. Luckily, most of the asteroids large enough to have differentiated into a core and mantle/crust have been blasted to bits and those pieces of core are floating around naked.

According to this chart the average concentration of gold in the Earth’s crust is 0.0031ppm. According to this PDF, the concentration of gold in meteorites varies, but certain iron meteorites (called “siderites” in the old study) contain up to 10ppm gold. In undifferentiated meteorites, the gold percentage is still much higher than the average for Earth’s depleted crust, with chondrites having from .1 to .37ppm. According to this page, the highest grade gold mines are at around 1 to 3ppm gold.

So asteroids range from “lower concentration than a rich mine but higher than a random handful of Earth’s crust” for stony meteorites to “similar to or greater than the gold concentration for the highest-yield mines” for iron asteroids. Plus other precious metals. Whether or not it would be possible in the short or long term to mine asteroids is questionable, but there is gold in them there floating hills.

16

If you’re going to mine an asteroid, you’re not going to do it for trash minerals like gold. You’re going to go for something valuable like iron.

17

Mining on earth usually consists of 2 or 3 stages.

First, the ore is ground up - hence the previously referenced steel balls. Put soft-ish rocks in a steel drum with a bunch of steel balls and gravity will help pulverize them to a powder. (See any problem yet?) There are rollers and jaw crushers that can break up the bigger bits (is how gravel is made) but nothing says “make mine powder” like heavy steel balls or rods in gravity. Of course, you add water to help with the grinding, and help carry away any heat generated. (See any other problems?)

For gold, this fine powder can then be given the industrial equivalent of “panning”, where stuff is sloshed around on a grooved vibrating table so gravity separates the heavier gold particles from the lighter rock. (Hmm, gravity again… and water)

Next, the separated concentrated gold flakes are dried (something actually much easier in space, if you don’t mind throwing away water) and melted so that gravity (again) separates the slag from gold. Slag of molten rock floats over the molten gold which is much denser.

For other metals, the principles are not much different - except we may add an electroplating step to refine the metal even further.

Given the right equipment, a spinning environment will substitute for gravity - but this requires a much larger piece of equipment. Something like the spinning wheel from 2001, but able to handle hundreds of tons of material pounding away all the time. It would be a major construction. Moving stuff in space with rockets gets very expensive, so I imagine it would be moored to the asteroid being eaten, so material could be moved with electric motors and conveyor belts or such. It would take decades or more to eat through something a few miles in diameter. you only want to send the finished product home where it needs rocket fuel.

Melting stuff is easy - solar reflectors - except how do you contain the result? Perhaps you could have solar cells and run electricity through the ore to melt it - we’re talking, again, some serious size solar cell farm.

In The Moon Is a Harsh Mistress Heinlein describes a linear motor acceleration launcher, an efficient way to “fire” a load toward earth where presumably it would be captured by a local tug craft and guided to where it was needed.

One concept would be to cast ingots in the shape of re-entry craft, and if some of the material burns off during re-entry, so what? Until the scale of metal production is so high we all start worrying about fine particulate metal oxides and nitrides in the atmosphere created by ablation of all those re-entry craft. maybe we could land them in Antarctica or Greenland where they cool off easily.

Basically, at this point we’re still decades and orders of magnitude away from industrial mining in space.

18

You don’t mine asteroids for the same materials or for the same purpose as terrestrial mines. You’re going for aluminum, iron, nickel and such to use to build your space habitats and factories, and carbon and water to synthesize organics from. They’re all so that you don’t have to spend gigabucks moving those same things into space from the Earth’s surface.

If anything you’re doing is going to be easier with gravity, you can land payloads on the Moon as easily as you can do them on Earth, and it’s phenomenally easier to get the refined materials back into space for use.

Gold and platinum will be handy industrial materials that should come out of the process, but no one’s going to mine asteroids for their monetary value alone.

19

I agree. The first asteroid mining will probably be for water, to supply some space based settlement. Rather than haul the stuff up through Earth’s gravity well, why not collect ice and purify it?

20

And you really think that an amount of gold that’s worth quadrillions at today’s prices will have absolutely no effect on the price of gold? There’s not all that much industrial demand for it. When it is useful, you don’t need very much of it because of how thin it can be made. Perhaps it would be used in more things as prices come down, but prices will still come down as there simply won’t be the demand for such a ridiculous amount of gold at today’s prices.