Logistics of how to mine an asteroid

Question

How would one go about mining an asteroid in a broad sense?

This question not in the mining itself, but location of the mining.

Say you have located an asteroid in that would like to mine. Which of the following do you do (the following are possible methods feel free to come with others)?

• Move the asteroid toward earth by either with a mass driver or gentle nudge so it can be refined later. Mine and refine in orbit or surface of earth.
• Take your refinery with you and refine the asteroid as it you mine it either sending the refined materials back to earth.
• Cut the asteroid into chunks and leave it behind for further refinement

Basic assumptions:

• Asteroid mining is economical -- economic basis is reduction of materials on earth
• Asteroid mining is based on objects a far away as Mars
• Technological hurdles: Fusion drives are in use, there is an independent colony on the moon, issues such as low gravity's effects on the human body have been resolved

Answer 1

TL:DR; you won't, because it won't be worth the effort. As soon as asteroid mining becomes a practical way of providing resources for Earth, the value of metals will plummet.

Someone else will do the mining, and will probably sell you the raw metals on the cheap.

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So, this is probably part economics, part safety and part orbital mechanics, and these things all kinda blur together.

Moving a refinery around the asteroid belt is energetically unfavourable, especially for a very large and heavy refinery. You have to inject yourself into a transfer orbit, trade off journey time for the amount of oomph you're prepared to impart to your refinery, wait a bit, and then rendezvous with the next prospect by matching orbits. Similarly, moving around large and heavy asteroids is going to be very challenging without the aid of large nuclear motors and lots of patience, and when you do start them moving they become a potentially serious hazard to all sorts of people and places, which limits where you might be allowed to move them to. Forget flying a billion tonnes of rock back to Mars or Earth... thats about as likely as you being allowed to drive a nuclear excavation charge through the centre of a major city.

Moving small rocks around is easier, but every single time you need to inject into a transfer orbit, coast, rendezvous, boost the rock into its own transfer orbit (probably with a suitable braking motor) and so on. Lots of hassle, lots of time, lots of rocks flying around at high speeds.

What you really want to do, then, is to claim the biggest unclaimed asteroid you can, and set up your refinery there, and suck it dry.

16 Psyche is one of the most massive bodies in the asteroid belt, weighing in at about 25 quadrillion tonnes. The surface of 16 Psyche seems to be about 90% metal, probably mostly nickel and iron, but no doubt there will be other heavy metals there. If the asteroid is as much as 1% iron by mass, it would have 250 trillion tonnes of iron. Current worldwide production of steel is under 2 billion tonnes a year, to give you some idea of the scale involved here (you'll need carbon to make the steel and 16 Psyche might not have enough, but there are plenty of carbonaceous asteroids out there you can mine for that). It could have more than a million years worth of iron and nickel, plus all sorts of "rare" metals (watch the value of gold and platinum crash). Other asteroids will provide vast quantities of aluminium and magnesium if 16 Psyche doesn't have enough of it.

What this probably means is that a few large asteroids like 16 Psyche will provide pretty much all the metal and mineral resources a growing civilisation could want, and even they represent a fraction of the belt's total reserves. The value of metal will just plummet, so there's simply no reason to worry about mining anything else. Just ask the people who are grinding up one of the big rocks to punt a nice of crude metal your way, probably with a fairly dumb robot tug attached. Probably cheap, and certainly a lot less hassle than faffing around with mining it all yourself.

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There is an exception to be made for consumable resources. Ice will become quite a valuable thing, because it is useful for habitats and life support, cooling, shielding, as a source of deuterium for fusion and as reaction mass for all manner of rockets.

Ice of course needs much less fancy refining, assuming you can find a relatively pure source. You'll be wanting to fly it back to the places it will be used, probably by setting up a little deuterium refinery and nuclear rocket or mass driver to get it going. Flying around big masses in the inner system is something that is likely to be highly regulated for safety reasons, so it won't be the purview of little wildcat mining operations. If you try pointing something dinosaur-killer sized at Earth you're going to get a lot of Loudness, Lawyers and Lasers, and if you're lucky they'll be in that order.

Leave the ice-pushing to the grownups.

Answer 2

I think the answer is a mixture of your first two options. The decision being made by economics

For asteroids with low but sufficient economic value, and low mass, the solution would be to alter the rock's velocity, and therefore orbital path, so it rendezvoused with the refinery. Assuming, for the sake of argument, that Mars and the Moon had major refineries facilities. A minimum energy path could be computed that brings the rock to one of either location from any coordinate along the asteroid belt. The length of the path might be years in some cases.

High mass asteroids might be regarded as too dangerous to deorbit towards our planets in case a malfunction repeats the events of the Yucatan that wiped out the dinosaurs. So for asteroids with high economic value and high mass, one could imagine a refinery traveling along the asteroid belt that broke up the asteroid, refining it down to useful materials. This big refinery would be relatively costly to accelerate and decelerate so it would only move to a new location once the local asteroid belt had been depleted of economic value.

The long path solution would likely create a futures market for deorbiting rocks based on estimates of content during the assay. This market would buy the rights of exploitation from the deorbiting agent -- might be an independent rock hound -- letting the belter get paid immediately for their work and they, the future market participant, gets paid when the rock is refined and is content sold on the open market.

This would also probably give rise to rock piracy or rock-jacking by altering the path of a deorbiting rock and redirecting it to a black-market refinery.

Answer 3

I would say the best option to go with is the Take your refinery with you and refine the asteroid as it you mine it, approach. A lot of asteroid mining in artworks and media depict asteroid mining as something like this. Finding a rock, digging a hole, working your way out and possibly building a nice habitat inside while you work. Now, this may work fine for the larger rocks but I haven't seen anyone plans for dealing with debris. Digging into a big rock inevitably means turning one big rock into a lot of small ones and that raises quite a few complications. You need to keep all that debris contained because A) You could lose everything you invested so much in mining out in the first place, which is bad, and B) You risk sending thousands of tiny relativistic bullets lose in a populated solar system, which is worse. So I like to imagine a lot of rockhopper minging vessels looking something like this. A kind of structure that can encircle the asteroid, have unfolding netting to keep debris contained, process all the material like a mobile refinery, and once every tiny pebble has been ground up and ran through the sieve, move onto the next big rock. This eliminates the debris problem, saves money on rocket fuel and construction, and any leftover rock and dirt can be recycled into farming soil. Waste not, want not.