It’s probably just a coincidence, but I find it interesting that one of Elon Musk’s companies (Tesla) has a huge demand for nickel and another one of Elon Musk’s companies (SpaceX) won a contract with NASA to explore 16 Psyche, an asteroid essentially made of nickel, and is working on a completely reusable rocket...

The problems with this theory (and with asteroid mining in general) is that it is extremely unlikely that anything you mine in space will be economical to get back down. Most people forget that it costs almost as much delta-V to get down as it does to get up in the first place -- if something was not worth the cost to launch it into space it is unlikely to be worth landing.

The problem with asteroid mining is that it faces one of the most expensive chicken-egg problems it is possible to imagine. Without industry in space there is no need for the bulk gathering of raw materials, but without the bulk raw materials it is not worth developing industrial processes for space and a zero-g environment.

> Most people forget that it costs almost as much delta-V to get down as it does to get up in the first place

Doesn't that depend on how you get it down.

Metal foam dropped from orbit into an ocean would float, you could have a retrieval vessel go pick it up.

Metal anything dropped from orbit at the speeds we are talking about would either burn up in the atmosphere or else hit the ocean surface and become lots of small chunks of something that is now sinking to the ocean floor. You need to shed a huge amount of delta-V just to get to the point where the landing site is described using any term other than 'impact crater.' Most of the mechanisms for dumping this energy tend to be a bit tricky to pull off and I am not sure, but there might be an upper limit after which ablation stops being a viable option.

If the foam ball you drop is large enough losses from ablation wouldn't be a big deal.

You can certainly get the speed down enough so that the words impact crater wouldn't be in the report, also you smack them into oceans not land (though smacking them into the desert would be an option I guess if you could shed enough speed).

For a 10 meter sphere of nickel foam with a density of 2000kg/m3 (so about 60% 'air' by volume) it's ~2000 miles per hour[1].

http://hyperphysics.phy-astr.gsu.edu/hbase/airfri2.html#c5

Fast but not insurmountable.

That sphere would be ~8000 tonnes of pure nickel minus ablative losses (which would reduce the impact speed).

Of course you'd want the density to be below 1000KG/m3 or it'd sink.

So a 10m sphere at 850kg/m3 would have a terminal velocity of ~1300 miles per hour - or about mach 2 and you'd be picking up about 3500 tonnes of pure nickel bobbing about.

I'd quite like to see that actually (from a good distance away).

3.4 million kg, traveling at 600 m/sec, and you think you would end up with a big ball of floating nickle? Okay....

Not a physicist, but my thinking would lead me to say that when this ball hits the water (after having already been heated a bit by ablation on the way down) it is going to compress into a pancake. Assuming the energy released at impact does not break the ball into lots of smaller pieces, the energy of the impact is going to vaporize a lot of water and melt a lot of nickle. I think what you are going to end up with after the large impact event is a compressed blob of nickle that is now rapidly sinking to the floor of the ocean.

We already know what happens to big chunks of metal from outer space that impact the surface of the earth, it tends not to be pretty. Oh yeah, and try to convince any country on the planet to let you drop your giant ball of awe-inspiring kinetic energy on a path that happens to cross over them. Not. Going. To. Happen.

When you have the ability to make it into foam in space, why not use that to make lifting bodies out of it, and let them glide down, instead of crashing like a stone?

Stop thinking in terms of projectiles. Just because the Space Shuttle came down like brick in a controlled crash doesn't mean there are no other ways to do this. Without the need for ablation, btw!

The lifting body idea is interesting, shape it so that it's got a flat side that self orientates (basically like an uncontrolled shuttle) and 'glide' (if you can call mach 1 gliding) it in, neat. You'd want to be very sure it was going to come down where you expected or you might affect rental prices.

I think one could aim for a https://en.wikipedia.org/wiki/Landing_footprint in the seas near the coastline without much trouble.

You can't 'glide down' from orbit. You need to dump your delta-V somewhere. Stop thinking of orbit as though this chunk of metal is suspended from some big balloon out there. _Everything_ in space is moving, 0.0% if it is moving at the right speed and direction to enter the atmosphere and soft land without a lot of external assistance.

I know that. I've written elsewhere how I imagine that. With modular thrusters which initiate the deorbiting, detaching when it is en route. Could be autonomous, could be 'tugboats' with human crew, I don't care. Doesn't really matter, as long as the lifting body of refined raw materials has the right weight to surface ratio, and therefore rarely even peaks above 400°C for a short time.

Meteorites that arrive on the Earth from outer space are most certainly a thing that happens sometimes, that's wear all our existing Mars rocks come from for instance. Whether something survives reentry depends on a lot of factors including the size of the object, the angle of re-entry, its composition, etc.

The thing is... we could outsource much of our current heavy- or other polluting industries 'up there', to finally remake the Planet of the Apes into the Garden of Eden, like it should be.

Wouldn't that be a nice goal?

Nickel is so common and cheap it is unlikely to be profitable to ship it to Earth. It's more likely that nickel and iron would be used as construction materials in space, to make satellites and stations cheaper by reducing the launch mass required.

The profitable stuff to ship to Earth would be platinum-group metals, which have values in the tens of thousands of dollars per kilogram. But those require much more capital investment, as you need to get to farther-off asteroids and do more intensive in-space refining.

I was just thinking about posting a comment about 16 psyche... I hadn't heard about the exploration mission, that should be pretty interesting. Iirc, 16 psyche is thought to possibly be a fragment of a planetary core and so it might contain a completely different proportion of metals than what you might find on the Earth's surface.

Mining an asteroid far away and then spend fuel to shuttle material from it to GEO or Moon seems rather uneconomical.

I would suggest finding a small enough (a few dozen kilotons) space rock made of a valuable / precious metal, and brought to it a large solar array and an ion gun. Metals make good ion gun fuel. Slowing the asteroid down to fall to an elliptic orbit around Earth, and then righting the orbit to put it on GEO or drop it to.the Moon seems doable with a rather limited use of mass. Technology permitting, a large enough solar sail could help slow down / steer the rock on its way towards Earth (or Moon, or Mars).

The problem is, a single accident or mistake can put the entire earth’s population at risk. It seems highly unlikely we’d bring big rocks back to earth.

The fuel cost to shuttle the materials back would be fairly negligible. The main cost to getting anything into space at the moment is the initial launch to LEO. (This equation changes if you're not actually launching your mining vessel from the earth's surface)

I suspect the value in asteroid mining will be for building things in space that will remain in space, due to the high cost of trying to launch material out of Earth's gravity well.

One theory in favor of space mining is that (and I personally believe this is wishful thinking) one asteroid might have a lot of titanium in it that would be worth trillions (and probably crash the titanium market).

But again, personally I think that's wishful thinking to try and get investors to push money into a space mining company. Based on nothing whatsoever, I believe most asteroids will be made out of fairly worthless materials.

The only substances that might have a chance to be profitably mined from asteroids are those that on Earth are concentrated at depths too great to be accessible and they are depleted at the Earth surface by thousands of times, or at least hundreds of times.

These elements are: 1. The 6 platinum-group elements 2. Rhenium and gold 3. Tellurium, selenium and germanium

Besides these elements, only indium might be profitable.

Indium is depleted only a little at the Earth surface, but its original abundance is very low, so additional extra-terrestrial sources could be useful.

From all the rare elements, indium is the one for which there are no good substitutes in its main applications.

Indium is completely irreplaceable in the best lighting sources (i.e. LEDs), in the best power semiconductor devices (with gallium nitride) and in the best transparent conductors (required e.g. for computer displays).

For transparent conductors there are great efforts to find a substitute and those might eventually be successful. Nevertheless until now all the alternatives have various disadvantages.

I thought the biggest cost of titanium today was extracting from the oxide, not the ore itself?

2016 prices: TiO2 $150/ton; metal $3750/ton — https://www.metalary.com/titanium-price/

Titanium ore is cheap, and is produced at a large enough scale the market wouldn't crash. The expensive metals are platinum-group metals (iridium, osmium, rhenium, &c), which go for tens of thousands of dollars per kilo.