https://en.wikipedia.org/wiki/Alexei_Leonov

https://en.wikipedia.org/wiki/Pavel_Belyayev (some interesting tidbits about the Voskhod 2 mission there)

I'm assuming that huge amounts of methane (or other suitable fuel) and oxygen will be wanted for propellant, though maybe ion propulsion makes that less essential.

The metals that are much more abundant on asteroids than on Earth will be dissolved in the Fe-Ni-Co metal in concentrations varying between 2 ppm for the most abundant (ruthenium) down to 0.05 ppm for the least abundant (rhenium).

While these very low concentrations are still thousands of times larger than the average concentrations on Earth, mining them on asteroids would still require processing thousands of tons of Fe-Ni-Co metal for a few kilograms of precious metals.

On asteroids that have never been melted, the processing could be easier, because most of the precious metals might be present in very small refractory grains dispersed between the grains of Fe-Ni-Co metal and silicate minerals and maybe a cheaper separation method could be found than for the case when they are in solution.

However, the same huge quantities of material need to be processed.

Right now, it is quite certain that this cannot be profitable.

Some time, in a more distant future, we can imagine a technology much more advanced than what we have now, which would enable sending some robots able to perform completely automatically the tasks of building from local materials some huge installations for energy collection, for mining and for extracting the desired elements, so that asteroid mining would require the transport in both directions, between Earth and the mined asteroid, of only very small quantities of materials and equipment.

Even if this is much beyond our current capabilities, it might become a necessity if we would exhaust the exploitable reserves for some of the least abundant elements, dispersing them in junk from which their extraction could become too costly.

On the other hand, there are numerous research projects now trying to replace the use of less abundant elements with the use of more abundant elements, in a lot of applications.

In most cases, it is likely that such substitution attempts are likely to succeed much earlier than the time when we would be able to mine those elements from outside the Earth.

A kilogram of nickel costs ~13$. And nickel makes up a mere 0.0009% of the earth's crust.

It's completely pointless to mine them, with the hope of returning them to Earth. It's also completely pointless to mine them, with the hope of using them in space, for many, many reasons.

1. A spacecraft factory employs thousands of people, and requires hundreds of millions of cubic feet of space.

2. The supply chains that feed a spacecraft factory employ hundreds of thousands of people, and require billions of cubic feet of space.

3. They also require a long tail end of chemical inputs that are not iron and nickel.

The difference between 'We have a space factory that is fed by an asteroid miner and builds more spacecraft/space factories' and 'We have a proof of concept where we spent a billion dollars to mine and refine 20 grams of iron, which we fed to a 3d-metal printer (Never mind all the other consumable inputs into it), to print a little figurine of a rocket' is rather large... And only the latter is achievable in my lifetime.

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.

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

Have you seen the reports on the new data coming out of the mission orbiting Bennu a few days ago? It's looking like small asteroids might be a bit less undifferentiated than we thought those the story isn't changing by that much.

https://www.space.com/asteroid-bennu-formation-history-osiri...

In retrospect I guess it makes sense that if 16 Psyche is a chunk of planetary core, then the sort of impact that created it would likely have turned it molten, and its internal weak gravity may then have caused all the heavy metals to sink to the middle before it cools.

At any rate, gold mining sounds like an easier problem than, say, trying to manufacture stainless steel in space in a way that makes economic sense. (We'll probably get there eventually if we're going to have any kind of real space economy, but bootstrapping is going to be hard.)

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.

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.

Says who? The solar constant on Earth is about 1360 W/m².

Due to the atmosphere, only about 1025 W/m² actually get to the surface.

Mars, just from applying the inverse-square law has an average solar constant of about 589 W/m². Due to the lack of clouds and thin atmosphere, most of that reaches the surface.

So basically you get more than half the energy per unit area than on Earth. Coupled with batteries or power-to-gas and even wind power, I see no major power problem on Mars.

It's not as if there's a lack of usable land for solar arrays or big stacks of batteries on Mars...

But that's besides the physics problems. It's not in any way simple to attach an ion rocket to an asteroid and change its orbit. Today's best ion engines used on probes deliver fractions of a Newton of thrust and requires several kilowatts of power to do so. That's just to accelerate a relatively small spacecraft (Dawn is a bit under 2 tons).

Adjusting the orbit of an asteroid of a non-trivial size with an ion engine would take orders of magnitude more fuel, power, and time than the Dawn probe. Even if by some magic you managed to mine the fuel from the asteroid itself, a technological feat unto itself, you still need power and time.

Power and time are doubly impacted because most asteroids rotate. Unless that axis of rotation is perfectly aligned with the desired trajectory you can only apply thrust for at best half the asteroid's rotation. Rotating is problematic for power generation. If the asteroid miner is solar powered it's panels would be in shadow half the asteroid's rotation so it needs extra mass and complexity for power storage. If it's nuclear powered it's radiators are in continual sunlight for half the asteroid's rotation so additional mass and complexity is needed to rotate them parallel to the bearing of the sun to remain effective.

Even with all that it could take centuries to move an asteroid of any significant size with ion engines. Even if it only took decades that is still a huge initial outlay with zero payback for decades. The only way that's even remotely sane is if you spammed every asteroid with probes to assess their composition and knew you were pulling in the Comstock Lode. But then you depressed the price of all the material and the whole effort barely pays for itself.

I.e. dropping a huge chunk of rare Earths onto Earth will make them not-so-rare and prices will collapse.

Damn, you just outlined a horror novel in space

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).

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!