[cftm]

I would argue that actually it does - in order to bring the world commodity market crashing, as is suggested by the article, it requires iron coming down to earth and bringing mass down the gravity well, safely, requires either a great deal of energy or something like a space elevator.

Under the assumption that no space elevator exists, then this argument is spot on. The iron outside of earth's gravity well would be cheap for building in space, the iron on earth would be "cheap" for building on earth.

Commodity movement in either direction wouldn't make sense, so two distinct markets for iron would exist.

[candiodari]

Gravity is a conservative force, so bringing the metal down with a space elevator will release exactly the same amount of energy as just crashing it into the surface. The rate may be different (though how would you dissipate that energy ? Note that there is essentially zero thermal contact with the athmosphere or anything else on a space elevator except at the bottom 20km or so)

That's one of the reasons why space miners are proposing to just crash the asteroids into desert areas.

[hedora]

Put another way, we should use a space elevator and electric generator to slow useful commodities down as they fall from space to earth.

If only rockets had regenerative brakes!

[transposed]

I thought of a pulley for some reason, and on the off chance it wasn't a completely ridiculous idea googled it: https://en.wikipedia.org/wiki/Lunar_space_elevator#Cross-Sec...

[M_Grey]

Grimaces

As though deserts were somehow magical "dead zones" we could afford to lose. On the other hand, we might reach a point where controlled ET impacts could be the only near-term way to generate the net cooling we need to survive climate change. Wouldn't that be a treat for a method of geoengineering!

A more realistic idea would be a Lunar base, probably automated. We crash asteroids into Luna, break them and process them there, then either rail-gun them into Earth orbit for an elevator grab, or a controlled descent into water.

That minimizes the Delta-v all the way, while still making concessions to a realistic need to process this stuff before "importing" it... i.e. crashing or "snatching" it.

[candiodari]

Why is that necessary ? We can control the speed of asteroid impacts without crashing them into the Moon.

Nobody (I hope) is suggesting just putting an asteroid on a crash course with earth. Rather the idea is to bring the asteroids in an orbit around the earth and/or the moon and then leave them there, biting off small chunks and deorbiting them one at a time. So what would impact would be something like 10-100 tons at a time, in 10 tons-at-a-time chunks, maybe even less (enough weight so they survive reentry, or maybe we package them to "fly"/crashland like the space shuttle)

So capturing an asteroid refers to moving them into a parking orbit around earth, nothing more.

And don't worry. Earth orbit is an unbelievably big place. If you don't want to be at special places (like geosync orbit, or just as close as possible), there is no shortage of space whatsoever.

[M_Grey]

Why take the risk? If anything goes wrong you either lose the asteroid with unpredictable results, or worse, it crashes uncontrollably. With the moon, you really don't have to care. It's also a useful "base" for any other exploration or industry we'd care to have, without having to overcome the Delta-v of something like Mars.

[candiodari]

I don't think you quite realize just how much energy we're talking about here. Most asteroids have enough mass, which at a realistic speed could shatter the moon.

If we shatter the moon, well, let's put it this we : at that point we're fucked. As in close to end of human race fucked. There will be worldwide constant meteor showers for years, which will impact with enough force to penetrate nuclear bunkers. Oceans will boil for years.

[CalChris]

Energy is conserved. Forces are reacted.

[Houshalter]

For iron maybe. Some metals are worth orders of magnitude more relative to their weight. Which would maybe make this economical. The article didn't elaborate much on it's composition of rarer metals though.

Once an industry exists transporting commodities to Earth, it will improve over time. Maybe eventually it will be economical for iron. Or maybe it could justify the cost of a space elevator.