prestonbarrows wrote:You've got it backwards.
Whatever method is used:
-- to go asteroid, attach device to send to earth in a controlled way (so it won't crash, and won't burn up -- very dangerous and improbable)
-- go to the asteroid, mine ore, return that
-- go to asteroid, mine ore, use for construction in space
and perhaps other possibilities.
Space mining might make sense for very esoteric things (helium3 on the moon, or some scarce metal that occurs in pure form on an asteroid); but terrestrial ores are $/ton; current prices for space transport for any purpose in any direction are many many many orders of magnitude more.
For example, for much of USA history, rocks that were 60% iron could be scooped right from the Mesabi range and put directly into a railroad car and from there into blast furnace. Tons and tons of iron (an entire mountain range's worth) was mined that way.
But there are no rail lines to space, and it's a longer journey.
From Wikipedia: "The plan has been met with skepticism by some scientists who do not see it as cost-effective, even though platinum and gold are worth nearly £35 per gram ($1,600 per ounce). An upcoming NASA mission (OSIRIS-REx) to return just 60g (two ounces) of material from an asteroid to Earth will cost about $1 billion USD"
For now, space mining is more of an irrational case of wishful thinking than even... fusion.