I didn't hear anything about a return trip from deep space. What would be a suitable size, 2 miles? Can you build something that will not tear itself apart while accelerating and breaking?No....
"Among the goodies to be found on near-earth asteroids are much-sought-after platinum, iron, nickel and sulfur as well as more obscure minerals that make excellent semi-conductors.
The equipment could also harvest water, which scientists believe holds the key to building propellants that will allow deep space exploration."
The purpose of mining to bring things back to earth is mineral mining. Water mining is to extend their travels further into space. in other words... they're not willing to start out across the desert until they have some oases to stop at
The heavy things are going to be gently lowered, right? The moon says that doesn't always happen. Wouldn't we have a better chance in using our existing energy supply to dig into this earth and exploit it as far as possible. Ie tap the heat from the lava under Yellowstone that not only powers North America it also cools it just enough that the explosion is averted
There is also the pushing in the opposite direction each and every time you land or leave the placeIf you took enough of it away, you would change its mass and would likely change how it reacts to gravatational fields. I am not sure how much you would have to take to have a significant effect.