There is a lot of talk in the media about deflecting asteroids away from the Earth in order to avoid catastrophic impact. This is often cited as a reason to carry out further research on the composition and structure of asteroids.
Whilst much of this talk is about the crude deflection of the path of an asteroid - what if you could more precisely control an asteroid - even a smaller one? All of a sudden I see this technology in human hands as a greater threat to Earth than if asteroid impacts were left to chance. There is a positive and a negative. The positive is that you could bring an asteroid into an orbit close to the Earth so that it could be mined. The negative is that an asteroid is the biggest weapon of mass destruction ever invented! The nation that masters the control of asteroids can control the Earth - it'll make nukes look like toys.
Looking at mining asteroids I start to think of the old tektite papers written by author's such as O'Keefe. These transfer tektites from the moon, along a very narrow corridor, to a precise place on Earth. Not very realistic for an impact event, but presumably feasible for an accurately aimed 'gun'. Having an asteroid in Earth orbit doesn't seem like a wise idea. Humans have a tendency to make mistakes and having an asteroid impact the Earth would be a bit of a big mistake. You'd never live that one down. To me it makes sense to have the asteroid orbit the moon. It could then be mined and moved to the Earth in smaller pieces.
So why am I thinking about this? Well after mining, the metals would need to be delivered to Earth. Tektites re-entered the atmosphere, so what can we learn from tektites? Firstly metal and glass behave very differently when passing through the atmosphere and this needs to be taken into account. Looking at Philippinites it would seem that a rotating perfect sphere may be an efficient way of delivering a material from space to the Earth's surface. The re-entry heat is evenly distributed, a perfect sphere that was already rotating would probably struggle to find a stable orientation, thus reducing ablation and loss of the precious mined material. The material could be mined by melting the asteroid and producing spheres from the melt. These small spheres of mined material could be aimed towards a desolate desert area or shallow water area for recovery with large magnets.
I think mining asteroids will happen in the future. It'll be interesting to see if tektite research is used. It will also be interesting to see the mining laws and how Earth's population will be protected from accidents.