Recently, I came across the concept of the Gravity Tractor for the first time. And I was intrigued.
A Gravity Tractor, as I understand it, is a concept for a small unmaned spacecraft which is launched into space, and sent to an asteroid. It rotates around it to change the direction of the asteroid. The major benefits is it's easy- no fancy rockets, no need for theoretical solar sails, no need to have any real understanding of the asteroids make up. The major downside is it's slow.
Now, every time I've come across this idea, people talk about using it to redirect an asteroid from impacting the Earth. This runs into the problem 'Can it redirect the asteroid in time?' since a Gravity Tractor is so slow.
But what about non-time-critical applications? Like mining asteroids?
Mining asteroids is hard because they're so far away- we'd need a very large ship to go all the way out to the asteroid belt and mine it and send resources back- and it would probably need to be manned.
But if those asteroids could be towed back to Earth orbit, suddenly mining them becomes a lot easier.
So- could a Gravity Tractor realistically be used to relocate mine-able asteroids closer to Earth? What size asteroids? What size ship would be needed? And what sort of time frame would it take?