Indeed, the mind bounds ahead with such endeavors approaching - what don't we just send a hundred micro-bots designed to harvest raw materials sufficiently well enough to construct on-sight new micro-bots, designed to harvest raw materials, and so on. Seems real easy, the more I think of it, to capture a comet and do something with it. Like, within the next 100 years or so, 'easy', that is - as in, well .. maybe getting easier and easier. Rockets and robots, babies, its all we'll need to get there and do stuff.