Why wouldn’t the original capturing device be made to collect samples and return to earth –something like escape pods? Sending astronauts must have a sophisticated purpose that requires judgment a machine cannot yet make
Sample return missions are pretty mundane, actually, especially when it comes to near Earth asteroids. NASA's basically written that off as "too easy" and assumes that other agencies and/or companies will try to do that anyway (DSI and Planetary Resources are preparing to do exactly that eventually). The whole point of capturing the asteroid is that you can put it in orbit of the moon where human explorers will be able to inspect it up close in a relatively cheap and short-term mission without having to break it apart or risk contaminating the samples. Also, that asteroid would inevitably be broken down for raw materials when they were done studying it; NASA probably figures they can find a good metallic asteroid with an abundance of platinum group metals and maybe kick off the start of a deep space gold rush.
Some of the space pundits are questioning NASA's mission as a pointless excuse to justify SLS/Orion, as there's no reason to send astronauts all the way to the moon merely to take a sample of an asteroid by hand. As the Mars rovers show, we can do a vast amount of science and manipulation without a manned presence, especially in the case of a very small target where a human's speed and agility are hardly necessary. In this case the mission profile seems more political than technical. Earlier in the asteroid program NASA was ignoring any asteroid candidates below about 500 meters as being unworthy of a visit. Those plans were aimed at sending a human deep-space mission to an asteroid in-situ, and nobody would spend a couple billion dollars to see an Orion fly for a month to pull up to a rock about the same size as an Orion. Then they apparently ruled out such a mission for budget and schedule reasons, so the goal would have to be less ambitious. Capturing a much smaller asteroid (perhaps 5 meters diameter instead of 500) and bringing it closer to us fit the bill, and that makes it easier to get an Orion mission to it. But if they brought it into Earth orbit (which wouldn't be an unworkable delta-V requirement) they could visit it with a Soyuz or Dragon on a Falcon v1.1, which doesn't justify building the SLS or the Orion. A remote sampling of the asteroid likewise fails to justify the manned spending. This seems to be a case where the mission exists to justify the program and the mission requirements are written to justify the type of equipment we're building. It will probably fall by the wayside as soon as they find a better justification for the same equipment. What they probably want to architect is having the Orion hook up with a manned asteroid processing facility in lunar orbit or L5, but that probably looked too expensive, long term, and easy to cancel.
Cables are going to have to be used. Astrnauts have to have them as guide ropes, or to brace themselves so as to apply force without knocking themselves into space. Cables also cut up the Kursk submarine you know. A solid nickel-iron slug cut be cut similarly. But here is the capper. Many asteroids--all of them probably--rotate/tumble. What cutting an asteroid does is turn it into a bola. Release one end of it at a certain time when facing a certain direction, and you convert rotational forces into translational ones--reducing engine/fuel costs. Call it David's sling
I love the idea of the ‘fill in the blank’ mining space race; after they master sample size retrievals, the fun will be in capturing their full claims and control landing them to earth