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It seems that most mining proposals involve landing on the body (blasting pieces of asteroids up from the surface for measurement has been proposed), would it be practical to exploit the volatile nature of cometary material (and availability of solar energy) to extract cometary material without having to land on the comet?

Scooping from the ion tail might be more practical (dust might require a more robust scoop) and desirable (comets are more special for their volatile content).

The cost of developing specialized comet mining technology (not just the scoop but also the navigation) would be spread over a smaller number of uses, so it is probably unlikely to be economically practical. However, this seemed like an interesting question.

(One of my concerns with landing on a comet was the perception of greater danger near Earth orbit--when the comet if fully active--than an asteroid.)

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    The advantage of asteroid mining is that there's very little mining involved; almost all of the resources are exposed, free to take. It's "bringing them home" that's the problem.

    What is most expensive in space? Air can be reused. Solar power is abundant as long as you don't fly too far away. The resources are there free for picking. What is most expensive is the ΔV.

    Blasting, picking, splitting asteroids, that's all baby level difficulty compared to accelerating the acquired material to speeds at which it will reach its destination within this decade or even century. Transport is the most significant cost in any space-based economy.

    Now, what would you pick, chasing a comet on elliptic orbit running far beyond orbit of Pluto, average ΔV comparable to that required to reach Saturn, struggling with not only slowing them down enough to get them to Earth but curving their orbit to make it circular instead of elliptic, or just bundle a bunch of mined material, strap it to a solar sail and gradually tack against the Sun until they reach their destination - then drop them on a desert or leave for Earth orbital manufacturing, and return the same "solar barque" using the same solar sail back to the asteroid belt where another batch of mined resources awaits, all that practically for free?

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    • $\begingroup$For a scooping mining vehicle, it might be possible to design the scoop to contribute to solar sail (and perhaps aerobraking?) acceleration. However, the consensus here is that comets are not worth the effort despite volatile richness (like mining the high-grade iron ore of Earth's core!).$\endgroup$
      – user56
      CommentedJul 25, 2013 at 15:10
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    Comets are typically on much higher energy trajectories compared to the asteroids looked at for mining. I suspect that that alone would make them un-economic.

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    • $\begingroup$So all methods of mining comets would be uneconomical. Sad because of their volatile richness. (Really wacky thought: could "aerobraking" [taking the coma as an atmosphere] be useful?)$\endgroup$
      – user56
      CommentedJul 25, 2013 at 14:53
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      $\begingroup$@Paul: Yes, aerobraking would be useful but only in the last phase. You need to be close enough and slow enough for it to be useful, and comets don't have enough gravity to provide useful distances through "atmosphere" for aerobraking. BTW, the mining might become economical once we spread out further from Earth. Think extrasolar travel "refueling station" beyond orbit of Pluto utilizing comets.$\endgroup$
      – SF.
      CommentedJul 28, 2013 at 9:33
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    Logistically it is not rewarding to capture, debris from an comets tail. Compare it to placing a net in a flood swollen river, sure you can capture lots of stuff, and the only energy is casting and retrieving the net.

    But the goal of mining is generally to acquire specific resources for specific needs. All mining on earth is focused in specific areas known or believed to harbor larger than average amounts of specific resources. It is reasonable to expect similar when mining resources in space.

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    • $\begingroup$If one was scooping from the ion tail (volatiles) would one not being effectively mining a hydrogen, oxygen, and carbon "ore" (mostly methane and water)? Also, aren't asteroid surfaces relatively homogeneous and other than type M not of "ore quality" (though mountain-removing copper mines indicate low grade ores can be profitably mined)?$\endgroup$
      – user56
      CommentedJul 25, 2013 at 14:47
    • $\begingroup$As Erik and SF, point out, they are moving fast. Unless you are moving fast in the same direction, your going to have to spend a lot energy getting to them. Probably more then you gain. It is a not uncommon theme in SF to nudge comets (and/or asteroids) into collision or orbital trajectories for a planet. This has been suggested as well for terraforming Mars, bombing the planet to increase the atmosphere.$\endgroup$
      – James Jenkins
      CommentedJul 25, 2013 at 23:03