On 6/15/07, Tom McCabe <[EMAIL PROTECTED]> wrote:
How exactly do you control a megaton-size hunk of metal flying through the air at 10,000+ m/s?
Clarifying this point on speed, in my view the asteroid would not hit Earth directly. Instead it would first make aerobrake maneuvers to enter Earth orbit and then to de-orbit. So, as far as I can see, its speed would be less-than orbital - <7,900 m/s . Still, a very high speed, granted.
The reason most metallic meteors survive is precisely because they are small- the drag deceleration exerted on an object is roughly inversely proportional to its size, because inertia goes up with r^3 while surface area (and hence drag) only goes up with r^2.
(...) Okay, that's a sound argument. In that case, the alternatives seems to be: (a) Cutting small shunks of a big metallic asteroid and then making controlled crashes of those. (This kind of reduces to the drop capsule method, but in a cruder - and perhaps cheaper - version.) (b) Or, for starts, target only tiny asteroids a few meters in length - the so called "meteoroids". Indeed I remember a project for moving meteoroids with solar sails (http://alglobus.net/NASAwork/papers/AsterAnts/paper.html - though in the case they were meant for processing in Earth orbit.) I wonder though if the economics of scale won't favor a less "distributed" model... As materials science progresses, perhaps there will be an alternative (c): making the mass-to-surface ratio of a larger asteroid go down artificially, by instanlling an inflatable, heat--and-friction resistant "shield" around the asteroid. An "asteroid parachute", so to speak. But that seems far more speculative than (a) and (b)... In any case, I think that the belief that asteroid mining is of use only for space construction due to energetics simply does not hold. There are ways around that - even if they are not so cool like crashing asteroids a hundred meters wide. :) ----- This list is sponsored by AGIRI: http://www.agiri.org/email To unsubscribe or change your options, please go to: http://v2.listbox.com/member/?member_id=4007604&user_secret=7d7fb4d8
