On Tue, 23 Oct 2007 08:26:08 -0700, Hop David wrote:

Michael Turner wrote:

I don't think hysteria is the right word. Large payloads would be harder
to control and a tiny error could change aerobraking to lithobraking. I
would call it "Deep Impact sensible fear". Again, I advocate payload
mass ceilings well below Tunguska size.

I'm still curious whether there might be a way to increase payload
mass and reduce terrestrial hazards by delivering asteroid-derived
payloads to Earth orbit in the form of large spherical shells of
material. As I've probably mentioned in this forum before, I was once
asked to look at an RFP for "demisable tanks" -- i.e., satellite fuel
tanks guaranteed to burn up on reentry. That inquiry went nowhere,
AFAIK. Which underscores a point: maybe you don't need ablative
shielding or heat-soaking tiles to bring stuff down intact. After
all, LEO satellite fuel tanks have been found in desert regions with
little more than scorch marks and dents from hitting the ground (at a
relatively low terminal velocity, obviously.) Maybe that's a bug for
satellite fuel tanks, but it's arguably a feature if you're interested
in aerobraking or aerocapture of resources delivered from cislunar or
interplanetary space.

Now let's say you want to deliver a lot of asteroid-mined metal to an
L-point, using aerobraking in the Earth's atmosphere. Blow the metal
up into a big, relatively thin-walled sphere. Maybe store some
asteroid-derived volatiles inside, which would coat the interior as
they freeze down to the point where you get into equilibrium with
sublimation losses.

Asteroid mined metal would come from a metallic asteroid which is
unlikely to have volatiles.

Actually, the stony chondrites are typically 10% metal or so, and metal
in a much more easily recovered form - the stuff can be magnetically
seperated from finely crushed rock, and there's reason to believe that
lots of stony chondrites have pre-crushed surfaces. If not, well, we
know how to make rock-crushers.

Metal asteroids, seem to be solid metal. Solid nickel steel, rather
like the stuff battleships used to be made out of. This poses certain
obvious problems for any wannabe asteroid-miner...


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