[ExI] (NASA.gov) NASA to chronicle close Earth flyby of asteroid (fwd)

spike spike66 at att.net
Sun Feb 17 18:01:07 UTC 2013

>... On Behalf Of Anders Sandberg

On 17/02/2013 03:10, spike wrote:
>> ... At those speeds I doubt it would break up the rock, but rather 
> would punch a clean cone-shaped hole...

>...There was a fair amount of that at the planetary defence conference I
attended two years back. Not so much fluid dynamics as granular media.  
If I understood the conclusions right, rubble piles are pretty good at
absorbing impacts - punching straight through requires a fairly thin

Ja that's what I realized when I started thinking about this again.  I was
visualizing a 10 ton class asteroid like the one that nuked the commies
Wednesday, so a rock perhaps a meter or two thick.  In retrospect I don't
think that conic-hole notion is correct at all, even if the momentum as an
escape path out the back.  I don't know what this high speed impact would

>... But everything depends in horrendously complex ways on exactly how the
rubble is organized, and this is simply not know. I think this was
recognized as *the* important unknown at the conference...

Ja, I cheerfully and abashedly retract my previous speculations.  {8^D

>...A bigger problem is actually getting whatever your payload is to the
NEO. If you detect it when it is within the Moon's orbit, typical spacecraft
take days  to go that kind of distance. NEOs can have huge delta-v excesses
compared to what we normally launch. So a good near/instant shield system
better have some very fast response units spread out in the volume. --
Anders Sandberg,

In evolution we have a notion known as preadaptation, an example being
feathers evolving for thermal control and attracting chicks, but turn out to
be great for flying.  We have pre-adapted anti-nuclear missile technology,
but it might be usable for breaking up incoming 10-ton class meteors.  THAAD
missiles and PAC3 missiles might be adaptable for end-game interception of
meteors, and they would already be stationed around population centers,
ready to fire on short notice.  

Reasoning: a previous post speculated that breaking up a meteor may be worse
than having it reenter as one piece, but this I refute.   Do consider that
the probability of a meteorite landing in a populated area is very small.
What injured all those commies was actually the sonic boom shattering glass
windows, and I can imagine it became very uncomfortable in those homes and
offices with the -10 degree temperatures which Russia provides in abundance
in February.  If we break up the rock into a thousand pieces even if just
before reentry, each fragment has its own ballistic coefficient.  The sonic
boom characteristics would be greatly mitigated.  This doesn't even require
a high-powered digital sim to verify: a sonic boom is a function of the
mass, cross sectional area and speed of the object.    

One big rock makes one huge shock wave, as we saw.  When fighter jet passes
by at supersonic speeds you know what happens.  When a bullet passes by at
the same speed, nothing happens.  A re-entering rubble pile makes a bunch of
smaller shock waves, some of which may interfere destructively with each
other, which might keep the hapless proles' windows intact and the Russian
winter outdoors where it belongs.


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