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

Anders Sandberg anders at aleph.se
Sun Feb 17 12:12:31 UTC 2013

On 17/02/2013 03:10, spike wrote:
> With that information, we might be able to estimate the momentum 
> transfer to the meteoroid, which I fear might be disappointingly 
> small. At those speeds I doubt it would break up the rock, but rather 
> would punch a clean cone-shaped hole. Of course our intuitions fail 
> for we have little or no experience in real life with impacts at 20 
> km/sec. I would like to see a good simulation of it however.

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 
asteroid. 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.

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,
Future of Humanity Institute
Oxford Martin School
Faculty of Philosophy
Oxford University

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