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

david deimtee at optusnet.com.au
Sun Feb 17 03:45:20 UTC 2013

On Sat, 16 Feb 2013 19:10:40 -0800
"spike" <spike66 at att.net> wrote:

> {8^D
>
> OK, I didn't state it very clearly.  Let me try it Damien Broderick
> style.
>
> You have perhaps seen what happens when a BB is fired at a glass
> window.  It often creates a cone-shaped punch-out, with the impact
> side hole the size of the BB and increasing in radius along the path
> of the BB.  When an impactor hits a meteoroid at sufficient velocity,
> we can expect a hole the size of the impactor on the impact side,
> increasing in radius as we go back, with a cone half angle of about 4
> to 8 degrees.
>
> 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.
>
> spike
>
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If you are changing the orbit, and the asteroid is rotating,
impacting off centre might work better.  If you remove a chunk that is
in motion relative to the centre of gravity, then the orbit will change
by the difference in velocity between the old and new centres of
gravity.

Hmm. thinking about it, if you hit the retreating side any momentum
transfer that did occur would probably be opposed by the change due to
this effect. Something else to consider before you shoot a rotating
asteroid, you want to hit the side that is rotating towards you for
maximum delta V.

-David.