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

spike spike66 at att.net
Sat Feb 16 22:33:27 UTC 2013

```>... On Behalf Of Tomasz Rola
...

>...Spike, I did not mean using nukes. They may be handy in some situations,
but in this case (10-100m impactors) I would like to try classic solution
first. Ram it, blow it, slow it down. And I wouldn't object if Earth had
some kind of "reactive armor" made of radars and missiles (to begin with
something). AFAIK an explosion in right place and time can change quite a
lot. Ask any modern tank... Regards,
Tomasz Rola

Tomasz ja, but be careful not to carry over analogies that don't work very
well.  The tank is way down here at the bottom of a sea of air, where the
shock waves from any explosion do most of the heavy lifting of wrecking
stuff and transferring momentum.  In the vacuum of space a nuke doesn't do
much.

Regarding your notion of a physical impact, this might transfer some
momentum, and here's how you estimate how much: find the speed of sound in
the rock, take the closing speed and calculate a cone going aft from impact
site outward along the path of the impact.  Then calculate a cone with the
longitudinal axis being the closing velocity and both transverse axes being
the speed of sound in the rock.  So if you have a closing speed of about 10
km/sec and you estimate the speed of sound in the rock at about a km/sec,
the half-angle of the cone is about 6 degrees.  So now the total momentum
transfer to the rock is calculated by estimating the surface area of that
cone, multiplying by the sheer strength of the rocky material.  That would
give you an area times a force per unit area, from which you estimate a
force.  You know the time span during which the force is being applied, so
we might be able to estimate the momentum transfer with that.  You end up
with a conic shaped hole in the rock, the size and shape of the impactor on
the impact side, an opening at perhaps 6 degrees going aft.  The rest of the
rock scarcely notice that anything has happened.

spike

```