# [ExI] Asteroid on track for possible Mars hit

spike spike66 at att.net
Mon Dec 24 02:03:33 UTC 2007

```> bounces at lists.extropy.org] On Behalf Of Stefano Vaj
...
>
> at the maximum speed a huge Orion vehicle may be able to attain in the
> available time?
>
> The deflection potential would seem much higher, as in some 3000
> explosions against one or two... Stefano Vaj

I don't understand 3000 explosions against one or two, but this notion is
what I thought of earlier today, or something kinda related to it.

For a rock 100 meters on a side, the deflection potential would not be great
for any of the schemes I have heard proposed involving a KEV.  My reasoning
is that to deflect a large object any appreciable amount with a KEV, one
would need to hit it from the side.  For something that is way out there,
hitting from the side is pretty much out of the question.  If it is coming
toward earth, all we really have available to us is a head on collision.
Think about it: if an object is headed our way, you don't have enough delta
Vee available to leave earth, then get way off to one side and then
accelerate enough towards the object from the side to make a hill of beans
difference in its path.

My notion then is not so much to deflect the rock but rather to attempt to
break it up intentionally, then deal with being smacked by many small
pieces.  If we have an opposite-direction collision, the closing speeds are
high enough that any KEV makes a broad shallow crater.  The material of the
KEV matters not, but only it's length from leading surface to trailing
surface.  The KEV vaporizes at the speed of sound in the KEV material and
the rock vaporizes at the speed of sound in the rock.

Recall that a Saturn V hoisted a lunar module and last stage to the kinds of
delta Vee needed to make a useable KEV.  I don't know the mass of all that
stuff, but for single digit estimates, I would say close enough to 10,000 kg
would cover everything that made it out to the moon: the propulsion unit,
the LEM, the reentry capsule, etc.  So let us assume a KEV about 1e4 kg with
a closing velocity of 20 km/sec.

My notion is that altho the impact blasts a wide shallow crater on the
surface, the shock wave *might* be sufficient to send cracks throughout the
rock.  No guarantee that it would break up.

Comets would surely be way easier to break up than rocks.

spike

```