In a message dated 3/26/04 9:30:18 AM, tango_dancer@... writes:

<< You won't be in for a big surprise for the very fact that you're

still alive and breathing. Almost all nuclear testing in the last

decades preceding the Nuclear Test Ban Treaty occured underground.

There are very interesting videos of the explosive effects as the

come to the surface. If simply detonating a buried H-Bomb was a

planet-busting event, we'd have all been history a long time ago.

A nuclear explosion is localized. We don't have planet buster bombs

yet. I think you're not fully grasping the scale of the moon. >>

An interesting tibit, before the first splitting of atom, many people were
afraid that if an atom was splitted, it would set off an uncontrollable chain
reaction that destroy earth itself. There were a LOT of sleepless nights of
checking and rechecking the numbers before Chicago lab would even start their
reactor.

Carl E. Mullin
visionary artist and entrepreneur
homo asteralis
ravenart@...
www.ravenartstudio.com

The more you love, the more you can love-and the more intensely you love.
Nor is there any limit on how many you can love.
If a person had time enough, he could love all of the majority who are decent
and just.
-Robert A. Heinlein (Time Enough For Love)

"Fear is the mind killer. Fear is the little death that brings total
obliteration." -- Dune

Freedom, Immortality, and the Stars!

Tangoman wrote:

> A nuclear explosion is localized. We don't have planet buster bombs
> yet. I think you're not fully grasping the scale of the moon.

To bust the Moon would presumably require every chunk of it attaining lunar
escape velocity?

Then I'd say 12+ trillion megatons at least. ;-)

Explanation...

Energy = G^3 * SQRT ( M^5 * rho * 4 * pi / 3 )

Energy is for escape velocity for body of mass M and density rho. G = grav
constant. Assumption of 4.2e15 J per megaton, SI units throughout, and a
spherical body.

Given that the world nuclear arsenal is maybe five thousand megatons
(http://www.thebulletin.org/research/qanda/worldarsenals.html) the Moon is
quite safe. ;-)

Regards,

Andy G

--- In spacesettlers@yahoogroups.com, "Andy Goddard"
wrote:
> Tangoman wrote:
>
> > A nuclear explosion is localized. We don't have planet buster
bombs
> > yet. I think you're not fully grasping the scale of the moon.
>
> To bust the Moon would presumably require every chunk of it
attaining lunar
> escape velocity?
>
> Then I'd say 12+ trillion megatons at least. ;-)
>
> Explanation...
>
> Energy = G^3 * SQRT ( M^5 * rho * 4 * pi / 3 )
>
> Energy is for escape velocity for body of mass M and density rho.
G = grav
> constant. Assumption of 4.2e15 J per megaton, SI units throughout,
and a
> spherical body.
>
> Given that the world nuclear arsenal is maybe five thousand
megatons
> (http://www.thebulletin.org/research/qanda/worldarsenals.html) the
Moon is
> quite safe. ;-)
>
> Regards,
>
> Andy G

LOL. I love it. Thanks for putting the numbers to the scenario.

TangoMan

Hi all!

Just as a follow-up to this thread, I was naively thinking that any
Earth-impacting asteroids could be drilled into and have nuclear detonations
set off deep within their cores, to break them apart. This would change the
vectors of much of the material of these asteroids, ensuring more "misses";
and both reduce the size and widen the spread of that shrapnel which would
reach the Earth's atmosphere.

Quick calculations using the formula from my earlier email show that objects
<10km across would be fragmented with small blasts (<5MT), and real
continent flatteners (20km diameter) could be blown apart with ~100MT
charges. (The graph of energy against size is strongly curved: by 40km
diameter the world nuclear arsenal is used up.)

But then it struck me that there's an easier, more efficient way to do this.
Statistical reports on ~10km asteroids show that most rotate with a duration
that can be plotted on a bell curve, with a peak at about 5.33 hours. The
bell curve shows a sharp cut-off at 2.27 hours. This rotational speed
corresponds to the maximum rotational speed that a collection of
gravitationally-bound rubble can do. Any faster, and the object will simply
fly to pieces. So how much energy would it take to spin up an asteroid to
this auto-destruct speed?

For a spherical or nearly spherical body, rotational kinetic energy is given
by:

0.2*M*r^2*omega^2

While the mass of these asteroids is large (typically 5*10^15 kg) the
rotational velocity is low, a few tens of thousands of radians per second,
and the necessary increment required to reach the break-apart speed is
equally low.

So. for objects with typical asteroidal density, it turns out that the
required energy figure is about a sixth of that required to blow the body
apart. (Lower densities need less energy still.) Couple this with the need
to not to have to drill (in microgravity, through loosely assembled rock
lumps, and to potentially great depths) and I think the spin 'em apart
strategy might have a lot going for it.

Additionally, this is possibly the best method for mining the asteroids.
Spin them up (presumably making a couple of areas highly radioactive in the
process) until you produce a cloud of lumps, gathered over the aeons, many
of which must presumably have been chipped off the larger asteroids which
will have differentiated into metal-rich strata, and therefore provide
easily accessible near-pure metals.

Apologies if this is well-known throughout the literature - I've not met the
idea before, but I can see my "back of an envelope" calculations suggest
it's the most attractive approach.

Regards,

Andy G

--- In spacesettlers@yahoogroups.com, "Andy Goddard"
wrote:

> While the mass of these asteroids is large (typically 5*10^15 kg)
the
> rotational velocity is low, a few tens of thousands of radians per
second,

Hi Andy,

Shouldn't the above have read thousandths rather than thousands?

Ed

"Never let it be said that your anal-retentive attention to detail
never yielded positive results" - Loki to Bartelby, "Dogma"

Oops! Well spotted! The maths is good, the text is wrong. :-)

Regards,

Andy G