Andy G wrote:
>... 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.

This technique seems to have been abandoned by everybody except
hollywood. Do the math on the level of destruction afflicted to a locale under
an impactor, versus the destruction done to the entire asteroid-facing
hemisphere when it's peppered with a shotgun blast of mountain sized
chunks.
More smaller detonations spreads the energy available more efficiently -in
terms of kilotons available related to damage inflicted to targets on the
ground, than a single large blast. It's why MIRVs have several smaller
warheads for a city area instead of a 100mt single warhead.
What's impossible to calculate is how a bomb placed at the core will affect an
asteroid which has been only poorly characterised to know all of its interior.
You won't save the planet by landing Bruce Willis and a few heroes and
quickly drilling and placing bombs, because they'll need to have a lot of time
to explore and study the rock, and then, maybe, place the bombs at the exact
precise place to shatter the rock to do the most help to the Earth (after
factoring spin and such).

It makes a much less exciting movie, but the best way would be to thoroughly
survey the asteroid while you're de-spinning it (many techniques available,
none requiring magic), then attach a solar or nuke thermal rocket to it, fed
from asteroidal ices. You only need to make it miss this one pass that it's
threatening, then it's gone out into the solar system. For effectively no
additional cost, keep the rocket firing, and use the near-miss you've created to
warp the course to swing past Venus a few turns around the Sun later. Use
that to swing it back past the Earth-Moon system again, for the final
maneuvers to place it into HEEO, where the mining facilities have been
placed to do the real work of turning it into useful things (as opposed to the
bootstrapping operation landed on it which just produces ices for reaction
masses and life support for the rotating crews riding it).

From: John Frazer [mailto:johnf4303@...]

> It makes a much less exciting movie, but the best way would be to
thoroughly
> survey the asteroid while you're de-spinning it (many techniques
available,
> none requiring magic), then attach a solar or nuke thermal rocket to
it, fed
> from asteroidal ices.

Or how about a mass-driver? The advantage there is that one might well
run asteroidal regolith through a solar oven process that desiccates the
soil and freezes the vapors out, storing the ice somewhere. Since you
(very wisely) wish to leave the door open on later material usage of the
asteroid, one would in this case be throwing away the least valuable
parts of the asteroid as reaction mass, rather than the most valuable.

Regards,

Mike Combs

>> It makes a much less exciting movie, but the best way
>>would be to attach a solar or nuke thermal rocket to
>>it, fed from asteroidal ices.
>
> Or how about a mass-driver?... one would in this case be
>throwing away the least valuable parts of the asteroid as
>reaction mass, rather than the most valuable.

An alternative which has been suggested is to land tools to bootstrap the
entire operation: metals to make foil mirrors to increase the output of the
facility are easy to make, as are the rails and equipment which are the bulk of
the mass driver track (rolled & stamped metals, drawn wire for cable, and
fused rock-dust "aster-crete/sinter-crete/concrete".
As time goes on, while the thing goes around the Sun a few times (while
crews are occasionally rotated or resupplied with finished goods they can't
produce as needed), the track length of the mass-driver engine lengthens,
driving up the exhaust velocity of the rocket.
There's a narrow race being run between the mission concepts of bring
everything needed to set it up and operate it straight from the cargo hold, or
instead bring more tools to build the dumb bulk parts which are by a large
margin the most of the cargo you'd need to bring to run the facility.

Is there really that much time from spotting the asteroid to collision?
Maybe it comes from the outer solar system or from outside of the solar
system.
Then it can be small, difficult to see and fast enough to be really
dangerous.
A few days advance warning might be all we have.

What do you think about the idea (not mine) to use Orion style
propulsion to intercept such asteroids? The scenario uses the Orion
vehicle as a kinetical bomb: don't slow down and rendevous, just speed
up! No fancy shock absorbers, but just enough so the unmanned ship can
stand the plasma pulses (or no shock absorbers at all?).

John Frazer wrote: