If they were sure a asteroid were going to hit the earth

Henry Spencer wrote:


While the threat undoubtedly got played up a bit by people with axes to
grind, the numbers came from the astronomers, who are not noted for their
huge military contracts.



Think of the radar and telescopic infrastructure related to asteroid
detection... "Jeez guys, looks like we're going to upgrade the VLA to
300 transmit receive dishes; anybody got a problem with that?"
"What's the trade-off?"
"We have to look for asteroids... for around an hour a day..."
"What are we going to do for the other 23 hours?"
"Win Nobel prizes..."
Meanwhile in Hawaii, the interior of the Mauna Kea volcano grew yet a
few degrees cooler as the 100 telescopes of the Keck Array began to
rotate their geothermal electrically driven domes in perfectly
synchronous motion; on each of them the proud insignia of The Global
Asteroid Protection Network- a small chicken wearing a blue helmet,
saluting with one wing, the other pointing to the heavens in perpetual
warning, reflected the starlight of the warm Hawaiian night.
After the required hour of asteroid hunting, the Keck boys decided to
show those VLA wimps who the real Studs of Stockholm were.

Pat

Scott Ferrin wrote:

This is basically just too short a time -- you can't debug the design,
even a fairly forgiving one, that quickly. You'd have to start with
hardware that was already developed or nearly so.




At this point though it's "do we try and maybe fail or do we not try
at all?"

I say we build a big rocketship on a rail launcher, then, after
stranding the cynical millionaire, and letting the pregnant dog on board
instead, we lift off for Zira.
This can be done in around a year's time.

Pat

On Thu, 13 Nov 2003 20:15:18 GMT, (Henry Spencer)
wrote:

In article ,
Scott Ferrin wrote:
I think you have failed to grasp just how powerful a big bomb is. :-)

I was looking at some of the underground detonations back in the day.
Even the biggest one (5 Mt) was contained...

By the standards of asteroid moving, 5 MT is still a pretty small bomb.
The MIT "Project Icarus" study specified 100-MT bombs, and they would have
preferred more -- that was just the largest bomb they thought could be
put together on 16 months' notice in the late 60s.

Yeah that's why I was suggesting a four or five stage nuclear warhead.





Orion wasn't using bare bombs -- they were planning to absorb most of the
X-ray pulse in the reaction mass wrapped around the bomb proper. What hit
the pusher plate was hot plasma, not X-rays. (Indeed, the fact that they
were talking about surface erosion tells you that! The X-ray pulse is too
penetrating to stop at the surface; it deposits most of its energy a few
centimeters *inside* whatever it hits.)

But how would that contribute to the reaction mass? If you're heating
subsurface materials it has no way to get out. You just end up with a
lot of hot material that goes nowhere.




(It is *gas* you want for efficient propulsion, not fragments.)

F=ma. Trying to vaporize the surface would result in very little "m"
and most of the "a" would not be directly away from the astroid.

Actually, it would be, simply because there's no other place for the gas
to go. If you heat material at one point -- say, with a surface burst --
then yes, it does expand more or less in a hemisphere. But if you heat
material over a wide area of the surface, it expands outward as a sheet of
gas, and the only major losses are at the edges; the gas in the middle has
nowhere to go except directly away, because it has other gas on all sides.

In a subsurface burst the "m" would be very high...

However, much of that energy will go to heating that large mass, which
contributes nothing at all to propulsion. It's only expanding gas which
pushes things. You are better off having the expanding gas push the
asteroid directly, rather than relying on it to push pieces away from
the asteroid.

Think of it like the difference between setting off the cartridge of a
5" gun out on flat ground and the recoil of the same cartridge in a
gun barrel. The one on the ground isn't going to fire that projectile
very far at all.


(Other things being equal, the latter *is* preferable, because you get the
most momentum from a given amount of energy by using the energy to push a
large mass away at low speed. But other things are not equal.)

...and the majority of it would be directed perpendicular
to the impact (the hole cut by the shaped charges would direct the blast).

Uh, no, some of the blast may squirt out the hole -- as hot gas -- but
there will be no particular tendency for the hole to direct the expansion
of rocks pushed by the blast.

The blast would also vaporize a significant about of material that
would also exit the hole.


Granted these are big ideas but it's an attempt to figure out how to
use current technology to move a LOT of weight.

People have looked at this before. Above-surface blasts generally look
best, especially if you are unsure of the structural integrity of the
asteroid. (Even the metallic asteroids aren't necessarily single pieces.)\



And most of them talk about a penetrating warhead though they
generally mean the kinetic type. Pound per pound a shaped charge is
the way to go (not to mention the structural integrity of the nuclear
warhead).

In message , Pat Flannery
writes


Henry Spencer wrote:


While the threat undoubtedly got played up a bit by people with axes to
grind, the numbers came from the astronomers, who are not noted for their
huge military contracts.


Think of the radar and telescopic infrastructure related to asteroid
detection... "Jeez guys, looks like we're going to upgrade the VLA to
300 transmit receive dishes; anybody got a problem with that?"
"What's the trade-off?"
"We have to look for asteroids... for around an hour a day..."
"What are we going to do for the other 23 hours?"
"Win Nobel prizes..."
Meanwhile in Hawaii, the interior of the Mauna Kea volcano grew yet a
few degrees cooler as the 100 telescopes of the Keck Array began to
rotate their geothermal electrically driven domes in perfectly
synchronous motion; on each of them the proud insignia of The Global
Asteroid Protection Network

Brilliant as usual, but it should be Completely Reliable Asteroid
Protection Network.
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Jonathan Silverlight wrote:


Brilliant as usual, but it should be Completely Reliable Asteroid
Protection Network.

How about Space Hazardous Impact Telemetry System?

Pat

"Henry Spencer" wrote in message
...
Above-surface blasts generally look
best, especially if you are unsure of the structural integrity of the
asteroid.

But they don't look like the special effects we've grown to love.
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in the works.

Pat Flannery wrote:


Scott Ferrin wrote:




It's kindof like pulling the lever on a slot machine. Pretty easy to
get a buck or two but not to many pull the million dollar payouts. I
wonder what the odds on any given day of say a 10 gigaton impact? Or
a one megaton impact in a city of over 50,000? Any stataticians out
there?

It seems that the numbers are getting steadily revised downwards; I
don't think it was a coincidence that the "asteroid threat" and
protection plan suddenly appeared right after Reagan's Star Wars system
got canceled.

Yep. Those out-of-work weapons guys arranged to have Shoemaker-Levy-9
smack into Jupiter.

They were also behind Walter & Luis Alvarez. The "discovery" of
Chicxulub is another massive hoax perpetrated by these schemers.

The numbers put forth by Shoemaker and others were good faith estimates.
I believe the Alvarez theory plus Jupiter's impact spurred funding for
NEO searches. And it is these searches that are making the old guesses
obsolete.

Suggestions that the numbers were cooked to benefit certain interests
makes me angry. If you want to tar someone's reputation please cite
evidence.

--
Hop David
http://clowder.net/hop/index.html

Henry Spencer wrote:

I think you have failed to grasp just how powerful a big bomb is. :-)
There is not a lot of difference between burying it a few meters and
detonating it on the surface. Besides, it is not clear that you want a
surface burst -- you may get a better propulsive effect by setting it off
at a modest altitude, where its X-ray flux can reach and vaporize a larger
area of surface. (It is *gas* you want for efficient propulsion, not
fragments.)


Aren't most asteroids thought to be piles of rubble? Would the momentum
be imparted to every fragment of the asteroid?

Perhaps a bomb would change the big bullet to shotgun pellets.

--
Hop David
http://clowder.net/hop/index.html

Derek Lyons wrote:
"Greg D. Moore \(Strider\)" wrote:

Note some have only been detected AFTER they've passed by the Earth.
Anything on a direct course is going to be hard to pick out due to lack of
relative motion to the stars.


hmm... In order to have a zero bearing rate, it will either have to
be *very* close, or traveling in a very unusual orbit.

IIRC the ones that worry the astronomers most is the retrograde ones,
as they are coming out of the suns glare.

D.

And the retrogrades have bigger velocities wrt Earth.

--
Hop David
http://clowder.net/hop/index.html

In message , Hop David
writes


Pat Flannery wrote:

It seems that the numbers are getting steadily revised downwards; I
don't think it was a coincidence that the "asteroid threat" and
protection plan suddenly appeared right after Reagan's Star Wars
system got canceled.

Yep. Those out-of-work weapons guys arranged to have Shoemaker-Levy-9
smack into Jupiter.

They were also behind Walter & Luis Alvarez. The "discovery" of
Chicxulub is another massive hoax perpetrated by these schemers.

The numbers put forth by Shoemaker and others were good faith
estimates. I believe the Alvarez theory plus Jupiter's impact spurred
funding for NEO searches. And it is these searches that are making the
old guesses obsolete.

Suggestions that the numbers were cooked to benefit certain interests
makes me angry. If you want to tar someone's reputation please cite
evidence.

I don't think anyone is saying that the numbers are being cooked, but
it's abundantly clear that the military is climbing on this particular
bandwagon with glee, as it's the only possible use for some of their
expensive toys.
And there's no doubt that there are 1000 other natural threats that will
kill more people in the next hundred years than any asteroid. As an
urgent problem, it's no more serious now than it was in the time of
Napoleon - or Julius Caesar - except that we will soon be able to deal
with it. Probably with a technology not yet invented.
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