From: James Rogers (jamesr@best.com)
Date: Tue Jan 14 1997 - 12:54:09 MST
At 03:17 PM 1/13/02 -0500, Michael Lorrey wrote:
>James Rogers wrote:
>> According to ASTM E-380-82 of Standards for Metric Practice, one ton TNT
>> nuclear equivalent is 4.184^9 Joules. This number is not the amount of
>> energy in a ton of TNT (which, BTW detonates at ~7000m/s in most military
>> forms), but a standardized unit with a historical name. In fact, one ton
>> TNT nuclear equivalent is defined as exactly 10^9 calories.
>
>I found a ref ona NASA page stating that one Megaton was 4.2 x 10^22
>ergs.
This is equivalent to the ASTM standard.
>>
>> >Freefall velocity from the moon is around 11km/s, so a minimum energy
>> >launch will give you 500 * 11000 * 11000 = 6 * 10^10 J. That's
>> >equivalent to about 6 * 10^3 kg of TNT, or 6 tons. Hence, a thousand times
>> >less than you claim. Sure you haven't got tons and kg confused?
>>
>> A one ton ferrous rock is pretty small. In fact, it amounts to a boulder
>> roughly 0.5-0.7 meters in diameter. Therefore, it is not surprising that it
>> only has an energy yield of 6*10^10 Joules.
>
>Yes it is quite small, and could easily be formed into the same
>stealthed shapes that Mark is puportin for nukes.
Stealth would play less a role for big rocks. Since a big rock is just "a
big rock" with no terminal guidance, and only kinetic energy as its energy
source, there is little you can do to defend against it. It is falling
whether you like it or not. The best you could do would be to modify the
trajectory.
>>
>> Just some quick comments on nuclear effects in the lunar environment:
>>
>> I checked all my civil engineering books and others to get real figures and
>> data. Assume a nuclear device with a yield of 1-Mt, which is a a few times
>> higher than the actual average yield of the current arsenal. An airburst
>> would have virtually no effect in the lunar environment, so we will assume a
>> ground burst. Assuming a theoretically perfect energy yield for a 1Mt
>> device, we have a total output of ~4*10^15 Joules. However, the vast
>> majority of the energy is harmlessly radiated, since an atmosphere and
>> surface living is required for these effects to have significance. The only
>> significant destructive force is the ground shock. Note that much of the
>> ground shock energy found in atmospheric environments is airslap induced
>> ground shock, and is therefore irrelevant. I assumed a depth of 2-meters,
>> since soil arching plays a significant role in shock resistance. After much
>> nasty calculation based on the above values, you will be disappointed to
>> learn that the safe distance from ground zero is between 500-1000 meters for
>> a 1Mt surface burst, depending on soil conditions. The reason is apparently
>> that virtually all the blast and cratering effects are consequences of
>> having an atmosphere, and soil doesn't propagate shock waves very well. In
>> fact, structures specifically hardened against nuclear blasts could survive
>> quite near ground zero, since non-airslap induced ground shock is attenuated
>> extremely rapidly.
>>
>> Note that this is not an exact science, and that there are many factors
>> involved. I was simply demonstrating that nuclear weapons lose most of
>> their effectiveness in subterranean lunar environments. Nuclear weapons are
>> hundreds of times more effective on earth.
>>
>
>Thanks for a more expert opinion James. Based on a reference I found of
>4.2 x 10^22 ergs per Megaton, I calculated 15 tons of TNT equiv. for the
>1 ton rock, so while I was seriously wrong in my own estimate, Mark was
>under by almost three times. I don't know why that number stuck in my
>brain, I had read it somewhere...
>
>Additionally, in terms of damage ability, large nukes have, even in
>atmosphere, an attentuating effectivness proportionate with their yeild.
>A 10 MT device will only have a damage area of between 4-8 times larger
>than a 300 KT device, which is why the powers have gotten away from
>using big nukes, as they are not as cost effective as using the same
>amount of material in four or more devices.
The scaling factor for nuclear weapons is (Yield1/Yield2)^(1/3), where
Yield1 and Yield2 are the yields of the nuclear devices in question. This
scaling factor is "ideal" for all explosives, nuclear or conventional. The
ideal case more or less holds up until about the 10Mt range, where the
exponent starts to decrease slightly due to "real" factors.
If you think about it, a cube root scaling factor makes perfect sense for
scaling one dimensional energy values in 3D space.
>For examply, a high altitude attack by 3-4 B-52s carrying conventional
>2000 lb HE bombs can damage as much area as a 10-20 KT nuke, though
>without the radiation effects. In fact, because the concussive
>shockwaves are from dozens of sources, rather than one device, they
>actually are more effective in their area of effectiveness.
The obvious reason for this being that a single large explosion is poorer at
distributing destructive energy than many smaller explosions that have been
spread out. You maximize the area of optimal destructive energy. Cluster
bombs are designed with the same principle in mind.
>Also, as James demonstrated, a big nuke htting a lunar target would have
>much closer actual damage equivalence to a much smaller device hitting
>an earth based target. While I do not know how to calculate the actual
>or estimated equivalence, I think that this is a significant factor to
>consider.
>
>If we look at a more proportionate device, like the Oklahoma bombing,
>that device, I beleive was estimated to be equivalent to a ton of TNT
>(please correct me with more accurate data).
The Oklahoma bombing was not equivalent to a ton of TNT. Although the truck
carried an estimated 1-1.5 tons of explosive, my "expert" estimate would be
a damage equivalence of about 1/4 ton of TNT based on the structural damage.
There are a several reasons why this is the case:
1) They were using an Ammonal-4 type explosive composition. These
compositions have detonation velocities of 3000-3500 m/s, depending on exact
composition and quality. Detonation velocity significantly impacts the
destructive capability of an explosive against building structures. Had
they been using TNT (detonation velocity ~7000 m/s) the damage would have
been far worse.
2) Ammonal-4 type explosive compositions typically exhibit incomplete
detonation. You rarely get the theoretical bang out of the explosive.
3) Ammonium Nitrate based explosives are low energy explosives. TNT is a
mid-to-high energy explosive. By their nature, TNT is significantly more
destructive.
WHAT I WOULD HAVE DONE DIFFERENTLY IF I WAS A TERRORIST:
I would have used nitromethane based racing fuel instead of diesel as a
sensitizer/fuel. Why? Twice the detonation velocity, complete detonation,
and energetics roughly equivalent to TNT.
Fortunately for the world, if terrorists were educated, they would probably
have a job other than terrorism. Ironically, Ammonal-4 type explosives (the
popular choice among terrorists) are poorly suited to building demolition.
Had a suitable explosive had been used in the World Trade Center bombing,
that building would not be standing.
-James Rogers
jamesr@best.com
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