l33telboi wrote:Mr. Oragahn wrote:No, you would use the exact formula provided on the blog which is behind your argument.
My argument is behind
this formula (also see the next post after that).
Not really. Remember, you talked about an equation that "let's you adjust what type of composition the asteroid is made of" and that while "it assumes zero gee", we couldn't "find a better suited formula because there quite simply is none", as "[it] fits every single parameter we need it to fit."
We're yet to see the one which allows you to input the composition parameter.
Considering that the simple one you used at SBC didn't have such a parameter, and that the only one which allowed to consider the material, via its density, was E = mX + mgh, although not used for asteroids, there were not many other choices than using this last one.
Squish wrote:From the paper, the generalized equation for surface blasts:
2.5x10^-3m per J^1/3.
(Edit: For a 3000 meter crater, that's 48.074 MT.)
Now you have brought
another formula, but seem a tad reluctant to use the blog's formula, minus the gravity-relative term (mgh), despite being directly associated to the quotation picked from the Glasstone blog.
You'll notice that the "no gravity argument" came hand in hand with the equation provided on the same page the quotation was taken from.
'No gravity' came hand in hand with the formula provided above, because it doesn't factor in gravity.
We don't know the parameters this other formula you brought, by citing Squishy, is allowed to be used for.
We've seen thus far that many crater formula for small yields do one single same thing: pick a given yield in kiloton, preferably a sub kiloton yield, divide by mass (defined by density and volume) of the corresponding crater, slap a small constant to that relative crater diameter, and that's it, you have an average energy per unit of volume to break or destroy it.
I still find this methodology quite poor if used for greater yields, because of the complete lack of care for the inverse square law, which I imagine could pass for small yields (<1 kT).
You ask me to prove the figure stated earlier, but for some reason I'm not allowed to actually use the formula used to obtain those figures? Come one, that's absurd. Have you noticed that your formula doesn't even factor in how hard it would be to crack a certain material?
It's not
my formula, I didn't even know about it until you mentionned the blog. By all means, it's yours, since it's the one that comes with the blog you cited as part of your evidence.
You use all sorts of formulas, add new ones, but not the very one found on the blog. Why is that?
Also, why do you say it doesn't address what's necessary to crack a certain material? None of them do, and Nige's formula is by far one that has shown to contain the most parameters for the simple that it contains the mass, obtained with the material's density.
It literally only deals with density. But even a school-child could point out that it's easier to break up a handfull of sand into smaller pieces then a solid rock.
Yet it's a
cratering formula which the author -- who couldn't understand how Glasstone and others super brains could miss the importance of gravity for so many years -- says can be used for all sorts of densities.
Equally, a school-child could point out that it's easier to break and crush a porous object made of a given material, than brake another object made of the same material, but which is not porous.
This can be verified in your very garden, with the soil mounds left by moles. Smashing the dry soil with the first barely leaves a mark, but if you'd move the escavated mass and carefully put it into a pot (in order to mimic the presence of that volume of earth like it had never left the ground), and tried to smash it, your fist would penetrate it easily.
All these nuke equations you presented are fine and dandy but none take into account that factor. Not even Wong's, as I said earlier on. A table on the blog shows that that a dry coral crater for a surface 1kT bomb is 1.1739 times bigger than for dry soil. That would mean that if we considered that the 1500 m radius for the crater was due to it being dry coral, the same device detonated on a dry soil surface would leave a crater with a radius of 1278 m. That alone with one of your formulas would return 32 megatons.
I also noticed, while observing the origins of the old formulas based on W (in kT) or J (in joules) that small differences creeped up, but didn't matter for small yields. However, when one would use those these formulas for higher yields, the differences would be multiplied in much noticeable ways.
Let's also rewind things a bit.
Glasstone's old formula worked this way, and was fairly simple in its construction:
For a dry soil, he estimated that a 1 kT device would leave a 120 feet wide crater (radius = 18.288 m). So to obtain the radius of a crater in feet, you had to do the following:
R = 60 x W^0.3
We may infer that the equation is almost primitive in a way. It's blunt. Small bomb makes small hole of dat size, urgh, bigger bomb makes same hole times bigger boom.
Wow.
Then things changed, casing density entered the stuff, and after more changes, came the introduction of gravity, for a final formula in 1994. Yet I don't see where they ever took care of the ISL. :/
Now, when I look at your first formula, the one picked from
SBC which gave you 51 megatons (51.62 MT more specifically), what do we see? Well, first, since you used in a zero gee environment, we can understand that it means g either is not present, or is but the term it belongs to returns 1 when p = 9.8 m/s².
So we see that it's a very close cousin of Glasstone's formula:
Diameter = 5 e-3 * J⅓ , with D in meters.
Let's see what this formula gives us for 1 kT.
1 kT = 4.184 e12 J. Therfore the diameter is:
D = 5e-3 * (4.184 e12)⅓
D = 80.57
Our 1 kT device laves a crater in dry soil that is 80.57 meters wide, for a radius of
40.285 meters.
One of the blog's tables says that a 1 kT surface detonation on such a soil would leave a crater with a radius of only
18.4 m. Considering that we're talking of low yields, the difference is monstruous.
A Russian test the 26th of november 1962, with a yield of 1.1 kT, detonated half a meter above the ground (which is the equivalent of putting the large bomb on the ground, with the core being 0.5 m above the surface), left a crater radius of 13.5 meters, and that possibly with one of these bigger casing devices (Glasstone often points them as being low yield/high mass devices), and as such, making a larger crater than an "efficient" device.
Again, the difference is baffling.
We could compare this with Johnnie Boy (0.5 kT), again, an old device, detonated 0.585 m above the ground.
By the formula, we obtain D = 63.95, so the radius is
31.975 m.
The real test begs to differ, with
R = 19 m.
Bufallo-2, 1.5 kT and detonated 0.2 m above the ground (almost peanuts) left a crater radius of
18.6 meters.
The formula argues that the radius should be
46.1 meters.
Now, can the detonations' heights of 0.5 meters matter? Possibly, but likely to a very minor degree.
To get a good bracketing idea, let's compare the formula with underground explosions then.
The Uncle test in 1951 is very interesting there. A 1.2 kT device, buried 5.2 meters below the surface, left a
78 m wide crater (R = 39 m). Adding to the casing the amplification of cratering, we also have depth, which matters a lot.
But what does the formula return for 1.2 kT?
A crater
85.62 meters wide!
It manages to make a bigger crater with an assumed more efficient device and, above all, a surface burst.
What about Sedan (1962)?
Yield, 104 kt. Buried 194 meters below the surface. Made a fantastic clean conical crater, with a radius of
186 meters.
The formula for the same yield, but a surfacic burst of a modern device?
R = 189.44 m
Finally, perhaps we can make a comparison between the estimated 184 m wide crater for a surface efficient 10 MT burst, from G&D's 1984 formula, and yours?
R = 867.9 m
When you look at the summary of the evolution of the formula, on the Glasstone blog it says the introduction of gravity brought the radius from 145 m to 92 m. We're nowhere close to the 867.9 m here.
A-HEM would be an
understatement!
Can we trust an equation that is obviously so wrong even for low yields? Not really, no. The problem is, what equation to use then?
And out of curiosity, have you tried scaling your figures down to say 15 megajoules and see what that gets you?
What figures? And why 15 megajoules?
That you don't know.
I do. It's statistitically provable that the average is far more likely to be closer to the real value then a conservative figure. This is simple logic. If you have a die with 10 sides, then the number 5 will most likely closer to the real figure then 1 whenever you throw it.
Still, googling average density returned you a nice number, but this number is pretty much totally useless and false.
First, the reason you don't know that 2.8 kg/m³ is a more probable scenario is because above all things, you need an asteroid that can have a crater of 3 km.
It means you'd need to work with asteroids being at the very least that wide, and wider. It completely reduces the whole sample to a new one, and we don't know what is the average density and composition of asteroids of that size.
Secondly, the exposé
assumes that the average asteroid if 10 km wide, despite establishing "that there are approximately 1 million asteroids of diameter 1 km or larger". That's to obtain an nice value that doesn't look completely bullshit, but it's just as good as the premise is: totally assumed and arbitrary.
Then the author and uses a spherical volume formula to obtain the average volume. Nevermind if asteroids of that size hardly meet the sphere criterium. Of course that would increase density, but it tells you just how accurage that exercise attempted to be: very little.
Now, the rubble pile model is very well favoured, and the
2007 Encyclopedia of the Solar System uses Mathilde as a reference.
Finally, if we look at wikipedia, for what it's worh, we see that our knowledge of the Kuiper Belt is still very limited. Still, observations made prove the existence of methane ice and water ice in the make up of several large objects.
Also, the overall mass of the belt varies a lot: 1/10th, 1/30th or 66 times Earth's mass, yet all are above the figure from that edu website you found, making it pointless as a reference.
Notice, by the way, that what you used only was the so called average mass of an asteroid of the Kuiper Belt.
But feel free to proceed with higher parameters, we'll see what you get.
High parameters would have us assume we're talking about a nickel/iron asteroids, you know, with a density around 8000 - 7000 kg/m^3.
I meant higher than the ones I suggested earlier on, below the 2.8 kg/m³ density. Use this one in E = mX if you want.
Hey, if you have some spare time, you may even plug the heavier densities, just for the kicks! :)
Next, the part about the famous "torpedo glow".