ApolloHoax.net
Off Topic => General Discussion => Topic started by: Andromeda on February 15, 2013, 02:13:25 AM
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Several meteors have exploded over the Urals. I didn't find out until I checked my Twitter feed this morning and saw Phil Plait's posts.
Doesn't look like anyone has been killed, but windows were blown out which caused injuries.
Things are still very confused at the moment and news is still coming in.
http://www.guardian.co.uk/science/2013/feb/15/meteorite-explosion-shakes-russian
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Wow, that was impressive.
I know from experience that these things often look much closer than they really are. In the mid 1960s in Maryland I saw a brilliant green fireball to the north that seemed to fall close by. It had actually landed in upstate New York.
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Turn down the audio before you press play!
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Over 500 people reported injured, mainly by damage caused by the shockwaves. Shockwaves were not caused by impact but the sonic boom of the object hitting the atmosphere. Just shows how high up that trail is and how fast the thing was moving. The trail took seconds to form, and had spread quite a bit before the shockwave hit. But then with the speed of sound being about 740 mph (averaging through the variation with altitude), if that trail formed 100 miles up it would take about 8 minutes to reach the ground.
Interesting from a human perception point of view. We see a streak and think it must be quite small and quite close, because we almost can't conceive of something moving that fast through the air....
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Current Russian estimates are: mass 10 tons, velocity 30 km/s. That works out to just about 1 kiloton TNT energy.
Most of it probably came out during that intensely bright flash lasting a second or two. A lot got turned into an atmospheric shock wave that did damage just as an airburst bomb would. But unlike a bomb that releases all its energy in ~1 us in a very small volume, here the energy was released over a much bigger volume of air so the peak temperatures were far lower and thermal radiation was nil. And of course radiation is nonexistent.
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Here's a horrifying thought. The current mass of the ISS is 450 tonnes, and orbital velocity at that altitude is maybe 7.5 km/s. And it's in an orbit low enough that it has to be frequently reboosted.
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Here's a horrifying thought. The current mass of the ISS is 450 tonnes, and orbital velocity at that altitude is maybe 7.5 km/s. And it's in an orbit low enough that it has to be frequently reboosted.
It's also made largely of hollow aluminum structures. I'd expect it to disintegrate at much higher altitudes, the energy being spread over a much larger ground area and a vastly larger number of much smaller shockwaves, with actual debris being a bigger hazard.
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Someone on my Facebook feed is saying, "Maybe the Mayans were just early!" Grrrrr.
But another person is asking how this ties in to the bigger one that's supposed to miss us. I have posited that it probably doesn't at all; can anyone tell me which of us is wrong?
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Someone on my Facebook feed is saying, "Maybe the Mayans were just early!" Grrrrr.
But another person is asking how this ties in to the bigger one that's supposed to miss us. I have posited that it probably doesn't at all; can anyone tell me which of us is wrong?
2012 DA14 will pass by traveling north. The Great Commie Meteor of 2013 was traveling west southwest. If they were related they would share the same orbit and therefore share the same ground path.
Russian meteor path plotted in Google Maps | Il Disinformatico (http://attivissimo.blogspot.com/2013/02/russian-meteor-path-plotted-in-google.html)
I've taken the Meteosat-10 image of the Russian meteoroid trail and used the Kazakhstan border that is digitally superimposed on Meteosat-10 images to align the image with the border in Google Maps. The result is shown above. The letter A indicates the city of Celyabinsk. The trail would appear to extend for approximately 320 kilometers (200 miles).
I hope this is useful in reconstructing the trajectory of the meteoroid. Please feel free to use the composite image: just link back to this post or mention my name (Paolo Attivissimo) in the credits.
(http://2.bp.blogspot.com/-8zjQpZviFL8/UR5VjmTMhdI/AAAAAAAAR-A/mfuq8_4eP8s/s1600/googlemaps-meteosat-matchup.png)
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Thank you!
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There is a discrepancy of three orders of magnitude in the mass estimates. Initially they were ~10 tons; now NASA is saying 10,000!
Velocity estimates range from 15 km/s to 30 km/s, which of course changes the kinetic energy by a factor of 4.
NASA's current estimate of the energy release is 500 kt. If so, then I agree an uncontrolled ISS entry would be nowhere near as bad.
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Most of the videos that include the bang start after the flash because they were taken manually by people with phone cameras. And most of the security and dashboard cameras running at the time of the fireball stop before the bang. But there are a few that show both, so I got interested in trying to estimate the altitude of the explosion. With that I hoped to use my references on nuclear weapons effects to estimate the energy release needed to give the observed effects on the ground.
The sunlight on the underside of the cloud is one qualitative clue of its minimum altitude, but I haven't checked to see what the ground elevation of the sun (which appears to have been just rising) was at that time.
In one dashboard camera I measure a flash-bang delay of 2 minutes 25 seconds. It does not appear overhead in that one so the resulting straight-line distance estimate of 46 km (based on an average speed of sound of 315 m/s) probably overestimates the altitude. It's hard to estimate elevation angle in these cameras, and some of the security footage doesn't show the fireball at all.
I'm sure there are all sorts of refraction effects that I'm not equipped to analyze.
There were actually quite a few nuclear weapons tests at similar altitudes by both the US and USSR, but I can't find any discussion of their blast effects. The reports are all about thermal and EMP effects, presumably because the blast is nil (mere broken windows would be pretty mild for a nuclear war).
Comments?
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The Nuclear Weapons Archive has a Repository of software of nuclear weapons effects but the good program (we.zip) is DOS based and I don't feel like fighting 64 bit Windows to make it work.
I was under the impression the shock wave that hit the city was from the sonic boom.
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The number I keep reading for the altitude of the blast is 12-15 miles.
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The Nuclear Weapons Archive has a Repository of software of nuclear weapons effects but the good program (we.zip) is DOS based and I don't feel like fighting 64 bit Windows to make it work.
You can try running it in DOSBox (http://www.dosbox.com/).
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The Nuclear Weapons Archive has a Repository of software of nuclear weapons effects but the good program (we.zip) is DOS based and I don't feel like fighting 64 bit Windows to make it work.
You can try running it in DOSBox (http://www.dosbox.com/).
That is exactly what I was referring to when I said I don't feel like fighting.
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Well, I managed to run it with DOSBox on my Linux machine. As in my experience DOSBox results are quite consistent across multiple platforms, it should work on Windows, too. No fiddling required - in my case, it involved only unzipping the archive to a directory, calling dosbox with that directory as an argument (it mounted it as C:) and running we.exe in the DOSBox window that had opened.
The Nuclear Weapons Archive page with the software is here:
http://nuclearweaponarchive.org/Library/Nukesims.html
And speaking of simulations, there's always the Earth impact calculator:
http://www.purdue.edu/impactearth
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I just played with that Purdue calculator, it's just what we're looking for.
The closest results I got were with: diameter, 18 m; density 3000 kg/m3; velocity 30 km/s; angle 20 deg; target sedimentary rock; observer distance 30 km. This yielded total energy 985 kt; average time between comparable impacts 109 yr; object begins breakup at 63.1 km; explodes at 33.6 km; residual velocity 24.1 km/s; airburst energy 350 kt; no crater; airblast arrives 2.27 min later; peak overpressure 194 Pa.
Some of these are in the ballpark but there are a few things I don't understand. Only about a third of the energy is released in the airburst. The fragments still have substantial velocity and the model doesn't say what happens to them. They certainly can't hit the ground with that energy as they're all going much faster than Mach 1 in even denser air, and being smaller they have lower ballistic coefficients. I think they should continue to generate a strong shock wave that will dissipate most of their energy.
The peak overpressure seems low; the tables I see say that small windows break at 0.1 psi; 10% of windows break at 0.3 psi; windows shattered, limited minor structure damage at 0.5 psi. This last one seems roughly comparable to what happened in Chelyabinsk, but 0.5 psi is about 3500 Pa, much more than the modeled 194 Pa. Maybe I was too far away at 30 km, but when I use anything smaller I get much less than the observed 2.4 minute delay.
I bet the maintainers of this model will recalibrate it with this event. After all, nothing like this has ever happened before in modern history.
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....average time between comparable impacts 109 yr
Interesting!!
Tunguska Event......1908
Chelyabinsk Event..2013
Difference: 105 yrs
Looks about right to me, although I am willing to bet that the Berwyn Mountain incident in 1974 (a.k.a. the "Welsh Roswell") was something similar to Chelyabinsk; a bright trail across the sky seen from Ireland in the west to Cornwall in the south and to the Midlands in the east, a loud explosion and what people in Llandrillo, Wales reported as a shaking "like an earthquake".
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The peak overpressure seems low; the tables I see say that small windows break at 0.1 psi; 10% of windows break at 0.3 psi; windows shattered, limited minor structure damage at 0.5 psi. This last one seems roughly comparable to what happened in Chelyabinsk, but 0.5 psi is about 3500 Pa, much more than the modeled 194 Pa. Maybe I was too far away at 30 km, but when I use anything smaller I get much less than the observed 2.4 minute delay.
I bet the maintainers of this model will recalibrate it with this event. After all, nothing like this has ever happened before in modern history.
That calculator is mostly edutainment. :) If you click on the "Documentation" link in the upper bar, you'll get a PDF with an article explaining the different models and the assumptions and simplifications they used.
I'm not even sure how the sound delay is calculated in the case of an airburst - the source parameter is "distance to impact site", not "to airburst", so this may be a possible source of the discrepancy. I skimmed the article, but couldn't find anything for sure.
Anyway, is it clear whether the broken glass was due to the "sonic boom" travelling shockwave, or the shockwave caused by the meteoroid disintegration event/explosion?
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I think it has to be the sonic boom.
While there are parallels between large bolides and nuclear weapons, especially in the total amount of energy released, there are some important differences.
A nuclear weapon releases all its energy in an instant (< 1 μs) and in a very small volume (~1 m3). It can do this in the air, on the surface or under ground or water. An asteroid's energy is entirely in its motion, and unless there's something to slow it down it cannot release that energy. In particular it cannot simply "detonate" in midair as a nuclear bomb can.
What it can do is to release that energy continuously as it decelerates in the air. If it breaks apart, its total surface area and energy release rate will suddenly increase, but it still won't "detonate". Unless perhaps it suddenly breaks apart into so many tiny pieces that decelerate so rapidly due to drag that all their remaining kinetic energies are released quickly enough to be considered an "explosion". But for a shallow trajectory like the Chelyabinks bolide, this didn't seem to happen. It seemed to release its energy more or less continuously over several seconds and quite a few km.
If there's still a lot of kinetic energy left when the object(s) hits the ground, then it/they will "detonate" and release all that energy in a very small volume and period of time. The effect will be much like the surface detonation of a nuclear weapon, with an incendiary thermal pulse, a blast wave and a crater, though no radiation of course.