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#11
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If they were sure a asteroid were going to hit the earth
"Scott Hedrick" wrote in message
.. . Uncountable telescopes in private hands. Not even possible to keep it a secret. The gubmint was able to keep an asteroid the size of Texas secret in Armageddon! Yet another factoid for my "Michael Bay is an artless hack" file. Mark |
#12
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If they were sure a asteroid were going to hit the earth
"Mark Hanson" wrote in message news:WJRrb.165024$e01.579447@attbi_s02... "Hallerb" wrote in message ... Do you think we would be told? Or would the adminstration keep it a secret to prevent panic? Lets assume its a BIG one.... Uncountable telescopes in private hands. Not even possible to keep it a secret. BIG one, probably impossible. Big enough to do some real damage, it's quite possible it would not be seen until to late. 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. Mark |
#13
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If they were sure a asteroid were going to hit the earth
"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. -- The STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to , as well as posted to sci.space.history and sci.space.shuttle for discussion. |
#14
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If they were sure a asteroid were going to hit the earth
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. The aerospace firms wanted to get big bucks to make something, and a asteroid stopper has the advantage that the odds it's going to get used in any particular year are very small indeed. If it is used, then either it works, and the companies that built it become heroes; or it doesn't work, and the investigation into corporate fraud is then actually a fairly small concern on the global scale of things. It's like somebody sold me a lotion to wear that they guaranteed would prevent shark attacks anytime I went swimming.....here in North Dakota. Pat |
#15
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If they were sure a asteroid were going to hit the earth
In article ,
Scott Ferrin wrote: 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? Really pretty unlikely. Impacts in the major-hydrogen-bomb class seem to be once a century or less, on average, and even their effects are mostly quite local. (The area of serious damage from Tunguska was about the size of a large city.) Earth's surface is mostly water, and even most of the land has quite low population densities. Cities cover only a very small fraction of the planet. The main risk to most cities is gigaton-plus impacts in oceans, because of ensuing tsunamis. Those can be devastating to coastal cities even if the impact itself is far away; tsunamis carry energy over long distances far more efficiently than blast waves in air do. ...Only a year to design AND put the thing together so things are going to be crude as in not extremely high tolerences... 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. ...So then you dust off the data for those 260" diameter solid motors they tested (any idea how long to make the propellant?) Slap some of those one something like Sea Dragon... I think you have failed to grasp just how big Sea Dragon was supposed to be. :-) Strap-ons of that size would increase its payload only a little. (And the capability to build them is not something we could re-establish quickly. Solids look easy but they are not; they are terribly sensitive to even the tiniest flaws in those big masses of fuel.) The idea being that you get the big nuclear warhead in just deep enough that when it goes off it blows out the side using the ejected fragments as reaction mass. If you just blow the thing on the surface... well it probably wouldn't do much. 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.) -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#16
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If they were sure a asteroid were going to hit the earth
In article ,
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. 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. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#17
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If they were sure a asteroid were going to hit the earth
On Thu, 13 Nov 2003 03:31:35 -0600, 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. The aerospace firms wanted to get big bucks to make something, and a asteroid stopper has the advantage that the odds it's going to get used in any particular year are very small indeed. If it is used, then either it works, and the companies that built it become heroes; or it doesn't work, and the investigation into corporate fraud is then actually a fairly small concern on the global scale of things. It's like somebody sold me a lotion to wear that they guaranteed would prevent shark attacks anytime I went swimming.....here in North Dakota. Pat The thing I find interesting is that they say there are sizable impacts on a yearly basis but they all seem to fall in the ocean ;-) |
#18
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If they were sure a asteroid were going to hit the earth
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?" ...So then you dust off the data for those 260" diameter solid motors they tested (any idea how long to make the propellant?) Slap some of those one something like Sea Dragon... I think you have failed to grasp just how big Sea Dragon was supposed to be. :-) Strap-ons of that size would increase its payload only a little. Yeah. IIRC Sea Dragon's liftoff thrust was suppose to be something like 72 million. I'm pretty sure even full length 260s were under ten. I figured it would be easier than the 325s or 380s they were kicking around back then :-) (And the capability to build them is not something we could re-establish quickly. Solids look easy but they are not; they are terribly sensitive to even the tiniest flaws in those big masses of fuel.) It would probably be easier then to just make the liquid engine bigger. The idea being that you get the big nuclear warhead in just deep enough that when it goes off it blows out the side using the ejected fragments as reaction mass. If you just blow the thing on the surface... well it probably wouldn't do much. 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 and it was just in dirt. (even still it was pretty amazing. Over a mile down. Check out the 11 Mb file here http://arcticcircle.uconn.edu/SEEJ/amchitka/) There is not a lot of difference between burying it a few meters and detonating it on the surface. I was thinking more along the lines of several hundred feet :-). Granted a 30 foot diameter shaped charge is nothing to sneeze at but I doubt it's beyond current technology. Two of them in tandem would get you three hundred feet in. Follow that with a long slim nuclear weapon that was tough enough to to survive a few lateral bounces and it could get most of the way to the bottom before going off. 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. Here's the problem with that. Surpisingly little of the surface would get vaporized. Back when they were doing testing to figure the erosion on the push plate on Project Orion they discovered that the erosion would be negligable and that something as simple as a very thin coat of oil would eliminate it altogether. (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. In a subsurface burst the "m" would be very high and the "a" would not be insignificant and the majority of it would be directed perpendicular to the impact (the hole cut by the shaped charges would direct the blast). Granted these are big ideas but it's an attempt to figure out how to use current technology to move a LOT of weight. |
#19
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If they were sure a asteroid were going to hit the earth
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. 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. Here's the problem with that. Surpisingly little of the surface would get vaporized. Back when they were doing testing to figure the erosion on the push plate on Project Orion they discovered that the erosion would be negligable... 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.) (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. (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. 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.) -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#20
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If they were sure a asteroid were going to hit the earth
Scott Ferrin wrote: The thing I find interesting is that they say there are sizable impacts on a yearly basis but they all seem to fall in the ocean ;-) There are lots of bolides though on a yearly basis; we didn't take into account that a lot of meteors explode in midair (particularly the carbonaceous chondrites) in the original figures. Mind you, a big one exploding over your head isn't going to be any fun- if Tunguska is anything to go by. Pat |
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