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Thread: Why not vaporize an asteroid or comet on a collision course with earth?

  1. #1
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    Why not vaporize an asteroid or comet on a collision course with earth?

    When talking about how one could potentially deal with a near earth asteroid or comet, one thing that is frequently stated right away is that "We can't just blow it up" and the analogy is made that this would only turn it from a single bullet into buckshot that would do at least as much damage if not more.

    Using a nuclear explosive might be useful for deflecting a hit, but it's always stated that we can't actually reduce an asteroid to vapor or turn it into dust which would then be dispersed into space.

    But I'd like to pose a question: Why not? It's clear that if you hit it with enough energy you'd reduce it to tiny particles or even to gas and if you had a large enough explosion, you could even blow it apart and scatter the remnants throughout space.

    I'd like to point out that there is no theoretical limit to the power or size of a Teller-Ulam h-bomb and three stage devices have been shown to be practical and have extreme power densities.

    When most think of a big h-bomb the first thing that comes to mind is the Russian RD-220 "Big Ivan" or "Tsar Bomba." It was tested in a modified version with a lead tamper and achieved a yeild of about 50 megatons. In fact, it would have achieved slightly over 100 megatons if tested at full yeild.

    However, when it comes to yeild to weight ratio, the RD-220 is actually not that good. A batter example of a highly effecient bomb is the American Mark-41. This bomb had a weight of just 4,850 kg and a yeild of 25 metric tons. Very large weapons of this type have been shown to be effective and when built so large, they can approach the theoretical maximum effeciency of over five and a half megatons per ton. The mk-41 was about 5.2 megatons per ton.

    As it becomes easier to achieve high effeciency in large nuclear devices, the yeild becomes linear to weight.

    The Ares-5 should be able to fling a good 50 tons into interplanetary space. If we assume that about 20 metric tons of ion engines, guidance systems, antennas and instruments is put onto a vehicle for the mission, this would still leave plenty of room for a 150 megaton warhead.

    Alternatively, the Ares-5 could launch 180 metric tons into a LEO parking orbit. It could launch a 180 metric ton warhead into the orbit and then a 180 metric ton EDS/guidance stage (or even two, utilizing three rockets) that would link up and propel it to the target. If low energy orbital transfers and ion engines were used, this ought to be enough to send it out of orbit. It might take a while to build up velocity. This would up the capacity to nearly a gigaton.


    If earth was really in danger from an asteroid, budget probably would not be much of an issue. If a dozen or so launches were made each year, for three or four years, it would be entirely possible to surround the asteroid with several gigatons worth of explosive energy. Either they could be sent on courses to meet at the asteroid or they could be left in a parking orbit and meet there all at once.

    Actually, I'd recon that a couple of gigatons ought to be enough to completely vaporize/ablate/pulverize a good sized asteroid. Possibly even less could do the job. And it's not impossible to deliver that kind of power to the asteroid or even comet.

    For reference: the 10 megaton Ivy Mike nuclear test was detonated at roughly ground level. It completely obliterated the small island it was located on and dug a crater 200 feet deep and a mile and a half across. It completely vaporized and/or pulverized hundreds of thousands of tons of hard coral rock. The fireball was nearly three miles wide.

    If earth is in danger, would you rather hit an asteroid just as hard as is necessary to push it off course, and hope that your calculations are right and everything goes according to plan? Do you really want it to *just barely* miss the earth? is that a good enough safety margin? Do you want to risk that if the trajectory calculations were off by a fraction of a percent it's the end of humanity? "oh sorry.. we wanted to be gentle and only use the minimum force, but we didn't anticipate that the solar winds would be ever so slightly greater, so instead of just barely missing us, it's going to just barely hit us."

    I sure as hell don't want that. I want that thing hit as hard as possible. Blowing it to smithereens would work for me.

    Explosive force can do it, if you use enough of it. There's a simple rule with brute force: If it doesn't work, that means you're not using enough of it.

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    I don't know the calculations to see whether it would be possible to vaporize a comet with a 1 gigaton nucelear warhead, but that's beside the point because even if you turn a comet into a cloud of water vapour, it's still carrying the same kinetic energy as if it's solid, all of which would be delivered to earth. Same thing with blowing up an asteroid.

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    I would imagine that all these pebbles atoms re-entering the atmosphere would heat things up unfortunately fast.

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    Quote Originally Posted by Drbuzz0 View Post
    ...Explosive force can do it, if you use enough of it. There's a simple rule with brute force: If it doesn't work, that means you're not using enough of it.
    This last is the most important part.

    1) while theoretically one can infinitely scale up nuclear devices, in practical terms 100-400 Megatons is about the upper end limit of modern weapon design potential.

    2) applying that energy in a manner so as to completely vaporize a mass of metal/rock in space is extremely difficult.

    3) these types of devices are not light or easy to launch to interplanetary intercept speeds.

    At some point in the future, such may be possible (but frankly, with the ability to accomplish this, capture and utilization make much more sense than "blasting to smithereens."), but such isn't possible today, or in the near term future.

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    Quote Originally Posted by Siguy View Post
    I don't know the calculations to see whether it would be possible to vaporize a comet with a 1 gigaton nucelear warhead,
    If you can't do it with a 1 gigaton warhead, you could do it with a ten gigaton warhead, or ten 1 gigaton warheads or even 20 500 megaton warheads.

    There's no upper limit to it. If it can't do it, build it bigger and build more of them.

    At the height of the cold war, the combined US and Soviet arsenals were equal to many many gigatons and we still do have most of that material lying around.


    Quote Originally Posted by Siguy View Post
    but that's beside the point because even if you turn a comet into a cloud of water vapour, it's still carrying the same kinetic energy as if it's solid, all of which would be delivered to earth. Same thing with blowing up an asteroid.
    If you blow it all into water vapor or even dust, it's not going to impact the earth in the same manner. If I throw an ice cube at you, it will hurt, but throw a cloud of water vapor with the same energy and it won't do much because it will mostly just blow right past you.

    If you vaporize a comet with several gigatons of nukes, then what you will do is create a big cloud that gets blown apart. You could actually do it enough that all the water molecules are shot off in different directions with enough velocity to leave a big void in the center.

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    Quote Originally Posted by Trakar View Post
    This last is the most important part.

    1) while theoretically one can infinitely scale up nuclear devices, in practical terms 100-400 Megatons is about the upper end limit of modern weapon design potential.

    You can actually build a big bomb out of stacking smaller ones together. It has been alleged that the AN602 bomb was actually four smaller independent warheads in one package. This is not entirely unreasonable.

    If need be, you could deliver the weapons as more than one payload. The speed of blast propagation does not preclude there from being many warheads that would detonate at the same time.


    The way I'd invasion this, you'd "land" several dozen warheads of a power of 50 to a few hundred megatons each on the asteroid, on different sides of it or orbiting very close to it. It might take a few years, maxing out rocket launch capacity to do this. You'd be sending up an enormous warhead every few of months on an Ares-V and a medium sized warhead at a rate of about one a month on a combination of Ariane-5, Proton, Atlas-5, Delta-IV Heavy, Zenit and Falcon-9 rockets. Of course, a centaur of similar to get it to interplanetary space reasonably fast

    Basically consider maxing out the world's capacity to build heavy rockets for a couple years, with each production facility working full tilt to crank out heavy lift vehicles as fast as they can and launch them with the biggest warhead you could fit on them.

    Once you have many gigatons of explosives in one place, you let it rip all at once.

    Difficult? Yes. But impossible? I don't see why, especially if it's a question of a civilization-ending asteroid.

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    If you could .... blow it up into smaller pieces, the very act of disintegrating it would cause pieces of it to accelerate laterally in directions "NOT TOWARD US" which is a good thing. But you need time. You can't do it 2 hours before impact.

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    Last edited by 01101001; 2010-Jan-04 at 04:31 PM.
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    Quote Originally Posted by Drbuzz0 View Post
    ...frequently stated right away is that "We can't just blow it up" and the analogy is made that this would only turn it from a single bullet into buckshot that would do at least as much damage if not more....Using a nuclear explosive might be useful for deflecting a hit, but it's always stated that we can't actually reduce an asteroid to vapor or turn it into dust which would then be dispersed into space...Why not?...
    Only the uninformed would say a NEO can't be vaporized. As you mentioned, the 10 megaton Ivy Mike test vaporized an entire island, and you can see the crater today: http://maps.google.com/maps?f=q&sour...29089&t=h&z=14

    http://en.wikipedia.org/wiki/Ivy_Mike

    Completely vaporizing threatening NEOs has been studied extensively and is possible. a 1,000 megaton device if properly placed could vaporize an asteroid about 1 km across:

    (3MB .pdf) http://www.osti.gov/bridge/servlets/...ble/509521.pdf

    However -- it's tricky to achieve that. The energy coupling of a surface detonation is poor, so this requires emplacing the device deep within the asteroid. The above paper discusses smaller nuclear charges which would create this emplacment shaft.

    Obviously each of those steps adds complexity and risk of something going wrong.

    For threatening NEOs, there are a wide range of possible actions. This varies based on size and warning time. Given a few years warning, a "gravity tractor" or other vehicle could nudge it off course.

    If warning time is only months to a year, the only option would be nuclear. Depending on the object size, mass, and trajectory, a stand-off detonation could push it off course without fragmenting it. That could be done with existing warheads and launch capability.

    The vaporization approach is essentially do or die on a single attempt. By contrast a series of stand-off detonations could progressively ramp up in intensity, giving time to observe the object behavior in between each shot.

    If the goal was vaporization of a 1km-size object, that would take at least a 1,000 megaton device. That would require design and construction.

    The maximum theoretical nuclear yield to weight ratio is 6 kilotons per kg, or 6 megatons per metric ton. If we assume a Delta IV Heavy could put 10,000 kg on an intercept trajectory, that's about 60 megatons, max.

    So the reason for not trying for vaporization becomes clear: it requires non-existent spacelift or orbital assembly, far more complex delivery and detonation, etc. All of those add complexity, time and risk, which you can ill afford with the entire planet in the balance.

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    I agree that nuking it is the best option. I disagree with the assertion that the remains of the asteroid if it wasn't deflected and was turned into smaller bits would cause more damage than a single impact. We get 1000 to 10,000 tons a day now in sizes ranging per day of about 40 centimeters, in a given year about 4 meters, and in a given century about 20 meters. This doesn't raise the tempreture of the earth by any measurable amount. But let's say the daily dose did raise the tempreture one millionth of a degree. If all of the chunks and dust hit the earth it would take 10 billion tons to raise the tempreture one degree.

    Let's call that our target asteroid. 10 billion tons, thirty times the weight of the Arizona crater meteor. To deflect it if it was headed bulls eye toward the earth it would have to be deflected by about 3500 miles by the time it reached us. If we hit it 35 days before impact we would have to make it move off course about 4 miles per hour to get it to miss. If we used one 20 megaton it would impart about one ton of explosive yield to each 500 tons of asteroid. Would one ton of explosive get 500 tons moving at 4 miles per hour? would 4 tons? Would 8 tons? Catch it 70 days in advance. 2 mile per hour deflection rate. Same goes for any pieces including dust. will they be moving or could we get them to move away from their course to earth by 2 to 4 miles per hour? In a "bunker buster" bomb going about 20 feet under the surface would propell about a million tons to a speed of about 10,000 miles ber hour. The reaction of our 10 billion ton asteroid would be about 1 mile per hour. Four 20 megaton bombs would get us what we want.

    Gravity tractor? A nuclear arsenal won't do it but a the gravity of a little bitty spacecraft will? And you still have to apply energy to get the asteroid to move. More than 20 megatons if a 20 megaton bomb won't do it.

    Lasers? They make wonderful tools but lousy weapons. More than 20, 80, 100 megatons? I don't think so. Besides the things turn and would be hard to keep a laser on one spot.

    Focused sunlight? Same problem and asteroids are hard to vaporize for a "vaporized material rocket" and out gassing of a comet would obscure any focused sunlight or laser light.

    There is an incentive for some people to promote gravity tractors, lasers, focused sunlight and encourage nuclear fears "oooh nooo, nuclear bombs, EEEGAAA!!!". (Aside from encouraging nuclear fears for political/economic reasons). For one thing gravity tractors, lasers and focused sunlight capable of doing the job don't exist. That absolves those who might be considered responsable for doing something from doing anything. It also creates an argument for funding gravity tractors, space lasers and focused sunlight. Money, money, money. Follow the money.
    Last edited by aastrotech; 2010-Jan-04 at 09:26 PM.

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    I think redirecting them would be better, as it's less energy intensive then blowing them up.
    And if we ever start using outer space for resources, it will still be available to us for mining.

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    Ideas like gravity tractors are based on the assumption that we have enough lead time (years at least, if not decades) for a relatively small force to significantly affect the asteroids course, so the comparison with nukes in the case of an asteroid 70 days out is a bit unfair.

    The idea of deflecting an asteroid with a nuke depends on how much of the nukes energy would be converted into kinetic energy. If the asteroid is a rubble heap it will deform under the blast, and the asteroid as a whole will hardly budge. A nice anology is hitting a baseball with a bat compared to hitting a lump of putty of the same weight and comparing how far they go. So a blast that breaks a solid asteroid into rubble might be self defeating for other reasons than turning one object into many.

    EDIT: If resource is no object, and we have to vapourise the thing, how much explosive force, nuclear and conventional, does the world have? how big an object could we break into vapour and/ or dust? how many launch vehicles would we need to hit an object in interplanetary space?

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    I've read that Russia plans to blow up a near Earth asteroid 99942 Apophis. I would love to see this happen. Nasa thinks it only has a 1 in 250,000 chance of hitting Earth, but could be as low as 1 in 37..

    I'd be more inclined to see the asteroid actually blown up, than altered off it's axis by some external force. I don't see how debris so far into space would effect Earth, but rather expand our knowledge.. like a been there, done that incase a real, true threat does present itself in the future.

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    Quote Originally Posted by Sententia View Post
    I've read that Russia plans to blow up a near Earth asteroid 99942 Apophis. I would love to see this happen. Nasa thinks it only has a 1 in 250,000 chance of hitting Earth, but could be as low as 1 in 37..

    I'd be more inclined to see the asteroid actually blown up, than altered off it's axis by some external force. I don't see how debris so far into space would effect Earth, but rather expand our knowledge.. like a been there, done that incase a real, true threat does present itself in the future.
    It is important to realize that objects in orbit continue in orbit, whether they are in a single piece or a cloud of expanding pieces, many of the larger pieces may even reform into a singluar object given time and opportunity. Spreading out the Apophis footprint, actually makes it more likely that some of its fragments will impact the Earth, given the imprecise knowledge and nature of the intended operation, we have very little way of determining the results of such a situation, it seems like an experiment that is fraught with potentially dangerous unforseens. If such an experiment is to be undertaken, it would be better to undertake if upon an object that is not in an Earth-crossing orbit.

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    Quote Originally Posted by marsbug View Post
    Ideas like gravity tractors are based on the assumption that we have enough lead time (years at least, if not decades) for a relatively small force to significantly affect the asteroids course, so the comparison with nukes in the case of an asteroid 70 days out is a bit unfair.
    On the other hand, something big enough to be a threat would (hopefully?) be visible in time, due to it's size.
    Right?

    The idea of deflecting an asteroid with a nuke depends on how much of the nukes energy would be converted into kinetic energy. If the asteroid is a rubble heap it will deform under the blast, and the asteroid as a whole will hardly budge. A nice anology is hitting a baseball with a bat compared to hitting a lump of putty of the same weight and comparing how far they go. So a blast that breaks a solid asteroid into rubble might be self defeating for other reasons than turning one object into many.
    Hmm, I remember reading in Mote in God's Eye, the idea of an asteroidal Orion, use a nuke to create a crater at the centre of gravity, then use successive nukes to propel it on a different trajectory. It was science fiction, but it felt to me to be reasonably plausible. I admit my knowledge of the principles of engineering are beyond amateur, however.

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    Quote Originally Posted by ravens_cry View Post
    On the other hand, something big enough to be a threat would (hopefully?) be visible in time, due to it's size.
    Right?


    Hmm, I remember reading in Mote in God's Eye, the idea of an asteroidal Orion, use a nuke to create a crater at the centre of gravity, then use successive nukes to propel it on a different trajectory. It was science fiction, but it felt to me to be reasonably plausible. I admit my knowledge of the principles of engineering are beyond amateur, however.
    Given an asteroid of the appropriate composition, that might be an interesting option.

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    Quote Originally Posted by marsbug View Post
    Ideas like gravity tractors are based on the assumption that we have enough lead time (years at least, if not decades) for a relatively small force to significantly affect the asteroids course, so the comparison with nukes in the case of an asteroid 70 days out is a bit unfair.
    It was supposed to be unfair. Gravity tractors are ridiculous. You missed my point. Longer lead time also gives a smaller explosive a better chance of deflecting it and more chances for larger bombs to blow it up.

    Quote Originally Posted by marsbug View Post
    The idea of deflecting an asteroid with a nuke depends on how much of the nukes energy would be converted into kinetic energy. If the asteroid is a rubble heap it will deform under the blast, and the asteroid as a whole will hardly budge. A nice anology is hitting a baseball with a bat compared to hitting a lump of putty of the same weight and comparing how far they go. So a blast that breaks a solid asteroid into rubble might be self defeating for other reasons than turning one object into many.
    Well a lump of putty would splatter and not much would hit the pitcher. But if I take your meaning as the asteroid would deform and absorb the energy? Then the question is what is the speed of the deformation? 2 miles per hour? 4 miles per hour? What is the escape velocity of our 10 billion ton target? 2 miles per hour? 4 miles per hour? .0000000856 miles per hour? If the deformation speed is greater than escape velocity it would blow apart. Combined with the numbers in my previous post that also answers your next question.

    Quote Originally Posted by marsbug View Post
    EDIT: If resource is no object, and we have to vapourise the thing, how much explosive force, nuclear and conventional, does the world have? how big an object could we break into vapour and/ or dust? how many launch vehicles would we need to hit an object in interplanetary space?
    As to re forming into one piece. That would take a couple of tens of millions of years at least if at all. If all the pieces have a speed greater than their escape velocity from their mutual center of gravity they never will and if less it would take millions of years for them to hit each other, bounce off etc. until their relative speeds are less than their escape velocity from their mutual center of gravity.
    Last edited by aastrotech; 2010-Jan-05 at 03:11 AM.

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    And.......... what if Russia's experiment throws the asteroid (which wasn't a problem) into the wrong direction,..... MAKING a problem. Nice,huh?
    You need to think these things through.

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    Quote Originally Posted by aastrotech View Post
    As to re forming into one piece. That would take a couple of tens of millions of years at least if at all. If all the pieces have a speed greater than their escape velocity from their mutual center of gravity they never will and if less it would take millions of years for them to hit each other, bounce off etc. until their relative speeds are less than their escape velocity from their mutual center of gravity.
    This makes the very big presumption that all or even most of the potentially very large pieces would be imparted with "escape velocity" changes in velocity from such a detonation. I see no reason to presume this, and see a non-negligible chance that you would end up with several large fragments that may temporarily drift apart but which could well end up regrouping within a few orbits if they aren't significantly gravitationally interacted with by other bodies in the intervening time.

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    Quote Originally Posted by danscope View Post
    And.......... what if Russia's experiment throws the asteroid (which wasn't a problem) into the wrong direction,..... MAKING a problem. Nice,huh?
    You need to think these things through.
    I'm not worried about debris entering out atmosphere. If the missile is coming from earth, and blows up in front of the asteroid chances are it would push any left over fragments backwards, and or opposite of being close to the Earth. It also depends how far out in the space the missile will detonate. Will it be in any radius of Earth? Will the missile be sent up months, maybe years before it does go off ? Theirs many questions to be answered before anything happens. But I don't see it as being a ridiculous idea by no means.

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    Quote Originally Posted by Sententia View Post
    I'm not worried about debris entering out atmosphere. If the missile is coming from earth, and blows up in front of the asteroid chances are it would push any left over fragments backwards, and or opposite of being close to the Earth. It also depends how far out in the space the missile will detonate. Will it be in any radius of Earth? Will the missile be sent up months, maybe years before it does go off ? Theirs many questions to be answered before anything happens. But I don't see it as being a ridiculous idea by no means.
    Until the energy of your detonation exceeds the kinetic energy of the asteroid (and that energy is effectively connected to the mass of the asteroid), you aren't going to be getting very much of any debris vectoring off along the path the asteroid came from. For the most part all of the resultant debris will continue along the original path, spreading out in a cone from the point of detonation (but a great deal depends upon the constitution of the asteroid and how effectively that blast energy is coupled to the mass of the asteroid). A standoff detonation, as you seem to be suggesting, may flash a few millimeters of surface rock to vapor and slightly alter the asteroid's orbit, but it generally wouldn't shatter much less vaporize the entire body.

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    Quote Originally Posted by Trakar View Post
    This makes the very big presumption that all or even most of the potentially very large pieces would be imparted with "escape velocity" changes in velocity from such a detonation. I see no reason to presume this, and see a non-negligible chance that you would end up with several large fragments that may temporarily drift apart but which could well end up regrouping within a few orbits if they aren't significantly gravitationally interacted with by other bodies in the intervening time.
    No. Any pieces that depart the mass will have off course momentum and will impart some off course momentum to the the rest. Already gave an illustration of the issue above.

    Any pieces that come back together will have as much energy as what blew them apart to begin with. They won't "drift" gently back together. They'll impact each other and blow themselves apart again. Some of their relative kinetic energy will convert to heat and eventualy they may lose enough to stick together again. It's called acretion. It takes so long we've never seen it happen with objects that small (10 billion to 100 billion tons or less). We've seen the results of it happening. We've developed some theories. We know some places where it should be happening, the asteroid belt, Saturn's rings. It just happens so slow we don't expect to see it happen. It boils down to a couple million years to reassemble an object like this.

    By the way, For a person with the handle "trakar" you've been making a lot of mistakes in your statements about the "track" of the asteroid. "explosion equals the asteroid's kinetic energy"? " vectoring off along the path the asteroid came from."? " Debris will continue along the original path"? These are not questions from me that I expect you to answer. These are statements by you that reveal a misunderstanding on your part of how these things move, can be moved, the forces and directions involved. Seems like you're not really on the same page.
    Last edited by aastrotech; 2010-Jan-05 at 09:10 AM.

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    Quote Originally Posted by danscope View Post
    And.......... what if Russia's experiment throws the asteroid (which wasn't a problem) into the wrong direction,..... MAKING a problem. Nice,huh?
    You need to think these things through.
    Presumably such an experiment would be done on an object that is sufficiently far away that there is no chance of that happening.
    As above, so below

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    Quote Originally Posted by danscope View Post
    And.......... what if Russia's experiment throws the asteroid (which wasn't a problem) into the wrong direction,..... MAKING a problem. Nice,huh?
    You need to think these things through.
    It's not like a game of billiards. It would take a lot to get an object to head to an object as tiny as Earth.

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    Quote Originally Posted by SolusLupus View Post
    It's not like a game of billiards. It would take a lot to get an object to head to an object as tiny as Earth.
    It is like billiards. Just on a very big table with a real soft and warped surface, very small and possibly mushy balls, very small pockets that move real fast and a really short stick. No bank shots unless you use gravity wells. Not much chance for combo shots. But it could be a game. Computer game maybe. Mars vs Earth maybe.

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    Quote Originally Posted by aastrotech View Post
    It was supposed to be unfair. Gravity tractors are ridiculous. You missed my point. Longer lead time also gives a smaller explosive a better chance of deflecting it and more chances for larger bombs to blow it up.



    Well a lump of putty would splatter and not much would hit the pitcher. But if I take your meaning as the asteroid would deform and absorb the energy? Then the question is what is the speed of the deformation? 2 miles per hour? 4 miles per hour? What is the escape velocity of our 10 billion ton target? 2 miles per hour? 4 miles per hour? .0000000856 miles per hour? If the deformation speed is greater than escape velocity it would blow apart. Combined with the numbers in my previous post that also answers your next question.
    No, that wasn't my meaning EDIT: to be clear: I did mean that the asteroid would deform, but not that the deformation itself was a problem, END EDIT. The point I'm trying to make about plastic deformation is that a rubblepile would transmit force poorly and unpredictably. Much of the energy could be lost as internal heat and vibrations due to friction and collisions between rocks, depending on how tightly packed the asteroid is. Voids in the asteroid would make the shockwaves propagate unevenly, so parts of the asteroid could be sent off at great speed and others hardly moved. In other words you might get an unpredictable splatter, with parts of the rock continuing on course and others leaving at high speed. Even a 50m rock could devastate a city, although thats still better than a 1 km rock devastating a continent. Worst case could be like hitting a water ballon rather than a solid object.

    Not that I'm saying explosives couldn't work, but theres no point trying to be efficient or subtle about it if you don't have time to investigate the asteroids structure properly. Work out the blast needed for the absolute worst case scenario, then triple it and apply that. Don't tap it whack it!

    And why are gravity tractors ridiculous? Its an efficient solution, allowing us to study the asteroid with the same ship we plan to move it with. You can't study an asteroid you've just pulverised.
    Last edited by marsbug; 2010-Jan-05 at 04:14 PM.

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    Quote Originally Posted by marsbug View Post
    You can't study an asteroid you've just pulverised.
    Spectroscopy should give some information.

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    Quote Originally Posted by aastrotech View Post
    ...I disagree with the assertion that the remains of the asteroid if it wasn't deflected and was turned into smaller bits would cause more damage than a single impact...
    A fragmented asteroid could easily cause more damage than a unitary impact. It's one reason nuclear MIRV warheads are used -- for a given throw weight, multiple smaller warheads do more damage over a wider area than a single big one.

    This is due to the inverse cube law, whereby blast damage falls off as the cube of distance. Increase distance from ground zero by 4 times, and blast damage drops by 4 cubed (64 times). That illustrates why the pilots who dropped the 55 megaton Soviet Tsar Bomba survived, despite being only 28 miles away when it detonated.

    If instead of a single 55 megaton device, 1,000 500 kiloton devices were spread out so their circles of total destruction overlapped, it would devastate a vastly wider area.

    The Barringer meteor crater in Arizona was caused by an approx 50 meter diameter meteorite, releasing about 5 megatons. A 1 km diameter NEO if finely fragmented to 8,000 equal-size pieces, EACH would produce damage similar to the Barringer crater meteor.

    It's like one huge bomb devastating one place, vs a full-scale nuclear attack by Russia devastating an entire continent (depending on the laydown pattern).

    If you could fragment the NEO to consistent baseball size particles, then they'd probably burn up in the earth's atmosphere. But how could you be absolutely certain of such perfect fragmentation?

    So the problem is obvious -- fragmenting can make things MUCH worse if not done perfectly. Yet with so many unknowns, achieving fragmentation dynamics with extreme confidence is impossible.

    For these reasons it would be safer to nudge it off course using either nuclear or non-nuclear methods, or totally vaporize it.

  29. #29
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    Quote Originally Posted by aastrotech View Post
    It is like billiards. Just on a very big table with a real soft and warped surface, very small and possibly mushy balls, very small pockets that move real fast and a really short stick. No bank shots unless you use gravity wells. Not much chance for combo shots. But it could be a game. Computer game maybe. Mars vs Earth maybe.
    So not like billiards.

  30. #30
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    Quote Originally Posted by glappkaeft View Post
    Spectroscopy should give some information.
    Fair point

    Another problem with deflecting a poorly understood asteroid with explosives is that without knowing how the mass is distributed you might end up spinning it without shifting its course much- like hitting a pool ball way off its center of mass will.

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