Solar Sail Projectiles

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grooble

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If you had some mass accelerated to 10% of light speed on a solar sail, could you use it to take out an asteroid? Would it have enough force to destroy one or move it?<br /><br />
 
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drwayne

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I ran some quick - back of the envelope numbers. Assuming that your .1C was essentially relative to the target asteroid, then the energy released is roughly 200 kilotons of TNT per kg of the weapon. So a metric ton weapon gives you 200 megatons of TNT.<br /><br />What that does to an asteroid, darn, I really do not know.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>
 
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grooble

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Yes, i've heard that before, but if its broken up, wouldn't a follow up nuke blast vaporise the smaller peices?<br /><br />
 
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henryhallam

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Initially I had the idea that even a fairly large nuke wouldn't actually be able to break the asteroid apart due to its gravitational binding energy (the way fairly large objects are held together - they aren't just huge coherent lumps of rock, they are actually held together by gravity) but having run the numbers this isn't right, because the G.B.E. of e.g. 2004MN4 is only half a gigajoule. So a nuke or very high speed projectile would have more than enough energy to overcome the GBE. In fact the chemical bonds holding it together may very well be stronger.<br /><br />HOWEVER, the energy required to actually vapourise the small pieces is much much greater. Referring to this page: http://www.madsci.org/posts/archives/mar2002/1015040902.Es.r.html<br />It is stated that in terms of the total energy needed to vapourise rock, the specific heat capacity is more significant than the latent heat of vapourisation (this is not the case with water but it does make sense given that the boiling point of rock is so high). So with the boiling point around 2850 K and the asteroid starting about 200 K (could be greater or less depending on its distance from the sun) you require 1080 * 2650 ~= 3 megajoules per kilogram of asteroid.<br /><br />With a medium-small sized asteroid such as 2004 MN4 (4.6 * 10^10 kg) this equates to around 10^17 joules to vapourise the asteroid. A "standard megaton" is 4.2 * 10^15 joules so... you need a 23 megaton nuke to vapourise the asteroid. Actually I'm surprised at how small that is. Of course the nuke would need to be bigger to account for energy lost but that's really not so much. Have I gone wrong somewhere in these calculations?<br /><br />Anyway even if you can vapourise the asteroid completely then your problems are not necessarily over. Could it maybe condense again? Even if it doesn't you are still adding that much energy to the atmosphere but I
 
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mrmorris

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<font color="yellow">"wouldn't a follow up nuke blast vaporise the smaller peices?"</font><br /><br />'Vaporize' means 'turn to vapor'. This essentially means that you're asking if the nuke would not only melt many many tons of solid rock, but also boil it. While I realize (or at least assume) that you didn't mean to be taken literally -- I bring this up as an example of where your thought processes are going off on this.<br /><br />Unless you've worked with explosives -- there's no real feel for what they do. I was a combat engineer and worked with TNT, C4, Ammonium Nitrate, and dynamite (the military grade -- not the nitro version). If you pile a sh*tload of explosives on top of the ground and light it off, what you get is a really big bang, and a very small crater. I mean ***very** small, depending on how hard the ground is, wed get craters an inch or less deep in the center and a foot or two in diameter even when using 20-30 pounds of TNT. This is because conventional explosions essentially create a very rapid expansion of gas. If something isn't directing or containing the expansion, it travels in the path of least resistance -- namely away from whatever solid object it is placed against. Explosions in space are even *less* destructive than ones on the ground, as there is no atmosphere to be expanded, and energy is transmittted only as radiation.<br /><br />In the case of a missile-delivered nuke hitting an asteroid, what would essentially happen (assuming it detonated on impact at ground-level) is that the nuke would go off. The conversion of matter to energy for the hydrogen would generate a huge amount of energy in the form of electromagnetic radiation (everything from radio to Gamma-Rays). The vast majority of this radiated energy would be directed *away* from the asteroid into open space. That portion which is directed toward the asteroid would impact the surface material -- much of which would melt and some of which would vaporize in an a
 
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henryhallam

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<font color="yellow"><br /> It still would not melt or vaporize a significant portion, however. At best, split it into more pieces.<br /></font><br /><br />Unless I have gone wrong with my calculations, I do think that a large nuke technically has enough energy to vapourise a small asteroid. It would probably have to be close to the middle of the asteroid though, otherwise you'd end up with a certain amount of VERY HOT vapourised rock which would carry most of the energy of the explosion, but this would leak out of the hole if it were too close to the edge and so it wouldn't have time to transfer its energy to the rest of the asteroid. In practice I agree with you, you wouldn't be able to vapourise very much of anything over about 10^11 kilograms in mass. And getting a nuke right into the middle would be difficult at best.<br /><br />Question: Would the splitting effect due to the expanding gases be fast enough that the gases could escape before transferring their energy to the rest of the rock, even if the explosion was right in the middle?
 
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edge_of_reason

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<<<If you had some mass accelerated to 10% of light speed on a solar sail, could you use it to take out an asteroid? Would it have enough force to destroy one or move it?>>><br /><br />If your your mass was accelerated going out radially away from the Sun, you would be in deep interstellar space by the time your sail hit 10% of c. So what asteroid were you thinking of impacting? It certainly wont be anything in the Solar System.<br /><br />Edge
 
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mrmorris

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<font color="yellow">"Unless I have gone wrong with my calculations"</font><br /><br />How are you handling losses? You're not going to get 100% efficiency -- or anything close to it. The further from the center of the explosion, the less energy from the radiant energy that will be transmitted to the material of the asteroid. Also, as the rock surrounding the explosion melts, then vaporizes -- it's going to expand <b>dramatically</b>. If there's a means of escape (i.e. the entry tunnel), much of the energy will end up escaping that way. If there is no entry tunnel, or the expanding gasses can't escape fast enough in that fashion, then the asteroid will fracture and you'll lose energy.<br /><br /><font color="yellow">"Question: Would the splitting effect..."</font><br /><br />Who knows? Certainly it's going to be dependent on the size of the asteroid, the size of the explosion, the material/density of the asteroid, the size of the entry hole, the presence or ansence of existing fractures in the asteroid, and a host of other variables that can't be computed with any modicum of certainty.
 
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spacester

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Good discussion, the best ever here on the subject, and we're just getting started.<br /><br />I would just also note that some (a lot?) of the energy would transfer into 'distortion energy'. The rock would compress like a coiled spring and then rebound. Without an atmosphere to dampen the energy, an isloated chunk would continue to vibrate seemingly indefinitely.<br /><br />If it was a solid chunk of rock or metal (unlikely IMO), you would be "ringing a very large bell". If the asteroid is a collection of chunks, you would be ringing them all at different levels of energy. Even if you break it apart from its original condition, you would be ringing a bunch of bells.<br /><br />As you say, the uncertainty would be very high. <div class="Discussion_UserSignature"> </div>
 
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scottb50

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This gets to the falacies of Armagedan. You blow it up and instead of a single object impacting at a certain point you have a number of objects impacting in a much larger area.<br /><br />it's all ballisticS. Look at the Patriot missle, or Bush's ABM system. The destruction of the vehicle spreads the debris over a larger area but it still will come down somewhere and it might make matters even worse because it is dispursed. Say a Nuke destined to destroy a silo in Montana is intercepted, instead of destroying a 20 mile radius it contaminates a 200 mile radius.<br /><br />If an asteroid is a threat blowing it up only expands it's destructive power over a larger area. A more realistic approach would be changing it's orbit, something nukes could not do. Landing mass drivers or attaching Nukes to provide momentum makes much more sense than simply blowing it up. <div class="Discussion_UserSignature"> </div>
 
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henryhallam

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<font color="yellow"><br /> A more realistic approach would be changing it's orbit, something nukes could not do. Landing mass drivers or attaching Nukes to provide momentum makes much more sense than simply blowing it up.<br /></font><br /><br />Completely agree with you here. But hypothetically if a small (few hundred-meters) asteroid could be blown up into vapour or very small pieces (we have established that this is very difficult to do, if possible at all) then even if it still impact the earth there would be little damage since the increased surface area allows the rock to burn up before it reaches ground level. On the other hand if the asteroid is bigger than a km or so then it will have enough energy to heat the atmosphere significantly, whether or not it is broken up. So for something that big, you're screwed unless you can push it out of the way in time.
 
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scottb50

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The only way you could do what you are talking about is doing what was done in armaggedon. Simply launching a missle at it won't push it away. <div class="Discussion_UserSignature"> </div>
 
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vogon13

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Light sail is a low mass, low acceleration technology. 10% C with an appreciable payload is going to take an enormous area of sail material, very very close to the sun. Not sure this is even remotely doable, regardless of the technology used to set it up. 10% C takes you from sun to earth in less than 2 hours. You see how difficult this is getting ? Think how much sunlight decreases from .01 AU to 1 AU.<br /><br />Rough rule of thumb, ~40G for 24 hours gets you to 10%C. As you move away from sun, acceleration decreases at square of the distance, this really sets you back. 40G from a light sail is incredible performance. Most concepts I've seen are less than 0.01G.<br /><br />Also, recall best efficiency for lightsail is radial to sun, so also navigation is problem, too.<br /><br />You can spread acceleration over longer period of time, at the cost of an even bigger sail, but you need to do most of your accel near sun due to that pesky square law thing. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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spacester

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<font color="yellow">. . . an isloated chunk would continue to vibrate seemingly indefinitely.</font><br /><br />Wrong. What a dope! What were you thinking? <img src="/images/icons/laugh.gif" /><br /><br />The vibration would die out due to internal heating resulting from the distortion energy cycles.<br />***<br />I've posted this white paper here several times over the years, maybe this time it will have an impact on the discussion.<br /><br />"Impact" . . . get it? It's a pun . . . <br /><br />oh never mind . . . <div class="Discussion_UserSignature"> </div>
 
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