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Question about missile defense systems and lasers

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  1. Aug 20, 2017 #1
    I was reading a news article about powerful lasers being used in missile defense systems, and I was wondering if multiple weak laser can work together to do the same job as one strong laser. For example can a thousand 1 Kw lasers in different locations be made to point at a single point on a fast moving target and cause an effect similar to a 1 Mw laser?
     
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  3. Aug 20, 2017 #2

    phinds

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    Theoretically I suppose so, but in practical terms it sounds ridiculous.
     
  4. Aug 21, 2017 #3

    boneh3ad

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    As long as they all focused on the exact same point so that you get the same beam intensity as the larger laser, then sure. That would be an extraordinary challenge to aim that precisely, though. In fact, given the unpredictable nature of density variations throughout the atmosphere, I'd say it would be effectively impossible since it will refract each beam slightly differently.
     
  5. Aug 22, 2017 #4
    Are you contemplating boring through the skin of the missile to disrupt internal systems?
    Or, perhaps blinding the missile by destroying or overloading the sensors?
    What type of missile - ballistic, cruise for example?
    Range to missile would most likely be a factor for focusing and effectiveness, through the atmosphere, as mentioned. Outer space?
    As well as intensity of the laser beam which could ionize the air and again render it in-effective.

    Just posting some areas that you could further investigate if you are inquisitive.
     
  6. Aug 22, 2017 #5
    This laser combining has been researched by DARPA some time back and met with little success. However with advancements in laser/optics this research has surfaced once again with some success. Some reading in the article lends some knowledge and difficulty in combining lasers.

    http://www.laserfocusworld.com/arti...ng-combining-beams-can-boost-total-power.html
     
  7. Aug 22, 2017 #6

    CWatters

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    They might not have to point at exactly the same point, just deliver enough energy to the missile to damage it.

    All my missiles have been polished to a mirror like shine :-)
     
  8. Aug 22, 2017 #7

    boneh3ad

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    Total energy doesn't matter for damage, though. Total energy per area, or intensity, matters. You could defocus a 1 MW laser so that it covered the continental united states and it would be harmless, but focused nearly to a point, it would poke a hole through just about anything.
     
  9. Aug 22, 2017 #8
    The area of a missile is much less then the areas of the united states. I'm guessing the missile can only shed excess heat to the surrounding air at a finite rate. If heat energy is continually added faster then it is taken away I imagine eventually the missile will get so hot it will fail for one reason or another. I'm not sure how many watts of laser such a thing would actually take though, but if most of the laser energy is converted into heat on the missile I can't help thinging a few GW or a TW would do it eventually.
     
  10. Aug 22, 2017 #9

    boneh3ad

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    Well the question would be whether you wanted to kill it with one big "POP!" before it is out of range or do you want to have to train your team of lasers on it over an extended period of time. The bigger lasers aren't working by putting a lot of energy into a small area in order to heat up the whole missile until it experiences thermal failure. They are working by putting a lot of energy into a small area so that a very small portion will fail and they can damage important internal components. For that, you need a lot of energy in a small area, i.e. a high intensity.
     
  11. Aug 22, 2017 #10

    CWatters

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    Don't they have re-entry heat shields? How does the heat of re-entry compare with a 1MW laser?
     
  12. Aug 23, 2017 #11

    boneh3ad

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    I don't know, but the lasers are designed to kill the missile in the boost phase before it reaches space. Really the goal is to rupture the fuel tank and cause the launch to fail, if I'm not mistaken.
     
  13. Oct 1, 2017 #12
    Thinking about this I find there are many details outside my knowledge. I guess what I'm wondering is if quantity can take the place of quality to some degree to make up for difficulties in precision you've mentioned. If just hitting the missile isn't enough precision to get the intensity required perhaps a larger quantity over a few square inches would be enough. Not really understanding the challenges I can only guess.

    There is a phrase I've heard that may pertain to this guess.

    "Good, Fast, Cheap: You Can Only Pick Two."

    This phrase seem to be applicable to many projects although I'm not sure if this is one of them. Still I feel like briefly examining it from such a perspective starting with a few definitions.

    We can define the project as directing a laser at some particular point on a missile in order to destroy it.

    We can define 'good' as directing as laser of adequate intensity at a targeted point on the missile for enough time to render the missile inoperable.

    We can define 'fast' as doing this very quickly which I'm sure is important given the speed of missiles.

    We can define 'cheap' as doing this inexpensively.

    Given these definitions, I'm guessing most missile defense system systems go for 'fast' and 'good'. This is how they achieve the intensity you've mention. I'm a bit curious if instead 'fast' and 'cheap' can be used by replacing the lost 'good' with greater numbers. Of course if you have to many numbers it's no longer cheap, but also maybe if you have enough numbers you can take advantage of economies of scale in production which would bring down costs.

    It seems like it might be a fun thing study if I was an engineer. Shame I didn't take that route.
     
    Last edited: Oct 2, 2017
  14. Oct 19, 2017 #13
    This was discussed at length when Reagan proposed his star wars defense system. The conclusion was that it is a lot easier to defend against a laser attack of a missile than design a laser to thwart the defenses. Some of the methods suggested to defeat a laser defense system were:
    1. Since mirrors are used to aim the lasers, if the missiles were more reflective than the mirror, the mirror would melt before the missile.
    2. Since the time to required to destroy the missile is relatively short, anything to lengthen the time needed to heat the missile beyond that short period would be effective. Two such methods are to spin the missile to spread the heat over a larger area and coating the missile with something like wax that will evaporate and dissipate the heat.
    3. Lasers also tend to dissipate while travelling long distances through air. The air in the center of the beam heats up more than at the edges causing the air to expand and behave like a concave lens.
     
  15. Oct 20, 2017 #14
    Not to derail this thread, but where I work we have modified the phrase
    "Good, Fast, Cheap: You Can Only Pick One."
     
  16. Oct 20, 2017 #15

    phinds

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    Sounds like you should find somewhere else to work
     
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