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Don't we simply need a missile covered with mirrors to defy these lasers? It's just a light bean albeit concentrated one, how hard can it be to deflect it? Ed

• tsbinz 7y ago
  "normal" mirrors don't really work for high-power lasers. If you try to reflect a high-power laser with your bathroom mirror, in the (very short) first moment it will reflect most of the beam, the part that's not reflected will burn the mirror and suddenly it's not a mirror anymore in the spot that the laser hits.
• baq 7y ago
  Mirrors aren’t 100% efficient which means they can be overwhelmed thermally and if you want your missile to be stealthy, you don’t want it reflective.
  • pauljurczak 7y ago
    Reflectivity and stealth are not mutually exclusive. As long as you don't reflect back to the radar antenna(s), you are invisible. In this case a cylindrical missile with 100% reflective conical front and ceramic fins would be very stealthy head-on.
  • naval-gazer 7y ago
    Reflective mirror surface is good for stealth if the angle is right.
• thaumaturgy 7y ago
  No, it doesn't work like that. The military is of course tight-lipped about exactly how powerful SHiELD is, but at least one site claims that the goal is 50kw [1]. That's a lot of power. A few years ago, a 30kw laser test made the rounds in news outlets for destroying a few targets during testing. [2] Mirrors don't perfectly reflect light in all frequencies. Mirrors are designed to reflect mostly visible light, lasers at this power level are infrared. Any imperfections in the reflective surface would immediately heat up, damaging the reflective surface, which would then heat up even more. And even if it were perfect, and were designed to reflect whatever frequency of radiation the laser's putting out, it's still not going to reflect 100% of the laser's output, and you've probably got yourself a material that's pretty impractical for a rocket. [1]: https://phys.org/news/2018-03-air-fighter-mounted-laser-summer.html https://phys.org/news/2018-03-air-fighter-mounted-laser-summ... [2]: https://newatlas.com/lockheed-martin-laser-truck/36377/ https://newatlas.com/lockheed-martin-laser-truck/36377/
  • wnkrshm 7y ago
    Since atmopsheric transmission windows dictate which kind of wavelengths you'd use for a laser weapon and which kinds of wavelengths can efficiently be created, multilayer coatings could conceivably reflect a lot of incoming power. In the 90s, the US DoD asked for 'laser armor' and got photonic crystal structures (1-d multilayer) that omnidirectionally reflect [1]. Further details about this are also available in the book "Photonic Crystals" (preprint for free here [2]). What is probably way easier though (and actually survives launch and particles hitting it and is already proven in practice) is to use ablative heat shields on missiles. The materials available are already optimized for mass vs. effectiveness due to the engineering constraints in space flight. Missile optics would probably need to be coated though or distributed. [1] https://www.osapublishing.org/ol/abstract.cfm?uri=ol-23-20-1573 https://www.osapublishing.org/ol/abstract.cfm?uri=ol-23-20-1... [2] http://ab-initio.mit.edu/book/ http://ab-initio.mit.edu/book/
    • AlanSE 7y ago
      > What is probably way easier though (and actually survives launch and particles hitting it and is already proven in practice) is to use ablative heat shields on missiles. The word "ablative" is typically used in reference to reentry. As the vehicle encounters incredible heat as it comes back into the atmosphere (due to compression heating or whatever), the shield intentionally has some part of its surface gradually boil off. Let me get what you're saying straight. Superpower A would launch an ICBM, and then Superpower B would then laser it as it flies through the air or space. As the missile absorbs the laser heat, its surface starts to boil off, but if the laser doesn't boil off enough, then the laser counter-attack on the missile could still be survivable.
      • 0xDEFC0DE 7y ago
        Plus delaying the time to destroy a single missile is still useful, even if it doesn't eventually make it, since an actual engagement is likely to involve more than one missile being launched. You could throw enough missiles to overwhelm a laser defense system and you might still come out cheaper than the laser defense system. </armchair-general>
• deleted 7y ago
  [deleted]
• fsh 7y ago
  That's actually a very good point. Standard dielectric mirror coatings can easily handle tens of kW hitting a ~1cm spot.
• Paraesthetic 7y ago
  I upvoted you, its a simple question, dont understand the downvoting. Its not everyone's field of expertise.
• pauljurczak 7y ago
  Mirrors would work for a low power laser, but not for what they were testing. There are other options though. The simplest one is a spiky elongated nose cone, which would dramatically reduce delivered power density for a missile on head-on trajectory. Add an ablative cone and you can defeat laser power levels realistically available in the near future, compact enough to be placed in a pod under a wing. Bear in mind that chemically powered laser will have limited number of shots available. Electrically charged one (with super-capacitor) will need significant delays between shots. In both cases they can be overwhelmed by a large enough number of missiles.
  • C1sc0cat 7y ago
    Would not the laser burning off the ablative armour disturb the trajectory ?
    • jacobush 7y ago
      Yep, but that could be countered by putting the missile in a spin (like a rifled bullet) or by active course correction.
    • wompawomp 7y ago
      Well, consider that a trajectory deviation for nuclear strikes is less meaningful inside of a 30 mile radius (might be helpful to a neighboring county). Also, the EMP would likely harm the laser. Meanwhile, laser batteries are probably only going to be protecting ships and their current port. So, better hope it's fleet week. The article mentions enticipated aircraft mounts. I wouldn't expect airborne lasers to scramble in time for most nuclear attacks. They'll only be used in the sense of dog fighting and suring offensive operations.
• onion2k 7y ago
  If you could make a flying retroreflector that looked like a missile you could get the plane to shoot itself down.
  • emiliobumachar 7y ago
    Insightful. But aiming back would be all kinds of hard. There's very little time before your contraption stops reflecting due to being burned by the unreflected portion of the initial beam.
    • aeternus 7y ago
      A retroreflector does not require aiming nor moving parts, it simply uses geometry to ensure that a lightbeam is always reflected back to its source. Retroreflectors are cheap to build and well-understood. It is a very interesting idea, the reflectors likely will burn but you could cover the missile with them. You only need to reflect enough to disable/weaken the emitter.
• arethuza 7y ago
  Good question - being in a somewhat cloudy part of the world I wonder what effect weather would have on this kind of system. Can you only defend yourself on clear days?
• naval-gazer 7y ago
  Despite what other commentators say, mirrors would work in theory. In fact lasers themselves have mirrors. High quality mirror material with > 99.8% reflectivity near infrared region would do the job. Multi layer metal substrate, usually copper based or fused silica to withstand thermal expansion and dielectric coating. High macroscopic surface quality is not needed. It's enough that it reflects. Even the mirrors used in laser erode. Laser weapon uses larger mirror area to focus tighter beam to the target. But unlike laser mirror missile surface don't have to withstand erosion long time and you can rotate the missile to divide the thermal power to larger area. There are practical reasons why the best practical option is not mirror but material with high thermal resistance. Hypersonic missiles already use those materials and they are protected against current generation of military lasers (50 to few 100s of kilowatts). You need megawatt lasers if you try shooting down HGV.
  • Haga 7y ago
    Could a plasma channel surge counter this and destroy the plane?
  • CWuestefeld 7y ago
    My grandfather worked on high-energy laser weapons back in the 70s. The laser would, indeed, melt their own mirrors. They had to develop a whole technology of self-deforming mirrors in order to avoid hot spots on the mirrors. From the descriptions that gramps used to give me, I'm not sure how what's described here is an advance over what he did back in the late 70s. I guess one thing is that back then, they were nowhere near being able to put the whole assembly into a pod that could be mounted on a fighter jet's wing. (gramps also worked on the Hubble Telescope, and spy satellites)
    • electrograv 7y ago
      One would hope that they have made fundamental improvements / innovations to the tech in those past 50 years[1], and they’ll just be keeping that advantage secret for a while. [1] Am I getting old or is it weird realizing that 1970 was almost 50 years ago?
• dboat 7y ago
  The way you asked the question implied that everyone working on the project must be kind of stupid. "simply" "how hard can it be" while showing a lack of expertise on the subject made you sound conceited. The question itself was fine and got interesting answers. Phrased differently, I don't think anyone would have downvoted you.
• hurtle_shurtle 7y ago
  > don't understand the downvoting You’re doing that ‘I am very smart and have found an obvious flaw sitting here that none of the professional missile engineers thought of’ thing. Makes a lot of people cringe.
  • craftyguy 7y ago
    Or they don't understand why their idea is flawed and would like someone to explain so that they may learn why. Also known as, asking questions is the pursuit of knowledge. That this is somehow lost on you makes me cringe, since it reminds me of reddit trolls.
    • Sabinus 7y ago
      "Don't we simply" "How hard can it be"
• nradov 7y ago
  Besides the other problems noted, mirrors and ablative shielding aren't really practical for guided missiles which target aircraft or ships. The missile needs an infrared/optical/radar seeker. So it would be difficult or impossible to find a material which would be electromagnetically transparent for the missile's own seeker but also protect it against incoming laser wavelengths.
• inflatableDodo 7y ago
  One defense is to make a missile that spirals around it's trajectory so it is hard to stay locked on.
• otakucode 7y ago
  Missile defense systems have always had a very basic and fundamentally insurmountable weakness that people just willfully ignore. It costs almost nothing to make more decoys, and it costs an astronomical amount to upgrade your system to track and handle more targets. Building any missile defense system is a nearly guaranteed way to destroy yourself. The enemy just builds more decoys for almost nothing, and then you go broke.
  • deleted 7y ago
    [deleted]
  • HeyLaughingBoy 7y ago
    Well, you do have to launch those decoys,which takes fuel. If they're aircraft-carried, now the airplane has to carry decoys instead of/in addition to live missiles, so it's now less effective. Once the missiles are launched, you need to navigate them actively towards the target at roughly the same flight profile as a real missle, otherwise why would the enemy bother engaging them? So they need guidance, which adds more cost and weight. In the end, you'll end up with a "decoy" that has everything the real missile has except for a warhead, so why not just put a warhead on it? At that point we're talking about just building more missiles, period.
    • asdff 7y ago
      So you are on to something. Why build big one missile that the laser will zap? Do it like your body does with sperm. Send a whole swarm of tiny missiles, overwhelm this huge engineering project, and one might get through.
    • otakucode 7y ago
      Usually, at least in the case of nuclear weapons, more missiles aren't used but more warheads, with the vast majority being decoys. The way the missiles work is that they break apart once they reach a certain point in the trajectory, making tracking far more difficult. It's the fundamental difference between adding more target tracking and handling capability to an anti-missile system (expensive) to just throwing out more cheap decoys. This has been an opposition to missile defense systems since the early 1980s when they were first introduced and I haven't read about any system that overcomes this weakness.
• pletnes 7y ago
  Even if the missile is not destroyed, optical sensor systems must necessarily absorb some light, and will probably be destroyed. This is a possible tactic employed by less powerful lasers, too.