8 ms·

So, is now when everyone starts to put mirrors on their missiles, tanks, and aircraft?

throwanem 10y ago
No, because the beam concentrates enough kinetic energy to go straight through whatever reflective material you have in mind.
- arethuza 10y ago
  I wonder what a 60kW laser would do to a tank? Not very much I'd have thought.
  - Maken 10y ago
    Could it make the reactive armour explode?
  - throwanem 10y ago
    You'd be right. It would need to dwell for considerable time on the same part of the tank's armor to have any meaningful effect, and even that would rely on slow, inefficient heating as a mechanism. (Assuming a rather improbable 100% kinetic energy transfer from a 60kW beam, that equates to about three .50 BMG rounds per second from contact range. That's a big round, but not big enough to have a significant effect on tank armor.) To address another commenter's point, it would not set off explosive reactive armor (ERA). While I don't have detailed information on the ERA compositions in common use, the constraints at hand effectively necessitate the use of relatively insensitive plastic explosives, broadly similar in characteristics to the well-understood C4. Such explosives require a shock wave, provided by a special device or (in the case of ERA) by the impact of a shaped charge, to detonate; heat and fire will not set them off. (Vietnam-era American soldiers burned pieces of C4 from Claymore mine charges as cooking fuel. The smoke was toxic, but that was the only danger.) You need a composition like this for ERA because it is not an actively controlled system. It's not as though there is a computer in the tank which detects an impact and detonates the corresponding ERA segments; the physical processes of such impacts play out far too quickly for such active control to work. ERA therefore has to work on a purely physical basis if it's going to work at all, and that means you need to use an explosive susceptible to detonation on impact. But you don't want an explosive that's very sensitive to impact, or to heat or fire, because you don't want to waste ERA or unnecessarily endanger infantry operating near the tank. (ERA's dangerous enough already that way without giving it a hair trigger!) So it's already not all that plausible that a beam like this might transfer enough energy, even on direct impact with a mass of such explosive, to set it off. But the impact won't be direct, because ERA isn't constructed of bare explosive blocks; there's always going to be a layer of metal, not armor but still relatively thick, between the explosive and the outside environment. This structure would intervene between the explosive and the beam, and would dissipate the transfer energy as heat. That might eventually set the underlying explosive on fire, but, for the reasons we've already covered, it would not cause a detonation.
- metalliqaz 10y ago
  Lasers are EM energy, not kinetic energy.
  - throwanem 10y ago
    What happens when a photon interacts with something that has mass?
    - RugnirViking 10y ago
      Mostly, thermal energy
      - throwanem 10y ago
        What happens when you dump thermal energy into bulk matter at a rate exceeding that at which that matter can dissipate heat?
        marcosdumay 10y ago
        The matter's temperature increases.
        throwanem 10y ago
        What happens when its temperature increases past the melting point?
        marcosdumay 10y ago
        It melts. I'm really not getting your point on the context here. The actual effects of this on a real target will depend on a huge number of variables (I bet it's great against stealth things, but cheap drones will start using aluminum paint).
        lkbm 10y ago

No, because the beam concentrates enough kinetic energy to go straight through whatever reflective material you have in mind.

arethuza 10y ago
I wonder what a 60kW laser would do to a tank? Not very much I'd have thought.
- Maken 10y ago
  Could it make the reactive armour explode?
- throwanem 10y ago
  You'd be right. It would need to dwell for considerable time on the same part of the tank's armor to have any meaningful effect, and even that would rely on slow, inefficient heating as a mechanism. (Assuming a rather improbable 100% kinetic energy transfer from a 60kW beam, that equates to about three .50 BMG rounds per second from contact range. That's a big round, but not big enough to have a significant effect on tank armor.) To address another commenter's point, it would not set off explosive reactive armor (ERA). While I don't have detailed information on the ERA compositions in common use, the constraints at hand effectively necessitate the use of relatively insensitive plastic explosives, broadly similar in characteristics to the well-understood C4. Such explosives require a shock wave, provided by a special device or (in the case of ERA) by the impact of a shaped charge, to detonate; heat and fire will not set them off. (Vietnam-era American soldiers burned pieces of C4 from Claymore mine charges as cooking fuel. The smoke was toxic, but that was the only danger.) You need a composition like this for ERA because it is not an actively controlled system. It's not as though there is a computer in the tank which detects an impact and detonates the corresponding ERA segments; the physical processes of such impacts play out far too quickly for such active control to work. ERA therefore has to work on a purely physical basis if it's going to work at all, and that means you need to use an explosive susceptible to detonation on impact. But you don't want an explosive that's very sensitive to impact, or to heat or fire, because you don't want to waste ERA or unnecessarily endanger infantry operating near the tank. (ERA's dangerous enough already that way without giving it a hair trigger!) So it's already not all that plausible that a beam like this might transfer enough energy, even on direct impact with a mass of such explosive, to set it off. But the impact won't be direct, because ERA isn't constructed of bare explosive blocks; there's always going to be a layer of metal, not armor but still relatively thick, between the explosive and the outside environment. This structure would intervene between the explosive and the beam, and would dissipate the transfer energy as heat. That might eventually set the underlying explosive on fire, but, for the reasons we've already covered, it would not cause a detonation.
metalliqaz 10y ago
Lasers are EM energy, not kinetic energy.
- throwanem 10y ago
  What happens when a photon interacts with something that has mass?
  - RugnirViking 10y ago
    Mostly, thermal energy
    - throwanem 10y ago
      What happens when you dump thermal energy into bulk matter at a rate exceeding that at which that matter can dissipate heat?
      - marcosdumay 10y ago
        The matter's temperature increases.
        throwanem 10y ago
        What happens when its temperature increases past the melting point?
        marcosdumay 10y ago
        It melts. I'm really not getting your point on the context here. The actual effects of this on a real target will depend on a huge number of variables (I bet it's great against stealth things, but cheap drones will start using aluminum paint).
        lkbm 10y ago