Navy Planning To Build Laser Cannon In Four Years 195
CowboyRobot writes "The US Navy is months away from requesting bids from contractors to construct a laser weapon for its ships, now that the technology is feasible. 'The key point came last April, when the Navy put a test laser firing a (relatively weak) 15-kilowatt beam aboard a decommissioned destroyer... the Martime Laser Demonstrator cut through choppy California waters, an overcast sky and salty sea air to burn through the outboard engine of a moving motorboat a mile away.'"
I'm Confused.... (Score:4, Interesting)
I'm confused. Surely the one thing a laser canon can't do is target things from over the horizon.
Re:Firing range (Score:5, Interesting)
It isn't entirely clear that the lasers will work(the demo with the lower powered unit burning an outboard motor took a pitifully long time and that was just a normal outboard motor. No attempt at optical countermeasures, no ablative coatings, no tricks at all); but it should be possible to keep photons on target where it wouldn't be possible for an autocannon to deliver bullets. Also, the navy is in the position where they are pretty much forced to operate on the assumption that something must work and lasers are among the more plausible contenders...
Basically, we have the world's largest investment in aircraft carriers, and stuff for them to carry, and they've been the navy's force-projecting pride and joy since approximately the point in WWII where it became clear that battleships were overpriced floating coffins against even fairly paltry aircraft. Now, if anti-ship missiles and the like cannot be intercepted by some sort of point defense system, it is the aircraft carrier's turn to go the way of the battleship. That would be 10s of billions of dollars worth of awkward(best case, HQ submits to the inevitable in time, the carriers are reduced to a mixture of rotting at the docks and punching defenseless little countries. Worst case, HQ doesn't submit to the inevitable, some scruffy band of militants with a budget so small that an American defense contractor wouldn't bother to steal it sinks something expensive and most of its crew).
This is for sort range tactical threats like boats (Score:4, Interesting)
This is a precision weapon for neutralizing things like Iranian speed boats or Yemeny boat bombs. You don't know if they are threat or not and so rather than blow up everything you disable it and if you make mistake you don't cause death or accidental wars. A laser can't fire over the horizon so it's not useful ship to ship or even ship to airplane. it's even somewhat hard to burn a spinning missile, especially if it is trying to avoid being tracked. (though it might be useful for that if they have enough juice.)
They discontinued the airborne laser program which to me makes more sense. Planes can't carry a lot of bomb weight but they have enormous power plants. Their modern mission are becoming increasingly precision oriented. With a laser can loiter and fry things as long as their fuel hold out. Plus like ships they have lots of cooling available.
Re:Hmm (Score:2, Interesting)
It's quite simple.
Let F be the force, E the energy of a single photon, p the momentum of a single photon, P the power of the laser, f the number of photons per time
For photons,
E = hc/lambda, p = h/lambda -> p = E / c
For each photon reflected, the mirror receives twice the impulse of the photon:
p_received = 2 * E / c
The number of photons per time is:
f = P/E
The force to the mirror is the impulse received per photon times the number of photons per time:
F = N * p_received / t = 2 * f * E / c = 2 * P / c
For a 15-kilowatt LASER, the force would be 1.0e-4 newtons.
Re:Hmm (Score:5, Interesting)
If this stays as a (relatively) short range weapon, which is likely given the way lasers work in the atmosphere, then I doubt that being able to trace the beam back to its source will matter much. A modern US destroyer is over 500 ft long. Based on the one mile range listed in the summary, it would be clearly visible, even to the naked eye.
Further, something big enough to take out an outboard motor, even scaled up, is at best, a point defense weapon (cruise missiles, very small surface craft, close in helicopters, etc.) Even something 10 times as powerful does not completely disable a frigate sized surface vessel before it can return fire with missiles, guns, and torpedo.
However, looking at the video, the time it takes to burn thru a thin-skinned outboard motor, on a boat that was barely moving, and making no effort to avoid the engagement, suggests that there is a long way to go before this could be a missile defense.
So the use case shrinks even further.
Most anti-ship missiles tend to cluster around a speed of 1000 km/h [wikipedia.org], which means they cover that last km in .27 seconds. And some US missiles arrive at over 4000 km/h.
Unless a massively scaled up version can track an incoming missile traveling that fast, and engage it, burn it, or blind it in that .27 seconds, its use as fleet CIWS seems limited at best. The only saving grace is the last km is usually (but not always) a head on straight in attack, making tracking easier.
Re:Too easy to defend against this (Score:4, Interesting)
You are right that the mirror will be destroyed pretty quickly, but for a short time it will be reflecting light back at the ship.
The 1 second was my assumption. I was thinking that the main advantage of the FEL over a conventional gun was the faster travel time for use against nearby fast-moving targets. In that case I think you need a really fast response time. I guess it depends on whether we are talking about inbound missiles or boats. For a boat, I agree you have lots of time, but then I don't see an advantage of the laser over a chain gun. For a missile you probably don't have much reaction time - probably only a few seconds if its a low altitude cruise missile. If you do have time, then again it seems a chain gun would work.
You are also right that adding ablative shielding to missiles will add weight. It would take some work to figure out how much is needed against a MW laser for a ~sonic speed missile.
I help design and commission the world's largest FEL (SLAC / LCLS) - they are quite complex and finicky machines. The FELs the navy is considering are a different type of machine (most likely superconducting recirculating linacs like the TJNAL FEL) but they remain very complex machines (Operating a SC linac on a rolling ship sounds very difficult to me).
Its not impossible to imagine one that could be kept ready for rapid use (1 or 30 seconds doesn't make a lot of difference), but it will be a LOT of work.
I have a reasonable understanding of the technology, but freely admit that I know nothing about the military application.
Ablative paint is better (Score:5, Interesting)
Re:Hmm (Score:4, Interesting)
A simpler solution is for navies to go underwater. In fact, all warfare is about to change: the future will involve few if any manned ships or airplanes, or indeed - manned combat.
Just as sailing ships gave way to steamships, and battleships gave way to carriers, the navies of the future will be quite different from the navies of today. I imagine that most naval vessels of the future will spend almost all of their time beneath the surface, and only occasionally surface to launch multitudes of small flying drones as needed. They will not need to surface at all to launch small swimming drones - and the ships themselves may not be manned.