Navy Planning To Build Laser Cannon In Four Years

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.'"

Comments

Hmm

[girlintraining]

So Navy's of tomorrow will have their ships covered in mirrors. Now, someone tell me why this won't work... because it seems like a really obvious way to divert a laser beam.

Re:Hmm

[houstonbofh]

High power lasers will smoke a typical mirror. There are reflective surfaces that could work, but you have to keep them perfectly clean. Not happening at sea for long... However, a laser will be easier to track back than a tracer round...

Re:Hmm

[KnightMB]

So Navy's of tomorrow will have their ships covered in mirrors. Now, someone tell me why this won't work... because it seems like a really obvious way to divert a laser beam.

Because a mirror does not reflect 100% of the energy, some will be absorbed, thus the laser will eventually burn through it. Super efficient mirrors are easy counter anyway, just lob some "buckshot" at the target to shatter the mirrors, then burn the ship up with the laser :-)

Re:Hmm

[Anonymous Coward]

Mirrors are not perfect, especially those exposed to the elements. Even a 99.9% reflective mirror (which would be impossible on a ship) would heat up quickly and discolour, and then all bets are off. Also lasers can use a wide range of frequencies outside of visible light which adds to the difficulty.

Re:Hmm

[Anonymous Coward]

High power lasers will smoke a typical mirror. There are reflective surfaces that could work, but you have to keep them perfectly clean. Not happening at sea for long... However, a laser will be easier to track back than a tracer round...

Maybe, maybe not.

If the laser light doesn't scatter much, the only one who can track it back to its source is the target.

But only AFTER getting blasted.

Of course, you could look out for the fricken' shark in the first place... ;-)

Re:Hmm

[Anonymous Coward]

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.

Re:Hmm

[Nidi62]

So Navy's of tomorrow will have their ships covered in mirrors. Now, someone tell me why this won't work... because it seems like a really obvious way to divert a laser beam.

Because the navies of tomorrow (or at least ours will) will also be armed with rail guns. Mirrors won't do much to stop that, and even if there's conventional armor underneath, the rail gun projectile, if it hits, will make them all but useless against a laser.

Re:Hmm

[Anonymous Coward]

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

[hey!]

High power lasers will smoke a typical mirror. There are reflective surfaces that could work, but you have to keep them perfectly clean. Not happening at sea for long...

Perfect defense against the laser isn't really the point. There's a range of conditions under which a laser of a given power can work fast enough to be effective against a quick moving target. Even painting something white would tend to narrow those conditions. Tests done in the 50s with nuclear heat flash showed that structures painted white survived while adjacent unpainted structures burst into flame.

Look at the the video in TFA. Note especially the cut in the editing; it would appear that it took some time for one of the black outboard engines of a stationary boat bursts into flames. The laser they're talking about building is only 7x as powerful as the one used in the demonstration. It's questionable whether such a laser could have that particular effect against a fast moving boat, much less something like a missile.

According to TFA, the point of the program is to get useful lasers onto ships earlier, but I question whether that's the right objective. What does the space, money, and manpower needed to mount such a weapon on a ship displace? Might it make more sense to spend that on something else while we continue research into lasers in a power range that would actually confer some kind of advantage when installed on a ship?

Re:Hmm

[busyqth]

That would be a devastating defense.
I'm sure the Navy will remember it next time they're up against a borg cube.

Re:Hmm

[Tyrannosaur]

Wouldn't the obvious solution be to create ships which absorb incoming energy and re-use it for their own use?

If I extend that "obvious solution" to apply to how to counter, say, nuclear weapons, you'll see why that won't work.

Re:Hmm

[DurnikBob]

Do you mean "your remaining eye"?

Re:Hmm

[Phanatic1a]

I wish people would cut this out.

Have you ever seen a high-energy mirror? It's not something you pick up at Bed, Bath & Beyond. They are expensive, they are fragile, they must be kept completely clean. The reflective surface has to be on the *front* of the mirror, not the rear, because there aren't materials transparent enough to pass high-energy laser light through without absorbing enough of it to react unpleasantly and spoil the reflection. So if there's something like a fingerprint, or a dust speck, on the reflective surface, that bit of crud absorbs the incident light, heats up/explodes, and damages the mirror coating. Which means it's not reflective anymore, which means that area of mirror coating now heats up/explodes and damages adjacent areas, leading to catastrophic failure of the mirror.

You are not going to put mirrors on your greasy *boats* that go bouncing around the surface of the *ocean* and have them remain clean enough to offer protection against a multi-kilowatt laser beam.

Re:Hmm

[icebike]

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, 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:Hmm

[Alan R Light]

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.

Re:Hmm

[tqk]

High power lasers will smoke a typical mirror.

Maybe, maybe not.

If the laser light doesn't scatter much, the only one who can track it back to its source is the target.

I'm not so sure either of these are correct. First, all you need to do is deflect the beam, not reflect it. "Point that thing at me, and one of your satellites is going to burn up!" Or, if you can split the beam into smaller pieces with multiple mirrors arranged around a cone pointed at the beam, you're done.

As for the second, I'd expect to see a plasma trail along the length of the beam consisting of steam and fried dust. That ought to be easily detectable.

Re:Hmm

[c0lo]

High power lasers will smoke a typical mirror. There are reflective surfaces that could work, but you have to keep them perfectly clean. Not happening at sea for long... However, a laser will be easier to track back than a tracer round...

Water; plenty around. Heat capacity: 4.18 J/(g*K).

1 kg of water at 25 C against 100kW => approx 3 secs to reach boiling point. I think I can pump a bit more than 1 kg of water (eventually mixed with some ink to absorb better) along the line of your incoming laser beam. Doesn't need to be totally aligned, just to intersect your beam for some length.
Alternatively, use a jet of water mixed with a medium that's highly dispersive on your wavelength (I don't know, possibly just air bubbles).

(it is said that soviet cosmonauts just used a pencil).

Re:Hmm

[icebike]

Surface forces have no defense against missile attacks, making them useless in a real war

Ah, not exactly true.
http://en.wikipedia.org/wiki/Close-in_weapon_system
http://www.raytheon.com/capabilities/products/searam/
http://en.wikipedia.org/wiki/RIM-116_Rolling_Airframe_Missile

Re:Hmm

[WindBourne]

Actually, that thin-skinned outboard is MUCH thicker than ANY missiles framing. As far as the boat goes, if it was moving on the ocean at say 30 MPH or better and it hit it, then I am impressed. The reason is that with computer tracking, a laser, or several lasers, will be able to hit a missile in one or more spots and blast it quickly. And if the chip is fast enough, it will be able to take out supersonic missiles. Of course, add in heavy rain or a snow-storm, and suddenly, lasers may not be such a great single defense.

I'm Confused....

[Catmeat]

“Subsonic cruise missiles, aircraft, fast-moving boats, unmanned aerial vehicles” — Mike Deitchman, who oversees future weapons development for the Office of Naval Research, promises Danger Room that the Navy laser cannons just over the horizon will target them all.

I'm confused. Surely the one thing a laser canon can't do is target things from over the horizon.

Re:I'm Confused....

[MightyYar]

Yup - the trick is just to design the laser so that the light slows down enough to get into a stable orbit... then you can just fire the laser and it will follow the contour of the earth. Things like mountains and hills can be overcome by firing it even more slowly in a ballistic trajectory.

Re:I'm Confused....

[Anonymous Coward]

He's using "just over the horizon" as a figure of speech, in the sense of time; i.e., the laser cannons that will be built in the near future. It's a poorly written sentence though, so the confusion is understandable.

Re:I'm Confused....

[scream at the sky]

“Subsonic cruise missiles, aircraft, fast-moving boats, unmanned aerial vehicles” — Mike Deitchman, who oversees future weapons development for the Office of Naval Research, promises Danger Room that the Navy laser cannons just over the horizon will target them all. I'm confused. Surely the one thing a laser canon can't do is target things from over the horizon.

I think he is using the word horizon as a metaphor for "coming soon" not a target on the literal horizon. Sloppy wording for sure, it took me a moment to process as well.

Too easy to defend against this

[joe_frisch]

If the attacking boat has a corner cube reflector there is a good chance of blinding people on the defending ship. Since the system needs to be ready for use without warning, the crew would need to always wear laser goggles.

You can protect a missile with an ablative shield - the sort used for re-entry vehicles. This doesn't need to be high tech - wood works surprisingly well (used by the Chinese for spacecraft years ago).

You could use a more diffuse beam to blind the crew of an attacking boat, but I think that violates the Geneva convention.

I'm also very skeptical about the 1MW -> 20' of steel / second. At a kilometer away, you probably have a spot size of around a centimeter. (it depends on wavelength, optics, etc, but that is the right ball park. Iron vaporization energy is 300KJ/mole or about 6KJ/gm. A 1cm long by 10M piece of iron is 1000 cc's or ~10^4 grams. So that's 60MJ to vaporize, or a minute, not a second to burn through. Of course the plume of iron vapor will disrupt the incoming beam so it will take a lot longer. This also assumes you can keep the beam perfectly focused.

The is also the question of whether a complex device like an FEL can be kept always ready to fire within a second. The light is much faster, but its not clear that when you include the time to ready and aim the weapon that the time to hit the target is faster than for a high speed gun.

Re:Too easy to defend against this

[DerekLyons]

If the attacking boat has a corner cube reflector there is a good chance of blinding people on the defending ship. Since the system needs to be ready for use without warning, the crew would need to always wear laser goggles.

Assuming the corner cube reflector is a front surface mirror, and has no dirt or dust or scratches or flaws - yes. Otherwise, the mirror is going to get smoked. Equally, it takes about thirty seconds or less for the crew to get under cover or to at least look away... so, no need for the crew to ever wear laser goggles except for the handful that must look in the direction of the target. (And you can cut the time down even further if you just want them to look away.)
 

You can protect a missile with an ablative shield - the sort used for re-entry vehicles. This doesn't need to be high tech - wood works surprisingly well (used by the Chinese for spacecraft years ago).

Put an ablative shield around the missile - and you've taken a good chunk out of it's range and payload as the shield now occupies weight and volume formerly dedicated to those things. That, or you've increased the impact on the launching platform as the missile is now larger and heavier. (As well as somewhat more expensive.) Keep in mind the wooden heatshields used by the Chinese were impregnated with (modestly high tech) epoxy, they weren't bare wood as the char has almost no strength.
 
 

The is also the question of whether a complex device like an FEL can be kept always ready to fire within a second. The light is much faster, but its not clear that when you include the time to ready and aim the weapon that the time to hit the target is faster than for a high speed gun.

No need for a second, ten to fifteen will do. (And I'll note that the claim that it needs to be a second is yours, not TFA's or the Navy's.)
 
(tl;dr version: Once again, the world doesn't work like most Slashdotters think it does, and Slashdotters haven't thought of something that actual knowledgeable people missed.)

Re:Too easy to defend against this

[joe_frisch]

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.

Re:Why China limitis rare earth exports

[joe_frisch]

FELs do usually use rare earth magnets, but the total amount of material isn't very large compared to disk drives and other commercial uses.

Re:BAD

[busyqth]

I tried to study Lenin, but I got arrested when I tried to break the glass surrounding his desiccated corpse.

Speaking of worker's revolution, you should have seen the call center after I told the drones that I was cutting them back to one bathroom break per eight hour shift. Well they were livid let me tell you! One guy even threatened to quit so I fired him for cause.
Now that was a revolution!

Just wait

[frankmu]

Will the Wave Motion Gun be next?

Re:Priorities.

[cold fjord]

I'm glad we have nothing else to spend money on besides toys for the military.

See this chart: Defense's Share of the Federal Pie and Economy Has Been Declining , in this report.

It's not for defense against major attacks

[Animats]

The Navy wants this so that, when they're dealing with a small boat that's causing a problem, they have an option between "ignore" and "blow them out of the water". Somalia pirates, smugglers, boats getting too close (see USS Cole) - things like that.

Re:Firing range

[wer32r]

I just came to think that it might be a counter-measure to the Iranian high-speed boats. iirc there was a discussion earlier on Slashdot about how difficult they might be to hit with traditional munitions.

Re:Firing range

[fuzzyfuzzyfungus]

I strongly suspect that this laser is intended as a replacement for existing point-defense systems(Phalanx). For longer ranges the navy also has a railgun scheme going, along with existing missiles and aircraft.

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).

And as a positive side effect...

[wisnoskij]

On a lower setting it can cook a perfect hotdog or marshmallow instantly.

This is for sort range tactical threats like boats

[goombah99]

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:Priorities.

[Idarubicin]

If you're going to quote that report, you could just as easily point to this figure.

In inflation-adjusted dollars, defense spending has been higher in the last five budgets than at any other point in the last fifty. The last time the DOD was spending more money in terms of real buying power was World War 2.

Ablative paint is better

[Kupfernigk]

Some military equipment has long been covered in ablative paint. Laser strikes, creates cloud of of particles which diffuse the beam preventing further damage. The identification of materials with suitable oxides or nitrides is left as an exercise for the reader.

Re:how much power does a 1MW laser need?

[joe_frisch]

With a superconducting recirculating LINAC driven FEL, I expect you could get 10-25% wall plug efficiency, but the present systems are way below that because there has so far been no need to optimize efficiency. OTOH, a superconducting linac on a moving platform like a ship raises all sorts of technical issues (for example the cavities are typically suspended by wires.......).

BTW: the above is a guess. Would take a real design study to get a solid number.

laser cannons are hard to scale

[slew]

A professor that I took a class from once mentioned in a lecture the primary difficulty of scaling a laser cannon.

With standard munitions, you send something over to the other ship and it blows up and releases all of its energy over there.
With a laser cannon you blow something up in your own ship and send a light beam over there with whatever laser efficiency you have.

Today, laser efficiency is about 30%, the math isn't very favorable.

Good luck with that

[WindBourne]

Salt water and dust on a mirror is pretty much guaranteeing that the laser is going to punch quickly through those mirrors.

Re:Good luck with that

[FranktehReaver]

Also, wouldn't the giant ship in the middle of the ocean be a good guess on where that blast came from? Speaking lasers have to fire in a line we wouldn't be planning any trajectories to shoot from where they cant see us to begin with.