Airborne Laser Gun 747

[Hardy Heinlin]

http://www.youtube.com/watch?v=oIbPpiSdHz8

My common sense tells me that this technology is useless when the targets have polished surfaces that mirror the light energy.

Isn't this just a big toy that helps the weapon industry, but not the military? It affects all plans regarding laser systems. A laser can destroy many things, even a white colored body, but not a mirror.

Just polish the missile's blank metal, don't paint it, and the whole laser defense is in vain. Why doesn't mention this anyone? Am I missing a certain physical law?

The laser itself is amplified by mirrors. If it could destroy mirrors, it would destroy itself.


Cheers,

|-|ardy

[frumpy]

I found that laser can be used to polish metal: (German only)

http://www.arnold-rv.de/UserFiles/file/Gepulster_Laserstrahl_poliert_Implantatoberflaechen.pdf


Reflection does not seem to be a problem:
http://en.wikipedia.org/wiki/Directed-energy_weapon

[Hardy Heinlin]

Reflection does not seem to be a problem:
http://en.wikipedia.org/wiki/Directed-energy_weapon

Where in this article did you read this? I couldn't find a hint.

[John Golin]

I think the mirrors are related to wavelength - so a polished surface in itself, while efficient at reflecting visible light, may not do so well at other wavelengths?

[Garry Richards]

As frequency increases reflectivity decreases and so absorption increases. Maybe an x-ray laser would penetrate a mirrored surface?

[frumpy]

Hardy, I should have done better homework. The problem of
reflection is not mentioned in the article, so I assumed it's no big deal.

I did some calculations on the energy. Its said that the
laser operates in the Megawatt-range, so the lowest
energy to assume is 1 Megawatt. Lowest absorption
of any material is a carbon-based coating, absorption
is at 0,045%. That means that 1 liter of water with the coating
around it and 1 second heat would warm up the whole thing
by 10° C. This does not seem to be much, but in reality I think
absorption is much higher. Also the laser is concentrated
on a small spot and g-force on rockets is usually high.

[John Golin]

Yes - from what I gather the intention is to heat up the rocket enough in the boost phase that it's structural integrity is compromised and it actually breaks up from aerodynamic forces...

Now the Navy rail guns - those are amazing!

[Hardy Heinlin]

I'm still not convinced :-)

I don't think they use frequencies higher than ultraviolet, maybe not even that.

I don't think they can focus a spot smaller than the size of a football on a target several miles away. The anti-blooming tricks may help to correct light beam direction changes, but not focus changes. Once the dot is blurred on the way through the turbulent airmass, you can't sharpen it again. That would be magic.

I don't think that a laser spot that size (football) can heat up a mirror to damaging temperatures. The rocket is built to stand high temperatures anyway.


|-|

[stekeller]

Well it has worked in tests...

https://www.youtube.com/watch?v=mq7ieXNoyVw

But the airplane is now stored in the Desert

http://www.theverge.com/2012/2/21/2814046/airborne-laser-testbed-canceled-boneyard

- Stekeller
KORD

[Hardy Heinlin]

I have no doubt that it has worked in tests with conventional un-mirrored targets.


|-|ardy



$5 billion did it cost, this experiment.

[Phil Bunch]

I'm still not convinced :-)

I don't think they use frequencies higher than ultraviolet, maybe not even that.

I don't think they can focus a spot smaller than the size of a football on a target several miles away. The anti-blooming tricks may help to correct light beam direction changes, but not focus changes. Once the dot is blurred on the way through the turbulent airmass, you can't sharpen it again. That would be magic.

I don't think that a laser spot that size (football) can heat up a mirror to damaging temperatures. The rocket is built to stand high temperatures anyway.


|-|

Hardy,

I share your skepticism, and apparently the US military agrees since it's not pursuing this project AFAIK.

It is now possible to substantially correct for atmospheric turbulence.  This technique, "adaptive optics", is now in common use at many or most of the major observatories.  They are also using laser beams to create a synthetic guide star to allow the telescope's primary mirror segments to correct for the real-time turbulence via adaptive optics.  It's quite a remarkable set of technologies, to say the least.  I have the impression that this has added much justification for constructing even larger earth-based telescopes for astronomy.

I had the impression that there were so many other issues with the 747-based laser cannon that atmospheric turbulence was probably not the biggest problem.  Of course the project was classified as top secret by the military, so the public will probably never know too much about it.

Here are some links to adaptive optics:

http://www.eso.org/public/teles-instr/technology/adaptive_optics.html

and

http://www.astro.caltech.edu/palomar/AO/