Re: Earth-surface-based antispacecraft lasers...
- From: LukeCampbell <lwcampbe@xxxxxxxxxxxxxxxx>
- Date: Thu, 20 Oct 2005 09:36:54 -0400
Johnny1a wrote:
You saw my post about this in the "defense for spacecraft against big lasers" thread? If not, that's where to start.Earth's atmosphere is transparent (more or less) to 'visible light' and some IR and radio-wavelength frequencies. For our purpose 'visible' light is probably the way to go.
Just how practical would ground-based laser weaponry be as an
anti-spacecraft weapon from LEO out to, say, twice the distance of GEO?
Assuming we can use any 'visible' wavelength (for some reason I'm
thinking green or blue, but that's not written in stone), and we've got
plenty of power (gigawatts available), can we make a _workable_ weapon
system out of this?
The best wavelengths for atmospheric penetration will vary considerably with atmospheric conditions, but for stuff we would tend to call clear air (ranging from hazy and smoggy but can still see the sky all the way to perfectly clean air) the best wavelengths will be somewhere in the 1 micron (near IR) to 0.5 micron (green) range. The shorter the wavelength, the better the beam can focus, but the more it will be scattered by air molecules and by particulates. The more particulates (haze, smog, mist, dust, pollen) the longer you will want your wavelength to reduce atmospheric scattering; the fewer particulates, the shorter you want your wavelength to keep a tighter focus.
One option might be a free electron laser. These can have their emission wavelength tuned over a moderate range (1 to 0.5 microns would be quite reasonable), and can approach 100% efficiency of turning electrical power to beam power.
With a big enough mirror and enough power, you can zap things out to GEO and further (heck, my original post was about zapping the moon from earth).
Makes the weapon inoperable for space based applications. Except - if you have gigawatts available, you may well be able to burn a hole through the clouds (technically, evaporate a hole through the clouds).The obvious problems (some of them):
Clouds
Haze
Atmospheric moisture
See above, about choosing your wavelength properly
WindsAdaptive optics let you correct for atmospheric turbulance, pre-defocusing the beam so any turbulance re-focuses it.
The need to shield the workings of the lasers from the elements (oneUse the design that astronomers use for their large telescopes, like the Keck. Put it in a dome that can open up.
problem the Lunar cannon doesn't face)
Vibrations in the ground and air around the facility
Not usually a problem.
It seems to me that this system would work best with a widely spreadIf it is feasable, use evacuated underground tunnels to propagate the beam between the projectors, in order to reduce losses due to scattering. If evacuation is not possible, just make sure the air is as clean as you can get it. Maybe you could keep the beam at a long wavelength for propagation (say 1 micron) and then send it through a frequency doubler to get 0.5 micron green if you need it.
array of projectors, so that local cloudcover or weather would not
silence the whole system. Also, a wide-territory array could 'hand
off' the focus as the target crossed the horizon.
Luke .
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- Earth-surface-based antispacecraft lasers...
- From: Johnny1a
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