Re: Solar powered lasers in space

On Sep 13, 9:44 pm, Alan Anderson <arand...@xxxxxxxxxxxxx> wrote:
In article <1189603948.133528.201...@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,

Willie.Moo...@xxxxxxxxx wrote:
4-wave mixing systems that use active holographic techniques to
control a powerful laser have allowed lasers to penetrate sputtering
vapor and maintain focus on a target by avoiding the sputtered
particles. The same techniques have been used to track targets.

At a distance of a few meters, the technique can deal with things in a
matter of microseconds.

These systems are easily adapted to controlling beams from space and
having the beams avoid unwanted targets while at the same time
illuminating desireable targets.

From LEO, the time delay is significant.

Thank you. You understand. I gave this example to illustrate the
power of adaptive optics properly set up. There are two factors, you
got one of them - time - the other is resolution. This is easily
computed by using the Rayleigh Criterion for Optics.

Yes the ability to penetrate dust and fog may be somewhat limited
because say from LEO - an altitude of say 300 km, response times are
milli-seconds, So, if a 10 micrometer particle moves 100 microns in 2
milliseconds, the adaptive optics will cast a shadow where it was a
millisecond ago. If particle separatoin is 500 micron - this may not
be a problem - all we're trying to do is project energy through the
dust and fog - we don't have to be perfect. So, in this instance -
defocusing the shadow by adjusting the optics a little, to create a
larger shadow centered on where the particle was - can work - up to a
certain particle speed and density.

So, if you go through all the calculations, it might be possible to
penetrate light haze and fog - but not heavier stuff. from LEO. From
GEO you just have to accept that you're going to be scattered by haze
and fog of any amount.

But that's okay - because you can operate in regions where haze and
fog are generally not an issue - high deserts for example.

The important thing is that even in GEO - where the altitude gives you
quarter second response times - you can accurately trace a receiver
and deliver power to it, and interrupt it if there's a large object
between the receiver and transmitter faster than most fuses work

The systemwill automatically cut off if fog or haze grows too thick.
The defocusing trick I just described, to penetrate light fog from low
altitude, will actually cut off power altogether at higher altitudes!
That is, if the shadows through a trick of optics cover the whole
beam, the beam is shut off.

Which combined with finding the target, cutting off the beam if
conditions weren't perfect is all you really need to do to have a safe
realiable service.

So, while I gave the ability to penetrate sputtering particles as an
example of the speed and accuracy possible with adaptive optics, I am
not saying we'll be able to deliver power from GEO through fog or
clouds - but the system properly adapted to the task is certainly fast
enough for tracking a target even if its moving, and interrupting
service to a panel that happens to have an object in the beam.

How high are the space-based beam emitters? Let's call it 300 km, so
the round-trip light travel time is a nice round 2 milliseconds.

Yep. At GEO 36,708 km - round trip travel times 244.72 milliseconds
- 122x longer still. I envision a system of satellites in GEO beaming
1 micron energy to the high desert to large centralized arrays
originally put up to collect solar energy. The energy density is 323
watts/m2 - which is no more than what the sun puts out during the day
in the IR. A 1/4 second response time means that a square meter of
surface will recieve a total of 81 joules before it cuts out. That's
8 millijoules per square cm. In a quarter second,8 milli-joules per
sq cm.

323 watts of IR energy fully absorbed by an object would be heated at
1/3 the rate at which the sun heats an object in broad daylight.

Is this dangerous? I don't think so. A 2,000 watt portable hair
dryer has a nozzle about 20 cm2 in area - that's 100 watts per sq cm -
and in 1/4 second it will deliver 25 joules per sq cm. -

So, I did this experiment - hold your hand in front of a hair dryiery
for 1/4 second at full blast. You'll feel it, but it won't be
dangerous.

Now, radiant energy is different than convection - which is how the
hair dryer works. But, that effects the rate and efficiency of the
heating - not the total amounts we're talking about. We're saying the
transfer is 100% in both cases. In actuality, if your hand, or
whatever is in the beam, reflects IR - then, heating will be far less
than in the case of convection. (air moving against your hand)


How
fast would you need to move your hand through the beam in order to
outpace its ability to avoid illuminating your thumb? Let's call the
width of your thumb a nice round 2 centimeters.

Yes, but even if there was no shadowing at all (which there is) and
your hand received the full brunt of the beam - it would recieve about
2 millijoules per square cm - compare this to 25 joules per sq cm you
get from a hair drying at full blast. You'll feel it - but it won't
damage you - much like tripping a fuse.

Remembrer fuses operate by limiting the amount of total energy that
gets discharged in a body. This works the same way.

Two centimeters in two milliseconds. That's a nice round ten meters per
second. And it's an easily achievable speed. Wave your hand quickly
through the beam and the system won't be able to avoid your thumb.

You are defining edge heating of a moving object in an extended beam.
Wave your hand quickly through a small beam and the leading and
trailing edges of your hand (in a perfectly focused system) would be
warmed but wouldn't get too hot before it left the beam. It takes
time for a given power level to deliver energy to your hand. That's
why you can flick a coal out of a hot fire back into the fire. That's
why you can get a jolt of electricity until the fuse kicks in - and
survive.

Hold you hand steady in the beam for a quarter second, and the beam
even if it originates at GEO will shadow your hand. Change the
optical setup slightly on the satellite, and you'll find the shadow in
the beam of your hand is magnified say 3x - and you will find that
even while moving you won't get edge heating.

All we need is a fuse, and the 4-wave mixing delivers that.

How b A
bird flying into the beam at a sedate ten miles per hour would have the
leading half inch of its head and wings exposed to the full strength of
the beam.

Yes edge effects. And the beam delivers a whopping 1/30th watts per
square cm around the edges of the bird. 1/3 full solar intensity,
1/3000th hair dryer intensity.

And he would get that heating effect for the entire time he flew
through the beam. Say the beam is 8 feet wide - so,at 10 mph the bird
is travelling 14.5 ft per second. He gets this heating effect for
about 55 milliseconds -

Now here's an interesting point..

A small beam, delivered at high intensity, is as safe as a big beam
delivered at low intensity.

A beam of 323 watt per sq m (1/3 watt/cm2) delivering 10 kW would have
an area of about 30 sq m. and be 6.2 m wide - about 20 feet. Our bird
would be in the beam 1-1/4 seconds. He would recieve 1/3 watts per sq
cm. So, he'd get less than 1/2 joule per sq cm.

A beam of 1,000,000 watts per sq m (100 watts/cm2 = hair dryer)
delivering 10 kW would have an area of 1/100h sq m and be 11.3 cm wide
- about 4-1/2 inches in diameter. Our bird would be in the beam 40
milliseconds. He would get zapped with 100 watts/cm2 - a total of 4
joules per sq cm.

If he landed on the reciiever and perched there - it would take 1/4
second for the beam to cut off. In the first case he'd recieve 1/12th
joule per sq cm. In the hypothetical hair dryer case - ultra high
intensity (not being considered for actual construction) he'd get no
more than 25 joules per sq cm. Again, hold your hand in front of a
2,000 watt hair dryer for 1/4 second and feel the effects.

And by putting a slight magnification in the beam optics - he'd be
safe there until he decided to leave. And the power would come on
about 1/8th second later.


A small aircraft flying at 200 knots would travel more than
20 cm in the time it takes for the active holographic technique to
respond.

Yes. There are edge effects that get progressively worse as speed and
distance increases. By careful design of the optical path, shadows at
the ground are magnified by a given factor, which eliminates those
effects within 1/8th second -

Which is my point.

Time and intensity determine how much energy is deposited on an
object. The system I describe can reduce that energy to safe levels -
allowing a safe relaible energy transfer method.

A large centralized array covering millions of acres would have well
defined corridors air traffic would fly over. There are actually
regions of the US where overflight is prohibited,and that happens to
be in some of the sunniest regions of the country. Those would be
ideal collector sites.

But even to an aircraft off course - it would be shadowed by the
satelite - even if located in GEO - in 1/8th second by casting a
magnified shadow back around the aircraft. At 323 Watts/m2 - it would
recieve 1/3 the energy of sunlight - for 1/4 second. At 1,000,000
watts/m2 - the same intensity as a hair dryer - the aircraft would
receive an IR heat load of 250 kJ per m2 - the same amount of energy
it would recieve sitting 4 minutes in the sun. A slight temperature
rise, but nothing destructive.

I'm not proposing 1,000,000 w/m2 - I'm proposing 323 W/m2 - but even
at the higher figure, heating effects are acceptable with a properly
engineered adaptive optics..

A smaller receiver for home or industrial use - would only be a few
meters wide - or at the higher level, a few cm wide - and an aircraft
flying thorugh even the higher intensity beams only a few cm wide -
would have no appreciable effect. Even in a city filled with millions
of beams.

Sure, you'd interrupt a beam for about as long as it takes for a
shadow of an aircraft to flash overhead during landing - but would it
hurt the aircraft? no. You would need some sort of capacitor or
something in your home system though to smoth out the power
fluctuations though.

But how big of a beam are we talking about
And that's the last I'm going to say about it.

Time and intensity are the determinants of how much energy is
delivered to an object. or could be delivered to an object. Beam
size is an important factor.to duration.

The length and style of the rest of your post have successfully
convinced me that you are indeed the William Mook you claim to be.
Congratulations.

yep.

I envision a progressively more sophisticated system being developed
over time. First, you have large centralized arrays of solar
collectors - these receive up to 1000 w/m2 when the sun shines - and
deliver 180 w/m2 electrical - for 1,600 hours per year - in sunny
regions. This is 288 kWh/m2. - making hydrogen from di water by
solar electrolysis - and delivering hydrogen to underground sites - by
pipeline - and delivering a constant supply of hydrogen to coal fired
plants, and hydrogenating the stranded coal into gasoline - is the
first step.

Adding a 1 micron beamed energy system delivering power at 323 watts
IR to the same installation - from GEo - 8,766 hours per year - with
85% efficiency - delivers 2,406 kWh/m2 - in addition to the solar -
increases the hydrogen production - and permits the sale of hydrogen
to augment dwindling oil supplies.

Adding other beamed energy sites around the world - provides direct
electrical power where needed.

Adding an array of reforming satellites at LEO - allows the extension
of the beamed energy system to homes.

Increasing the intensity from 323 watts/m2 to 30,000 watts/m2 allows
the beamed energy system to be used by ground sea and air systems

Increasing the intensity from 30,000 watts/m2 to 1 MW or higher per m2
allows the beamed energy system to be used by space systems
..


.

Relevant Pages

  • Re: Possible spacecraft weapons systems.
    ... let's assume a spacecraft with a zero-point energy ... Even for point blank range CIWS, where the beam spread ... large lens which focuses the beam onto a small spot on the target. ... The zone plate free electron laser weapon design ...
    (rec.arts.sf.science)
  • Re: Solar powered lasers in space
    ... Increasing energy density to 1,000,000 W/m2 and use in flight ... a powerful beam can be switched in phase by a weak ... there are logical layers in ... built into the phase conjugate mirror its far more reliable and safe ...
    (sci.space.policy)
  • Re: Orion Drive space battle
    ... diode lasers just have terrible beam quality. ... energy not extracted as coherent photons remains in the electron beam, ... You say below particle ...
    (rec.arts.sf.science)
  • Negative Energy
    ... energy' photons (anti-photons wouldn't be correct, ... Freezing Dark Death Beam on ... photons (anti-photons wouldn't be correct, ... Negative momentum particles would be VERY noticeable in the particle ...
    (rec.arts.sf.science)
  • Re: Conventions that dont suck?
    ... energy, energy has mass, and mass warps space-time. ... output were put into a narrow beam. ... fluctuations in power level due to the the quantization of the waves ... One advantage of gamma ray frequencies is it's "easy" (at least in ...
    (rec.arts.sf.fandom)