Re: Solar powered lasers in space

On Sep 17, 3:40 am, Ian Parker <ianpark...@xxxxxxxxx> wrote:
On 14 Sep, 20:30, Willie.Moo...@xxxxxxxxx wrote:



On Sep 14, 9:33 am, Ian Parker <ianpark...@xxxxxxxxx> wrote:

40% seems a very high efficiency for a laser, but even if this figure
is accepted there is one overiding problem. At noon in a desert you
have about 1kw/m^2 coming in through solar power anyway. The obvious
question to me is why not have solar power in the desrt and be done
with it. Lets generate power and split water into hydrogen and oxygen
in the desert using the energy that comes from the Sun anyway. Why
have a space laser as an intermediate stage?

Is it to get power 24/7? Well you have to be above LEO to effectively
extend the desert day.

You add the satellite to lower costs... that's the point. You lower
costs by increasing the capital utilization of the equipment.

BACKGROUND - SOLAR PANELS

PHYSICS
The sun is a thermal source emitting all colors. Silicon has a
specific bandgap energy at 1,108 nm which absorbs all wavelengths
shorter than that bandgap color, and converts each color with an
efficiency of the ratio of the wavelength absorbed relative to the
bandgap wavelength. So, 1,100 nm is almost perfectly absorbed. 550
nm is converted to electrical action at 50% efficiency 275 nm is
converted to electrical action at 25% efficiency - because the bandgap
energy is fixed. ALL the energy of wavelengths longer than 1108 nm
is lost - its converted with 0% efficiency. Summing across all the
wavelengths in a real system - you get about 180 watts electrical for
each 1000 watts solar put in.

Could I say at once as a general preamble that I feel we should keep
an open mind on all possible systems. In talkinf avout 1108nm you are
assuming two things - Photovoltaics & Silicon for photovoltaics. If
that is true then you are correct. There are however alternatives.

1) Biological - Here yellow is the wavelength for photosynthesis, just
over 500nm.
2) Raise steam & drive a turbine- Here wavelength is unimportant.

UTILIZATION
Now in a desert region we have in North America the equivalanet of
1,600 hours of sunlight per year. That's because of seasonal
variation and cosine effects. The sun at dawn and dusk illuminates
the terrain at an angle. Its only at noon at certain times of the
year that you get peak power. All other times light comes in at an
angle and is lower intensity. So, you have an effective peak power
output of 1,600 hours.

This is true. You are now thalking about GEO. Some earlier postings
mentioned LEO. At GEO utilisation is indeed 24/7 (almost) there is an
eclipse season. At the equinoxes this is about 1hr 10min per night
around midnight. Away from equinoxes you have 24/7.





OUTPUT AND COSTS
Energy is measured in kWh. So, each kW of panel from sunlight
produces in this scenario 1,600 kWh.

The cost of this system is lets say $1,000 per peak kilo-watt - and it
has a lifetime of 20 years. That means you're paying $50.00 a year
for the equipment. If you borrowed the money and paid it back over 20
years, you'd pay more like $100.00 a year for the equipment. Lets say
there are no other costs to keep it simple - since these are the main
costs. Then you're paying $100 for 1,600 kWh - that's 6.25 cents per
kWh.

BACKGROUND LASER POWER SAT

LASER POWER PHYSICS

Lets ADD a powersat that beam laser energy at 1,000 nm (1 um) onto
this same panel array. The laser energy is converted by the silicon
with nearly perfect efficiency. 1,0000 nm / 1,108 nm = 90.25% -
scattering in the air subtracts another 5% - So, for each 1,000
watts of laser you get 850 watts electrical.

INTENSITY
If we decide to emit the same 1,000 watts per square meter the sun
produces, using a solar pumped laser in space, then we obtain 850
watts electrical per square meter on the ground. This adds to the 180
watts electrical each square meter produces from sunlight.

COST OF PEAK WATT ON THE GROUND
This is the first advantage of a power sat. We said it cost $1 per
peak watt for the solar panel installation in our example above. This
is $180 per square meter of panels. Reusing the same installation for
a solar power receiver at the intensity described above means that
$180 per square meter is spread across 850 watts electrical output
from the satellite. So, the ground station costs are reduced from $1
per peak watt to ,

$180/850 = $0.212

21.2 cents per peak watt - for the ground statoin side - or $212 per
peak kW.

UTILIZATION

The solar pumped laser is at GEO - hovering stationary above the panel
array. The laser satellite illuminates the panels nearly all the time
and totals.nearly 8,766 hours per year - except for a few minutes when
Earth's shadow eclipses the satellite.

.
OUTPUT AND COSTS
Like the solar panels, the energy is kWh, so each kW of panels and
satellite produces a total of 8,766 hours of satellite power per
year.

Lets say that each kilowatt of solar laser power on orbit costs
$6,000. A satellite is mostly thin film highly reflective plastic
focusing sunlight onto a special device called a fabrey-perot cell -
filled with materials that lase at 1,000 nm. This laser beam passes
through a window of special adaptive optical window that adjusts the
beam in response to a controlling pilot beam from the panel array on
the ground so that the power safely and reliably falls on the panels
and nowhere else.

This is quite interesting. I feel that this concept should be extended
further. A set of lasers such as you describe can be made much more
capable with a few changes. These changes are quite compliocated and
perhaps a little bit difficule to understand but they would not add
greatly to the cost. What you weant on your window is a piezoelectric
system capable of putting a delay of half a wavelength in or out.

If you take a pattern at infinity (in fact the Earth will still be in
the Fresnel region - not quite infinity) and take a Fourier Transform
you get the pattern that has to transmitted. One thing - The radiation
intensity is real (we are not worried about the phase (angle in Argand
diagram). Our laser outlets are only capable of varying phase angle
not intensity. However by giving freedom to phase we can achieve a
general pattern by varying phases alone. This means.

1) The system is capable of being focussed either into a very small
region or into a more diffuse region.

2) The system will focus on a number of spots simultanously some
diffuse some points.

Thought - Could an asteroid be moved by concentrating laser light onto
it?

http://groups.google.co.uk/group/sci.space.policy/browse_frm/thread/4...

Lasers were not mentioned in the NASA report, perhaps they should have
been. I think too it was a great pity that Rand Simberg saw fit to
hijack the discussion.

Personally I am not sure I like the idea of nuclear bombs, where there
is an alternative.

Actually the concepts of LISA, the concept of a large space
(fragmented) telescope and the concept of laser arrays are very much
bound up. With active phase control you can always reach the
diffraction limit and you can work out with 1.22lambda/d just what
that is.

Launch costs are approximately $10,000 per kg and construction costs
in the aerospace business are around $2,500 per kg. The costs of raw
materials are nil compared to these costs. The bulk of the weight of
the satellite is the thin film material - and so knowing the thickness
of this the efficiency of converting sunlight to laser light - we can
compute the area of the film and its weight - and add a correction to
estimate what the laser and controls would weigh - and multiply by the
figures above to get a preliminary estimate of satellite costs - and
see that $5 per watt is accurate.

Launch costs is again an interesting one. If you have an energy system
it will (I presume) go from LEO to GEO using ion drive.

- Ian Parker- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

If all goes well, within the first decade of the full operation of
those Willie Moo laser cannons will start to pay their own way in
clean energy for their R&D and deployment, and if still working after
that first spendy decade is when Earth will start to obtain whatever's
the energy that's no longer going into sustaining his space based
platform of lasers and otherwise of those multiple receiving stations.

The all-inclusive energy that such R&D, deployment and servicing is
going to demand is rather significant, and that's only if nothing goes
all that terribly wrong or wares out. Whereas the LSE-CM/ISS tether
dipole element deployed platform of multiple laser cannons, that'll if
need be reach to within 2r of mother Earth is also doable, and being
far more capable of delivering clean energy to his battery of laser
cannons that'll offer much greater combined energy density. If I were
in charge, I would gladly provide this tether extended platform and
the spare teraWatts of energy.

His terrestrial based solar energy conversions (mostly applied
directly into creating LH2) are actually a whole lot more doable as
is, at not 1% the R&D or much less of any spendy fly-by-rocket and
subsequent pollution factors. However, for some silly reason the
notions of using solar or any renewable energy in order to produce
those nifty energy products of h2o2 and aluminum is Willie Moo taboo.
Go figure (I guess in Willie's world we'll have to keep forever using
nukes, as well as burning off coal, oil and natural gas for the
makings of h2o2 and aluminum, and thus forever creating those extra
mega tonnes of CO2 and NOx).
- Brad Guth -

.

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