Karl,

A 'structure' composed of trillions of mass produced 'cells' does have
an advantage, as long as all the 'cells' operate together optically.
Discrete structures separated by millions of meters can operate
together optically via conjugate optics, as described here;

http://ol.osa.org/abstract.cfm?id=7073

Not only can light be reflected from an array of discrete components
as if the entire array of components were operating as a single
optical element, but the reflected light can be amplified via laser
action;

http://ol.osa.org/abstract.cfm?id=8347

So, for these reasons I have assumed that the entire 'structure' -
regardless of how its assembled, acts as a single optical element 2
million kilometers - or 2 billion meters - in diameter.

So, the limits of resolution of a 2 billion meter diameter optical
element is easily computed.

http://www.mellesgriot.com/products/optics/gb_2_3.htm

The diameter of the airy disk is;

sin(theta-r) = 2.44 * lambda / r

and

r = 1e9 m
lambda = 1e-6 m

so

sin(theta-r) = 2.44e-15 ~ 2.44e-15 radians ~1.4e-13 degrees

This implies at various distances most of the energy (86.5%) will fall
within a disk of a particular diameter.

A light year is the distance light travels in one year. So, this is;

3e8 * 3600 * 24 * 365.25 = 9.467e15 meters

A spot that is

2.44e-15*9.467e15 = 23.1 meters in diameter

can be reliably illuminated by an optical element 2e9 meters in
diameter at this distance by 1 micron wavelength light. Tighter
resolutions can be achieved at higher wavelengths. Green light for
example would have an airy spot half this size.


Of course, illuminating smaller portions of the sphere reduces the
effective size of the optical element you're dealing with. Anyone in
the solar system requiring power would only need interrogate a small
portion of this 2 million kilometer diameter optical element.

A kilometer diameter sized spot could be formed to power a laser light
sail or laser sustained rocket up to 40 light years from sol at 1
micron and up to 80 light years from sol in green light. Up to 160
light years in UV. Response times could be a problem. Because you
must wait round trip times in one spot for the power to respond to
your request for it. In these instances it may be preferable to set
up automated equipment to deliver 'waves' of power - like a surf on
the beach - that repeat in well defined spaces and patterns. That way
to make use of the energy, all ships must do is communicate with the
automated equipment as to the times dates and places of the next
series of light surf.

Radio telescopes could communicate information great distances
allowing the coordination of deep space travel from star to star.
They could also allow the collection of electronic payment for use of
energy. So, fees could be collected from great distances
automatically over long periods of times. The size, scope and length
of time such economic entities could exist would be unprecedented in
human history. Against these vast economic powerhouses even present
day governments pale by comparison.

Of course, controlling the output of entire stars and reliably
delivering that output anywhere in a volume up to 100 light years from
that star is also unprecedented in human history. Such capacity would
give our species immediate access to the galaxy and would likely end
poverty as we know it. Although I would suspect poverty as we don't
know it now would likely continue.



(Karl Hallowell) wrote in message . com...
(william mook) wrote in message om...
Ian Stirling wrote in message ...
william mook wrote:
The ultimate in solar collectors must be the deposition of solar
collectors onto the solar surface. The sun puts out 3.86x10^26 watts
of power. Distributed over a sphere whose radius is equal to the
radius of Earth's orbit this falls to a little less than 1,400 watts
per square meter. But on the solar surface this energy density
exceeds 60 megawatts per square meter! Clearly, if we could figure
snip
But of course, we need to figure out how to make something work
reliably on the solar surface. Which I haven't done.

Trivial matter of engineering...
60Mw/m^2 is not a big problem.
A millimeter of copper will only have about 140C across it at 60Mw/m^2.

The problem is the cooling.
You can only radiate to the sky, no convection is possible.
It may be possible to get a hair under solar temperatures by using
coatings that are more efficiant radiators than the solar atmosphere
(no absorbtion bands) but you'r still looking at well over 5000K.

This is a problem, as everything melts at this temperature.

It's probably easier to move out a bit, as you'r not charged by
the square meter for solar surface.

Well, following up on this idea.

The melting point of Copper is 1,357K the melting point of W is 3695K.
This translates to;

Solar Surface: 5770K 64 MW/m2 - Surface (400,000 km from center)
MP Carbon: 3800K 12 MW/m2 - 522,000 km (922,000 km from
center)
MP Tungsten: 3695K 10 MW/m2 - 610,000 km (1,010,000km from
center)
MP Copper: 1357K 195 KW/m2 - 6,830,000 km (7,230,000)

Still 50 million miles inside of Mercury's orbit..

Peak radiation color is;

Solar Surface: 5770K 502 nm Blue/Green
MP Carbon: 3800K 763 nm Dark Red
MP Tungsten: 3695K 785 nm Deep Red
MP Copper: 1357K 2,137 nm Infrared

A carbon film 1,000,000 km in radius and 1 micron thick would have a
volume of 12,566,370,614,359,172,953 cubic meters and weigh
28,487,962,182,752,245,086 metric tons.

A solid ball of carbon this size would have a diameter of 145 km.

A fancy carbon nanotube structure composed of lots of empty space
encompassing the sun might mass 1 quintillion tons which would be 48
km in diameter before deployment. Think of a wire mesh reduced to the
scale of carbon tubes.

Could we concievably process a ball of carbon 50 km across, and unfold
it to embrace the entire output of the sun?

Why not?

There is sufficient resources in the asteroid belt to do this -
carbonaceous chondrites would do nicely.

GaAs lasers would radiate at this wavelength. Carbon nanotubes could
be structured to emit laser light at any wavelength when energized.
Combined with conjugate optical techniques the bulk of this energy
could be made to radiate at any color or mix of colors anywhere.

And we could make use of the entire output of the sun!

Of course, we'd have to take care to keep the Earth and other planets
illuminated as they are now.

This is also a technique that could manage the increasing brightness
of the sun over the aeons - by controlling the output falling on Earth
and the other planets - its possible to maintain present conditions
for astronomical time periods.

Rather than a single large structure, this is likely to be achieved by
a host of small structures. It makes it easier to pass light through
since one could orient the structures edgewise to the Sun whenever
they pass through the plane of the Solar system.

Care needs to be taken with Earth since the radiating structure would
still have the heat output of the Sun. That coupled with the
illumination that would be required means that the Earth gets heated
in two ways.

Power transportation is also a problem. Visible (or UV) light lasers
should be able to illuminate efficiently throughout the inner Solar
system, but it'll take significant surface area or higher frequencies
to beam power out to say Uranus (IMHO). Still dissipation appears to
be a problem to me particularly outside the Solar system. You will
need to find a better way to transport power there.


Karl Hallowell