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...100 MW of Space Solar Power ...per single launch!



 
 
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  #221  
Old December 24th 09, 08:01 PM posted to sci.space.policy,sci.space.history,sci.physics
Dr J R Stockton[_54_]
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Posts: 7
Default ...100 MW of Space Solar Power ...per single launch!

In sci.space.history message
, Tue, 22 Dec 2009 11:19:42, Sylvia Else

posted:

What you seem determined to ignore is that the microwave part is a
separate assembly. It is not an integral part of the solar absorber.
Its thermal requirements have to be addressed separately.


Now you are getting into mere engineering.

You seem now to understand that a passive body at Earth's distance from
the Sun, if the same colour all over, will have a temperature of
approximately zero degrees (C or F, it does not matter; but not K).

And, I think, that a mirror facing the Sun will be much cooler, because
it returns energy rather than absorbing it.

The solar cells do absorb energy; but to a considerable extent they do
not themselves dissipate it as heat. as long as they are thermally
connected to the back, they will stay cool.

Now **IF** those cells were all wired to a centre (like the cells on
ISS), where there is a GIANT RF Generator of significantly less than
100% efficiency illuminating an Arecibo or Lovell type RF mirror, then
there would be a local cooling problem with the oscillator; it would be
necessary to transfer heat to the backside of the array, facing the 3K
universe.

So one should not do it that way,

Among the solar cells, distribute a large number of phase-controlled RF
Generators, wired to the local cells and thermally connected to their
backsides. See Wiki "Pave Paws" for an example of such a RF radiating
system.

Note that there is not no substantial electric power interconnect, and
no substantial thermal interconnect. Just a lightweight phase-
controlling-signal system, and enough structure to hold the cells in
place.

--
(c) John Stockton, near London.
Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
Correct = 4-line sig. separator as above, a line precisely "-- " (RFC5536/7)
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  #222  
Old December 24th 09, 08:15 PM posted to sci.space.policy,sci.space.history,sci.physics
Dr J R Stockton[_54_]
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Posts: 7
Default Phased Array [was: ...100 MW of Space Solar Power ...per single launch!]

In sci.space.history message c918ca7a-391a-4c74-a32e-1ba2dd82c8c0@a32g2
000yqm.googlegroups.com, Tue, 22 Dec 2009 11:34:21, Geoffrey A. Landis
posted, in reply to me:
)

The latest idea seems to be to have a number of separately-launched
units close together (a near-filled sunlight receiver), not coupled by
structure but needing active guidance to keep together, and transmitting
phase-coherently across the entire fragmented array.


It doesn't matter how "nearly filled" the sunlight receiver is; what
matters is how nearly-filled the microwave transmitter is. If there
are gaps between the transmitter elements, those gaps will produce
grating lobes, which will reduce the energy of the beam by a fraction
equal to (sum of the individual apertures)/(area of the aperture if it
were completely filled).


I think I underestimated your "Widely separated".

Without analysis, ISTM that one does want the structures close together,
not for visible or RF "optical" reasons, but since it's probably easier
for other vehicles to avoid them that way. But it may be better to have
them far enough apart to be dodged independently.

--
(c) John Stockton, nr London, UK. Turnpike v6.05.
Web URL:http://www.merlyn.demon.co.uk/ - w. FAQish topics, links, acronyms
PAS EXE etc : URL:http://www.merlyn.demon.co.uk/programs/ - see 00index.htm
Dates - miscdate.htm estrdate.htm js-dates.htm pas-time.htm critdate.htm etc.
  #223  
Old December 25th 09, 02:03 AM posted to sci.space.policy,sci.space.history,sci.physics
Sylvia Else
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Posts: 1,063
Default ...100 MW of Space Solar Power ...per single launch!

Dr J R Stockton wrote:
In sci.space.history message
, Tue, 22 Dec 2009 11:19:42, Sylvia Else

posted:
What you seem determined to ignore is that the microwave part is a
separate assembly. It is not an integral part of the solar absorber.
Its thermal requirements have to be addressed separately.


Now you are getting into mere engineering.

You seem now to understand that a passive body at Earth's distance from
the Sun, if the same colour all over, will have a temperature of
approximately zero degrees (C or F, it does not matter; but not K).

And, I think, that a mirror facing the Sun will be much cooler, because
it returns energy rather than absorbing it.

The solar cells do absorb energy; but to a considerable extent they do
not themselves dissipate it as heat. as long as they are thermally
connected to the back, they will stay cool.

Now **IF** those cells were all wired to a centre (like the cells on
ISS), where there is a GIANT RF Generator of significantly less than
100% efficiency illuminating an Arecibo or Lovell type RF mirror, then
there would be a local cooling problem with the oscillator; it would be
necessary to transfer heat to the backside of the array, facing the 3K
universe.

So one should not do it that way,

Among the solar cells, distribute a large number of phase-controlled RF
Generators, wired to the local cells and thermally connected to their
backsides. See Wiki "Pave Paws" for an example of such a RF radiating
system.

Note that there is not no substantial electric power interconnect, and
no substantial thermal interconnect. Just a lightweight phase-
controlling-signal system, and enough structure to hold the cells in
place.


You're just not thinking this through. The solar panel has to remain
pointed at the sun. The output microwave power has to be directed at
Earth. The two directions rotate 360 degrees with respect to each other
every 24 hours. Changing the phase of the elements is all very well, but
the effective aperture of the transmitting antenna would be reduced as
the panel gets foreshortened as seen from Earth. Further the individual
transmitting elements, which presumably do not emit isotropically, would
themselves have to be rotated relevative to the panel.

Sylvia.

  #224  
Old December 25th 09, 09:30 AM posted to sci.space.policy,sci.space.history,sci.physics
Pat Flannery
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Posts: 18,465
Default ...100 MW of Space Solar Power ...per single launch!

Dr J R Stockton wrote:
Among the solar cells, distribute a large number of phase-controlled RF
Generators, wired to the local cells and thermally connected to their
backsides.


could you then turn the temperature differential at the two ends of the
system into a thermoelectric generator, to add more electrical power to
that generated by the solar cells themselves?

Pat
  #225  
Old December 25th 09, 10:01 AM posted to sci.space.policy,sci.space.history,sci.physics
Pat Flannery
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Posts: 18,465
Default Phased Array [was: ...100 MW of Space Solar Power ...persingle launch!]

Dr J R Stockton wrote:
Without analysis, ISTM that one does want the structures close together,
not for visible or RF "optical" reasons, but since it's probably easier
for other vehicles to avoid them that way. But it may be better to have
them far enough apart to be dodged independently.


There is microgravity to contend with here as well as electrostatic
charging and repulsion.
The microgravity fields of the individual elements will cause them to
try and clump together if there isn't some sort of structure connecting
them; once they get close enough their similar electrical charges will
cause them to repel each other - the end result will be that the forces
balance at some point, and they all start settling into a stable
geodetic lattice of points with equal spacing between each of the elements.*
Unfortunately, that stable shape is a sphere, so they start interfering
with each other's microwave transmissions and getting into each other's
shadows.
But then the tidal forces get hold of them, as the ones on the side of
the sphere facing away from Earth are in higher orbits than the ones on
the side facing Earth, and the periods of the two orbits are subtly
different. The details of what happens next in a system with dozens or
hundreds of individual satellites in it would take a computer to
simulate, but I don't think their behavior is simple by any means.

* I think this effect was observed with the peeling insulation blanket
fragments on the HST visible during the Shuttle's approach during the
first repair mission. They seemed to be floating in a cloud around the
telescope, rather than either being pulled into it by its tiny gravity
field or drifting away from it due to the influence of different air
drag versus mass characteristics or photon pressure from the sunlight
striking them.

Pat


  #226  
Old December 25th 09, 05:43 PM posted to sci.space.policy,sci.space.history,sci.physics
Peter Fairbrother
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Posts: 100
Default ...100 MW of Space Solar Power ...per single launch!

Sylvia Else wrote:

You're just not thinking this through. The solar panel has to remain
pointed at the sun. The output microwave power has to be directed at
Earth. The two directions rotate 360 degrees with respect to each other
every 24 hours. Changing the phase of the elements is all very well, but
the effective aperture of the transmitting antenna would be reduced as
the panel gets foreshortened as seen from Earth.


Yes.

Further the individual
transmitting elements, which presumably do not emit isotropically, would
themselves have to be rotated relevative to the panel.


No - that's what a phased array does. The individual elements radiate
over about 2 steradians, or almost half a sphere. The elements of the
array create a beam by interfering with each other, and the timing of
the phases to the elements changes the direction of the beam.

BTW an array can also create two or more beams, by varying the timing of
the phases to the elements - but this involves complex electronics. This
technique is used on some military radar arrays, but it might be
unsuitable for a very large array in space.

Think of two beams incident on the array, and the phase pattern that
would make. Then drive the elements to that pattern, and you get beams
(roughly speaking).

However the transmitting array would most likely be pointed directly at
the Earth station all the time, with only minor phase changes for
precise steering (or alternatively the phases of the elements might be
fixed, in order to make it less complex, and the array oriented precisely).


-- Peter Fairbrother
  #227  
Old December 25th 09, 11:19 PM posted to sci.space.policy,sci.space.history,sci.physics
BradGuth
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Posts: 21,544
Default ...100 MW of Space Solar Power ...per single launch!

On Dec 25, 8:43*am, Peter Fairbrother wrote:
Sylvia Else wrote:
You're just not thinking this through. The solar panel has to remain
pointed at the sun. The output microwave power has to be directed at
Earth. The two directions rotate 360 degrees with respect to each other
every 24 hours. Changing the phase of the elements is all very well, but
the effective aperture of the transmitting antenna would be reduced as
the panel gets foreshortened as seen from Earth.


Yes.

Further the individual

transmitting elements, which presumably do not emit isotropically, would
themselves have to be rotated relevative to the panel.


No - that's what a phased array does. The individual elements radiate
over about 2 steradians, or almost half a sphere. The elements of the
array create a beam by interfering with each other, and the timing of
the phases to the elements changes the direction of the beam.

BTW an array can also create two or more beams, by varying the timing of
the phases to the elements - but this involves complex electronics. This
technique is used on some military radar arrays, but it might be
unsuitable for a very large array in space.

Think of two beams incident on the array, and the phase pattern that
would make. Then drive the elements to that pattern, and you get beams
(roughly speaking).

However the transmitting array would most likely be pointed directly at
the Earth station all the time, with only minor phase changes for
precise steering (or alternatively the phases of the elements might be
fixed, in order to make it less complex, and the array oriented precisely).

-- Peter Fairbrother


If Sylvia Else and most others if this Usenet/newsgroup were any more
negative or naysay, they'd form into an HLC antimatter singularity or
black hole and suck all of us along with them.

The SSP is at best something less than ideal, with considerable energy
losses and somewhat spendy infrastructure. However, that's still a
whole lot better than continually polluting our frail environment with
expanded and intensified carbon footprints, or that of having to
survive WW3 because of global warming from terrestrial Big Energy
alternatives getting too spendy for those of us that are not rich and
powerful. (personally, I seem to have a private yacht and jet gap, not
to mention none of those brown-nosed minions)

~ BG
  #228  
Old December 26th 09, 01:39 AM posted to sci.space.policy,sci.space.history,sci.physics
Sylvia Else
external usenet poster
 
Posts: 1,063
Default ...100 MW of Space Solar Power ...per single launch!

Peter Fairbrother wrote:
Sylvia Else wrote:

You're just not thinking this through. The solar panel has to remain
pointed at the sun. The output microwave power has to be directed at
Earth. The two directions rotate 360 degrees with respect to each
other every 24 hours. Changing the phase of the elements is all very
well, but the effective aperture of the transmitting antenna would be
reduced as the panel gets foreshortened as seen from Earth.


Yes.

Further the individual
transmitting elements, which presumably do not emit isotropically,
would themselves have to be rotated relevative to the panel.


No - that's what a phased array does. The individual elements radiate
over about 2 steradians, or almost half a sphere. The elements of the
array create a beam by interfering with each other, and the timing of
the phases to the elements changes the direction of the beam.


As you say, half a sphere - not isotropic. Allow it to turn far enough
away from the intended beam direction and it won't work. Stockton
appears happy for it to turn through 360 degrees per day.

Sylvia.

  #229  
Old December 26th 09, 01:42 AM posted to sci.space.policy,sci.space.history,sci.physics
Sylvia Else
external usenet poster
 
Posts: 1,063
Default ...100 MW of Space Solar Power ...per single launch!

BradGuth wrote:
On Dec 25, 8:43 am, Peter Fairbrother wrote:
Sylvia Else wrote:
You're just not thinking this through. The solar panel has to remain
pointed at the sun. The output microwave power has to be directed at
Earth. The two directions rotate 360 degrees with respect to each other
every 24 hours. Changing the phase of the elements is all very well, but
the effective aperture of the transmitting antenna would be reduced as
the panel gets foreshortened as seen from Earth.

Yes.

Further the individual

transmitting elements, which presumably do not emit isotropically, would
themselves have to be rotated relevative to the panel.

No - that's what a phased array does. The individual elements radiate
over about 2 steradians, or almost half a sphere. The elements of the
array create a beam by interfering with each other, and the timing of
the phases to the elements changes the direction of the beam.

BTW an array can also create two or more beams, by varying the timing of
the phases to the elements - but this involves complex electronics. This
technique is used on some military radar arrays, but it might be
unsuitable for a very large array in space.

Think of two beams incident on the array, and the phase pattern that
would make. Then drive the elements to that pattern, and you get beams
(roughly speaking).

However the transmitting array would most likely be pointed directly at
the Earth station all the time, with only minor phase changes for
precise steering (or alternatively the phases of the elements might be
fixed, in order to make it less complex, and the array oriented precisely).

-- Peter Fairbrother


If Sylvia Else and most others if this Usenet/newsgroup were any more
negative or naysay, they'd form into an HLC antimatter singularity or
black hole and suck all of us along with them.


I've expressed some concerns about the economics. Otherwise I have no
particular issue with the concept. I've pointed to some of the technical
challenges, but that's not being negative, IMHO.

However the implementation as envisaged by Stockton just won't work
properly.

Sylvia.
  #230  
Old December 26th 09, 11:42 PM posted to sci.space.policy,sci.space.history,sci.physics
Peter Stickney[_2_]
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Posts: 124
Default ...100 MW of Space Solar Power ...per single launch!

Pat Flannery wrote:

jmfbahciv wrote:
Pat Flannery wrote:
jmfbahciv wrote:

You don't know how bad things can get. Snow, sleet, and frozen
rain can coat anything with inches of stuff in that region.


I live in North Dakota, and the same thing can happen around here,
despite it being as flat as a billiard table.
This could mean that the rectennas are limited to the southern parts of
the continent to escape being covered in ice.
In regards to satellite TV that's inconvenient, but when your power grid
is relying on it it becomes critical.
They are better in the south anyway, as a GEO SPS is higher in the sky
from there, so the rectenna array can be more round in shape.


Pat,
As a North Country Sasquatch, coming from the shadow of Mt. Washington
itself, I have to say that you don't have a clue wrt the weather in that
region. When we talk about inches, it's in multiples of 4.
People from up there move to North Dakota for the nicer climate.
The conditions that BAH are referring to are such that candidates for the
Amundson/Scott Station are trained there, so that they won't complain about
the conditions at the South Pole.
The Standard Issue Walking Stick for the Mt. Washington Observatory in
winter is a 5' steel pry bar. Anything else and you'll blow away.

More s.s.h content - The Andover, ME, satellite uplink/downlink station
isn't vary far from there.
Oh, yeah - the Regional High School for Bethel, and Lock Mills, ME, and the
surrounding villiages is Telstar Regional High.

--
Pete Stickney
Who can make lunch out of a red Jordan's Hot Dog, a bag of Humpty-Dumpty
Potato Chips, and a bottle of Moxie.
 




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