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From: Dr J R Stockton on 24 Dec 2009 14:01
In sci.space.history message <008e5048$0$16926$c3e8da3(a)news.astraweb.com
>, Tue, 22 Dec 2009 11:19:42, Sylvia Else <sylvia(a)not.at.this.address>
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. *@merlyn.demon.co.uk/?.?.Stockton(a)physics.org
Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links.
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Do not Mail News to me. Before a reply, quote with ">" or "> " (RFC5536/7)
From: Sylvia Else on 24 Dec 2009 20:03
Dr J R Stockton wrote:
> In sci.space.history message <008e5048$0$16926$c3e8da3(a)news.astraweb.com
>> , Tue, 22 Dec 2009 11:19:42, Sylvia Else <sylvia(a)not.at.this.address>
> 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.

From: Pat Flannery on 25 Dec 2009 03:30
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
From: Peter Fairbrother on 25 Dec 2009 11:43
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
From: BradGuth on 25 Dec 2009 17:19
On Dec 25, 8:43 am, Peter Fairbrother <zenadsl6...(a)zen.co.uk> 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
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