--- In spacesettlers@yahoogroups.com, Al Globus wrote:
> I've done the calc several times and get about the same number.

I've done the calc several times also, over many years, and in different ways. I always come up with Earth intercepting about one 2 billionth of the sun's power.

The paper also said: "just 600 solar power satellites, 1 km radius each, could supply a terawatt (one trillion watts) [Assuming 10% end to end efficiency] of energy continuously and extremely predictably."

Assuming a minimum (because the produced electric-power is supposed to be continuous) solar flux density of 1321 watts/sqm, the amount of solar power intercepted by such an SPS fleet would be 600 * .7854 * 1e6 * 1321 watts/sqm = 622.5 gigawatts. Multiplying that by your 10% efficiency figure gives us only 62.25 gigawatts (to the busbar?). Even increasing the assumed solar flux density to 1400 or 1500 watts/sqm wouldn't bring the total to anywhere near a terawatt.

Next, it says: "Nine thousand such satellites could produce the equivalent of all the energy produced today (roughly 15 TW)."

That would be true if the first part were true -- which it wasn't. Each of the above 1 km radius SPS units delivers 600 / 62.25 GW = .10375 GW. To produce 15 TW would require 15000 GW / .10375 GW = 144,579 SPS units.

Next: "At a 10 km radius, fewer than 400 satellites are necessary."

That's a bit more realistic, but it's because it doesn't jibe mathematically with the previous claims. However, the real answer is that 1,446 satellites would be necessary. They wouldn't fit in GEO (only 264,869 km in circumference) since they would each need to be at least 109x their diameters away from each other and from communications satellites to avoid shadowing. (That doesn't account for the bunching-up caused by solar light pressure distorting the orbits, which bunching-up would create a need for even more spacing.) Even without any comsats in the way, they would need GEO to be 20 km * 109 * 1,446 = 3,152,280 km in circumference.

On Jan 30, 2012, at 9:02 PM, hitssquad wrote:

>
> --- In spacesettlers@yahoogroups.com, Al Globus wrote:
> > I've done the calc several times and get about the same number.
>
> I've done the calc several times also, over many years, and in
> different ways. I always come up with Earth intercepting about one 2
> billionth of the sun's power.
>
> The paper also said: "just 600 solar power satellites, 1 km radius
> each, could supply a terawatt (one trillion watts) [Assuming 10% end
> to end efficiency] of energy continuously and extremely predictably."
>
> Assuming a minimum (because the produced electric-power is supposed
> to be continuous) solar flux density of 1321 watts/sqm, the amount
> of solar power intercepted by such an SPS fleet would be 600 * .7854
> * 1e6 * 1321 watts/sqm = 622.5 gigawatts. Multiplying that by your
> 10% efficiency figure gives us only 62.25 gigawatts (to the
> busbar?). Even increasing the assumed solar flux density to 1400 or
> 1500 watts/sqm wouldn't bring the total to anywhere near a terawatt.
>
It looks like I made a mistake somewhere in the calcs. Given one
million square meters and 1,000 watts/m2 thats a gigawatt. 10%
efficiency (end to end) leads to 100 MW. 600 of those is only 60 GW,
so I was definitely wrong.

For the next two weeks I'm pretty busy with a deadline, but I was
planning to do a re-look at this paper anyway and I'll redo them (with
greater care this time, hopefully). I'll fix it.

Thanks.

--- In spacesettlers@yahoogroups.com, Al Globus wrote:
> I was planning to do a re-look at this paper anyway

OK. I figured it was a work in progress. I'm looking forward to it.

> Thanks.

You're welcome. I hope my feedback helped and that my math wasn't off. Please feel free to email me at yahoo.

Next, it says: "Nine thousand such satellites could produce the equivalent
of all the energy produced today (roughly 15 TW)."

...

Would it be possible to safely transmit so much power by microwave to
Earth? What would be the area of the ground antennas?

Personally, to tell the truth, I feel uncomfortable with power satellites,
unless someone can prove with 99.99% confidence that all this microwave
will not zap the Earth. (Unfortunately blind trust in scientists and
engineers is no longer possible, considering the present state of our
planet in the age of science and technology. )

Still, I would support an experimental satellite.

Theoretically speaking large amounts of power can be generated in space.
One way to transmit power would be to have only the transmitting antennas
at geosynchronous orbit. Power generating satellites can be further back,
which will beam their power to these antennas.

Regards,
Selvaraj

On 31 January 2012 10:32, hitssquad wrote:

On Feb 1, 2012, at 8:41 AM, sraj wrote:

> Next, it says: "Nine thousand such satellites could produce the
> equivalent
> of all the energy produced today (roughly 15 TW)."
>
> ...
>
> Would it be possible to safely transmit so much power by microwave to
> Earth?

I've calculated the heating, it is completely trivial. Much less
than 1/1000th or a degree if memory serves.

Analysis is need to see if beams would promote atmospheric chemistry.

It should be noted that an awful lot of electromagnetic energy passes
through the atmosphere today. Consider the Sun.

> What would be the area of the ground antennas?

Large, but quite a bit smaller than needed to generate the same power
with ground solar.

>
> Personally, to tell the truth, I feel uncomfortable with power
> satellites,
> unless someone can prove with 99.99% confidence that all this
> microwave
> will not zap the Earth.

If by zap, you mean damage a multi-thousand km rock, no. There are
specific effects that can happen and the choice of frequency makes a
big difference. Part of any major SSP project has to be an
environmental impact report. There's good reason to believe the EIR
will come out fine, but it hasn't been done. To do it properly
requires some fairly serious money, a lot more than SSP has ever
received.

It's important to remember that the alternatives, coal, gas, oil,
ground solar, wind, nuclear all have environmental impacts, some of
them pretty nasty. What SSP has to do is be better, not perfect.

I hope that someone gets it worked out. SPS will be very important for
Mars for several reasons. One reasons is the dust storms on Mars which could
put ground based solar out of service for 60 to 120 Martian days a year.

John Wayne Smith,
1000 Planets Research Co.

In a message dated 2/1/2012 9:53:33 P.M. Eastern Standard Time,
alglobus@... writes:

On Feb 1, 2012, at 8:41 AM, sraj wrote:

> Next, it says: "Nine thousand such satellites could produce the
> equivalent of all the energy produced today (roughly 15 TW)."
> ...
> Would it be possible to safely transmit so much power by microwave to
Earth?

I've calculated the heating, it is completely trivial. Much less
than 1/1000th or a degree if memory serves.

Analysis is need to see if beams would promote atmospheric chemistry.

It should be noted that an awful lot of electromagnetic energy passes
through the atmosphere today. Consider the Sun.

> What would be the area of the ground antennas?

Large, but quite a bit smaller than needed to generate the same power
with ground solar.

> Personally, to tell the truth, I feel uncomfortable with power
> satellites, unless someone can prove with 99.99%
> confidence that all this microwave will not zap the Earth.

If by zap, you mean damage a multi-thousand km rock, no. There are
specific effects that can happen and the choice of frequency makes a
big difference. Part of any major SSP project has to be an
environmental impact report. There's good reason to believe the EIR
will come out fine, but it hasn't been done. To do it properly
requires some fairly serious money, a lot more than SSP has ever
received.

It's important to remember that the alternatives, coal, gas, oil,
ground solar, wind, nuclear all have environmental impacts, some of
them pretty nasty. What SSP has to do is be better, not perfect.

> (Unfortunately blind trust in scientists and engineers is no longer
possible,
> considering the present state of our planet in the age of science and
technology. )

> I hope that someone gets it worked out. SPS will be very important for
> Mars for several reasons. One reasons is the dust storms on Mars which could
> put ground based solar out of service for 60 to 120 Martian days a year.

Here's an article about building rectennas on Mars from local materials:

http://science.nasa.gov/science-news/science-at-nasa/1999/msad03mar99_1/

It would be surprising to me if SPS got implemented on Mars before Earth, but you never know.

Another thing I find interesting about this article is that it attributes the original idea of making propellant on Mars from local materials to O'Neill.

Regards,

Mike Combs

From: spacesettlers@yahoogroups.com [mailto:spacesettlers@yahoogroups.com] On Behalf Of jwsmith42000@...
Sent: Wednesday, February 01, 2012 9:28 PM
To: spacesettlers@yahoogroups.com
Subject: Re: [spacesettlers] If only GEO were 3e6 km in circumference (was Earth inter...

I hope that someone gets it worked out. SPS will be very important for
Mars for several reasons. One reasons is the dust storms on Mars which could
put ground based solar out of service for 60 to 120 Martian days a year.

John Wayne Smith,
1000 Planets Research Co.

In a message dated 2/1/2012 9:53:33 P.M. Eastern Standard Time,
alglobus@... writes:

On Feb 1, 2012, at 8:41 AM, sraj wrote:

> Next, it says: "Nine thousand such satellites could produce the
> equivalent of all the energy produced today (roughly 15 TW)."
> ...
> Would it be possible to safely transmit so much power by microwave to
Earth?

I've calculated the heating, it is completely trivial. Much less
than 1/1000th or a degree if memory serves.

Analysis is need to see if beams would promote atmospheric chemistry.

It should be noted that an awful lot of electromagnetic energy passes
through the atmosphere today. Consider the Sun.

> What would be the area of the ground antennas?

Large, but quite a bit smaller than needed to generate the same power
with ground solar.

> Personally, to tell the truth, I feel uncomfortable with power
> satellites, unless someone can prove with 99.99%
> confidence that all this microwave will not zap the Earth.

If by zap, you mean damage a multi-thousand km rock, no. There are
specific effects that can happen and the choice of frequency makes a
big difference. Part of any major SSP project has to be an
environmental impact report. There's good reason to believe the EIR
will come out fine, but it hasn't been done. To do it properly
requires some fairly serious money, a lot more than SSP has ever
received.

It's important to remember that the alternatives, coal, gas, oil,
ground solar, wind, nuclear all have environmental impacts, some of
them pretty nasty. What SSP has to do is be better, not perfect.

> (Unfortunately blind trust in scientists and engineers is no longer
possible,
> considering the present state of our planet in the age of science and
technology. )

Mike, Thank you for that link. One thing it shows is something that I have
been saying for many years: Technology is never outdated - It is just
superceded.
I have looked back as far as 3000 years to get ideas but somehow missed
this one.

Again, Thank You!

John Wayne Smith
1000 Planets Research Company

In a message dated 2/2/2012 9:39:53 A.M. Eastern Standard Time,
mikecombs@... writes:

> I hope that someone gets it worked out. SPS will be very important for
> Mars for several reasons. One reasons is the dust storms on Mars which
could
> put ground based solar out of service for 60 to 120 Martian days a year.

Here's an article about building rectennas on Mars from local materials:

http://science.nasa.gov/science-news/science-at-nasa/1999/msad03mar99_1/

It would be surprising to me if SPS got implemented on Mars before Earth,
but you never know.

Another thing I find interesting about this article is that it attributes
the original idea of making propellant on Mars from local materials to
O'Neill.

Regards,

Mike Combs

From: spacesettlers@yahoogroups.com [mailto:spacesettlers@yahoogroups.com]
On Behalf Of jwsmith42000@...
Sent: Wednesday, February 01, 2012 9:28 PM
To: spacesettlers@yahoogroups.com
Subject: Re: [spacesettlers] If only GEO were 3e6 km in circumference (was
Earth inter...

I hope that someone gets it worked out. SPS will be very important for
Mars for several reasons. One reasons is the dust storms on Mars which
could
put ground based solar out of service for 60 to 120 Martian days a year.

John Wayne Smith,
1000 Planets Research Co.

In a message dated 2/1/2012 9:53:33 P.M. Eastern Standard Time,
alglobus@... writes:

On Feb 1, 2012, at 8:41 AM, sraj wrote:

> Next, it says: "Nine thousand such satellites could produce the
> equivalent of all the energy produced today (roughly 15 TW)."
> ...
> Would it be possible to safely transmit so much power by microwave to
Earth?

I've calculated the heating, it is completely trivial. Much less
than 1/1000th or a degree if memory serves.

Analysis is need to see if beams would promote atmospheric chemistry.

It should be noted that an awful lot of electromagnetic energy passes
through the atmosphere today. Consider the Sun.

> What would be the area of the ground antennas?

Large, but quite a bit smaller than needed to generate the same power
with ground solar.

> Personally, to tell the truth, I feel uncomfortable with power
> satellites, unless someone can prove with 99.99%
> confidence that all this microwave will not zap the Earth.

If by zap, you mean damage a multi-thousand km rock, no. There are
specific effects that can happen and the choice of frequency makes a
big difference. Part of any major SSP project has to be an
environmental impact report. There's good reason to believe the EIR
will come out fine, but it hasn't been done. To do it properly
requires some fairly serious money, a lot more than SSP has ever
received.

It's important to remember that the alternatives, coal, gas, oil,
ground solar, wind, nuclear all have environmental impacts, some of
them pretty nasty. What SSP has to do is be better, not perfect.

> (Unfortunately blind trust in scientists and engineers is no longer
possible,
> considering the present state of our planet in the age of science and
technology. )

--- In spacesettlers@yahoogroups.com, Al Globus wrote:
>
>> What would be the area of the ground antennas?
>
> Large, but quite a bit smaller than needed to generate the same power
> with ground solar.

Nope. Not "quite a bit smaller" at all, not if all the energy needs are
going to be met, instead of just baseline electrical energy needs.

That would require about 8 percent of the entire land area of the
lower-48 U.S.

Also area for ground-based solar can be put on top of things that are
already there: buildings, houses and parking lots.

> Nope. Not "quite a bit smaller" at all, not if all the energy needs are
> going to be met, instead of just baseline electrical energy needs.

Quite a bit smaller for the same total amount of energy delivered. I remember back in the day initially seeing a comparison between rectennas and ground-based solar arrays indicating the former would only take up 1/40 the land area as the latter for the same total amount of power overall. Then later I saw the number changed to 1/30. But even with the later estimate, we're far better off surrendering land to rectennas than to ground-based solar arrays.

> Also area for ground-based solar can be put on top of things that are
> already there: buildings, houses and parking lots.
But we can also put rectenna arrays above things that we couldn't put solar arrays, like croplands and ranchlands.

Regards,

Mike Combs
Internet Marketing Communications
903-868-6314

[E2E Logic http://www.ti.com/e2e-logic]

From: spacesettlers@yahoogroups.com [mailto:spacesettlers@yahoogroups.com] On Behalf Of William
Sent: Thursday, February 02, 2012 4:09 PM
To: spacesettlers@yahoogroups.com
Subject: [spacesettlers] Re: If only GEO were 3e6 km in circumference (was Earth intercepts one part in)

--- In spacesettlers@yahoogroups.com, Al Globus wrote:
>
>> What would be the area of the ground antennas?
>
> Large, but quite a bit smaller than needed to generate the same power
> with ground solar.

Nope. Not "quite a bit smaller" at all, not if all the energy needs are
going to be met, instead of just baseline electrical energy needs.

That would require about 8 percent of the entire land area of the
lower-48 U.S.

Also area for ground-based solar can be put on top of things that are
already there: buildings, houses and parking lots.

Al Globus wrote:
>> What would be the area of the ground antennas? Large, but quite a bit smaller than needed to generate the same power with ground solar.
From: William wlm_efn@...
"Nope. Not "quite a bit smaller" at all, not if all the energy needs are going to be met, instead of just baseline electrical energy needs.
"That would require about 8 percent of the entire land area of the lower-48 U.S.
"Also area for ground-based solar can be put on top of things that are already there: buildings, houses and parking lots.

No one was saying these are mutually exclusive options for society. Come to think of it, has anyone said the ground antennas couldn't also be placed along with solar panels. If there is a large solar installation, couldn't it also have ground antennas installed on the same real estate?

> Come to think of it, has anyone said the ground antennas couldn't also be placed along with solar
> panels. If there is a large solar installation, couldn't it also have ground antennas installed on
> the same real estate?

Geoffrey Landis has written papers on this very proposal. He views SPS and ground-based solar as complementary, not competing.

Regards,

Mike Combs

From: spacesettlers@yahoogroups.com [mailto:spacesettlers@yahoogroups.com] On Behalf Of Matt Gallimore
Sent: Friday, February 03, 2012 11:14 AM
To: spacesettlers@yahoogroups.com
Subject: Re: [spacesettlers] Re: If only GEO were 3e6 km in circumference (was Earth intercepts one part in)

Al Globus wrote:
>> What would be the area of the ground antennas? Large, but quite a bit smaller than needed to generate the same power with ground solar.
From: William wlm_efn@...
"Nope. Not "quite a bit smaller" at all, not if all the energy needs are going to be met, instead of just baseline electrical energy needs.
"That would require about 8 percent of the entire land area of the lower-48 U.S.
"Also area for ground-based solar can be put on top of things that are already there: buildings, houses and parking lots.

No one was saying these are mutually exclusive options for society. Come to think of it, has anyone said the ground antennas couldn't also be placed along with solar panels. If there is a large solar installation, couldn't it also have ground antennas installed on the same real estate?

On Feb 3, 2012, at 9:13 AM, Matt Gallimore wrote:

> Al Globus wrote:
> >> What would be the area of the ground antennas? Large, but quite a
> bit smaller than needed to generate the same power with ground solar.
> From: William wlm_efn@...
> "Nope. Not "quite a bit smaller" at all, not if all the energy needs
> are going to be met, instead of just baseline electrical energy needs.
> "That would require about 8 percent of the entire land area of the
> lower-48 U.S.
> "Also area for ground-based solar can be put on top of things that
> are already there: buildings, houses and parking lots.
>
SSP receivers work 24/7, potentially have greater energy density, and
the input energy is at a known frequency so a lot more juice can be
delivered per unit area. With some frequencies, e.g., microwaves, you
can use the land under the antenna for agriculture.

Ground solar is a 'duh' for roof tops, and there is real progress.
I'm hoping my next roof is electric. That said, I'd prefer to keep as
much of the rest of Earth as green as possible.