Space Solar Power - A possible way of Reducing Rectenna size?

One of the drawbacks of SSP is the size of the Earth based rectenna.
This isn't an engineering challenge, but near populated areas will be
a planning permission issue. In the UK, it's hard enough to get
planning permission to put up a wind turbine. Even the offshore 1GW
wind farms have had to go through a 3 years approvals process.

SSP doesn't scale well. The original reference designs have a 5GW
beam transmitted from a 5km diameter transmitter to a 5km diameter
rectenna. I can't think of anywhere in the UK where you'd get
planning permission for a 5km rectenna, except perhaps offshore. Even
then ....

One way of reducing the size of the Earth based rectenna is to increase
the size of the space based rectenna. This though increases the power
density and the cost of the space structure.

A question: How do you steer a multi-gigawatt microwave transmitter? Is
it steered electronically? If so, is it possible to switch the beam
across say, 10 rectennas, perhaps 10 times per second?

Consider a 20GW powersat, with a 20km diameter transmitter. This needs
an Earth based rectenna of only 1.25km diameter. However, beaming all
20GW to this one site would make the beam unsafe (about 15KW/m2). If
instead the beam was switched across 10 rectennas, each getting 0.01
seconds every 0.1 second, the average beam power density would be a
relatively safe 1.5KW / m2. Each rectenna produces only 2GW, so as a
source its much more manageable, and a 1.25km diameter rectenna might
get planning permission.

Disadvantages:
- The transmitter is 16 times more massive, carrying 4 times the power.
- Some capacitance is needed at the rectenna - though with clever
design it might be possible to get an AC current out of the rectenna
directly.
- The device could now be used as weapon (but then so can a nuclear
power station)

Is this possible?

On Jan 24, 3:35 pm, "Alex Terrell" wrote:

SSP doesn't scale well. The original reference designs have a 5GW
beam transmitted from a 5km diameter transmitter to a 5km diameter
rectenna. I can't think of anywhere in the UK where you'd get
planning permission for a 5km rectenna, except perhaps offshore. Even
then ....

Simple solution: shut off all electric power to the region that refuses
to allow rectennae on land purchased for that purpose.

Same for nukes.

On Jan 24, 4:35 pm, "Alex Terrell" wrote:

One of the drawbacks of SSP is the size of the Earth based rectenna.

I have a solution. Eliminate it entirely. No rectenna, no problem.

On Jan 24, 4:35 pm, "Alex Terrell" wrote:
One of the drawbacks of SSP is the size of the Earth based rectenna.
...
SSP doesn't scale well. The original reference designs have a 5GW
beam transmitted from a 5km diameter transmitter to a 5km diameter
rectenna.

One way of reducing the size of the Earth based rectenna is to increase
the size of the space based rectenna. This though increases the power
density and the cost of the space structure.

If memory serves, one of the main reasons for the big
receiving antenna was to keep power density below a
level that could start to affect the environment, like
mid-beam birds and such.

- Ed Kyle

"Alex Terrell" wrote in message
oups.com...
One of the drawbacks of SSP is the size of the Earth based rectenna.
This isn't an engineering challenge, but near populated areas will be
a planning permission issue. In the UK, it's hard enough to get
planning permission to put up a wind turbine. Even the offshore 1GW
wind farms have had to go through a 3 years approvals process.

SSP doesn't scale well.



This JPL presentation claims that SSP can bypass
photovoltaics and microwaving completely, by using a
light trap that directly converts sunlight into a high
power laser using fiber optics. And use the laser
beam as a source of transmission to earth or
other points in space.
http://space-power.grc.nasa.gov/ppo/...eaming_TIM.pdf


And in this presentation, from the Univ of Alabama, of
possible laser power beaming technologies, they speculate
such a power beam could be used for thrust.

".1 GW of average optical power converted
to thrust lifts 1 Metric ton to orbit"

And they conclude this is possible for receiver size
for laser transmission.

"Terrestrial system is moderate size (3m x 1m for 1 MW),
which allows location on a vehicle, could be developed in the
near term (2-5 years) with focused program, and can serve
as a stepping stone to the space SHEL Laser."

http://space-power.grc.nasa.gov/ppo/...IM_9-11-02.pdf


This link summarizes much of the latest research in SSP.

Nasa Glenn Research Center
Space Solar Power Concept And Technology Maturation Program
Technical Interchange Meeting (SCTM TIM
http://space-power.grc.nasa.gov/ppo/publications/sctm/


Of course much of this is still very speculative, but
what if we gave our best and brightest that
HUNDRED BILLION over twenty years?

What kind of advances might they come up with
if already they envision having the ability to
.....power cars... directly from space.

Or power colonies and space craft.
Literally..power space craft as in thrust.

But we're going to put a shelter for a few
astronauts on the moon and mars instead.
To look for fossils and establish colonies for
....dozens and well, maybe a dozen people.

You know, how many conspiracy nuts are out
there that imagine Big Corporate America
is hiding those tires that never wear out.
Or that magic perpetual motion machine
etc etc.

Well ya know, the more I read about how the
Vision for Space Exploration came to be.
The more I read about the advances and potential
of SSP.The more I read about how the White House
canned the X-33. And how all these things seemed
to happen in that period just before and after 9/11.

The more I think this is IT~

A Texas oilman long known to be beholden to Lockheed
....trashing solar power and reusable spacecraft
....for the sake of quick and easy profits....naw...only
....in the movies. Never happen, we'd have to be
nuts to even think it...right?

I think they would, and have, done just that.




s

In article .com,
Alex Terrell wrote:
A question: How do you steer a multi-gigawatt microwave transmitter? Is
it steered electronically?

Correct. Oh, there are alternatives, but for such a big transmitting
antenna, electronic steering is overwhelmingly the preferred solution.

If so, is it possible to switch the beam
across say, 10 rectennas, perhaps 10 times per second?

Better: it is possible to generate multiple beams *simultaneously* --
with electronic steering of a zillion-element transmitter, you can shape
the output distribution to have peaks in several directions rather than
just one. (Each beam is still subject to the same fundamental limits on
how tight it can be; this trick doesn't get around that.)
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

On Jan 24, 5:23 pm, "Ed Kyle" wrote:
On Jan 24, 4:35 pm, "Alex Terrell" wrote:

One of the drawbacks of SSP is the size of the Earth based rectenna.
...
SSP doesn't scale well. The original reference designs have a 5GW
beam transmitted from a 5km diameter transmitter to a 5km diameter
rectenna.

One way of reducing the size of the Earth based rectenna is to increase
the size of the space based rectenna. This though increases the power
density and the cost of the space structure.If memory serves, one of the main reasons for the big
receiving antenna was to keep power density below a
level that could start to affect the environment, like
mid-beam birds and such.

I thought it was almost entirely to keep the size of the transmitting
antenna (which, after all, has to be launched into space) under
control. I could be wrong.

- jake

"Alex Terrell" wrote:

:- The device could now be used as weapon (but then so can a nuclear
ower station)

How can a nuclear power station be used as a weapon?

--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn

On 25 Jan, 03:01, "Jake McGuire" wrote:
On Jan 24, 5:23 pm, "Ed Kyle" wrote:

On Jan 24, 4:35 pm, "Alex Terrell" wrote:

One of the drawbacks of SSP is the size of the Earth based rectenna.
...
SSP doesn't scale well. The original reference designs have a 5GW
beam transmitted from a 5km diameter transmitter to a 5km diameter
rectenna.

One way of reducing the size of the Earth based rectenna is to increase
the size of the space based rectenna. This though increases the power
density and the cost of the space structure.If memory serves, one of the main reasons for the big
receiving antenna was to keep power density below a
level that could start to affect the environment, like
mid-beam birds and such. I thought it was almost entirely to keep the size of the transmitting
antenna (which, after all, has to be launched into space) under
control. I could be wrong.

Both to reduce the size of the transmitting antenna, and to limit the
radiation flux.

It is unlikely the transmitting antenna would be launched from Earth,
unless a space elevator arrives before a moon base.

On 25 Jan, 02:53, (Henry Spencer) wrote:
In article .com,

Alex Terrell wrote:
A question: How do you steer a multi-gigawatt microwave transmitter? Is
it steered electronically?Correct. Oh, there are alternatives, but for such a big transmitting
antenna, electronic steering is overwhelmingly the preferred solution.

If so, is it possible to switch the beam
across say, 10 rectennas, perhaps 10 times per second?Better: it is possible to generate multiple beams *simultaneously* --
with electronic steering of a zillion-element transmitter, you can shape
the output distribution to have peaks in several directions rather than
just one. (Each beam is still subject to the same fundamental limits on
how tight it can be; this trick doesn't get around that.)
--
Thanks. This implies to an advantage for power sats over the 5GW
reference design.

The right strategy might be to start with one powersat, and just keep
building it up as big as possible. Though of course, this goes against
the issue of redundancy. Though if one 20GW power sat is exporting to
20 rectennas across a continent, the temporary loss of 20GW might be
bearable.

At what size do tidal forces become an issue (rather than a design
factor) in Geostationary Orbit?

Perhaps in 2100 we could have 50TW from 1,000 50GW power sats. (Still
masses about half an O'Neill cylinder).