>From what I've been able to gather, on Earth the rectenna farm for a
SPS would be about 10 kilometers in diameter, more if it is situated
at a higher latitude.

My assumption is that it must be this size because we want to limit
the microwave power density, and thus are optimizing rectenna size
to power density. If we had a "Death Ray" beam dense with microwave
we could do with a smaller rectenna. Is this correct? Of course, I
understand why we don't want a powerful beam.

If my assumption is correct in that beam strength can be multiplied,
then would it be possible to have multiple Lunar Solar Satellites
supporting the mining and launching operations on the moon, and have
ALL of the LSS beaming down to one rectenna farm on the moon.

Anybody have any indormation on the limits of power density that a
rectenna farm can absorb, or do you really need a 10 km diamter farm
PER 5 GW satellite?

Thanks for the information.

Actually the diameter is diffraction limited due to the
wavelength of the microwaves. You physically can't focus the
beam down more than that from that distance, without increasing
the size of the transmitter. In fact the receiver/transmitters
diameters are inversely proportional to each other.

victoriatangoman wrote:

>>From what I've been able to gather, on Earth the rectenna farm for a
> SPS would be about 10 kilometers in diameter, more if it is situated
> at a higher latitude.
>
> My assumption is that it must be this size because we want to limit
> the microwave power density, and thus are optimizing rectenna size
> to power density. If we had a "Death Ray" beam dense with microwave
> we could do with a smaller rectenna. Is this correct? Of course, I
> understand why we don't want a powerful beam.
>
> If my assumption is correct in that beam strength can be multiplied,
> then would it be possible to have multiple Lunar Solar Satellites
> supporting the mining and launching operations on the moon, and have
> ALL of the LSS beaming down to one rectenna farm on the moon.
>
> Anybody have any indormation on the limits of power density that a
> rectenna farm can absorb, or do you really need a 10 km diamter farm
> PER 5 GW satellite?
>
> Thanks for the information.
>

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding
technological civilization?"
- Gerard O'Neill

Ian, Thanks for that clarification, but what I'm trying to get a
response to is whether multiple beams can come down onto ONE
rectenna farm. How much energy can the rectenna panels absorb?

--- In spacesettlers@y..., Ian Woollard wrote:
> Actually the diameter is diffraction limited due to the
> wavelength of the microwaves. You physically can't focus the
> beam down more than that from that distance, without increasing
> the size of the transmitter. In fact the receiver/transmitters
> diameters are inversely proportional to each other.
>
> victoriatangoman wrote:
>
> >>From what I've been able to gather, on Earth the rectenna farm
for a
> > SPS would be about 10 kilometers in diameter, more if it is
situated
> > at a higher latitude.
> >
> > My assumption is that it must be this size because we want to
limit
> > the microwave power density, and thus are optimizing rectenna
size
> > to power density. If we had a "Death Ray" beam dense with
microwave
> > we could do with a smaller rectenna. Is this correct? Of course,
I
> > understand why we don't want a powerful beam.
> >
> > If my assumption is correct in that beam strength can be
multiplied,
> > then would it be possible to have multiple Lunar Solar
Satellites
> > supporting the mining and launching operations on the moon, and
have
> > ALL of the LSS beaming down to one rectenna farm on the moon.
> >
> > Anybody have any indormation on the limits of power density that
a
> > rectenna farm can absorb, or do you really need a 10 km diamter
farm

victoriatangoman wrote:

> How much energy can the rectenna panels absorb?

Rectantennas can take more power than anyone is ever likely to
point at them, kilowatts/m^2 atleast.

One big issue though is that there are NO stable lunar orbits
at all.

The idea with the geosynchronous power sats is that they hang
over a particular point in the sky. This simplifies the design
enormously. There aren't any geosynchonous orbits around the
moon either.

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding
technological civilization?"
- Gerard O'Neill

Isn't L1 stable in two of the three axis. It's only about 30,000 km
from the surface and might present a more elegant solution to power
for a moon based mining and launching facility.

Also, what material are the rectennas made from. Can it be
manufctured on the moon?

--- In spacesettlers@y..., Ian Woollard wrote:

Well, a rectenna mainly consists of wire, capacitor and
diode(s), so it depends whether you have the manufacturing base
for that; you may well be able to import the capacitors and
diodes though.

victoriatangoman wrote:

> Isn't L1 stable in two of the three axis. It's only about 30,000 km
> from the surface and might present a more elegant solution to power
> for a moon based mining and launching facility.
>
> Also, what material are the rectennas made from. Can it be
> manufctured on the moon?
>
> --- In spacesettlers@y..., Ian Woollard wrote:
>
>>victoriatangoman wrote:
>>
>>
>>>How much energy can the rectenna panels absorb?
>>>
>>
>>Rectantennas can take more power than anyone is ever likely to
>>point at them, kilowatts/m^2 atleast.
>>
>>One big issue though is that there are NO stable lunar orbits
>>at all.
>>
>>The idea with the geosynchronous power sats is that they hang
>>over a particular point in the sky. This simplifies the design
>>enormously. There aren't any geosynchonous orbits around the
>>moon either.
>>
>>--
>>- Ian Woollard (ian.woollard@t...)
>>
>>"Is a planetary surface the right place for an expanding
>>technological civilization?"
>>- Gerard O'Neill
>>
>

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding
technological civilization?"
- Gerard O'Neill

Thanks for the info. Such a scheme would allow more power to come
online for the mining base without need to continualy expand the
rectenna farm.

Also, when the launching from the base diminishes, perhaps because
of increasing asteroidal imports, then the power sats
are "reasonably" mobile and perhaps can be utilized in geosynchronus
orbit.

As for orbit at L1, of course, the orbit will need to be maintained
for such a massive structure. The other consideration would be power
from lunar surfacem either at equator or pole. But what this does is
it ties the power facility to the lunar surface forever.

It would be interesting to more thoroughly examine the bootstrapping
process and the economics of the polar versus L1 scenario, to
determine which is most plausable. Of course, I'm completely
discounting nuclear power because of earth launch concerns, and
equatorial power and storage as viable options. My analysis of the
polar/L1 situation is about a week away. I'd love to hear opinions
on which makes the most sense.

--- In spacesettlers@y..., Ian Woollard wrote:
> Well, a rectenna mainly consists of wire, capacitor and
> diode(s), so it depends whether you have the manufacturing base
> for that; you may well be able to import the capacitors and
> diodes though.
>
> victoriatangoman wrote:
>
> > Isn't L1 stable in two of the three axis. It's only about
30,000 km
> > from the surface and might present a more elegant solution to
power

--- In spacesettlers@y..., Ian Woollard wrote:
>
> The idea with the geosynchronous power sats is that they hang
> over a particular point in the sky. This simplifies the design
> enormously. There aren't any geosynchonous orbits around the
> moon either.
>
> --

That is only partially true. By definition, "geosynchronous" orbits
can only orbit the earth. However, L4 and L5 are stable orbits
which orbit the earth-moon system in one month = one lunar rotation,
so a SPS at these libration orbits would always point at the same
two spots on the moon.

:) ed

PS I have been desperately searching for a way to fund my robotics
work, and so have taken a job as a camp cook on far northern oil
rigs; I just got back tonight after spending just over a week at a
camp at more than 59 degrees north, the furthest north I have ever
travelled. These rig camps are very much like what I had envisioned
a moon base would be like, particularly in terms of isolation and
logistics, and in the types of people present... if I ever write a
science fiction story set in a moonbase, I already have a large cast
of characters to draw from :)