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.

> >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.
>

Partially true. Another point is that having a low concentration
beam allows the use of a relatively small transmitting antenna.
Getting a tighter beam involes launching a bigger antenna.

>
> 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.
>

I am sorry, I do not follow this at all.

Why have multiple lunar satellites ? One not just one big one ?

>
> 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?
>

No hard data. Note that as the power density increases, the waste heat
per unit area will increase, so the rectenna will run at higher
temperatures. Heat rejection on the Moon is a difficult problem, and
this would make it more difficult.
If the rectenna gets too hot the conversion elements will burn out.

>
> 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.
>

No, this is not viable.

A single large transmitter antenna is more efficient than many small
antennas. Small antennas lose most of their energy in sidelobes.

>
> > >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.
> >
> Partially true. Another point is that having a low
concentration
> beam allows the use of a relatively small transmitting antenna.
> Getting a tighter beam involes launching a bigger antenna.
>
> > 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.
> >
> I am sorry, I do not follow this at all.
>
> Why have multiple lunar satellites ? One not just one big one ?

As I've discovered, launching mass via a mass driver is a very
energy intenisve endeavor. If you're interested in the actual
numbers I've been able to derive, I've been posting most of my
calculations over in the space settlers group.

I'm just pursuing an intellectual exercise, trying to see what is
involved in getting an infrastructure in place. My curiousity
started with the mamoth task of an Island 3, but now that I'm
further into it, I'm working at a bootstrapping scenario.

To answer your question, I'm inclined to favor the position of
having multiple 5 GW SPS in lunar L1 orbit, because when, or if, the
lunar operations need less power, those SPS could, with some effort,
be transferred to GSO.

Also, I'm assuming that a 5 GW SPS would be "on-line" sooner than a
10 GW, etc. It gets the power to the lunar operation that much
sooner.

>
> > 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?
> >
> No hard data. Note that as the power density increases, the
waste heat
> per unit area will increase, so the rectenna will run at higher
> temperatures. Heat rejection on the Moon is a difficult problem,
and
> this would make it more difficult.
> If the rectenna gets too hot the conversion elements will burn out.

Good points. I wonder what the limits are? Doing some simple math, a
10 KM diamter rectenna field, absorbing 5 GW would average at 63.63
watts/meter ^2. How much more could be absorbed? 5x 10x?

I wonder how much heat absorption the panels would take on the moon
before we could kill two birds with one stone. Circulate a fluid to
pick up the waste heat from the rectenna's and make use of that heat
for additional energy.

> --- In ssi_list@... charles radley
> >
> To answer your question, I'm inclined to favor the
> position of
> having multiple 5 GW SPS in lunar L1 orbit, because
> when, or if, the
> lunar operations need less power, those SPS could,
> with some effort,
> be transferred to GSO.
>

Feeding a single rectenna from multiple indepdent
antennas is impossible, the beams will intefere and
tend to cancel each other out.

If you really want 5 separate transmitters, then you
have two options, either

1) link all the transmitters together into a phased
array, that it effectively a single antenna, or

2) Cable all the 5 spses together an feed their
microwave
outputs through a single transmitter antenna.

> Also, I'm assuming that a 5 GW SPS would be
> "on-line" sooner than a
> 10 GW, etc. It gets the power to the lunar operation
> that much
> sooner.
>

I do not follow this logic at all.

At least, I do not understand why it would drive the
need for multiple SPSes.

A single SPS could start out as 5 GW and be expanded
to
give 10 GW output. This would be done by adding
solar panels. For a constant power density, the
transmitter antenna size needed for a 10 GW station
would actually be smaller than for a 5 GW station. If
the same size antenna is used it could be defocused by
changing the surface profile shape thus spreading out
the beam as required.

>
> > --- In ssi_list@... charles radley
> > >
> > To answer your question, I'm inclined to favor the
> > position of
> > having multiple 5 GW SPS in lunar L1 orbit, because
> > when, or if, the
> > lunar operations need less power, those SPS could,
> > with some effort,
> > be transferred to GSO.
> >
> Feeding a single rectenna from multiple indepdent
> antennas is impossible, the beams will intefere and
> tend to cancel each other out.
>
> If you really want 5 separate transmitters, then you
> have two options, either
>
> 1) link all the transmitters together into a phased
> array, that it effectively a single antenna, or
>
> 2) Cable all the 5 spses together an feed their
> microwave
> outputs through a single transmitter antenna.

Very good points. Thank you. Of the two options which do you think
is the easiest to implement?

>
> > Also, I'm assuming that a 5 GW SPS would be
> > "on-line" sooner than a
> > 10 GW, etc. It gets the power to the lunar operation
> > that much
> > sooner.
> >
> I do not follow this logic at all.
>
> At least, I do not understand why it would drive the
> need for multiple SPSes.
>
> A single SPS could start out as 5 GW and be expanded
> to
> give 10 GW output. This would be done by adding
> solar panels. For a constant power density, the
> transmitter antenna size needed for a 10 GW station
> would actually be smaller than for a 5 GW station. If
> the same size antenna is used it could be defocused by
> changing the surface profile shape thus spreading out
> the beam as required.

So, if I'm understanding you correctly, a SPS could be transmitting
power to a rectenna as a "work in progress." Either continually
being expanded; or expanded and the power is brought on in stages.

What would have to be done to the transmitting antenna to allow the
added power to be transmitted? Exactly, what would be required
to "change the surface profile?"

OF course the alternative is to have a power station at the lunar
Pole and transmit via cable to the equatorial base. I see a number
of advantages with this scenario, but the drawback is that the whole
power generation facility is tied to the moon forever. With SPS,
they are somewhat mobile. What do you think?