What's wrong with this idea?

--- In spacesettlers@y..., Ian Woollard wrote:
> victoriatangoman wrote:
>
> So all you need to do is switch off one transmitter and turn on
the
> other and you can supply extra power. I suppose in theory you
could
> point it just about anywhere, provided you were prepared to wait
for the
> antenna to swing across and lock in.

Thanks for your insight. Maybe you can help with this question too.
If the overhead SPS is beaming power to the rectenna, would there be
any issue with waveform interference if another SPS from a few time
zones away, beamed in a portion of its power, but that power is
coming in at a different angle than from overhead?

>
> >2.) A super-sized SPS, with multiple transmitter arrays, serving
> >multiple rectenna farms in a narrow longitudinal band. This could
> >provide power balancing between different utilities. Also by
> >extending this concept to a larger scale, could a Super-Size SPS
> >serve multiple utilities across the hemispherical line, thus
> >providing power to summer peak loads while the other hemispehre
is
> >experiencing winter?
> >
> Yeah, don't see why not; it looks very doable. The only question
is
> whether there is enough market south of the equator.
>
> >3.) A transfer of microwave power to and from multiple orbiting
SPS
> >in order to take power where it is needed. This prevents
designing
> >SPS capacity for peak power load. Thus, a SPS orbiting above a
> >longitude in the night, can beam a portion of its power across
> >space, perhaps relayed by other SPSs, to a SPS above a daylight
> >longitude.
> >
> I'm less certain this works so well. Well, it works, but the
> transmitters are typically much smaller than the rectenna
(actually
> according to the equation I've seen the product of their areas is
> related to the distance you're sending it.). So you'd end up
building
> huge rectennas to make this work, and you'd need them to be in
space.
> That's probably prohibitively expensive in launch costs right now,
> although in the long run the costs are probably not an issue at
all (in
> the context of space settlement).

After some analysis, I too have some doubts about how well this will
work. The over riding factor will be what is the value of
electricity that is generated in the middle of the night that you
can't sell. If that value is zero, then it might be worth trying to
sell it in another market despite the huge transmission losses.

Consider the following, radius of earth is 6,378.1 km, GEO is 35,786
km above earth surface, thus 2 SPSs with 1 relay, would entail two
legs for the transmission, each 59,629 km. This is compared to the
35,786 km from SPS to the rectenna.

Please check me on these calculations. If we designate power
received at rectenna from overhead SPS to be 100%, then power
received at the relay would be 36%. Is there further loss, in the
process of, not the distance involved of, redirecting the energy?
Now when the power is received at the destination SPS, it will be at
9%. But this is power coming from the dead of night across the
globe. Our time offset is 12 hours between the two SPSs. What is the
value of that power if there is no use for it at its designated
rectenna? I would contend it has no value. So beam it to another
rectenna whose market demands that power, even if we can only get 9%
of that power across that distance.

If we use just the line-of-sight scenario we are limited to, at
most, a 120 degree separation, with a direct line transmission of
73,030 km between the two SPSs. The received power would be 24% of
that received at the rectenna directly underneath the sending SPS.
Our time offset is 8 hours between the two SPSs. Now, we have more
power received at the final SPS, but it came from a market that is 8
hours offset from us. The question arises, does that sending market
have as much excess power to send as the one that is offset 12
hours? I don't know.

>
> You could try having multiple repeaters though, that way the
antennas
> are much smaller... The issue with this is efficiency, as you'd
lose
> power with each hop, but also, for any significant distance you're
> talking kilometer antennas. And the distances from one side of the
> earth, the long way is 100,000 km or so if you have multiple hops.

To address your concern I'll just throw an idea out without having a
clue as to its feasability. We use microwaves to beam energy from
SPS to rectenna because they travel through the atmosphere without
too much attenuation, but is this necessarily the best form in the
vacuum of space. Could the inter-SPS transfers occur as laser light?
We'd still face the dreaded inverse square loss issue, but wouldn't
laser light resolve the problem of kilometer long rectennas in space?