Beamed Power

>>
>>Yeah? And? These power stations aren't THAT expensive. Few tens of
>>millions or so. Maybe one hundred million.
>>
> And then some. They come in about $1 billion per gigawatt.

Ok, I was assuming a power of around 100 megawatts, so I was
about right.

>>Oh, well, lets assume an arbitrary 1kg/m^2. Sounds in the ballpark
> I would rather have some real numbers. Anybody got any references ?

So would I but lets see if we're in the ballpark first.

> 1 kg / m^2 for something only 1mm thick sounds high to me.
> What material is it made from ? Aluminum ?

Ok, about 1/7 of a millimeter for aluminium.

>>(that would make it less than 1mm thick, but in space that's probably
>>not totally out of the question.) Cost to GEO is about ~$10000 per kg.
> Sure, could it be even less than 1 mm thick ?

Yes, but its limited by resistive heating I think.

>>You need atleast 1km^2, that's 1 million m^2.
>>Therefore one GEO transmitter would cost atleast 10 billion.
> Good, that is one data point.
>
> Now, let us look at the assumptions.
>
> What is the thickness for the antenna material ?
> If it were thinner, let us say like kitchen aluminum Foil.
> I just measured some, it weighs in at 0.0475 kg per square metre,
> thickness is unspecified,
> looks like less than 0.1 mm

It's not clear its upto the job though.

> 1 km^2 would be 10e6 m^2 = 47,500 kg
>
> Cost to GEO from Earth surface about $ 475 million US.

Marginal. In the ballpark though.

> Also, does it need to be solid Aluminum ? Can we use aluminized mylar
> or Kapton ? A lot lighter.

Aerials have to conduct, you make it too thin it melts.

> Does it need to be solid surface ? Would a mesh be OK ?

Yes. But the amount of conductor stays the same, and the
surface area goes down... less cooling. You're in a
vacuum, only radiative cooling.

> The O'Neil designs were for about 1 Gigawatt per square kilometre of
> antenna.

1 Gigawatt/km^2 = 1kw/m^2. Sounds like it my be too much for
aluminium foil. You'd need to do some more checking.

For an example of what happens to aluminium foil when the
power goes too high, stick an AOL CD in a microwave for a
few seconds, next to a glass of water; label side up is
best. (It WON'T wreck the microwave, provided you include the
glass of water.)

> So my numbers give about $ 1 billion or two per gigawatt.
> In the same ball park as terrestrial power systems.

>>You may need two in fact, one for receive, one for transmit. That
>Yes, we need two at least.

Not necessarily. A diffraction grating can make a directional
mirror. In theory it might be possible to point a diffraction
grating at the ground station. In practice that may not be
possible due to mechanical misalignment issues.

Still, I'm wondering whether an electronically steerable
diffraction grating could be constructed. Might be very much cheaper
as you only need one surface.

> Microwave telecom systems routinely go tens of kilometres, so that is a
> good experience base.

Not really, but their power efficiency is mostly irrelevant, only
received power and the cost of the antennas.

> You stated that SPS beams would be less intense than cell phones, ergo
> less hazardous.
>
> Or did you mean that cell phones may yet turn out to be hazardous ?

There's a risk that its hazardous. The evidence is weak though. And
it doesn't seem to get more strong with careful study, which
probably means it's junk science. Still, its very difficult to prove
something safe. The public have a very skewed perception of risk,
any NEW risk is looked at very carefully, particularly when it
doesn't directly benefit them. The public probably won't think this
benefits them, unless the electricity price ends up half the old
cost or something.

> CR.
>

civilization?"