Digest Number 509

I see what you mean about laser beaming. Yes, it definitely makes
mroe sense. I'm with you

except . . .

do you think that Dubya would be happy with a multi-gigawatt
concentrated laser in orbit.

Wouldn't that be considered a WMD because of its energy density?

Just a thought.

TangoMan

--- In ssi_list@... Ian Woollard
> You're not getting me; I'm saying for laser power beaming between
L1 and
> the lunar surface for example, the worst PV you can find can give
you
> 50% efficiency, under a dollar per watt or so, including the laser
and
> PV. And you can use direct sunlight when it's available as well.
>
> Microwave is great for returning power to earth, because it
punches
> through the clouds, but there's no weather on the moon, and so
it's
> going to be more expensive by the time you've laid out multiple
square
> kilometers of rectenna. I mean, microwaves don't focus down worth
a
> damn from any distance unless you have huge antenna at each end.
Light
> is easy.
>
> >--- In ssi_list@... Ian Woollard
> >
> >>
> >>
> >>
> >>>Lasers are not much use, because the rectenna would simply be
PV
> >>>
> >>>
> >arrays are low conversion efficiency.
> >
> >>>
> >>>
> >>>
> >>>
> >>Do you have a reference for that low conversion efficiency? The
> >>
> >>
> >best PVs
> >
> >>are now at about 30% when used with sunlight,
> >>
> >>
> >
> >True enough, but I'm not ready to accept that a SPS will be using
> >the most efficient PV available because if they have to be
> >constructed from orbital resources, I wonder if we'll be able to
> >acquire the Group III or V periodic table elements to alloy with
> >gallium arsenide, indium, copper indium diselenide, gallium
indium
> >phosphide, and germanium.
> >
> >I think it more likely that a simpler silicon PV cell will be
used
> >because it will be more easily manufactured from lunar silicon
using
> >the Czochralski or float zone method in a zero-g or lunar
> >environment.
> >
> >I think that there is a chance that PV technology and solar
> >thermal/sterling engine may not even be used. With the abundance
of
> >ilmenite in the lunar regolith, after we extract the iron and an
> >oxygen atom we'll be left with titanium dioxide, which when
> >impregnated with a dye can replace the semiconducting material
used
> >in PV cells to create a voltage. This may be a cheaper technology
to