Re: "Concerned citizens" only hope for SPS......by Dr. Gerard K. O'Neill

"Alex Terrell" <alexterrell@xxxxxxxxx> wrote:

:
:Len Lekx wrote:
:> On Thu, 02 Nov 2006 21:04:37 GMT, Fred J. McCall
:> <fmccall@xxxxxxxxxxxxx> wrote:
:>
:> >Again, talks about 5GW and not the 20GW being claimed. This one
:> >assumes you're building most of the stations on the Moon and lofting
:> >it from there.
:>
:> But it's still larger than the 500MW system you're thinking of...
:> :-)
:
:5GW is the standard reference design. The trickiest bits of scaling
:would seem to be:
:
:1. Very large commutstors
:2. Wiring which increases with the cube of linear dimensions
:3. Gravitational tides

You left out "getting that much mass up with no ROI", which is the
problem that dwarfs all the rest.

:However, in principle no reason why 400km2 can't deliver 40GW to the
:ground.

In principle, no reason why we can't just stick a really big
thermocouple through the middle of the Sun, but it's bloody unlikely.

:> >[This is why I favor the Moon over Mars as a goal for large permanent
:> >habitation, by the way.]
:>
:> Hey - an idea we share!
:>
:> >: Why does it all have to come from Earth? Part of the concept is to
:> >It all has to come from Earth because of the solar cell efficiencies I
:> >cited. You're not going to be making multi-layer multi-spectral cells
:>
:> Why, oh WHY does everybody think that solar cells are the ONLY way
:> that SPS can be built????? Solar-thermal has generating efficiencies
:> that are (correct me if I'm wrong...) greater than solar cells.
:> Mirrors are cheaper than solar cells, so can be made larger for the
:> same cost.
:>
:Who care'sabout effiency?

The folks who have to:

1) Get all the mass up there.

2) Keep it all pointed appropriately.

3) Keep it all together.

4) Pay the bills until something comes on line.

:What counts is cost per KWhr.

And moving mass around and managing the mass of your station is part
of that cost.

:I don't rule
:out solar thermal, but consider that space photovoltaic must work on an
:automated processes where you throw in silicon and/or other ingredients
:to a hopper and out come ~0.1mm thick solar sheets - the solar sheets
:could be very low cost indeed. (Amorphous Si:H seems to come out below
:this thickness).

All magically automated by, uh, what, precisely? Oh, and take your
conversion efficiency down to around 12%-15% AT BEST. You now need a
bigger array.

:> >in space for a long, LONG time (and you need something to make them
:> >out of). If you want to drop the efficiency back to somewhere between
:> >1/4 and 1/3 of what I assumed (increase size of required array
:> >appropriately) you can perhaps get started making the things on the
:> >Moon.
:>
:> I've got no problem with that... :-)
:>
:> >If by 'space-based industrial capability' you mean actually making the
:> >things in space (rather than on one of the balls of dirt), then that's
:> >really, REALLY probably not going to happen for structures of this
:> >size. You'd have to get the raw materials from somewhere, which puts
:> >you in the asteroid moving business or increasing your launch
:> >requirements by orders of magnitude to send up raw material to feed
:> >your space industry.
:>
:> Why not? Granted, it won't happen TOMORROW... but at some point in
:> time, lunar and asteroid mining will provide a lot of raw material.
:
:I could well see a situation where given the infrastructure, the
:marginal cost of the satellites is very low indeed. (No maintenance,
:automated extrusions, very large scale structures etc). And the raw
:material requirements are not that great. One 1km diameter NEO could
:provide all the raw material needed for several TW of power.

In other words, all magically happening, including getting that 1km
NEO to your 'space factory'.

In case you haven't noticed, the odds of a robotic mission to fix
Hubble were considered so low as to not be worth the attempt.

:> >Because 50 MW isn't enough to meet local demand. Why do you think we
:> >don't build 20 GW units here on Earth?
:>
:> Ummm... because nobody wants that much coal waste anywhere near
:> where they live...? :-)
:
:I could imagine that China could well build 20 nuclear plants near
:Shanghai.

And why not one really, REALLY big one, instead?

:> >As I expected, mere hand waving. There is no real reason to expect
:> >the cost of the second one to drop precipitously at all.
:> >Unfortunately, this is what it all to frequently comes back to with
:> >SPS fans - "... and then a miracle happens ...".
:
:There are reasons to expect the unit cost to be very low indeed.

And yet nobody seems to be able to put any forward that don't assume
one or more miracles along the way.

:Its
:just the $100 billion that's needed to get the show on the road which
:is the problem.

There's a reason for this. It's the lack of a real business case that
anyone finds believable.

You'd be better off working toward that than assuming "and then a
miracle comes to pass".

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw
.

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