> My past calculations lead me to believe that a 10GW
> SPS would cost $70B; ignoring non-recurring costs.

The ISS solar power system currently weighs ~100,000 kg and provides
~100 kW at the panel connections.
http://en.wikipedia.org/wiki/ISS_Solar_Arrays#Truss_and_solar_array_as
sembly_sequence
http://en.wikipedia.org/wiki/ISS_Solar_Arrays#Solar_arrays

That works out to ~1,000 kg/kW. If we assume a launch cost of
$1,000/kg to GEO, such a solar power system scaled linearly would
cost $1 million/kW = $1 billion/MW = $1 trillion/GW, just to launch.

If about half of the ~$100 billion spent so far on the ISS is
attributable to the solar power system, the cost would be $50
billion/100kW = $0.5 billion/kW = $0.5 million/W = $0.5
quadrillion/GW.

By the way:

If we figure that each square meter of sun-facing Earth-orbital space
receives 1,320 watts, that each array is 420 (35 x 12) square meters,
and that each array produces 32.8 kW at the panel connectors,
conversion efficiency is only 5.9%. The conversion efficiency works
out to even less, if we count the spaces between the arrays that can
be seen in these pictures:
http://en.wikipedia.org/wiki/ISS_Solar_Arrays#Solar_arrays

> That assumes that everything is launched from earth at
> a reasonable estimated (and industry supported) RLV cost
> of $500/kg, and NASA's baseline 10,000tons per GW
> estimate from two decades ago.

My above ~1,000 kg/kW figure for the ISS power system converts to ~1
billion kg/GW, or ~1 million tons/GW. It seems that, in practice,
things aren't working out quite as well as they did on decades ago
paper.

> If we instead assume that the material comes from the moon,
> we can probably cut that estimate in half, down to $3B.

If you are referring to launching rocks from the moon, why not
compare that to the cost of launching single-stage pressure-fed
steel/aluminum/titanium high-tolerance (big, dumb, cheap) rocket
bodies (partly filled with whatever other raw materials might be
needed) using TRW's lunar-lander proven ultra-low-cost pintle (non
showerhead) injection architecture.
http://en.wikipedia.org/wiki/Kestrel_(rocket_engine)

The fuel cost is supposedly somewhere south of $10/lb of payload to
LEO:
http://yarchive.net/space/rocket/fuels/fuel_costs.html

> That works out to ~1,000 kg/kW.
> conversion efficiency is only 5.9%.

No one will disagree with you that the ISS is a horrible design in every one
of its thousands of NASA mandated grotesque details.

> If we assume a launch cost of
> $1,000/kg to GEO, such a solar power system scaled linearly would
> cost $1 million/kW = $1 billion/MW = $1 trillion/GW, just to launch.

But no one will take you seriously when you start claiming that the ISS is
some kind of irrifutable proof that we cannot do better.

> By the way:

> > That assumes that everything is launched from earth at
> > a reasonable estimated (and industry supported) RLV cost
> > of $500/kg, and NASA's baseline 10,000tons per GW
> > estimate from two decades ago.
>
> My above ~1,000 kg/kW figure for the ISS power system converts to ~1
> billion kg/GW, or ~1 million tons/GW. It seems that, in practice,
> things aren't working out quite as well as they did on decades ago
> paper.

If you are incapable or unwilling to understand the difference between the
kind of solar array used by the ISS, and the kind used by an SPS, then the
modorator needs to remove you from this list for trolling.

> If you are referring to launching rocks from the moon, why not
> compare that to the cost of [big dumb boosters]?

Because luna electrical launch delivering simple baulk material will
undercut BDBs in a long term project.
Because RLVs will very probably undercut BDB in launching complex earth
equipment.

Kestral is a bird, not a rocket engine

GAry 7