Solar Power Satellites

--- In spacesettlers@yahoogroups.com, "Combs, Mike"
"I'm curious to know if we're debating you, or essentially debating
Zubrin by proxy."

I had my word processor set to automatically hyphenate. Also, I'm
told that the way to make a statement is to "Tell them what you're
going to say; say it; then tell them what you said." I skipped one
of these three steps.

I'm not aware that Robert Zubrin has written on this subject. Can
you tell me the title of his work on this subject?

"So what the above implies is that it might take 1/10 the output of a
nuclear reactor just to maintain orientation of this satellite.
Maintaining orbital altitude wouldn't even enter into it since there
is no significant drag at GEO altitude."

Station keeping consists of controlling the generation, conversion
and transmission of electricity, monitoring and communications,
aiming the solar panels and the power beam, other orbital,
rotational, and orientation adjustments, monitoring and dealing with
static electric, magnetic, vibration and oscillation issues, and
keeping the whole thing stable.

The power satellite will be subject to perturbations from
gravitational and magnetic anomalies on the Earth, Earth-Moon-Sun
interactions, coronal mass ejections, the influence of Jupiter and
Venus, and many others. Also, I don't think you can just point the
thing at the Sun, and let it go at that. The satellite will revolve
around the Earth every 24 or so hours in an orbit inclined to the
elliptic by differing amounts as the seasons progress, and subject to
other rotational effects of the Earth.

I estimated that the total energy cost for all of this would be about
39 megawatts (1300 watts/m2 * 10^7 meters of solar arrays * 30% solar
cell efficiency * 1%). The International Space Station (ISS) uses
about 65 kilowatts of electricity, but it doesn't use electricity for
orbital, rotational, or orientation adjustments. I haven't found any
way to determine the electrical equivalent of the ISS thrusters, but
I'm sure it would represent a substantial fraction of the total
energy use of the Station.

When one considers that the power satellite will weight about 100
times as much as the ISS, and that it will process a solar flux of 13
gigawatts in a facility that is about 10,000 times as large as the
ISS, a few hundred times as much equivalent electricity use including
the orbital, rotational, and orientation adjustments seems in the
ballpark.

"I've never read anything about SPS to imply that anything beyond
passive cooling would be necessary."

The ISS uses liquid ammonia radiators to dissipate heat. The power
satellite would process an enormously greater energy flux. I think
the heat issue alone could be a show stopper. About 13 million
kilowatts (kws) of energy will impinge on the power satellite nearly
continuously. Of this, about 1.95 million kws (13 million kws * 30%
solar panel efficiency * 50% efficiency converting electricity into a
power beam) is transmitted to Earth, and an equal amount will be
deposited on the power satellite as heat. About half (or moresolar
panels aren't designed to reflect sunlight) of the remaining 9.8
million kws will be deposited as heat on the solar array, and the
balance will be reflected.

6.85 million kws of heat will have to be radiated into space.

"the equivalent of only one shuttle mission per year.. SPS advocates
assumed yet more advanced space transportation systems with
capabilities far beyond even the hypothetical Shuttle ones."

With the "shuttle equivalent missions," I am assuming an equivalent
mission (about 7 crew and 22 tons of cargo), but at 1/10 the cost to
LEO, and 1/5 the cost to geostationary orbit. I think a ten fold
reduction in cost would represent some significant advancement.

Bob