[extropy-chat] Space elevator numbers I
hkhenson at rogers.com
Tue Feb 13 19:31:07 UTC 2007
I am not sure this is the right place to be discussing this. If anyone
knows of a better place, please let me know.
If we want a non nuclear solution to the carbon and energy crisis, we need
to put some numbers on it. Displacing coal for power generation in the US
would take about 300 Gw. That's 30 10 Gw or 60 5 Gw SPS.
SPS designs are projected to be in the 1-2 kg/kw range. I.e., a 5 Gw SPS
would mass 5,000 to 10,000 metric tons. This business is urgent, so let's
figure displacing all the US coal fired plants in about a year. So 360
days/60 plants means we need to build a 5 Gw plant every 6 days. Roughly
(and ignoring the short tons to metric tons) figure lifting 10,000 tons
every 5 days to GEO or 2000 tons a day.
Back in the space colony days Dr. O'Neill used to say that getting out of
the earth's gravity was equal to going up a 4000 mile high mountain. I
recalculated it from escape velocity and got 3998 miles. Close enough. :-)
Approximating GEO to be at escape, and because orbital energy is
partitioned equally between velocity and potential, the energy requirement
is to haul 2000 tons per day up a 2000 mile high mountain. (The other half
of the energy is extracted from the earth's rotation.)
Using English units (you can rework it in metric) that's 4 million pounds x
10 million feet or 4 x 10 ** 13. ft-pounds/day, or about 900,000 hp (660 Mw)
For reference, the aircraft carrier Enterprise can crank out about 280,000
hp. (210 Mw)
So the lift power required is in the range of 2/3rds of a Gw.
Climbers using beamed power and electrical motors to go up a cable are in
the range of 1% efficient. Which means something like 66 Gw of power would
be required to lift the parts for a 5 Gw power sat every 5 days. That's
not impossibly bad, the power sat would pay back its lift energy cost in 66
(to be continued)
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