Great analysis, thanks.
Any change if we manufacture the panels in space. Lifting robotic
manufacturing station first and then refuel with raw materials?
learner
On Sep 2, 2009, at 2:10 PM, hkhenson wrote:
Sept. 1 (Bloomberg) -- Mitsubishi Electric Corp. and IHI Corp. will
join a 2 trillion yen ($21 billion) Japanese project intending to
build a giant solar-power generator in space within three decades and
beam electricity to earth.
A research group representing 16 companies, including Mitsubishi
Heavy
Industries Ltd., will spend four years developing technology to send
electricity without cables in the form of microwaves, according to a
statement on the trade ministry's Web site today.
http://www.bloomberg.com/apps/news?pid=20601101&sid=aJ529lsdk9HI
http://www.bloomberg.com/apps/news?pid=20601080&sid=aF3XI.TvlsJk
I responded on a closed mailing list. Here is a copy with deletions.
snip
"Transporting panels to the solar station 36,000 kilometers above the
earth=92s surface will be prohibitively costly, so Japan has to
figure out
a way to slash expenses to make the solar station commercially
viable,
said Hiroshi Yoshida, Chief Executive Officer of Excalibur KK, a
Tokyo-based space and defense-policy consulting company. =93These
expenses
need to be lowered to a hundredth of current estimates,=94 Yoshida
said by
phone from Tokyo.
I get the same number close enough. Current price to GEO $20,000/
kg; required for space based solar power to displace fossils by
being substantially less expensive (1-2 cents per kWh) is $100/kg, a
factor of 200.
"Step 1: Rocket Equation...
Needed 100 t/hr to GEO, $100/kg. Try a two stage to GEO. Required
14 km/sec, get the first 4 km/sec with a mass ratio 3 hydrogen/
oxygen rocket. To get the remaining 10 km/sec with a mass ratio 2
means an average exhaust velocity of 15km/sec.
Because you stage far short of LEO, the second stage must have
relatively high thrust so 60 km/sec ion engines won't do. Ablation
laser propulsion (well understood physics) with an average exhaust
velocity of 15 km/sec will provide over a g at 4 GW. The suborbital
path keeps the second stage out of the atmosphere long enough (15
minutes) for the laser to push the second stage into geosynchronous
transfer orbit.
At 4 payloads an hour (working the laser full time), each payload to
GEO needs to be 25 t. So the laser stage is 50 t, the first stage
50 t (16%structure) and 200 t propellant. On takeoff it masses 300
tons, less than a 747. A large airport handles a lot more traffic
than 8 747 takeoffs and landings an hour.
Step 2: A miracle occurs...
Hard engineering, no miracles permitted. Not easy, the laser might
eventually cost $40 billion. To get started (to positive cash flow)
came out to $60 billion on a first cut proforma analysis.
Step 3:
snip
A UK company, Reaction Engines, has an inordinately clever approach
to boost the effective exhaust velocity so as to actually put
positive payloads into LEO with hydrogen/oxygen single stage to
orbit. What they are doing is recovering a lot of the energy that
goes into liquefying hydrogen and using that to compress air to
rocket chamber pressures up to 26km and Mach 5+. Google for them.
Also see http://www.theoildrum.com/node/5485
Keith
PS. A lot of the mass of a thermal power satellite is heat sink
fluid. That can be made from finely ground rock and a little gas.
Decouples gas pressure from the amount of heat the pseudo fluid can
carry. Seems a shame to be shipping up sacks of cement dust. We
are looking into the payback time for a moving cable space elevator
through L1 to the lunar surface. Existing materials are good enough
for the cable--without taper. 15 MW is enough to lift 33 tons per
hour. Feed lunar dirt through a vibratory ball mill and presto heat
sink fluid.
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