[ExI] Slashdot Hardware Story | Japan Plans $21B Space Power Plant

hkhenson hkhenson at rogers.com
Thu Sep 3 14:48:13 UTC 2009

At 05:00 AM 9/3/2009, Stefano Vaj wrote:

>On Sep 1, 4:54?pm, Samantha Atkins <sjatk... at gmail.com> wrote:
> > http://hardware.slashdot.org/story/09/09/01/1656246/Japan-Plans-21B-S...

  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.



I responded on Slashdot.  Here is a copy with additions/deletions.


Tekfactory put his finger squarely on the problem. $500/pound is 
close enough to $1000/kg and that is ten times to high for space 
based solar power to undercut fossil fuels. The Japanese recognize this.

"Transporting panels to the solar station 36,000 kilometers above the 
earth's 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. "These 
expenses need to be lowered to a hundredth of current estimates," 
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.

Design to cost. Start with the rocket equation:

Needed 100 t/hr to GEO, $100/kg. Try a two stage to GEO. Requires 14 
km/sec, get the first 4 km/sec with a mass ratio 3 hydrogen/oxygen 
rocket. Four km/sec is easy to do, ask Elon Musk. 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 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 mass ratio 2 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 eight 747 takeoffs and landings an hour.

Hard engineering and not cheap.  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.

A UK company, Reaction Engines, has an inordinately clever approach 
to boost the effective exhaust velocity so as to put payloads (12 
tons) 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 cool and compress air to rocket chamber 
pressures up to 26km and Mach 5+. Google for them. Also see 
http://www.theoildrum.com/node/5485 if you want more details.

Added new thoughts from the space elevator conference.

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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