[ExI] Hemingway test program.

Keith Henson hkeithhenson at gmail.com
Wed Feb 19 19:37:17 UTC 2014


Ran this through the clear writing program and worked on it till
junior high kids could read it.

Scope of the problem

Humans need to replace ~15 TW of power from fossil fuel with a cheap
non-carbon source over the next 20-25 years.

"Cheap" here is from Gail Tverberg's article
http://theenergycollective.com/gail-tverberg/266116/oil-prices-lead-hard-financial-limits

and her discussion at a conference on power satellites where $30-50
per bbl oil was OK for vibrant economies.

If power satellites are a possible solution, then we need to consider
number of areas of knowledge to analyze the project.  This list is not
exhaustive.

Economics

For a low maintenance, no fuel power source, the cost per kWh is
~1/80,000 of the capital investment.  Thus, $800/kW capital cost would
provide 1 cent per kWh power, $1600 would cost 2 cents per kWh, etc.
(One cent/kWh is $10/MWh.)

Chemistry and electro chemistry

Synthetic oil cost about $10/bbl for the capital equipment.  This was
what the Sasol plant in Qatar cost.  It also takes electrolytic
hydrogen and biomass or CO2 from the atmosphere.  The CO2 is close to
free.  The hydrogen for a bbl of oil takes two MWh of power.  Thus
$10/MWh power would provide $30/bbl oil and $20/MWh would make $50/bbl
oil.  Synthetic liquid transportation fuels need vast amounts of low
cost electrical power.  Hydropower is this inexpensive, but there is
not enough hydropower to solve the problem.

Orbital mechanics

Describes the velocity change needed to reach to LEO and the transfer
from LEO to GEO.  There are other orbits besides equatorial GEO.
Geosynchronous Laplace orbits take less station keeping.  Molniya
orbits are good for high latitude locations.

"Rocket science," the rocket equation

It is critical to understand the reaction mass fraction required for a
given delta V and a particular exhaust velocity.  Low exhaust velocity
results in low payload fractions.  This is the motivation for the high
investment in a 3 GW propulsion laser.  With laser propulsion, it
takes two stages to GEO.  Even then, we need to convert the entire dry
mass of the second stage into power satellite parts for economics to
work out.

Microwave optics

The microwave frequency sets the power satellite size.  At 2.45 GHz,
(the most proposed wavelength), the transmitter in space needs to be a
km in diameter.  The rectenna on the ground is 10 km east to west for
a power satellite on the same longitude as the rectenna.  Higher
frequency decreases the size of both antennas, but increases the
atmospheric absorption

Geometry and geography figure into the launch system.  The launches
need to be to the east (to take advantage of the earth's rotation).
It must be on a coast near the equator, especially if using laser
propulsion.  A glance at a globe will show that there are few such
locations.

Geometry also figures into the power satellite and laser propulsion
design.  The 23 deg tilt of the geosynchronous orbit and the need to
keep sunlight off radiators complicates the design.

Laser optics

The same microwave optics equation sets the optical aperture size to
focus a high-powered laser beam on a vehicle.  For 808 nm, a ten-meter
mirror will focus to 4 meters over the distance from GEO to LEO.

Thermodynamics

Cooling the propulsion laser is a thermodynamics problem.  Three GW of
waste heat takes over 8.5 square km of area.  Low pressure steam is
the heat transfer fluid of choice.

Skylon

The Skylon vehicle comes into this story twice.  It is the vehicle of
choice to lift ~15,000 tons for the initial laser propulsions station.
 Modified with laser hydrogen heaters in the wings, it can go into
orbit with a much higher payload fraction.  A laser boosted Skylon is
the only vehicle proposed that will provide the throughput power
satellites need.

[No wonder people don't understand the proposal]



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